http://www.eoearth.org/ Thu, 01 Jan 1970 00:00:00 GMT 15 en-us cutler@bu.edu http://www.eoearth.org/e/i/header_logo.gif http://www.eoearth.org/ http://www.eoearth.org/article/Water_governance <a href='/article/Water_governance'><img border='0' src='/upload/thumb/b/be/Fig_1_water_governance.JPG/250px-Fig_1_water_governance.JPG' width='100'/></a> <p>The water sector worldwide is increasingly characterized in terms of a crisis situation. The unique and complex characteristics of the water resource entail complex social, political, and economic implications in its management. The water crisis is mainly a crisis of governance and the management forms under which water has been historically governed. In light of the problems in the water sector, public-private partnerships have been increasingly advocated and adopted throughout the world. Proponents of partnerships have often appealed to the financial gains, cost reductions, efficiency gains, environmental compliance, human resource developments, and increased services which have followed private sector engagement. Opponents of partnerships have appealed to the price increases, imbalance of power, labor disputes, inequities, environmental damage, and increased risks associated with private sector participation in water services. This paper reviews these debates to conclude that evidence can be found in support of either position. The paper argues that this dichotomous debate has lead to inconclusive and unconstructive discussions among interested parties. The paper recommended that focus be re-directed away from ideological positions on privatization towards a focus on the principals and standards which can make private participation work for the public good when it is chosen. </p> <p><a href='/article/Water_governance'>Read Full Article...</a></p> http://www.eoearth.org/article/Water_governance Fri, 09 May 2008 13:55:31 GMT http://www.eoearth.org/article/Supertanker <a href='/article/Supertanker'><img border='0' src='/upload/thumb/a/a0/Supertanker.jpg/250px-Supertanker.jpg' width='100'/></a> <p>The term supertanker originally applied to the class of tankers too large to transit international canals while carrying cargo, and currently defined by two ship classes: Very Large Crude Carriers (VLCCs) between ~200,000 and ~300,000 deadweight tons (dwt) and Ultra Large Crude Carriers (ULCCs) greater than ~300,000 dwt. Supertankers are a remarkable technological response to <a href="/article/Market">market</a> conditions that promoted economies of scale without apparent bound in the 1960s, 70s, and 80s. </p><p>The first modern tanker (tanks integral with hull) was the ~3000 dwt &#39;Glukauf&#39;, built in 1886. Until the 1950s, most crude oil was <a href="/article/Petroleum_refining">refined</a> at source and transported to market in products tankers, sized between 12,000 and 30,000 dwt. Larger vessels became economically feasible when oil companies began locating refineries near energy markets, although the <a href="/article/Suez_Canal%2C_Egypt">Suez Canal</a> restricted tanker size. Energy market shifts and the 1956 closure of the Suez Canal created new routes, removing geographic barriers to construction of the first VLCCs and ULCCs. Fully-loaded supertankers (especially efficient diesel-powered VLCCs built in 1990s) reduced unit shipping costs dramatically, but partial loads could not sustain economies of scale; many were scrapped in the 1980s and 90s or used for storage. </p><p>The largest supertanker ever built was the 555,843 dwt &#39;Seawise Giant&#39;, refitted in 2004 as a floating storage and offloading unit named the &#39;Knock Nevis&#39;. Current supertanker sizes are defined by <a href="/article/Market">market</a> conditions providing an economic upper bound and geophysical limitations defining the number of routes and ports (or offshore terminals) that these very large vessels can safely serve. </p> <p><a href='/article/Supertanker'>Read Full Article...</a></p> http://www.eoearth.org/article/Supertanker Thu, 08 May 2008 15:19:13 GMT http://www.eoearth.org/article/Impact_of_ozone_on_Mediterranean_forests <a href='/article/Impact_of_ozone_on_Mediterranean_forests'><img border='0' src='/upload/thumb/8/84/Days_with_90_ppb_info_exceedancees%2C_2006.gif/300px-Days_with_90_ppb_info_exceedancees%2C_2006.gif' width='100'/></a> <p>Tropospheric <a href="/article/Ozone">ozone</a> (O₃) concentrations are increasing all over the world. The troposphere extends to between 10 and 18 kilometers above the surface of the Earth and consists of many layers. Ozone is more concentrated above the mixing layer, or ground layer. Ground-level ozone is a serious problem because of its environmental effects. Ground level ozone pollution is pronounced in <a href="/article/Region">regions</a> with strong photochemical activity, such as the <a href="/article/Mediterranean_Basin">Mediterranean Basin</a>. For a general description of the Mediterranean basin climate and vegetation, see &quot;<a href="/article/Mediterranean_conifer_and_mixed_forests">Mediterranean conifer and mixed forests</a>&quot;. </p><p>The physical and chemical processes affecting O₃ formation vary greatly even within the Mediterranean Basin. In summer, the Western basin is under the influence of weak levels of Azores anti-cyclonic subsidence, low <a href="/article/Wind">winds</a>, and strong insolation. These conditions favor massive photochemical production of O₃, with development of mesoscale processes and recirculation within air masses. During the same period, the Eastern basin is under conditions of weak ascent and strong advection, i.e. the Etesian winds, that largely inhibit the development of recirculation, even if peaks of 150-220 parts per billion (ppb) occur. The boundary between the two major O₃ formation areas is located over Italy. Due to its central position in the Mediterranean, Italy may be considered as a hot-spot for O₃ and representative of O₃ <a href="/article/Impact_of_ozone_on_health_and_vegetation">impacts on Mediterranean vegetation</a>. </p><p>Southern Europe is affected by dangerous ground level <a href="/article/Ozone">ozone</a> concentrations. In 2006, the frequency of ozone level exceedances was higher than in previous years, though not as high as in the record year 2003. The European Environmental Agency reports that the highest one-hour ozone concentration occurred in Italy. Other high hourly ozone concentrations were reported in Austria, France, Italy, Portugal, Romania and Spain (Figure 1). North-western, central and eastern Europe did not escape either. </p><p>In the <a href="/article/Mediterranean_Basin">Mediterranean Basin</a>, the detrimental impact of <a href="/article/Ozone">O₃</a> on forests remains largely under-investigated. Detecting plant, or vegetative effects is necessary to give biological significance to O₃ standards. Field evidence of direct effects of O₃ on Mediterranean forests are controversial. Significant relationships between O₃exposure and effects (crown transparency, radial growth and foliar symptoms) often fail. Possible causes for this discrepancy are: </p><ul><li>The critical level established to protect Mediterranean forests against ozone is inappropriate. Ozone effects on trees have been mainly inferred from controlled-condition experiments on seedlings rather than multi-factorial analysis of forest conditions in the field. Extrapolating O₃ sensitivity from young to mature trees creates substantial overestimations. A number of studies have raised doubts about conclusions drawn from O₃ exposures in closed and open-top chambers. In addition, the current approach used by the European Union (EU) to assess and predict risk to vegetation is based on the concept of exposure of vegetation to <a href="/article/Atmospheric_composition">air</a> concentrations of <a href="/article/Ozone">ozone</a> rather that on uptake of this substance by vegetation. The exposure-based approach is functionally wrong, as effects are caused by the amount of ozone uptaken into the leaf and detoxified inside the leaf (flux). The complexity of this approach, however, may interfere with an extensive use for <a href="/article/Risk_assessment">risk assessment</a> and still needs to be evaluated;</li><li>Response indicators are improper or improperly investigated. Ozone effects on plants are aspecific. Thus, all indicators are ambiguous. Multivariate statistical analysis may help in decoding the role of different predictors. It is somehow surprising that we are searching for O₃ effects on tree radial growth under field conditions, when experiments have not yet determined if ambient O₃ levels actually impair it; and<br /></li><li>Site and plant characteristics increase O₃ tolerance in Mediterranean vegetation. Mediterranean forest vegetation appears to be adapted to face oxidative stress factors, such as elevated O₃ concentrations, drought and high <a href="/article/Solar_radiation">radiation</a>, including UV-B. Some reasons to explain why Mediterranean vegetation may tolerate potentially harmful O₃ concentrations are: sclerophyllous leaves (little intercellular air space, thick cuticle and cell wall, high <a href="/article/Stomata">stomatal</a> density); low gas exchange rates; emission of volatile organic compounds (VOC); and active antioxidant pool. The prevailing environmental conditions in the <a href="/article/Mediterranean_Basin">Mediterranean Basin</a> (excess light, elevated <a href="/article/Temperature">temperature</a>, reduced <a href="/article/Precipitation_and_fog">precipitation</a>) reduce stomatal conductance (and thus the uptake of <a href="/article/Ozone">ozone</a>) at the time of the highest O₃ levels, and promote sclerophylly, VOC emission, and content and activity of antioxidants. </li></ul> <p>In conclusion, Mediterranean forests are at the highest ozone risk in Europe because of the high ozone concentrations they experience. Even if field injury is not as high as expected on the basis of concentration-based standards, visible ozone-like foliar injury has been observed for several years on a number of tree species in Spain, France and Italy at permanent <a href="/article/Monitoring">monitoring</a> sites where high O₃ concentrations occur. Visible <a href="/article/Ozone">ozone</a>-like <a href="/article/Impact_of_ozone_on_health_and_vegetation">injury to vegetation</a> is often in the form of spotty brown discolorations on leaves (Figure 2). Two Mediterranean pine species &ndash; <em>Pinus ponderosa</em> and <em>P. halepensis</em> &ndash; are among the most symptomatic conifers under field conditions. This suggests that ozone affects Mediterranean forests, even if the extent of ozone impairment is still to be quantified. </p> <p><a href='/article/Impact_of_ozone_on_Mediterranean_forests'>Read Full Article...</a></p> http://www.eoearth.org/article/Impact_of_ozone_on_Mediterranean_forests Wed, 07 May 2008 15:42:13 GMT http://www.eoearth.org/article/Mid-latitude_cyclone <a href='/article/Mid-latitude_cyclone'><img border='0' src='/upload/thumb/5/51/Cyclone_family_US.gif/250px-Cyclone_family_US.gif' width='100'/></a> <p>Mid-latitude or frontal cyclones are large traveling atmospheric cyclonic storms up to 2000 <a href="/article/Meter">kilometers</a> in diameter with centers of low <a href="/article/Atmospheric_pressure">atmospheric pressure</a>. An intense mid-latitude cyclone may have a surface pressure as low as 970 millibars, compared to an average sea-level pressure of 1013 millibars. Normally, individual frontal cyclones exist for about 3 to 10 days moving in a generally west to east direction. Frontal cyclones are the dominant weather event of the Earth&#39;s mid-latitudes forming along the polar front (Figure 1). </p><p>Mid-latitude cyclones are the result of the dynamic interaction of warm tropical and cold polar air masses at the polar front. This interaction causes the warm air to be cyclonically lifted vertically into the <a href="/article/Atmosphere_layers">atmosphere</a> where it combines with colder upper atmosphere air. This process also helps to transport excess energy from the lower latitudes to the higher latitudes. </p><p>The mid-latitude cyclone is rarely motionless and commonly travels about 1200 kilometers in one day. Precise movement of this weather system is controlled by the orientation of the polar jet stream in the upper troposphere. An estimate of future movement of the mid-latitude cyclone can be determined by the <a href="/article/Wind">winds</a> directly behind the cold front. If the winds are 70 kilometers per hour, the cyclone can be projected to continue its movement along the ground surface at this velocity. </p> <p>Figure 3 describes the patterns of <a href="/article/Wind">wind</a> flow, surface pressure, fronts, and zones of <a href="/article/Precipitation_and_fog">precipitation</a> associated with a mid-latitude cyclone in the Northern Hemisphere. Around the low, winds blow counterclockwise and inwards (clockwise and inward in the Southern Hemisphere). West of the low, cold air traveling from the north and northwest creates a cold front extending from the cyclone&#39;s center to the southwest. Southeast of the low, northward moving warm air from the subtropics produces a warm front. Precipitation is located at the center of the low and along the fronts where air is being uplifted. </p><p>Mid-latitude cyclones can produce a wide variety of precipitation types. Precipitation types include: rain, freezing rain, hail, sleet, snow pellets, and snow. Frozen forms of precipitation (except hail) are common with storms that occur in the winter months. Hail is associated with severe <a href="/article/Thunderstorm">thunderstorms</a> that form along or in front of cold fronts during spring and summer months. </p> <p>Figure 4 describes a vertical cross-section through a mature mid-latitude cyclone. In this cross-section, we can see how air <a href="/article/Temperature">temperature</a> changes as we move from behind the cold front to a position ahead of the warm front. Behind the surface position of the cold front, forward-moving cold dense air causes the uplift of the warm lighter air in advance of the front. Because this uplift is relatively rapid along a steep frontal gradient, the condensed water vapor quickly organizes itself into cumulus and then cumulonimbus clouds. Cumulonimbus clouds produce heavy precipitation and can develop into severe <a href="/article/Thunderstorm">thunderstorms</a> if conditions are right. Along the gently sloping warm front, the lifting of moist air produces first nimbostratus clouds followed by altostratus and cirrostratus. <a href="/article/Precipitation_and_fog">Precipitation</a> is less intense along this front, varying from moderate to light showers some distance ahead of the surface location of the warm front. </p> <p>Frontal cyclone development is related to polar jet stream processes. Within the jet stream, localized areas of air outflow can occur because of upper air divergence. Outflow results in the development of an upper air vacuum. To compensate for the vacuum in the upper <a href="/article/Atmosphere_layers">atmosphere</a>, surface air flows cyclonically upward into the outflow to replenish lost mass. The process stops and the mid-latitude cyclone dissipates when the upper air vacuum is filled with surface air. </p> <p>Mid-latitude cyclones cause far less damage than tropical cyclones or <a href="/article/Tropical_weather_and_hurricanes">hurricanes</a>. Hurricanes involve much greater amounts of atmospheric energy exchange. As one goes away from the equator, the energy available to fuel a weather system decreases as the amount of <a href="/article/Solar_radiation">solar radiation</a> and <a href="/article/Heat">heat</a> declines. Mid-latitude cyclones can have <a href="/article/Wind">winds</a> as strong as what is associated with a weak hurricane. But, this is a rare occurrence. Frontal cyclones tend to be most disruptive to human activity during winter months. Winter storms can produce heavy snowfalls or freezing rain which slows down transportation, snaps powerlines, and kills vegetation. In January 1998, a winter storm in eastern North America resulted in more than 20 human deaths, billions of dollars of damage, the loss of electrical power in some areas for up to two weeks, and the destruction of many deciduous trees because of the weight of ice (Figures 5 and 6). </p><p><big><strong>Further Reading</strong></big> </p> <ul><li> <a href="http://www.physicalgeography.net" class='external text' title="http://www.physicalgeography.net">PhysicalGeography.net</a> </li></ul> <p><a href='/article/Mid-latitude_cyclone'>Read Full Article...</a></p> http://www.eoearth.org/article/Mid-latitude_cyclone Tue, 06 May 2008 14:52:46 GMT http://www.eoearth.org/article/Reptile <a href='/article/Reptile'><img border='0' src='/upload/thumb/f/ff/Reptile1.gif/250px-Reptile1.gif' width='100'/></a> <p>Reptiles do not form a distinct evolutionary group as birds and mammals do. Rather, the Class Reptilia consists of four orders which are very different from each other. For example, lizards are more closely related to birds than to turtles! </p><p>As a result, reptiles are as easily defined by what they aren&#39;t as by what they are. </p><p>As opposed to mammals and birds, reptiles have neither fur nor feathers, but scales. Reptiles can not be confused with amphibians because reptiles have dry, water-proof skin and eggs, as well as internal fertilization and more advanced circulatory, respiratory, excretory, and nervous systems. </p> <p><a href='/article/Reptile'>Read Full Article...</a></p> http://www.eoearth.org/article/Reptile Mon, 05 May 2008 14:11:22 GMT http://www.eoearth.org/article/Supply_and_demand <a href='/article/Supply_and_demand'><img border='0' src='/upload/thumb/9/95/Supply_Curve_for_Apartments_graph.gif/250px-Supply_Curve_for_Apartments_graph.gif' width='100'/></a> <p>We will start with the following thought experiment. Suppose there is a condominium apartment building where all the apartments are identical, and each apartment has a different owner. Suppose that a number of them might be interested in selling their apartments. For the purposes of this thought experiment, we will assume that they are all well-informed and interested primarily in their potential monetary gain. </p><p>Each owner has a slightly different idea of what would be an acceptable price. No owner will accept less than $91,000 for his or her apartment. At a price of $91,000, one owner is willing to sell. At a price of $92,000, two owners are willing to sell. In fact, it turns out that each time the price rose by $1,000 there is one more owner willing to sell an apartment. None would be willing to sell at $90,000. </p> <p><a href='/article/Supply_and_demand'>Read Full Article...</a></p> http://www.eoearth.org/article/Supply_and_demand Fri, 02 May 2008 17:34:27 GMT http://www.eoearth.org/article/Region <a href='/article/Region'><img border='0' src='/upload/thumb/4/43/World_Regional_map.jpg/400px-World_Regional_map.jpg' width='100'/></a> <p>Regions are artificial constructs that <a href="/article/Geography">geographers</a> use to divide the world into sections which can then be compared with other units or studied in more detail on their own. Their defining feature is that the phenomena being studied exists in greater concentration within the boundaries than it or they do outside of it. We have been made familiar with their use since grade school when we were first introduced to a map of the world with the continents or the seven seas labled. But regions can be as large as a hemisphere or as small as a city block. As scholars progress in their study of the discipline, they utilize more specific and complex types of regions to understand spacial relationships. Rather than size, it is the criteria chosen that establishes the boundaries. There are several different kinds of regions. </p> <ol><li><b>Formal</b> (also referred to as <b>uniform regions</b>) </li><li><b>Functional</b> <ol><li><b>Nodal</b> </li><li><b>Network</b> </li></ol> </li><li><b>Vernacular</b> </li></ol> <p><b>Formal regions</b> are frequently used to outline governmental, physical, cultural and economic areas. Some familiar examples include, Canada, the Rocky Mountains, the Islamic World, or the rice-growing areas. <b>Functional regions </b> are frequently used for service areas, for example, areas served by a particular utility company. <b>Nodal regions</b> are a particular type of functional region that is defined by the point-to-point nature of activity. For example if we wanted to identify places in the United States that have a certain number of telephone calls placed to London over a given period of time, these locations would be represented by points on a <a href="/article/Maps">map</a>, rather than a particular contiguous area. <b>Network regions</b> describe networks of activity&mdash;for example, delivery routes. </p><p>Vernacular regions are constructed by peoples' perception and therefore vary in extent from person to person. They exist because people refer to them as if they are real. Perfect examples are provided by the terms <i>Midwest</i>, <i>Dixie</i>, and <i>Down East</i>. If you gave people maps of the United States and asked them to drawn a line around any of these regions their boundaries would vary considerably. </p> <p><a href='/article/Region'>Read Full Article...</a></p> http://www.eoearth.org/article/Region Thu, 01 May 2008 15:23:28 GMT http://www.eoearth.org/article/Montreal_Protocol_in_transition <a href='/article/Montreal_Protocol_in_transition'><img border='0' src='/upload/thumb/e/e9/Ozone_hole.gif/250px-Ozone_hole.gif' width='100'/></a> <p>Even as the negotiators were hammering out the final com­promises in Montreal in September 1987, an unprecedented international scien­tific expedition was under way in <a href="/article/Antarctica">Antarctica</a>. Using specially designed equipment placed in balloons, satellites, a DC-8 fly­ing laboratory, and a converted high-altitude U-2 spy aircraft, scientists were tracking stratospheric chemical reactions and measuring minute concentrations of gases. Preliminary results, announced about two weeks after the <a href="/article/Montreal_Protocol_on_Substances_that_Deplete_the_Ozone_Layer">protocol&#39;s</a> sign­ing, indicated high stratospheric chlorine presence and the worst-ever seasonal drop in <a href="/article/Antarctic_ozone_hole">Antarctic ozone</a>.</p> <p>Six months later, in March 1988, a joint NASA-NOAA press conference released the Ozone Trends Panel Report, a comprehensive international scientific assessment of all previ­ous air- and ground-based stratospheric trace gas measure­ments, including those from the 1987 Antarctic expedition. The conclusions were stunning: no longer a theory, ozone layer depletion had at last been substantiated by hard evi­dence. The analysis established that between 1969 and 1986, stratospheric ozone over heavily populated <a href="/article/Region">regions</a> of the northern hemisphere, including North America, Europe, and the Soviet Union, China, and Japan, had diminished by small but significant amounts. And CFCs and halons were now im­plicated beyond dispute – including responsibility for the ozone collapse over Antarctica.</p> <p>The new scientific findings were profoundly disquieting. The most alarming implication was that the models on which the <a href="/article/Montreal_Protocol_on_Substances_that_Deplete_the_Ozone_Layer">Montreal Protocol</a> was based had proven incapable of predicting either the chlorine-induced <a href="/article/Antarctica">Antarctic</a> phenomenon or the extent of ozone depletion elsewhere. Most probably, therefore, they were underestimating future <a href="/article/Ozone">ozone</a> losses.</p> <p>Scientific studies now indicated that if existing <a href="/article/Atmospheric_composition">atmospheric</a> concentrations of chlorine and <a href="/article/Bromine">bromine</a> were merely stabil­ized, the <a href="/article/Antarctic_ozone_hole">Antarctic ozone loss</a> would be permanent. In order for ozone levels over Antarctica gradually to recover, and to avoid possibly crossing similar unforeseen thresholds in the future, it would be necessary to restore atmospheric chlorine concentrations (then at three parts per billion and rising) to levels at least as low as those prevailing in the early 1970s, namely, two parts per billion. </p> <p>The original CFCs and halons would be phased out more rapidly than any of the negotiators at Montreal could have dreamed possible.</p> <p>Although the work of protecting the ozone layer is still not completely finished, the major challenges have been successfully addressed. The industrialized countries have either phased out, or are in process of phasing out, all of the major <a href="/article/Ozone">ozone</a>-depleting substances as well as the less-damaging transitional chemicals. Developing countries have also accepted phase-out schedules as a great wave of new technologies is being diffused around the world. </p> <p>Now, the ozone layer is slowly beginning to recover.</p> <p><a href='/article/Montreal_Protocol_in_transition'>Read Full Article...</a></p> http://www.eoearth.org/article/Montreal_Protocol_in_transition Wed, 30 Apr 2008 12:57:28 GMT http://www.eoearth.org/article/Accelerator-driven_nuclear_energy <a href='/article/Accelerator-driven_nuclear_energy'><img border='0' src='/upload/thumb/6/67/Spallation.jpg/250px-Spallation.jpg' width='100'/></a> <p>The essence of a conventional <a href="/article/Nuclear_power_reactor">nuclear power reactor</a> is the controlled fission chain reaction of uranium-235 (²³⁵U) and plutonium-239 (²³⁹Pu). This produces <a href="/article/Heat">heat</a> which is used to make steam to drive a turbine. The chain reaction depends on having a surplus of neutrons to keep it going (fission of ²³⁵U requires one neutron input and produces on average 2.43 neutrons). </p><p>For many years there has been interest in utilizing <a href="/article/Thorium">thorium</a> (Th-232) as a nuclear fuel since it is three times as abundant in the Earth's crust as <a href="/article/Uranium">uranium</a>. Also, all of the mined thorium is potentially useable in a reactor, compared with the 0.7% of natural uranium, so some 40 times the amount of energy per unit mass might be available. A thorium reactor would work by having Th-232 capture a neutron to become Th-233 which decays to uranium-233, which then fissions. The problem is that insufficient neutrons are generated to keep the reaction going. </p><p>More recently, there has been interest in transmuting the long-lived transuranic radionuclides (the actinides neptunium, americium and curium particularly) formed by neutron capture in a conventional reactor and reporting with the high-level waste. If these could be made into shorter-lived radionuclides such as fission products, the management and eventual disposal of high-level radioactive waste would be easier and less expensive. As it is, most radionuclides (notably fission products) decay rapidly, so that their collective radioactivity is reduced to less than 0.1% of the original level 50 years after being removed from the reactor. However, the main long-lived ones are actinides. </p><p>Accelerator-driven systems (ADS) address both of these issues. ADSs are seen as safer than normal fission reactors because they are subcritical and stop when the input current is switched off. This is because they burn material which does not have a high enough fission-to-capture ratio for neutrons to enable criticality and maintain a fission chain reaction. It may be thorium fuel, or actinides which need 'incineration'. </p> <p><a href='/article/Accelerator-driven_nuclear_energy'>Read Full Article...</a></p> http://www.eoearth.org/article/Accelerator-driven_nuclear_energy Tue, 29 Apr 2008 13:29:39 GMT http://www.eoearth.org/article/Accelerator-driven_nuclear_energy <a href='/article/Accelerator-driven_nuclear_energy'><img border='0' src='/upload/thumb/6/67/Spallation.jpg/250px-Spallation.jpg' width='100'/></a> <p>The essence of a conventional <a href="/article/Nuclear_power_reactor">nuclear power reactor</a> is the controlled fission chain reaction of uranium-235 (²³⁵U) and plutonium-239 (²³⁹Pu). This produces <a href="/article/Heat">heat</a> which is used to make steam to drive a turbine. The chain reaction depends on having a surplus of neutrons to keep it going (fission of ²³⁵U requires one neutron input and produces on average 2.43 neutrons). </p><p>For many years there has been interest in utilizing <a href="/article/Thorium">thorium</a> (Th-232) as a nuclear fuel since it is three times as abundant in the Earth's crust as <a href="/article/Uranium">uranium</a>. Also, all of the mined thorium is potentially useable in a reactor, compared with the 0.7% of natural uranium, so some 40 times the amount of energy per unit mass might be available. A thorium reactor would work by having Th-232 capture a neutron to become Th-233 which decays to uranium-233, which then fissions. The problem is that insufficient neutrons are generated to keep the reaction going. </p><p>More recently, there has been interest in transmuting the long-lived transuranic radionuclides (the actinides neptunium, americium and curium particularly) formed by neutron capture in a conventional reactor and reporting with the high-level waste. If these could be made into shorter-lived radionuclides such as fission products, the management and eventual disposal of high-level radioactive waste would be easier and less expensive. As it is, most radionuclides (notably fission products) decay rapidly, so that their collective radioactivity is reduced to less than 0.1% of the original level 50 years after being removed from the reactor. However, the main long-lived ones are actinides. </p><p>Accelerator-driven systems (ADS) address both of these issues. ADSs are seen as safer than normal fission reactors because they are subcritical and stop when the input current is switched off. This is because they burn material which does not have a high enough fission-to-capture ratio for neutrons to enable criticality and maintain a fission chain reaction. It may be thorium fuel, or actinides which need 'incineration'. </p> <p><a href='/article/Accelerator-driven_nuclear_energy'>Read Full Article...</a></p> http://www.eoearth.org/article/Accelerator-driven_nuclear_energy Tue, 29 Apr 2008 13:21:32 GMT http://www.eoearth.org/article/Marine_nitrogen_cycle <a href='/article/Marine_nitrogen_cycle'><img border='0' src='/upload/thumb/0/0b/Marine_N_cycle.JPG/350px-Marine_N_cycle.JPG' width='100'/></a> <p><a href="/article/Nitrogen">Nitrogen</a> (N) is an essential macronutrient the non-availability of which in suitable form or concentration often limits biological production both in the terrestrial and marine environments. It is a polyvalent element that occurs in oxidation states ranging from –3 to +5. Molecular nitrogen (N₂), the dominant constituent of our <a href="/article/Atmospheric_composition">atmosphere</a>, is the most abundant form of nitrogen on Earth. However, the triple N-N bond makes N₂ almost inert, and only a few microorganisms have the capability to utilize (fix) N₂, converting it to the more easily utilizable combined nitrogen forms – initially ammonia (NH₃), or its protonated species, ammonium (NH₄⁺) that is terminally oxidized to nitrate (NO₃^-) by nitrifying bacteria. Nitrification, a chemoautotrophic process, is carried out by a consortium of <a href="/article/Bacteria">bacteria</a> and involves production of intermediates such as nitrite (NO₂^-), and <a href="/article/Nitrous_oxide">nitrous oxide</a> (N₂O) as a byproduct. Due to the oxidizing nature of the Earth’s surface environment, including most of the oceanic water column, NO₃^- is by far the most abundant combined nitrogen species in aquatic systems. However, nitrogen occurs in the most reduced form in biological materials and so when primary producers utilize NO₃^- as the nitrogenous nutrient, it must be reduced to the –3 state; most plants are enzymatically equipped for this purpose. Nitrifiers also oxidize reduced nitrogen released from the decaying organic matter and excreted by organisms. Biological and chemical fixation of N₂ that occurs on a smaller scale through lightning must somehow be compensated by N₂ production in order to maintain the <a href="/article/Atmospheric_composition">atmospheric</a> N₂ content constant over <a href="/article/Geologic_time">geological time scales</a>. This is achieved through the process of denitrification that occurs in anaerobic environments. It involves the reduction of NO₃^- to N₂ with NO₂^-, nitric oxide (NO) and N₂O as intermediates. Another pathway of N₂ production is the anaerobic ammonium oxidation (anammox; NH₄⁺+ NO₂^- &rarr; N₂ + 2H₂O) which, in contrast to denitrification, is carried by chemoautotrophic bacteria. </p><p>Uptake by <a href="/article/Phytoplankton">phytoplankton</a> often results in the nearly complete depletion of inorganic combined forms in sunlit, stratified surface waters of the <a href="/article/Ocean">ocean</a>, whereas sinking of organic debris and its degradation and consequent release of inorganic <a href="/article/Nitrogen">nitrogen</a> causes the latter to accumulate in the subsurface layers along with other macronutrients such as phosphate. Reflux of NO₃^- to the euphotic zone through upwelling and vertical mixing largely regulates primary production except in remote areas (high-nutrient low-chlorophyll regimes) such as the equatorial Pacific and the Southern Ocean where low concentration of a micronutrient (<a href="/article/Iron">iron</a>) appears to limit photosynthesis. In areas characterized by low dissolved inorganic nitrogen (DIN) concentration in surface waters, dissolved organic nitrogen (DON) may be the most abundant form of combined nitrogen and hence an important nitrogen source for both primary and secondary producers. However, most of the DON pool in the ocean is relatively refractory. As in the case of phosphate, NO₃^- concentration exhibits an inverse relationship with <a href="/article/Oxygen">oxygen</a> concentration, and increases downstream of the deep-water flow, being the lowest in the North Atlantic and the highest in the North Pacific. </p><p>Rate of N-fixation in the <a href="/article/Ocean">ocean</a> is poorly constrained; its estimate having risen steadily in recent times currently stands at about 135 Tg N a^-1 (1 Tg = 10¹² g). This is comparable with total inputs of combined <a href="/article/Nitrogen">nitrogen</a> to the ocean by river runoff (~35 and 45 Tg N a^-1 in the dissolved inorganic and particulate organic forms, respectively) and atmospheric deposition (~50 Tg N a^-1), a substantial fraction of which is believed to be of anthropogenic (human-made) origin. Of the various loss terms of combined nitrogen from the ocean, <a href="/article/Air_pollution_emissions">emission</a> of N₂O to the <a href="/article/Atmospheric_composition">atmosphere</a> (4-7 Tg N a^-1) is quantitatively not important for the oceanic combined nitrogen budget, even though for the atmosphere itself it represents a major source of N₂O. The burial rate in the sediments is also quite modest (~25 Tg N a^-1). The most important loss terms are sedimentary and water-column denitrification. The former occurs in all parts of the ocean, especially along the continental margins, because anaerobic conditions required for the onset of denitrification are usually reached within a few millimeters to a few centimeters below the sediment-water interface. However, sedimentary denitrification rate is highly variable, and this together with limited measurements makes estimates of sedimentary denitrification highly uncertain (ranging from 180 to 300 Tg N a^-1). One would expect the extent of water-column denitrification to be better constrained due to the geographical restriction of vigorous denitrification to just a few well-demarcated sites - within the <a href="/article/Oxygen">oxygen</a> minimum zones (OMZs) of the eastern tropical Pacific and the northwestern Indian Ocean (Arabian Sea). However, current estimates of water-column denitrification also vary widely (from 65 to 150 Tg N a^-1). </p><p>A part of the uncertainty in water-column N₂ production arises from the fact that most estimates are based on the deficiency in NO₃^- within the OMZs relative to the concentration expected from the nearly-constant relative changes in <a href="/article/Carbon">C</a>:<a href="/article/Nitrogen">N</a>:P:<a href="/article/Oxygen">O</a> in seawater due to biological activity (the Redfield Ratios: 106:16:1:138), whereas the recently discovered anammox process supported by measurements of N₂/Ar suggests that the extent of N₂ production might substantially exceed ‘nitrate deficits’. Although with the lower ends of ranges for both sedimentary and water column denitrification, it is possible that the oceanic combined nitrogen budget could still be in a steady state, it is more likely that in the present day <a href="/article/Ocean">ocean</a>, losses of combined <a href="/article/Nitrogen">nitrogen</a> significantly exceed inputs. The proponents of the non-steady state believe that the ocean oscillates between a net source and net sink of combined nitrogen on time scales of hundreds to tens of thousand of years, and the associated changes in the combined nitrogen inventory affect the oceanic capacity to sequester atmospheric <a href="/article/Carbon_dioxide">carbon dioxide</a> (CO₂), thereby modulating, in part, climatic (glacial-interglacial) cycles. Those who believe in a balanced budget, argue that oceanic nitrate/phosphate atomic ratio (~15) is quite similar to the “Redfieldian” ratio of 16 in <a href="/article/Plankton">plankton</a> and the intercept of the linear nitrate/phosphate relationship is very close to zero. This in conjunction with the domination of the budget by biological sources and sinks &ndash; nitrogen fixation and denitrification, which may be tightly coupled &ndash; is expected to favor “homeostasis” that would opposes large imbalances. Thus, it is possible that the present imbalance in combined nitrogen budget could either be a transient phenomenon, or it may represent an increase in the oceanic denitrification rates during the “Anthropocene” due to human activity. </p><p><b>Further Reading</b> </p> <ul><li> Codispoti, L. A., Brandes, J. A., Christensen, J. P., Devol, A. H., Naqvi, S. W. A., Paerl, H. W., and Yoshinari, T.: The oceanic fixed nitrogen and nitrous oxide budgets: Moving targets as we enter the anthropocene?, Sci. Mar., 65, 85-105, 2001. </li><li> Gruber, N.: The dynamics of the marine nitrogen cycle and its influence on atmospheric CO₂, in: <i>The Ocean Carbon Cycle and Climate</i>, edited by: Follows, M., and Oguz, T., Kluwer Academic, Dordrecht, 97-148, 2004. <a href="http://www.amazon.com/dp/1402020864/?tag=encycofearth-20" class='external text' title="http://www.amazon.com/dp/1402020864/?tag=encycofearth-20">ISBN: 1402020864</a> </li></ul> <p><a href='/article/Marine_nitrogen_cycle'>Read Full Article...</a></p> http://www.eoearth.org/article/Marine_nitrogen_cycle Mon, 28 Apr 2008 15:06:05 GMT http://www.eoearth.org/article/Predation <a href='/article/Predation'><img border='0' src='/upload/thumb/4/44/LadybirdPredation.jpg/250px-LadybirdPredation.jpg' width='100'/></a> <p>Predation is an interaction between species in which one species uses another species as food. Predation is a process of major importance in influencing the distribution, abundance, and <a href="/article/Species_diversity">diversity of species</a> in ecological communities. Generally, successful predation leads to an increase in the population size of the predator and a decrease in population size of the prey. These effects on the prey population may then ripple out through the ecological community, indirectly changing the abundances of other species. One example of such indirect effects of predation involves the trophic cascade. As the name implies, a trophic cascade occurs when the effects of predation &quot;cascade&quot; down the food chain to affect plants or other species that are not direcrtly eaten by the predator. Typically, a trophic cascade involves a predator feeding on herbivores and reducing their abundance, which then releases plants from grazing pressure and increases the biomass of vegetation. In addition to such ecological effects of predation, which occur on time scales of one or a few generations of the organisms involved, predation has also played, and continues to play, a major role over evolutionary time in molding the phenotypes of many species. </p> <p><a href='/article/Predation'>Read Full Article...</a></p> http://www.eoearth.org/article/Predation Fri, 25 Apr 2008 15:19:06 GMT http://www.eoearth.org/article/Glacier <a href='/article/Glacier'><img border='0' src='/upload/thumb/a/af/Antarctica_glacier.gif/250px-Antarctica_glacier.gif' width='100'/></a> <p>Various types of paleoclimatic evidence suggest that the climate of the Earth has <a href="/article/Earth%27s_climatic_history">varied over time</a>. The data suggest that during most of the Earth&#39;s history, global <a href="/article/Temperature">temperatures</a> were probably 8 to 15° Celsius warmer than they are today. However, there were periods of times when the Earth&#39;s average global temperature became cold; cold enough for the formation of alpine glaciers and continental glaciers that extended in to the higher, middle and sometimes lower latitudes. In the last billion years of Earth&#39;s history, glacial periods have started at roughly 925, 800, 680, 450, 330, and 2 million years before present (B.P.). Of these ice ages, the most severe occurred at 800 million years ago when glaciers came within 5 degrees of the equator. </p><p>The last major glacial period began about 2,000,000 years B.P. and is commonly known as the Pleistocene or Ice Age. During this glacial period, large glacial ice sheets covered much of North America, Europe, and Asia for long periods of time. The extent of the glacier ice during the Pleistocene, however, was not static. The Pleistocene had periods when the glaciers retreated (interglacial) because of mild temperatures, and advanced because of colder temperatures (glacial). Average global temperatures were probably 4 to 5° Celsius colder than they are today at the peak of the Pleistocene. The most recent glacial retreat began about 14,000 years B.P. and is still going on. We call this period the Holocene epoch. </p><p>In North America, the Pleistocene glaciers began their formation in the higher altitudes of the Rocky Mountains, and high-latitude locations in Greenland and north-central Canada. From these locations, the ice spread in all directions following the topography of the landscape. In North America, the glaciers from the Rocky Mountains and north-central Canada met each other in the center of the continent creating an ice sheet that stretched from the <a href="/article/Ocean">Pacific</a> to the <a href="/article/Ocean">Atlantic Ocean</a>. At their greatest extent, the ice sheets of North America covered most of Canada and extended into the United States to a latitude of about 40° North. </p><p>A similar pattern of glaciation has also been scientifically documented in Europe and Asia. In Eurasia, ice sheets had their birth place in the Alps Mountains, Scandinavia, northern British Isles, and northern Siberia. The ice sheets of Eurasia, however, did not form a single ice sheet through convergence and their furthest extent south was limited to a latitude of about 45° North. </p> <p><a href='/article/Glacier'>Read Full Article...</a></p> http://www.eoearth.org/article/Glacier Thu, 24 Apr 2008 14:22:00 GMT http://www.eoearth.org/article/Mauna_Loa_curve <a href='/article/Mauna_Loa_curve'><img border='0' src='/upload/thumb/5/58/Mauna_Loa_map.png/250px-Mauna_Loa_map.png' width='100'/></a> <p>Since 1958, the concentration of <a href="/article/Carbon_dioxide">carbon dioxide</a> (CO₂) in the <a href="/article/Atmospheric_composition">atmosphere</a> has been measured daily at Mauna Loa Observatory, Hawaii (19°32' N, 155°35' W). Mauna Loa Observatory is located on the Island of Hawaii at an elevation of 3,397 meters above mean sea level) on the northern flank of Mauna Loa volcano. Established in 1957, Mauna Lao Observatory has grown to become the premier long-term atmospheric monitoring facility on Earth and is the site where the ever-increasing concentrations of global atmospheric CO₂ were determined. The observatory consists of 10 buildings from which up to 250 different atmospheric parameters are measured by scientists and engineers. </p><p>This air is relatively free from local pollutants, and so is thought to be representative of air in the northern hemisphere. CO₂ measurements at Mauna Loa show two movements. Since 1958, there has been a general increase in the atmospheric concentration of CO₂ due to the <a href="/article/Combustion">combustion</a> of fossil fuels and deforestation. The data also show an annual <a href="/article/Carbon_cycle">cycle</a>. Each year, the concentration of CO₂ rises and falls. The curve is also known as the "Keeling curve", named for <a href="/article/Keeling%2C_Charles_D.">Charles D. Keeling</a> (1928-2005), an American pioneer in the <a href="/article/Monitoring">monitoring</a> of carbon dioxide concentrations in the atmosphere. </p> <p><a href='/article/Mauna_Loa_curve'>Read Full Article...</a></p> http://www.eoearth.org/article/Mauna_Loa_curve Wed, 23 Apr 2008 14:22:24 GMT http://www.eoearth.org/article/Global_warming <a href='/article/Global_warming'><img border='0' src='/upload/thumb/f/f3/Global_temp_2007.jpg/300px-Global_temp_2007.jpg' width='100'/></a> <table border="2" cellspacing="0" cellpadding="0"><tr><td> <p><a href='/article/Global_warming'>Read Full Article...</a></p> http://www.eoearth.org/article/Global_warming Tue, 22 Apr 2008 14:32:22 GMT http://www.eoearth.org/article/Natural_capital_and_economic_growth <a href='/article/Natural_capital_and_economic_growth'><img border='0' src='/upload/thumb/f/f4/Wetland1.jpg/225px-Wetland1.jpg' width='100'/></a> <p><a href='/article/Natural_capital_and_economic_growth'>Read Full Article...</a></p> http://www.eoearth.org/article/Natural_capital_and_economic_growth Mon, 21 Apr 2008 15:28:22 GMT http://www.eoearth.org/article/Natural_capital_and_economic_growth <a href='/article/Natural_capital_and_economic_growth'><img border='0' src='/upload/thumb/f/f4/Wetland1.jpg/225px-Wetland1.jpg' width='100'/></a> <p><a href='/article/Natural_capital_and_economic_growth'>Read Full Article...</a></p> http://www.eoearth.org/article/Natural_capital_and_economic_growth Mon, 21 Apr 2008 15:27:07 GMT http://www.eoearth.org/article/Seagrass_meadows <a href='/article/Seagrass_meadows'><img border='0' src='/upload/thumb/6/67/Posidonia.jpg/300px-Posidonia.jpg' width='100'/></a> <p>Seagrasses are angiosperms that are restricted to life in the sea. Seagrasses colonized the sea, from terrestrial angiosperm ancestors, about 100 million years ago, which indicates a relatively early appearance of seagrasses in angiosperm evolution. With a rather low number of species (about 50-60), seagrass comprise &lt; 0.02% of the angiosperm flora. Seagrasses are assigned to two families, Potamogetonaceae and Hydrocharitaceae, encompassing 12 genera of angiosperms containing about 50 species (Table 1). Three of the genera, <em>Halophila</em>, <em>Zostera</em> and <em>Posidonia</em>, which may have evolved from lineages that appeared relatively early in seagrass evolution, comprise most (55%) of the species, while <em>Enhalus</em>, the most recent seagrass genus, is represented by a single species (<em>Enhalus acoroides</em>, Table 1). Most seagrass meadows are monospecific, but may develop multispecies, with up to 12 species, meadows in subtropical and tropical waters.</p> <h1 align="left"> Adaptations to colonize the Sea</h1><p>The colonization of the sea required a number of key adaptations including (1) blade or subulate leaves with sheaths, fitted for high-energy environments; (2) hydrophilous pollination, allowing submarine pollination (except for the genus <em>Enhalus</em>) and subsequent propagule dispersal; and (3) extensive lacunar systems allowing the internal gas flow needed to maintain the <a href="/article/Oxygen">oxygen</a> supply required by their below-ground structures in anoxic sediments. Seagrass species are all clonal, rhizomatous plants, a necessary adaptation for angiosperm growth in the high-energy marine environment. The rhizome is responsible for the extension of the clone in space, as well as for connecting neighboring ramets, thereby maintaining integration within the clone. The growth rates of seagrass rhizomes vary from a few centimeters per year in the larger, slow growing species, to more than 5 <a href="/article/Meter">m</a> yr^-1 in the smallest species. These horizontal extension rates result in estimated times to develop seagrass meadows ranging from less than 1 year, for fast-growing species (<em>Halophila</em>, <em>Syringodium</em> and <em>Cymodocea</em> species), to centuries for the slowest growing ones (e.g. <em>Posidonia oceanica</em>, Photo 1). </p> <h1 align="left"> Seagrass Distribution and Habitat </h1> <p align="left">Seagrasses occur in all coastal areas of the world, except along Antarctic shores. The four most obvious habitat requirements of seagrasses are a marine environment, adequate rooting substrate, sufficient immersion in seawater and illumination to maintain growth. Seagrasses are found in waters with salinity greater than 10‰ in estuaries to salinities of about 45‰, in hypersaline coastal environments. Seagrass grow from the intertidal, where they are exposed to full sunlight during the emersion periods to depths receiving, on average, 11% of the irradiance incident just below the water surface, allowing seagrasses to grow deeper than 40 m in the clearest <a href="/article/Ocean">ocean</a> waters. Most seagrass species are confined to sandy to muddy sediments, although some species can grow over rock. High sediment mobility by currents and waves, causing successive burial and erosion, may cause seagrass mortality. Consequently, highly mobile, but otherwise suitable, sandy sediments, may be bare of seagrass cover. High inputs of organic matter, which stimulate bacterial activity, are conducive to seagrass mortality due to the accumulation of phytotoxic compounds, such as sulphide. The organic matter concentrations of sediments supporting seagrass growth is generally less than 6% of the dry weight, with redox potentials spanning from highly oxidized to moderately reduced (&gt; - 100 mV). Seagrass encounter suitable conditions along a global area estimated at about 0.6106 km², equivalent to 10% of the coastal ocean, an estimate of seagrass cover that involves considerable uncertainty. </p> <h1 align="left"> Seagrass Functions </h1> <p align="left">Seagrass form extensive meadows (Photos 1 and 2), which are highly productive and often support high biomass, with a global average biomass of about 180 g C m^-2 an average net production of about 400 g C m^-2 yr^-1, ranking amongst the most productive ecosystems in the biosphere. These estimates represent, when scaled to the estimated global cover of seagrasses, a contribution to marine primary production of 0.61015 g C yr^-1, or about 1.13% of the total marine primary production. Because herbivory rates are low in most seagrass meadows, most of their primary production is either stored in the sediments or exported to neighboring ecosystems. Seagrass bury about 27 Tg C year^-1, or about 12% of the total <a href="/article/Carbon">carbon</a> storage in marine ecosystems. Hence, seagrasses are important components of the marine carbon cycle, being responsible for a significant fraction of the net CO₂ uptake by marine biota. </p><p align="left"> </p><p align="left">Seagrass meadows enhance the <a href="/article/Biodiversity">biodiversity</a> of coastal waters. They harbor, virtually without exception, more animals and more species than nearby unvegetated areas. The fish fauna of seagrass meadows can be of considerable diversity, typically reaching more than 100 species in any one region, often dominated by juvenile specimens, as seagrass meadows often play a nursery role. The largest animals that are associated with the seagrass habitat are the green turtle, <em>Chelonia mydas</em>, and species of the order Sirenia (sea cows), notably the dugong <em>Dugong dugon</em>, and the West Indian manatee <em>Trichechus manatus</em>. These animals are the largest marine herbivores, and forage over seagrass meadows. A second manatee species, <em>T. senegalensis</em> (the West African manatee) may also consume seagrass, but data on this animal are scanty. </p><p align="left">Seagrass meadows have other important ecological functions. They improve water quality by reducing the particle loads in the water and absorbing dissolved nutrients. Seagrass stabilize sediments, diminishing sediment resuspension while promoting sedimentation. Seagrass meadows dissipate wave energy and protect coastlines. In addition, a significant fraction of seagrass production accumulated in the beach, as beach-cast detritus, where they deliver carbonate materials that nourish the beach and contribute to dune formation. </p> <h1 align="left"> Conservation issues </h1> <p align="left">Seagrass meadows are believed to be experiencing a world-wide decline, with global loss rates estimated at 2-5% year^-1, compared to 0.5% year^-1 for tropical forests. The causes for seagrass loss are multiple and include disease, extreme events, such as hurricanes and typhoons, burial by shifting sand, excess nutrient inputs to coastal waters and a reduction of water and sediment quality associated to <a href="/article/Eutrophication">eutrophication</a>, and overgrowth by opportunistic algae, leading to seagrass loss, excess organic supply from aquaculture and effluents, water quality deterioration by excess sediment inputs, mechanical damage from fishing activities, coastal engineering and boat activities; climatic extremes, such as heat waves and associated hypoxic events; displacement by invasive species, and excessive herbivory. Whereas actions are being taken to curb these trends, including legislation to protect seagrass meadows, transplanting efforts, and monitoring efforts to detect change, there is, as yet, no evidence that the associated recoveries compensate for the losses. </p> <p><a href='/article/Seagrass_meadows'>Read Full Article...</a></p> http://www.eoearth.org/article/Seagrass_meadows Fri, 18 Apr 2008 14:28:12 GMT http://www.eoearth.org/article/Land-use_and_land-cover_change <a href='/article/Land-use_and_land-cover_change'><img border='0' src='/upload/thumb/a/af/Brazil_deforestation.jpg/250px-Brazil_deforestation.jpg' width='100'/></a> <p><strong>Land-use and land-cover change</strong> (<strong>LULCC</strong>); also known as <strong>land change</strong>) is a general term for the human modification of Earth&#39;s terrestrial surface. Though humans have been modifying land to obtain food and other essentials for thousands of years, current rates, extents and intensities of LULCC are far greater than ever in history, driving unprecedented changes in ecosystems and environmental processes at local, regional and global scales. These changes encompass the greatest environmental concerns of human populations today, including climate change, <a href="/article/Biodiversity">biodiversity</a> loss and the pollution of water, soils and air. Monitoring and mediating the negative consequences of LULCC while sustaining the production of essential resources has therefore become a major priority of researchers and policymakers around the world.</p> <p><a href='/article/Land-use_and_land-cover_change'>Read Full Article...</a></p> http://www.eoearth.org/article/Land-use_and_land-cover_change Thu, 17 Apr 2008 14:36:07 GMT http://www.eoearth.org/article/Market_dynamics <a href='/article/Market_dynamics'><img border='0' src='/upload/thumb/d/d4/Surplus%2C_Shortage%2C_and_Equilibrium_graph.gif/250px-Surplus%2C_Shortage%2C_and_Equilibrium_graph.gif' width='100'/></a> <p>While <a href="/article/Supply_and_demand">supply-and-demand</a> analysis can be a very useful tool, not every <a href="/article/Market">market</a> is a perfectly competitive spot market with smoothly-functioning double-auction mechanisms. Markets may be characterized by market power, differentiated goods, imperfect information, long-term contracts or very different approaches to price determination. An issue of particular importance to <a href="/article/Macroeconomics">macroeconomics</a> is the question of the speed at which real-world price adjustments take place. </p> <p>How long will it take our hypothetical condo traders to reach equilibrium? Minutes? An hour? A day? The theory of <a href="/article/Supply_and_demand">supply and demand</a> doesn’t tell us. The graphs represent a static model. </p><p>Some markets, like stock markets in which traders are constantly yelling bids to each other, clear quickly. But what if you don’t have everyone in a room, agreeing on trades minute-by-minute? For example, consider the market for shirts. When you go into a clothing store, you see a rack of shirts and, on their tags, a given price. The price probably reflects a mark-up by the retailer over what he or she paid to a distributor to get the shirts. The distributor in turn probably charged a mark-up over the price charged by the manufacturer. Now, if the shirts are overpriced, they won’t sell very well. In the terms we introduced, there will be a surplus. If the market worked like the perfect doubleprice and quantity to get it just right, similar to what we saw for our hypothetical apartment market in Figure 1. The price would fall, the surplus of shirts would disappear immediately, and equilibrium would be restored. </p><p>In a realistic, complicated case such as this one, however, there is actually a chain of markets involved—the manufacturer sells to the distributor, the distributor to the retailer, and the retailer to the final buyer. A quick adjustment of prices is unlikely. More commonly, while retailers may mark down the prices on the shirts they have in stock in order to clear them out, this drop in the price won’t immediately travel back up the supply chain. In the next order the retailers place with their distributors, the retailers may just ask for a smaller quantity of shirts, at the price at which the distributor is offering them—especially if the retailer is small relative to the distributor and has little power to bargain over prices. Any changes in prices or quantities at the manufacturing level will only develop over time, as the manufacturers see the level of their inventories either rise (because the shirts are not selling) or fall (because the distributors order more). </p><p>Because of the time it takes for all these things to happen, some economists believe that the most likely first response to a surplus situation is that manufacturers will cut production—perhaps laying off workers—rather than reducing their price. In this case, the quantity produced adjusts to meet the quantity demanded at a given price, rather than the price adjusting to clear the <a href="/article/Market">market</a>. If such quantity adjustments happen economy-wide, unemployment could rise. </p><p>Suppliers may also be reluctant to change rapidly the prices they offer due to menu costs—literally, the costs of changing the prices listed on such things as order forms and restaurant menus. In real-world markets, we generally expect market forces arising from surpluses and shortages to exert pressure on quantities and/or prices in the direction of equilibrium. This is why it is important to be familiar with the model of <a href="/article/Supply_and_demand">supply and demand</a>. But we can’t be sure that that these pressures will be strongly felt, or that an equilibrium will actually be reached. The pure market forces we have examined in our hypothetical perfectly competitive, spot, double-auction market are not the only forces in the world, nor do these forces always work smoothly and quickly. Factors such as union contracts, lengthy production processes, information problems, and other factors can slow down adjustment to equilibrium—or mean that a market equilibrium doesn’t even exist. </p> <p><a href='/article/Market_dynamics'>Read Full Article...</a></p> http://www.eoearth.org/article/Market_dynamics Wed, 16 Apr 2008 14:40:38 GMT http://www.eoearth.org/article/History_of_taxation_in_the_United_States <a href='/article/History_of_taxation_in_the_United_States'><img border='0' src='/upload/thumb/5/56/Tax_Collections1913-2000_US_graph.gif/200px-Tax_Collections1913-2000_US_graph.gif' width='100'/></a> <p>The tax mechanisms used during first 150 years or so of U.S. tax history bears little resemblance to the current system of <a href="/article/Taxation_in_the_United_States">taxation</a>. First, the U.S. Constitution restricted “direct” taxation by the federal government – meaning taxes directly on individuals. Instead, the federal government relied on indirect taxes including taxes on imports (tariffs) and excise taxes. Tariffs were the major source of U.S. government receipts from the beginning of the nation up to the early 1900s. For example, in 1800, custom duties comprised about 84% of government receipts. Internal federal revenue collections (which exclude tariffs on imports) as recently as the early 20th century were primarily derived from excise taxes on alcohol. In 1900 over 60% of internal revenue collections came from alcohol excise taxes with another 20% from tobacco excise taxes. </p><p>Another important difference is the scale of government taxation and expenditures relative to the entire economy. Government spending is currently a major portion of the total U.S. economy – in 2002 government expenditures and investment at all levels comprised about 20% of total economic output. In the late 1800s government expenditures were responsible for only about 2% of national output (earlier data on national output are not available). The role of government has become more prominent as a result of expansion of military activity and an increase in the provision of public services. Consequently an overall trend of increasing <a href="/article/Taxation_in_the_United_States">taxation</a> is evident, although we’ll see that this trend has recently stabilized or reversed. </p><p>The Constitutional framers were wary of a government’s power to tax. Taxation of the American Colonies by a distant and corrupt England was a driving force behind the American Revolution. Consequently, they believed in decentralized taxation and delegated most public revenue collection to localities, which relied primarily on property taxes. During peacetime the federal government met its expenses through relatively modest excise taxes and tariffs. During wars, such as the War of 1812, federal taxes were temporarily raised to finance the war or pay down the ensuing debts. Once the financial crisis passed, taxes were reduced in response to public opposition to high tax rates. </p><p>Like previous wars, the Civil War initiated an increase in both excise tax and tariff rates. Government revenue collections increased by a factor of seven between 1863 and 1866. Perhaps the most significant tax policy enacted during the Civil War was the institution of the first national income tax. Concerns about the legality of the tax, considering the Constitution’s prohibition of direct taxation, were muted during the national emergency. The income tax rates were low by modern standards – a maximum rate of 10% along with generous exemptions meant that only about 10% of households were subject to any income tax. Still, the income tax generated over 20% of federal revenues in 1865. After the war, few politicians favored the continuation of the income tax, and in 1872 it was allowed to expire. </p><p>The impetus for the modern federal income tax rests not with a wartime emergency but with the Populist movement of the late 1800s. The tax system in place at the time, based primarily on excise taxes on alcohol and tobacco, was largely regressive. The Populists revived interest in an income tax as a means to introduce a <a href="/article/Taxation_in_the_United_States">progressive tax</a> based on ability to pay. They saw it as a response to excessive monopoly profits and the concentration of wealth and power. In other words, the tax was not envisioned as a means to generate significant additional public revenue but as a vehicle of social justice. </p><p>A federal income tax, with a large exemption of $4,000, was instituted in 1894 but the Supreme Court ruled it unconstitutional in 1895. Over the next couple of decades proposals were made for a constitutional amendment to establish a federal income tax. While these attempts were defeated, support for federal income taxation gradually increased. Eventually, in 1913 the 16th Amendment to the U.S. Constitution was ratified creating the legal basis for the federal income tax. </p><p>While the initial income tax was <a href="/article/Taxation_in_the_United_States">progressive</a>, it was less radical than many desired. In fact, many conservatives expressed guarded support for the measure to prevent a more significant tax. While the income tax was targeted towards the wealthy – in the first few years only about 2% of households paid any income tax – tax rates of only 1%-7% prevented it from generating significant revenues. </p> <blockquote>“...virtually none of the income tax proponents within the government believed that the income tax would become a major, yet alone the dominant, permanent source of revenue within the consumption-based federal tax system.” (<i>Brownlee, 1996, p.45</i>)</blockquote> <p>These views were to quickly change as the nation required a dramatic increase in revenues to finance World War I. </p> <p><a href='/article/History_of_taxation_in_the_United_States'>Read Full Article...</a></p> http://www.eoearth.org/article/History_of_taxation_in_the_United_States Tue, 15 Apr 2008 14:35:34 GMT http://www.eoearth.org/article/Sustainable_future <a href='/article/Sustainable_future'><img border='0' src='/upload/thumb/3/30/Urban_and_Rural_Populations_of_the_World.JPG/250px-Urban_and_Rural_Populations_of_the_World.JPG' width='100'/></a> <p align="left"> </p><p align="left">Historically humans were able to live within a system of finite resources. Long ago humans had access to a large amount of natural resources and a seemingly unlimited amount of available land. Humans also had a limited population, they consumed very little, and also produced a limited amount of pollutants that the environment was mostly able to assimilate or transform into safe byproducts. Unfortunately, increased population, increased <a href="/article/Essential_economic_activities">consumption</a>, and advances in technology have increased our individual and collective impact on the environment (i.e., our <a href="/article/Ecological_footprint">ecological footprint</a>). Thus, the world now faces serious challenges in terms of long-term <a href="/article/Economic_growth">economic growth</a>, societal prosperity, and environmental stewardship.</p><p> It took the human population hundreds of thousands of years to reach a population of 1 billion. The world&#39;s population now exceeds 6 billion and is expected to reach 9 to 10 billion sometime this century before leveling off (see Figure 1). Tied to this <a href="/article/Human_population_explosion">increase in population</a> are increases in personal resource consumption in most parts of the world.</p> <p align="left">The United Nations Environment Programme (UNEP) lists ten existing or emerging environmental issues the world currently faces (Table 1). Issues such as population growth, climate change &amp; variability, rising consumption, loss of <a href="/article/Biodiversity">biodiversity</a>, and freshwater depletion (and associated water scarcity) are clearly recognized as major environmental challenges. And importantly, all these issues point to one fundamental aspect of <a href="/article/Sustainability">sustainability</a>, that is, the economic and social well being of every citizen and Nation is dependent on the health of the environment. </p><p align="left">As an example of how humans are consuming environmental resources in a non-sustainable manner, some scientists estimate that over 25% of the Sun’s energy, that reaches the Earth and is incorporated into ecosystems, is now appropriated by human beings. Think about it, two more doublings of the human impact on the world’s natural resources (from 25% to 50% and then from 50% to 100%) would result in 100% of the Earth’s net primary production being utilized by humans. This scenario can be accomplished through a combination of population increase, <a href="/article/Economic_growth">economic growth</a> that is based solely on consumption, and advances in technology that allow an even greater proportion of the Earth’s natural resources to be appropriated.</p> <p>Of course this scenario of human’s capturing 100% of the Earth’s net primary production is an <a href="/article/Ecology">ecological</a> impossibility because it leaves ecosystems with nothing. This scenario would also be dire for humans because of our well established dependency on ecosystems for social and economic prosperity. </p> <p><a href='/article/Sustainable_future'>Read Full Article...</a></p> http://www.eoearth.org/article/Sustainable_future Mon, 14 Apr 2008 14:17:37 GMT http://www.eoearth.org/article/Recycling <a href='/article/Recycling'><img border='0' src='/upload/thumb/9/96/Curbside_recycling.jpg/300px-Curbside_recycling.jpg' width='100'/></a> <p>Recycling is the process of turning used products into raw materials that can be used to make new products. Its purpose is to conserve natural resources and reduce pollution. Recycling reduces energy consumption, since it generally takes less energy to recycle a product than to make a new one. Similarly, recycling causes less pollution than <a href="/article/Essential_economic_activities">manufacturing</a> a new product, and conserves raw materials. It also decreases the amount of waste sent to landfills or incinerators. Although people have always reused things, recycling as we know it today emerged as part of the modern environmental movement. </p><p>During World War II, Americans experimented with conservation and recycling as a matter of national security. Afterward, 1950s middle class life unapologetically adopted the ethics of expansion and newness. As more and more middle-class Americans began to express environmental attitudes, the wastefulness of modern <a href="/article/Essential_economic_activities">consumption</a> became obvious to more and more consumers. More Americans than ever before became willing to integrate such practices into their lives as part of a commitment to the environment. For instance, most children born after the 1980s assume the &quot;recycle, reduce, and re-use&quot; mantra has been part of the U.S. since its founding. In actuality, it serves as a continuation of the cultural and social impact of <a href="/article/Earth_Day_%2770:_What_It_Meant">Earth Day 1970</a> and the effort of Americans to begin to live within limits. </p><p>Belittled by many environmentalists, recycling often seems like busy-work for kids with little actual environmental benefit. However, such a minor shift in human behavior suggests the significant alteration made to many humans&#39; view of their place in nature by the late 1900s. This change in worldview, caused by many political, social, and intellectual shifts, forced humans in developed nations to question their lack of restraint. In particular, the culture of consumption of post-World War II America re-enforced carelessness, waste, and a drive for newness. Environmental concerns contributed to a new &quot;ethic&quot; within American culture that began to value restraint, re-use, and living within limits. This ethic of restraint, fed by over-used landfills and excessive litter, gave communities a new mandate in maintaining the waste of their population. Re-using products or creating useful byproducts from waste offered application of this new ethic while also offering new opportunity for <a href="/article/Economic_growth">economic profit and development</a>. </p><p>Non-profit recycling centers began opening around the country, followed by municipal recycling programs. Today, most U.S. communities have such programs. A typical program asks people to separate their recyclables from their trash before placing them at the curb for collection. To encourage recycling, some communities also charge residents for the quantity of trash put out for collection. The most commonly recycled household items are paper and cardboard; metal, glass, and plastic containers and packaging; and <a href="/article/Yard_waste">yard waste</a>. Recycling the recovered materials is simple for metals and glass; they can be melted down, reformed, and reused. Yard waste can be <a href="/article/Composting">composted</a> with little or no equipment. Paper, the most important recycled material, must be mixed with water, and sometimes de-inked, to form a pulp that can be used in papermaking. Plastics recycling requires an expensive process of separation of different resins. </p><p>In the US, plastics are all numerically coded according to type, including: polyethylene terphthalate (PETE or PET; 1) an example of these plastics are virtually all soft drink bottles, high density polyethylene (HDPE; 2) an example would be detergent bottles, polyvinyl chloride (PVC; 3), sometimes used for water or oil bottles but now rare in food beverage packaging, due to concerns about its environmental hazards; low density polyethylene (LDPE; 4) often used for plastic bags, polypropylene (PP; 5) examples are some yogurt containers and bottle caps, and polystyrene (PS; 6) used to make Styrofoam containers. Number 7 seen on some packaging, refers to all plastics other than these six. It is not a single plastic material. </p><p>The American Chemistry Council reports that in the US in 2005, 922 million pounds of HDPE bottles (those thick plastic bottles like milk jugs and laundry detergent bottles) were recycled, as were over one billion pounds of PET and PP bottles, although they note that this represents only about 25-30% of all recyclable bottles. The majority of this is attributed to PET, as PP recycling is rare, and a large part of the recycling of bottles comes from the 11 states with deposit legislation. </p><p>Depending on the type, plastics can be recycled into anything from fiberfill to polyester-like fibers, to blue recycling bins, or plastic lumber furniture. Fleece is an example of a textile that can be produced from recycled plastics. While many companies still rely on “virgin” polyester to produce fleece, there are now several “eco-fleece” products on the <a href="/article/Market">market</a> that are made primarily or entirely from recycled bottles. </p><p><br /> <strong>Further Reading</strong> </p> <ul><li> Strasser, Susan. <em>Waste and Want: A Social History of Trash</em>. NY: Owl Books, 2000. <a href="http://www.amazon.com/dp/0805065121/?tag=encycofearth-20" class='external text' title="http://www.amazon.com/dp/0805065121/?tag=encycofearth-20">ISBN: 0805065121</a> </li><li> Zimring, Carl A. <em>Cash for Your Trash: Scrap Recycling in America</em>. Rutgers University Press, 2005. <a href="http://www.amazon.com/dp/0813536863/?tag=encycofearth-20" class='external text' title="http://www.amazon.com/dp/0813536863/?tag=encycofearth-20">ISBN: 0813536863</a> </li></ul> <p><a href='/article/Recycling'>Read Full Article...</a></p> http://www.eoearth.org/article/Recycling Fri, 11 Apr 2008 13:37:28 GMT http://www.eoearth.org/article/Whale_communication_and_culture <a href='/article/Whale_communication_and_culture'><img border='0' src='/upload/thumb/9/90/Wccfig1.humpback.jpg/250px-Wccfig1.humpback.jpg' width='100'/></a> <p>One of the most compelling fields in whale biology is the study of communication and culture. Odontocetes, or toothed whales such as dolphins and sperm whales, propagate sound waves to echolocate, allowing them to detect objects and organisms with sonar. Mysticetes, or baleen whales, have vocal folds, or cords, that allow them to generate the loudest biological sounds on earth. Some cetologists have found that these sounds also indicate the presence of cultural lineages. Groups of killer whales maintain their own vocal dialects, despite interaction with other orcas. Dolphins appear to possess some of the core properties of grammar and syntax, fundamental to human language.</p> <p><a href='/article/Whale_communication_and_culture'>Read Full Article...</a></p> http://www.eoearth.org/article/Whale_communication_and_culture Thu, 10 Apr 2008 14:31:00 GMT http://www.eoearth.org/article/Topographic_maps <a href='/article/Topographic_maps'><img border='0' src='/upload/thumb/b/b2/Contour_line_map.jpg/250px-Contour_line_map.jpg' width='100'/></a> <p>A topographic map is a detailed and accurate two-dimensional representation of natural and human-made features on the Earth&#39;s surface. These <a href="/article/Maps">maps</a> are used for a number of applications, from camping, hunting, fishing, and hiking to urban planning, resource management, and surveying. The most distinctive characteristic of a topographic map is that the three-dimensional shape of the Earth&#39;s surface is modeled by the use of contour lines. Contours are imaginary lines that connect locations of similar elevation. Contours make it possible to represent the height of mountains and steepness of slopes on a two-dimensional map surface. Topographic maps also use a variety of symbols to describe both natural and human-made features such as roads, buildings, quarries, lakes, streams, and vegetation. </p><p>Scale is important in the detail a map can show and the area it can cover. Topographic maps produced by the Canadian National Topographic System (NTS) are generally available in two different scales: 1:50,000 and 1:250,000. Maps with a scale of 1:50,000 are relatively large-scale covering an area approximately 1,000 square kilometers. At this scale, features as small as a single home can be shown. The smaller-scale 1:250,000 topographic map is more of a general purpose reconnaissance-type map. A map of this scale covers the same area of land as sixteen 1:50,000 scale maps. </p><p>In the United States, topographic maps have been made by the United States Geological Survey (USGS) since 1879. Topographic coverage of the United States is available at scales of 1:24,000, 1:25,000 (metric), 1:62,250 (one inch to 1 mile), 1:63,360 (Alaska only), 1:100,000 and 1:250,000. </p> <p><a href='/article/Topographic_maps'>Read Full Article...</a></p> http://www.eoearth.org/article/Topographic_maps Wed, 09 Apr 2008 14:19:20 GMT http://www.eoearth.org/article/Topographic_maps <a href='/article/Topographic_maps'><img border='0' src='/upload/thumb/b/b2/Contour_line_map.jpg/250px-Contour_line_map.jpg' width='100'/></a> <p>A topographic map is a detailed and accurate two-dimensional representation of natural and human-made features on the Earth&#39;s surface. These <a href="/article/Maps">maps</a> are used for a number of applications, from camping, hunting, fishing, and hiking to urban planning, resource management, and surveying. The most distinctive characteristic of a topographic map is that the three-dimensional shape of the Earth&#39;s surface is modeled by the use of contour lines. Contours are imaginary lines that connect locations of similar elevation. Contours make it possible to represent the height of mountains and steepness of slopes on a two-dimensional map surface. Topographic maps also use a variety of symbols to describe both natural and human-made features such as roads, buildings, quarries, lakes, streams, and vegetation. </p><p>Scale is important in the detail a map can show and the area it can cover. Topographic maps produced by the Canadian National Topographic System (NTS) are generally available in two different scales: 1:50,000 and 1:250,000. Maps with a scale of 1:50,000 are relatively large-scale covering an area approximately 1,000 square kilometers. At this scale, features as small as a single home can be shown. The smaller-scale 1:250,000 topographic map is more of a general purpose reconnaissance-type map. A map of this scale covers the same area of land as sixteen 1:50,000 scale maps. </p><p>In the United States, topographic maps have been made by the United States Geological Survey (USGS) since 1879. Topographic coverage of the United States is available at scales of 1:24,000, 1:25,000 (metric), 1:62,250 (one inch to 1 mile), 1:63,360 (Alaska only), 1:100,000 and 1:250,000. </p> <p><a href='/article/Topographic_maps'>Read Full Article...</a></p> http://www.eoearth.org/article/Topographic_maps Wed, 09 Apr 2008 14:18:01 GMT http://www.eoearth.org/article/Biome <a href='/article/Biome'><img border='0' src='/media/approved/e/ec/Konza_Prairie.jpg' width='100'/></a> <p>Biomes organize the biological communities of the earth based on similarities in the dominant vegetation, climate, geographic location, and other characteristics. Aspects of the physical environment such as precipitation, <a href="/article/Temperature">temperature</a>, and water depth, have a strong influence on the traits of species living in that environment, and thus biological communities experiencing similar environmental conditions often contain species that have evolved similar characteristics. There is no single classification of biomes that is agreed upon by all scientists because different scientists wish to emphasize different characteristics by their definition. Historically however, biomes have been identified and mapped based on general differences in vegetation type associated with regional variations in climate and terrain.</p> <p><a href='/article/Biome'>Read Full Article...</a></p> http://www.eoearth.org/article/Biome Tue, 08 Apr 2008 21:25:53 GMT http://www.eoearth.org/article/Biome <a href='/article/Biome'><img border='0' src='/media/approved/e/ec/Konza_Prairie.jpg' width='100'/></a> <p>Biomes organize the biological communities of the earth based on similarities in the dominant vegetation, climate, geographic location, and other characteristics. Aspects of the physical environment such as precipitation, <a href="/article/Temperature">temperature</a>, and water depth, have a strong influence on the traits of species living in that environment, and thus biological communities experiencing similar environmental conditions often contain species that have evolved similar characteristics. There is no single classification of biomes that is agreed upon by all scientists because different scientists wish to emphasize different characteristics by their definition. Historically however, biomes have been identified and mapped based on general differences in vegetation type associated with regional variations in climate and terrain.</p> <p><a href='/article/Biome'>Read Full Article...</a></p> http://www.eoearth.org/article/Biome Tue, 08 Apr 2008 21:25:30 GMT http://www.eoearth.org/article/Biome <a href='/article/Biome'><img border='0' src='/media/approved/e/ec/Konza_Prairie.jpg' width='100'/></a> <p>Biomes organize the biological communities of the earth based on similarities in the dominant vegetation, climate, geographic location, and other characteristics. Aspects of the physical environment such as precipitation, <a href="/article/Temperature">temperature</a>, and water depth, have a strong influence on the traits of species living in that environment, and thus biological communities experiencing similar environmental conditions often contain species that have evolved similar characteristics. There is no single classification of biomes that is agreed upon by all scientists because different scientists wish to emphasize different characteristics by their definition. Historically however, biomes have been identified and mapped based on general differences in vegetation type associated with regional variations in climate and terrain.</p> <p><a href='/article/Biome'>Read Full Article...</a></p> http://www.eoearth.org/article/Biome Tue, 08 Apr 2008 21:24:38 GMT http://www.eoearth.org/article/Biome <a href='/article/Biome'><img border='0' src='/media/approved/e/ec/Konza_Prairie.jpg' width='100'/></a> <p>Biomes organize the biological communities of the earth based on similarities in the dominant vegetation, climate, geographic location, and other characteristics. Aspects of the physical environment such as precipitation, <a href="/article/Temperature">temperature</a>, and water depth, have a strong influence on the traits of species living in that environment, and thus biological communities experiencing similar environmental conditions often contain species that have evolved similar characteristics. There is no single classification of biomes that is agreed upon by all scientists because different scientists wish to emphasize different characteristics by their definition. Historically however, biomes have been identified and mapped based on general differences in vegetation type associated with regional variations in climate and terrain.</p> <p><a href='/article/Biome'>Read Full Article...</a></p> http://www.eoearth.org/article/Biome Tue, 08 Apr 2008 21:21:31 GMT http://www.eoearth.org/article/Lichen <a href='/article/Lichen'><img border='0' src='/upload/thumb/4/43/Tidal_zone_showing_marine_lichens.jpg/200px-Tidal_zone_showing_marine_lichens.jpg' width='100'/></a> <p>Lichens have traditionally been referred to as a prime example of a symbiotic relationship. Each lichen consists of an intimate association between a fungus and a species of algae. The algae within the lichen photosynthesizes, providing food for both symbionts. The fungus protects the alga from harmful light intensities, produces a substance that accelerates photosynthesis in the algae, and absorbs and retains <a href="/article/Physical_properties_of_water">water</a> and minerals for both organisms. There is physiological and ultrastructural evidence that suggests the fungus <a href="/article/Parasite">parasitizes</a> the algae in a controlled fashion and, in some instances, actually destroys the algal cells. There are about 25,000 species of lichens known and they are capable of living in environmental conditions that kill most other forms of life. The number of aquatic lichens is limited as most live under the blazing <a href="/article/Solar_radiation">sun</a> often on bare <a href="/article/Composition_of_rocks">rocks</a>. Aquatic lichens typically live in the intertidal zone along <a href="/article/Coastal_zone">sea shores</a> or in shallow <a href="/article/Stream">streams</a>. </p> <p><a href='/article/Lichen'>Read Full Article...</a></p> http://www.eoearth.org/article/Lichen Tue, 08 Apr 2008 21:20:46 GMT http://www.eoearth.org/article/Biome <a href='/article/Biome'><img border='0' src='/media/approved/e/ec/Konza_Prairie.jpg' width='100'/></a> <p>Biomes organize the biological communities of the earth based on similarities in the dominant vegetation, climate, geographic location, and other characteristics. Aspects of the physical environment such as precipitation, <a href="/article/Temperature">temperature</a>, and water depth, have a strong influence on the traits of species living in that environment, and thus biological communities experiencing similar environmental conditions often contain species that have evolved similar characteristics. There is no single classification of biomes that is agreed upon by all scientists because different scientists wish to emphasize different characteristics by their definition. Historically however, biomes have been identified and mapped based on general differences in vegetation type associated with regional variations in climate and terrain.</p> <p><a href='/article/Biome'>Read Full Article...</a></p> http://www.eoearth.org/article/Biome Tue, 08 Apr 2008 19:03:54 GMT http://www.eoearth.org/article/Vertical_farming <a href='/article/Vertical_farming'><img border='0' src='/upload/thumb/6/60/C_Jacobs_VFs_solar.jpg/200px-C_Jacobs_VFs_solar.jpg' width='100'/></a> <p>The advent of <a href="/article/Agriculture">agriculture</a> ushered in an unprecedented increase in the human population and their <a href="/article/Domestication">domesticated animals</a>. Farming catalyzed the transformation of hunter-gatherers into urban dwellers. Today, over 800 million hectares is committed to agriculture, or about 38% of the total landmass of the Earth. Farming has <a href="/article/Land-use_and_land-cover_change">re-arranged the landscape</a> in favor of cultivated fields and herds of cattle, and has occurred at the expense of natural ecozones, reducing most of them to fragmented, semi-functional units, while completely eliminating others. Undeniably, a reliable food supply has allowed for a healthier life style for most of the civilized world, while the very act of farming has created new health hazards. </p> <p>For example, the transmission of numerous infectious disease agents - avian influenza, rabies, yellow fever, dengue fever, <a href="/article/Malaria">malaria</a>, trypanosomiasis, hookworm, <a href="/article/Schistosomiasis">schistosomiasis</a> - occur with relentlessly devastating regularity at the tropical and sub-tropical agricultural interface. Emerging infections, many of which are viral zoonoses (e.g., Ebola, Lassa fever), rapidly adapt to the human host following encroachment into natural environments. Exposure to <a href="/article/Toxicity">toxic</a> levels of some classes of agrochemicals (<a href="/article/Pesticide">pesticides</a>, fungicides) and trauma are two other significant health risks associated with traditional agricultural practices. Over the next 50 years, the human population is expected to rise to at least 8.6 billion, requiring an additional 10⁹ hectares to feed them using current technologies. That quantity of farmland is no longer available. Thus, alternative strategies for obtaining an abundant and varied food supply without encroachment into the few remaining functional ecosystems must be seriously entertained. </p><p>If traditional farming could be replaced by constructing urban food production centers - vertical farms - then a long-term benefit would be the gradual repair of many of the world’s damaged ecosystems through the systematic abandonment of farmland. In temperate and tropical zones, the re-growth of hardwood forests could play a significant role in <a href="/article/Carbon_capture_and_storage">carbon sequestration</a> and may help reverse current trends in global climate change. Social benefits of vertical farming include the creation of a sustainable urban environment that encourages good health for all who choose to live there; new employment opportunities; fewer abandoned lots and buildings; cleaner air; and an abundant supply of safe drinking water. </p> <p><a href='/article/Vertical_farming'>Read Full Article...</a></p> http://www.eoearth.org/article/Vertical_farming Tue, 08 Apr 2008 15:31:09 GMT http://www.eoearth.org/article/Mauna_Loa_curve <a href='/article/Mauna_Loa_curve'><img border='0' src='/upload/thumb/5/58/Mauna_Loa_map.png/250px-Mauna_Loa_map.png' width='100'/></a> <p>Since 1958, the concentration of <a href="/article/Carbon_dioxide">carbon dioxide</a> (CO₂) in the <a href="/article/Atmospheric_composition">atmosphere</a> has been measured daily at Mauna Loa Observatory, Hawaii (19°32' N, 155°35' W). Mauna Loa Observatory is located on the Island of Hawaii at an elevation of 3,397 meters above mean sea level) on the northern flank of Mauna Loa volcano. Established in 1957, Mauna Lao Observatory has grown to become the premier long-term atmospheric monitoring facility on Earth and is the site where the ever-increasing concentrations of global atmospheric CO₂ were determined. The observatory consists of 10 buildings from which up to 250 different atmospheric parameters are measured by scientists and engineers. </p><p>This air is relatively free from local pollutants, and so is thought to be representative of air in the northern hemisphere. CO₂ measurements at Mauna Loa show two movements. Since 1958, there has been a general increase in the atmospheric concentration of CO₂ due to the <a href="/article/Combustion">combustion</a> of fossil fuels and deforestation. The data also show an annual <a href="/article/Carbon_cycle">cycle</a>. Each year, the concentration of CO₂ rises and falls. The curve is also known as the "Keeling curve", named for <a href="/article/Keeling%2C_Charles_D.">Charles D. Keeling</a> (1928-2005), an American pioneer in the <a href="/article/Monitoring">monitoring</a> of carbon dioxide concentrations in the atmosphere. </p> <p><a href='/article/Mauna_Loa_curve'>Read Full Article...</a></p> http://www.eoearth.org/article/Mauna_Loa_curve Mon, 07 Apr 2008 14:13:43 GMT http://www.eoearth.org/article/Water_governance <a href='/article/Water_governance'><img border='0' src='/upload/thumb/b/be/Fig_1_water_governance.JPG/250px-Fig_1_water_governance.JPG' width='100'/></a> <p>The water sector worldwide is increasingly characterized in terms of a crisis situation. The unique and complex characteristics of the water resource entail complex social, political, and economic implications in its management. The water crisis is mainly a crisis of governance and the management forms under which water has been historically governed. In light of the problems in the water sector, public-private partnerships have been increasingly advocated and adopted throughout the world. Proponents of partnerships have often appealed to the financial gains, cost reductions, efficiency gains, environmental compliance, human resource developments, and increased services which have followed private sector engagement. Opponents of partnerships have appealed to the price increases, imbalance of power, labor disputes, inequities, environmental damage, and increased risks associated with private sector participation in water services. This paper reviews these debates to conclude that evidence can be found in support of either position. The paper argues that this dichotomous debate has lead to inconclusive and unconstructive discussions among interested parties. The paper recommended that focus be re-directed away from ideological positions on privatization towards a focus on the principals and standards which can make private participation work for the public good when it is chosen. </p> <p><a href='/article/Water_governance'>Read Full Article...</a></p> http://www.eoearth.org/article/Water_governance Fri, 04 Apr 2008 14:48:19 GMT http://www.eoearth.org/article/Tax_subsidies <a href='/article/Tax_subsidies'><img border='0' src='/upload/thumb/0/07/Kalinin_nuclear_plant.jpg/300px-Kalinin_nuclear_plant.jpg' width='100'/></a> <p>Tax subsidies are the result of selective <a href="/article/Taxation_in_the_United_States">tax legislation</a> that benefit particular groups of people or industries in the economy. In effect, they share the costs of certain actions between the private sector and the government and impact investment decisions by increasing the expected returns associated with a particular pattern of economic activity. Tax subsidies may be applied in a number of ways to any one or a combination of economic variables (land, labor, <a href="/article/Capital">capital</a>). </p><p>While some provisions (e.g., the general investment tax credits) may be available to an entire class of economic activity, such provisions may still be viewed as subsidies because other classes of economic activity are placed at a relative economic disadvantage. In this case, for example, the government has made a decision to favor <a href="/article/Capital">capital</a>-based productive methods rather than alternatives (such as labor). Similarly, subsidies to new investment favor <a href="/article/Supply_and_demand">supply</a> expansions (such as new power plants) over improved efficiency in the use of existing capacity (such as many demand-side management approaches) and constitute a de facto governmental choice of the method by which to meet <a href="/article/Market">market</a> <a href="/article/Supply_and_demand">demand</a>. </p><p>Tax subsidies are generally measured in reference to a normative or baseline <a href="/article/Taxation_in_the_United_States">tax system</a>, and estimates assume no other changes in the tax code. Each tax expenditure is calculated assuming that there is no interaction with other provisions. As a result, the estimates can't be added directly together without errors. As it is very difficult to estimate the potential interactions from simultaneous removal of multiple subsidies, though, most analyses do add the tax expenditure values together anyway. </p><p>Since the government forgoes revenue that would have been collected had there been no special legislation and must make up those revenues through higher taxes on other economic activities, these policies have real costs. These costs are classified as "tax expenditures." Within the United States, we are lucky in that two separate groups (the U.S. Treasury and the Joint Committee on Taxation) both independently estimate tax expenditures associate with current and proposed legislation. Many states and countries have no information at all about these special tax rulings. As a general rule of thumb, where there is no light the largest mushrooms grow. However, even within the U.S., the estimates for tax losses for the same provision by the two bodies can differ by hundreds of millions of dollars. The estimation methods or assumptions are not made public, so improving the accuracy of these estimates is not clear-cut. </p><p>The stated goal of tax subsidies, according to the U.S. General Accounting Office, is to promote some policy objective such as "<a href="/article/Economic_growth">economic growth</a> or a desirable expenditure pattern by taxpayers." However, there is a great deal of disagreement over whether particular tax benefits typically encourage "socially desirable" economic behavior. Further, even if the policies are effective, they are static and may become ineffective or counterproductive as circumstances (be they demographic, technological, or economic) change. For example, percentage depletion allowances were significantly expanded when crucial minerals were needed for war efforts. As these initial conditions changed, the policies did not necessarily evolve with them. </p><p>In summary, tax subsidies are neither inherently right or wrong. They are inherently distortionary, however, in that they alter patterns of economic activity to promote particular areas (targeted by Congress) that would not necessarily have received investment or consumer <a href="/article/Supply_and_demand">demand</a> in the absence of the <a href="/article/Subsidies_and_market_interventions">government intervention</a>. The subsidies need to be considered as a real cost when evaluating alternative long-term energy options. These costs include the direct cost of increased <a href="/article/Taxation_in_the_United_States">taxes</a> in other areas to individual taxpayers, and the indirect costs to the economy as a whole through the distortionary effect of the subsidies on R&amp;D, investment, and <a href="/article/Consumption_and_consumer_sovereignty">consumption</a> patterns. </p><p>There are a few issues to keep in mind regarding our net tax expenditure estimates. First, special taxes on energy have been treated as negative subsidies if they are used for general revenue purposes. If they are earmarked for specific energy-related uses, such as <a href="/article/Oil_spill">oil spill</a> cleanup, they are considered user fees and are netted from the total government cost of dealing with the particular energy-related problem. Second, energy-payments such as royalties reflect a return to the resource-owner for selling the oil or minerals in question, and are not a tax. Finally, given the fact that the data regarding Treasury losses from tax provisions are somewhat crude and that interactions between the various tax preferences are not incorporated into these data, our quantification of the tax subsidy magnitude should be viewed as an estimate. </p> <p><a href='/article/Tax_subsidies'>Read Full Article...</a></p> http://www.eoearth.org/article/Tax_subsidies Thu, 03 Apr 2008 14:25:29 GMT http://www.eoearth.org/article/Electromagnetic_radiation <a href='/article/Electromagnetic_radiation'><img border='0' src='/upload/thumb/0/06/Spectrum.jpg/350px-Spectrum.jpg' width='100'/></a> <p>Radiation (from Latin <em>radiare,</em> &#39;to emit beams&#39;) is energy transmitted through space as particles or electromagnetic waves or the process of their emission. All objects above the <a href="/article/Temperature">temperature</a> of absolute zero (-273.15° Celsius) radiate energy to their surrounding environment. Particle radiation refers to the radiation of energy by means of small, fast-moving particles that have energy and mass. <strong>Electromagnetic radiation</strong> is emitted in discrete units known as photons that travel at the speed of light as electromagnetic waves. Electromagnetic energy is classified by increasing energy or decreasing wavelength into radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma-rays (Figure 1). </p><p>Radiation is separated into two categories, ionizing and non-ionizing, to denote the energy and danger of the radiation. Ionizing radiation is radiation in which an individual particle carries enough energy to ionize an atom or molecule. Corpuscular ionizing radiation consists of fast-moving, charged particles such as electrons, positrons, or small atomic nuclei. Thermal, epithermal, and fast neutrons interact with atomic nuclei creating secondary ionizing radiation and are called indirectly ionizing radiation. Electromagnetic ionizing radiation includes X-rays and gamma-rays. Ultraviolet light also can ionize an atom or molecule, but is referred to usually as non-ionizing radiation. The amount of ionizing radiation, or &#39;absorbed dose&#39; is measured in grays. One gray (Gy) is one joule of the energy deposited per kilogram of mass. Some types of radiation, such as neutrons or alpha particles, are more biologically damaging than photons or fast electrons when the absorbed dose from both is equal. To estimate this, dose equivalent, in a unit called the sievert (Sv), is used. Regardless of the type of radiation, one sievert of radiation produces the same biological effect. High radiation doses tend to kill <a href="/article/Cells">cells</a>, while low <a href="/article/Dose">doses</a> tend to damage or alter the genetic code of irradiated cells. The effect of very low doses is a subject of current debate. </p><p>Visible light is a form of electromagnetic radiation that can be perceived by our eyes. Light has a wavelength of between 0.40 to 0.71 micrometers (µm). Figure 1 illustrates the various spectral color bands that make up light. The sun emits only a portion (44%) of its radiation in this zone. <a href="/article/Solar_radiation">Solar radiation</a> spans a spectrum from approximately 0.1 to 4.0 micrometers. The band from 0.1 to 0.4 micrometers is called ultraviolet radiation. About 7% of the sun&#39;s emission is in this wavelength band. About 48% of the sun&#39;s radiation falls in the region between 0.71 to 4.0 micrometers. This band is called the near (0.71 to 1.5 micrometers) and far (1.5 to 4.0 micrometers) infrared . </p><p>The amount of electromagnetic radiation emitted by a body is directly related to its <a href="/article/Temperature">temperature</a>. If the body is a perfect emitter (black body), the amount of radiation given off is proportional to the 4th power of its temperature as measured in <a href="/article/Kelvin">Kelvin</a> units. This natural phenomenon is described by the Stephan-Boltzmann Law. The following simple equation describes this law mathematically: </p> <p>According to the Stephan-Boltzmann equation, a small increase in the temperature of a radiating body results in a large amount of additional radiation being emitted. </p><p>In general, good emitters of radiation are also good absorbers of radiation at specific wavelength bands. This is especially true of gases and is responsible for the Earth&#39;s <a href="/article/Greenhouse_effect">greenhouse effect</a>. Likewise, weak emitters of radiation are also weak absorbers of radiation at specific wavelength bands. This fact is referred to as Kirchhoff&#39;s Law. Some objects in nature have almost completely perfect abilities to absorb and emit radiation. We call these objects black bodies. The radiation characteristics of the sun and the Earth are very close to being black bodies. </p><p>The wavelength of maximum emission of any body is inversely proportional to its absolute <a href="/article/Temperature">temperature</a>. Thus, the higher the temperature, the shorter the wavelength of maximum emission. This phenomenon is often called Wien&#39;s Law. The following equation describes this law: </p> <p>Wien&#39;s Law suggests that as the temperature of a body increases, the wavelength of maximum emission becomes smaller. According to the above equation, the wavelength of maximum emission for the sun (5,800 <a href="/article/Kelvin">Kelvins</a>) is about 0.5 micrometers, while the wavelength of maximum emission for the Earth (288 Kelvins) is approximately 10.0 micrometers. </p><p>A graph that describes the quantity of radiation that is emitted from a body at particular wavelengths is commonly called a spectrum. The following two graphs describe the spectrums for the sun and Earth (Figure 2 and Figure 3). </p> <p>  <br /> </p><p>The graphs in Figures 2 and 3 illustrate two important points concerning the relationship between the <a href="/article/Temperature">temperature</a> of a body and its emissions of electromagnetic radiation: </p> <ol><li> The amount of radiation emitted from a body increases exponentially with a linear rise in temperature (see above Stephan-Boltzmann&#39;s Law). </li><li> The average wavelength of electromagnetic emissions becomes shorter with increasing temperature (see above Wien&#39;s Law). </li></ol> <p>Finally, the amount of radiation passing through a specific area is inversely proportional to the square of the distance of that area from the energy source. This phenomenon is called the Inverse Square Law. Using this law we can model the effect that distance traveled has on the intensity of emitted radiation from a body like the sun. Figure 4 suggests that the intensity of radiation emitted by a body quickly diminishes with distance in a nonlinear fashion. </p><p>Mathematically, the Inverse Square Law is described by the equation: </p> <strong>Intensity = I/d²</strong> <p>where <em>I</em> is the intensity of the radiation at 1d (see Figure 4) and <em>d</em> is the distance traveled. </p><p>The decrease in intensity with distance is not linear when graphed (Figure 5). </p><p><strong>Further Reading</strong> </p> <ul><li> <a href="http://www.physicalgeography.net" class='external text' title="http://www.physicalgeography.net">PhysicalGeography.net</a> </li></ul> <p><a href='/article/Electromagnetic_radiation'>Read Full Article...</a></p> http://www.eoearth.org/article/Electromagnetic_radiation Wed, 02 Apr 2008 14:18:39 GMT http://www.eoearth.org/article/Oil_spill <a href='/article/Oil_spill'><img border='0' src='/upload/thumb/7/7d/Exxon_valdez_aground.jpg/250px-Exxon_valdez_aground.jpg' width='100'/></a> <p>An oil spill is the accidental petroleum release into the environment. On land, oil spills are usually localized and thus their impact can be eliminated relatively easily. In contrast, marine oil spills may result in oil pollution over large areas and present serious environmental hazards. The primary source of accidental oil input into seas is associated with oil transportation by tankers and pipelines (about 70%), whereas the contribution of offshore drilling and production activities is minimal (less than 1%). Large and catastrophic spills releasing more than 30,000 tons of oil are relatively rare events and their frequency in recent decades has decreased perceptibly. Yet, such episodes have the potential to cause the most serious ecological risk (primarily for sea birds and mammals) and result in long-term environmental disturbances (mainly in <a href="/article/Coastal_zone">coastal zones</a>) and economic impact on coastal activities (especially on <a href="/article/Marine_fisheries">fisheries</a> and mariculture). </p><p>Public concern over marine oil spills has been clearly augmented since the 1967 Torrey Canyon <a href="/article/Supertanker">supertanker</a> accident off the UK coast, when 100,000 tonnes of spilled oil caused heavy pollution of the French and British shores with serious ecological and fisheries consequences. More recently, the highly publicized 1989 spill of the <em>Exxon Valdez</em> in <a href="/article/Prince_William_Sound%2C_Alaska">Prince William Sound, Alaska</a> caused unprecedented damage to the fragile Arctic system. Since then, impressive technical, political, and legal experience in managing the problem has been gained in many countries and at the international level, mainly through a number of Conventions initiated by the International Maritime Organization (IMO). As a result of the <a href="/article/Exxon_Valdez_oil_spill">Exxon Valdez oil spill</a>, the U.S. passed legislation requiring all newly built tankers to have a double hull. </p><p>When the oil reaches the shoreline, on rocky shores some components of the oil evaporate, leaving behind the heaviest components and turning the oil into tar. On rocky shores with surf, the tar will erode away from the wave action, and biological communities will return rather quickly. In <a href="/article/Marsh">marshes</a>, however, oil can sink down below the surface and remain for many years. Oil accumulated in marsh sediments undergoes some microbial breakdown, but it is slow. Low-energy environments like marshes are the most vulnerable and show the slowest rates of recovery from oil spills. Effects of a rather small oil spill in Falmouth, MA in the late 1960s were seen to last for a decade by a team of scientists from the nearby Woods Hole Oceanographic Institute. It is seldom that a spill occurs right in an area that has been intensively studied prior to the spill. Fiddler crabs were particularly sensitive, and were still affected after seven years. The oil affected their burrow construction – the burrows did not go straight down, but leveled off to a horizontal plane. While this was not a problem during the summer, when winter came the crabs were not below the freezing zone of the marsh as they should have been and froze to death. Benthic communities took about a decade to return to normal. After 30 years, some abnormalities still are noted in fiddler crab burrows in the oiled areas. </p><p>Marshes and sediments in <a href="/article/Prince_William_Sound%2C_Alaska">Prince William Sound</a> in Alaska retained oil from the massive oil spill of the <em>Exxon Valdez</em> in 1989 for many years, affecting the development of fish embryos on the bottom. After ten years, pockets of oil remained in these <a href="/article/Marsh">marshes</a>, and mussels, clams, ducks and sea otters showed evidence of harm in some localized areas. Remedial actions after oil spills are controversial, and some of the cures (e.g. aggressive cleaning with large heavy equipment) may be worse than the original problem, as was seen in the attempted clean up after the <a href="/article/Exxon_Valdez_oil_spill">Exxon Valdez oil spill</a>. </p><p><strong>Further Reading</strong></p><ul><li>Patin, Stanislav and Elena Cascio (Translator), 1999. <a href="http://www.offshore-environment.com/index.html" class='external text' title="http://www.offshore-environment.com/index.html">Environmental impact of the offshore oil and gas industry</a>. EcoMonitor Pub, East North Port, N.Y. <a href="http://www.amazon.com/dp/0-9671836-0-X/?tag=encycofearth-20" class='external text' title="http://www.amazon.com/dp/0-9671836-0-X/?tag=encycofearth-20">ISBN: 0-9671836-0-X</a> </li><li>Patin, Stanislav, 2004. <a href="http://www.sciencedirect.com/science?_ob=ArticleURL&amp;_udi=B7GGD-4CM9GC0-7X&amp;_rdoc=1&amp;_hierId=40165&amp;_refWorkId=222&amp;_explode=39816,40165&amp;_alpha=P&amp;_fmt=summary&amp;_orig=na&amp;_docanchor=&amp;_idxType=AU&amp;view=c&amp;_acct=C000050221&amp;_version=1&amp;_urlVersion=0&amp;_userid=10&amp;md5=363d97b258fc147442d4870d7fa85763" class='external text' title="http://www.sciencedirect.com/science? ob=ArticleURL&amp; udi=B7GGD-4CM9GC0-7X&amp; rdoc=1&amp; hierId=40165&amp; refWorkId=222&amp; explode=39816,40165&amp; alpha=P&amp; fmt=summary&amp; orig=na&amp; docanchor=&amp; idxType=AU&a