Daugava River
The wide Daugava River at Riga, Latvia. @ C.Michael Hogan
The Daugava River drains portions of the countries of Latvia, Belarus and Russia, prior to discharging to the Gulf of Riga. Also known as the West Dvina River, this watercourse is the fourth largest river discharging to the Baltic Sea catchment.
This 1005 kilometer long river has suffered environmental damage from agricultural runoff and from hydroelectric dam construction, with major impacts dealt in the Soviet era of collective farming. In ancient history the Daugava estuary was a locus of prehistoric settlement, and later marked one of the eastern limits of the voyages of the Vikings.
Contents
Geology
The lower Daugava valley (nearest the Gulf of Riga) was formed in relatively recent times, as glacial meltwater formed incision on the relatively level terrain near the Baltic Sea coast; these events occurred in the early Holocene, approximately 11,000 years before present. The relatively soft upper soils that were cut by the Daugava can be characterized in most of the Daugava basin in Latvia are chiefly sandy till and other glacio-lacustrine sand. Subsequently after the most recent Ice Age, lacustrine sediments and peat were deposited by riverine flow.
The Valdai hills serve as part of the watershed boundary of the Daugava River; this mountain range marks the regional frontier of glaciation during the most recent Ice Age.
Hydrology
Watershed of the Daugava River. In Russia, the Daugava River presents as an outflow from Lake Dvineca; at that outlet in the Valdai Hills, the Daugava channel width is a mere six to eight meters. By the time the Daugava reaches the Belarus/Latvia border, the channel is approximately 200 meters wide and flows through a relatively narrow valley about 500 meters in breadth. In coastal Latvia the Daugava achieves a width of 370 to 750 meters, with a typical depth of about five to fifteen meters.
The major tributaries of the Daugava in its Latvian reaches are the Ogre River and the Aiviekste River.
Water quality
Upstream of the Latvian town of Jekabpils the pH has a characteristic value of about 7.8; in this reach the calcium ion has a typical concentration of around 43 milligrams per liter; nitrate has a concentration of about 0.82 milligrams per liter (as nitrogen); phosphate ion is measured at 0.038 milligrams per liter; and oxygen saturation was measured at eighty percent. The high nitrate and phosphate load of the Daugava is instrumental to the buildup of extensive phytoplankton biomass in the Baltic Sea; other European rivers contributing to such high nutrient loading of the Baltic are the Oder and Vistula Rivers.
The Lielupe River, a Latvian tributary, is considered biologically dead from the heavy loading of toxic water pollutant discharges. At the end of the Soviet period in Latvia, discharge to the Leilupe of toxic hospital waste and municipal wastewater sludge reached a level of 250,000 metric tons per annum. The Leilupe was closed to swimming in 1982, with bacteria counts reaching one half million per liter, among the worst of any world surface water.
In Belarus, water pollution of the Daugava is considered moderately severe, with the chief sources being treated wastewater, fish-farming and agricultural chemical runoff (e.g. herbicides, pesticides, nitrate and phosphate).
Aquatic biota
European sturgeon. Illustrations de Ichtyologie ou histoire naturelle générale et particulière des Poissons Bloch, Marcus Elieser, J. F. Hennig, Plumier, Krüger, Pater, Schmidt, Ludwig, Bodenehr, Moritz
The chief marine mammal in the Daugava is the European otter (lutra lutra). The Daugava estuary, along with estuaries of the Gauja and Parnu Rivers, is an important repository of aquatic organisms for the Gulf of Riga itself.
The crustaceans Lamprogena pulchella, Ergasilus briani, E.sieboldi and Tracheliastes polycopus occur in the Daugava River; L.pulchella occurs as well as the Salaca River, another Latvian river that discharges to the Gulf of Riga. Fish nematodes found in the Daugava River include Rhabdochona denudata, Pseudocapillaria tomentosa and Raphidascarus acus. Other fish parasites in the Daugava River include members of the Myxobolus genus, including M.dispar, M.minutus, M.exiguus, M.Muelleri, and M.nemetzeki.
There are 50 fish species found in the Daugava basin, six of which are non-native. The European sturgeon (Acipenser sturio) is now considered extirpated in the Daugava estuary and Gulf of Riga as a whole; this critically endangered fish historically spawned in the lower Daugava, and has suffered local extinction from overfishing and water pollution.
Ecoregions
Boggy sarmatic mixed forest near the Latvian mainstem of the Daugava. @ C.Michael Hogan There are two principal ecoregions within the Daugava watershed. The dominant ecoregion that occupies the vast majority of the catchment basin is the Sarmatic mixed forests ecoregion. A smaller portion of the Russian element of the basin is covered by the Scandinavian and Russian taiga.
In the Sarmatic mixed forests, deforestation has eliminated about 78 percent of the tree cover, mostly through agricultural land conversion. In addition to the dominant canopy—Scots pine and Norway spruce intermixed with some broadleaf species—there are a number of shrubs, wildflowers, grasses and mosses that inhabit the mid-tier and forest floor. Common low-growing shrubs include Bilberry (Vaccinium myrtillus) and Heather (Calluna vulgaris). Widespread ferns seen on forest floors include Western Brackenfern (Pteridium aquilinum) and Mountain Bladderfern (Cystopteris montana). Common mosses found in the more mesic soils are Broom Forkmoss (Dicranum scoparium), Stairstep Moss (Hylocomium splendens), Red-stemmed Feathermoss (Pleurozium schreberi), Ostrich Plume (Ptilium crista-castrensis) and Common Hair Moss (Polytrichum commune).
Hydroelectricity
The largest hydroelectric plant on the Daugava River is the Plavinas facility, conceived by the central planning of the Soviet Union, who controlled Latvia at the time of its development in the late 1950s and early 1960s. This 868 megawatt plant was built invoking the concept of clean renewable energy, but in fact resulted in the inundation of large amounts of cultural treasures as well as habitat of a number of rare plant species.
In some cases such as at the Rizhskaya hydroelectric facility on the Daugava, there are engineered fish passages to encourage fish movement on the river, in spite of the dam.
History
City of Daugavpils in 1912, situated along the Daugava. Source: Sergei Mikhailovich Prokudin-Gorskii Collection (Library of Congress) For millennia, the mouth of the Daugava and other shores of the Gulf of Riga were settlement locations of early humans, carrying out an initial hunter-gatherer subsistence, and utilizing the waters of the Daugava estuary as fishing and gathering areas for aquatic biota. Beginning around the sixth century AD, Viking explorers crossed the Baltic Sea and entered the Daugava River, navigating upriver into the Baltic interior.
In medieval times the Daugava was an important navigation trading route for transport of furs from the north and Byzantine silver. The Riga area was a key element of settlement and defence of the mouth of the Daugava at least as early as the Middle Ages, as evidenced by the now destroyed fort at Torņakalns on the west bank of the Daugava at present day Riga. Since the Late Middle Ages the western part of the basin has come under various national rule; for example the Latvian town of Daugavpils, located on the western Daugava, has variously been under papal rule as well as Slavonic, Polish, German and Russian sway until Latvian independence at the end of the Cold War.
References
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