Vistula Estuary

Category: Marine and Oceanic Biomes.

Geographic Location: Europe.

Summary: A unique coastal marine environment, this estuary hosts rich marine and avian populations, but needs every effort to counteract damage from reckless anthropogenic activities upstream.

Shared by Russia and Poland, the Vistula Estuary is one of the largest transboundary estuaries in the southern Baltic Sea. Sometimes called Vistula Bay or Vistula Gulf, the estuary is unusual in that it takes the form of a mainly freshwater lagoon— an arm-shaped, elongated body of water 57 miles (91 kilometers) long, its width ranging from 5 to 8 miles (8 to 13 kilometers). The estuary covers an area of 330 square miles (855 square kilometers). Approximately 44 percent of the drainage basin area lies in Poland, while 56 percent falls in Russia. The total surface area of the catchment basin of the estuary is 9 square miles (24 square kilometers) within both countries.

While some brackish waters from the Baltic Sea circulate past the extremely long sand bar that separates the two bodies, most of the inflow to the lagoon comes from the Vistula River, the longest river of Poland. The Vistula River originates on the western slopes of the Carpathian Mountains in southeast Poland and flows northwest through the cities of Krakow, Warsaw, and Torum before reaching the lagoon. This is a total length of 677 miles (1,090 kilometers). Also adding freshwater input to the estuary are Nogat and Pregolya, two major eastern streams of the Vistula River delta. They enter the lagoon by the Strait of Baltiysk in Gdańsk Bay.

The sand bar, one of the longest such features in the world, is known as Vistula Spit; about 50 kilometers) long, it varies from .25 to 1.5 miles (0.4 to 2.5 kilometers) wide. There are built-up stretches in the form of small beach towns, some with extensive tree cover, mainly on the lagoon side. Beaches on the sea side are generally kept clear for wildlife, as well as tourism.

The Vistula Estuary is quite shallow, with an average depth of 7 feet (2 meters) and a maximum depth of 16 feet (5 meters). The water volume is estimated to be 0.5 cubic miles (2 cubic kilometers). Exposed to both marine and continental impacts, climate in the estuary is mainly temperate. Summers are cool, with an average temperature of 63 degrees F (17 degrees C), while the winter temperatures average approximately 39 degrees F (4 degrees C). Average annual precipitation ranges from 24 to 33 inches (600 to 850 millimeters).

Biodiversity

The Vistula Estuary is a biologically productive ecosystem with its foundation built upon plankton, in such forms as 34 species of Rotatoria, 16 of Cladocera, and 21 of Copepoda. Further up the food chain are 42 fish species. Herring, bream, pikeperch, and eel are among the most abundant and valuable commercial fish species here. Other species include perch, flounder, ruffe, burbot, ziege, roach, and trout.

Marine mammals, mainly seals and porpoises, venture in and out of the estuary, no doubt drawn by both the relative ease of securing prey and the relative safety from larger predators.

Hundreds of thousands of birds on the Scandinavian-Iberian Flyway make the Vistula Estuary a major stop. Some 240 species of birds touch down here, with more than 100 selecting some part of the lagoon area as a nesting zone. The largest European colony of great cormorants has established itself at Katy Rybackie here, numbering over 30,000.

The sandspit is the dominant feature along the north side of the estuary; it features a variety of dune habitats, and even forested swaths on the higher areas that also support small human settlements. There are marshlands near the mouths of the rivers, mostly clustered around the eastern and southeastern reaches of the lagoon. Here dwell reptile and amphibian species that either dodge the preying birds or turn predator and attack nests. Adjacent to the Vistula marshland is the Elblag upland, where mammals such as otter, muskrat, and rodents are found in some abundance.

Threats and Conservation

Polluted waters from upstream farms and industries—only lightly regulated for most of the twentieth century—have long plagued this estuary. Phosphorus, oil, nitrogen, mercury, cadmium and zinc were among the most-noted substances causing widespread problems. Things began to turn around in the wake of political changes, following the 1989 collapse of the former Soviet Union. Several years of stagnant economic activity gave the ecosystem something of a breather, but recent economic boom years have once again raised fears that the waterways here will be seen as dumping grounds. However, there is now a better-established environmental point of view in much decision making and administrators recognize the value of intact biomes in attracting tourism revenues, as well as in supporting the longstanding fishing industry here.

Real dangers to the ecological balance include the ongoing warming of the Baltic Sea waters, offshore algal blooms, and the changes in the foodweb that these pressures may foretell. The crash of the cod fishery in the North Sea and Baltic Sea indicate that other species may move into that ecological niche, which may cascade other significant changes that would reach to the Vistula Estuary. The construction of various dams and levees to modify the river for agriculture and development purposes has altered the river to such as extent that the Vistula is far more prone to flooding in the twenty-first century.

The huge cormorant rookery here is so successful at taking fish from the waters that, combined with commercial fisheries, it is thought to lead to periodic declines in bream and pike perch through overfishing. Even climate change is looked at in terms of its interaction with the cormorants, as the flock is seen to gain breeding-season days as average temperatures rise, meaning the population is on track to grow still more. (On the other hand, earlier successful breeding by the cormorant flock often leads to earlier departure for other fishing grounds. This phenomenon has been recorded as taking place nearly four weeks earlier than normal over the last several decades in various parts of Europe.)

There are various invasive species that the natives have given some ground to, although few are considered especially harmful. One such nuisance is the Chinese mitten crab, introduced a century ago and still playing havoc with fishing gear.

Quite a few nature reserves dot this biome, and most of them are havens for the vast numbers of migratory birds that stream through twice each year. They range from Vistula Spit Landscape Park, Sea-Holly Dunes, and Vistula Spit Beeches (also on the spit are two bird sanctuary areas, Katy Rybackie and Gull Sandbank) to three other areas favored by both large and small flocks, amounting to well over 100 species in each case. These are Elblag Bay, Nogat Estuary, and Druzno Lake.

There are two year-round, no-fish corridors in the lagoon, established to help ensure that sufficient spawning and fry development activity can take place in support of the commercial fishery here.

Bibliography

Miotk-Szpiganowicz, GraŜyna, Joanna Zachowicz, and Szymon Uścinowicz. “Palynological Evidence of Human Activity on the Gulf of Gdansk Coast During the Late Holocene.” Brazilian Journal of Oceanography 58 (2010).

Naumenko, E. N. “Zooplankton in Different Types of Estuaries (Using Curonian and Vistula Estuaries as an Example).” Inland Water Biology 2, no. 1 (2009).

Paturej, Ewa and Marek Kruk. “The Impact of Environmental Factors on Zooplankton Communities in the Vistula Lagoon.” International Journal of Oceanological and Hydrobiological Studies 40, no. 2 (2011).

“The Rising Risk of Flooding in Poland.” PreventionWeb, 13 June 2022, www.preventionweb.net/news/rising-risk-flooding-poland. Accessed 18 Aug. 2022.

Rolbiecki, Leszek and Jerzy Rokicki. “Parasite Fauna of the Eel, Anguilla anguilla (Linnaeus, 1758), From the Polish Part of the Vistula Lagoon.” Wiadomooeci Parazytologiczne 52, no. 2 (2006).