Impact of new, navigable canal through the Vistula spit on the hydrologic balance of the Vistula lagoon (Baltic Sea)

Abstract

The object of research - the Vistula Lagoon is one of the two lagoons on the Polish coast, which is of great importance not only from an economic point of view, but also an environmental one. The purpose of the paper is to provide calculations on the current water balance for the Vistula Lagoon, before and after construction of a canal through the Vistula Spit. This is important because the construction of a new connection between the Vistula Lagoon and the Baltic Sea can result in changes in the lagoon's water balance, which in turn cause changes in the Vistula Lagoon biotic and abiotic environment. In addition, we wish to update the estimate of the water exchange between the Vistula Lagoon and the Baltic Sea through the Strait of Baltiysk and to estimate the exchange through the Vistula Spit canal after it is fully open. The main works consisted of researching source materials from various state institutions, which allowed to calculate the water balance of the Vistula Lagoon and perform mathematical modeling. These data include the amount of precipitation and evaporation, the amount of inflow from the catchment, the amount of inflow from polders, underground supply, the amount of inflow and outflow through the Strait of Baltiysk. The largest portion of the water received by a coastal lagoon comes from the adjacent ocean. In this case, it is about 75%. In addition, an array of catchment sources yields 20% of the studied lagoon's water. The Strait of Baltiysk constitutes the main outflow pathway for water exiting the Vistula Lagoon – close to 98% of outflow. Simulations have shown that the construction of the Nowy Swiat ship canal will not alter the water balance in the Vistula Lagoon to a meaningful extent. The problems that may emerge include those related to changes in the local biotic and abiotic environment due at the construction stage or in the period that follows resulting from the disturbance of highly polluted lagoon floor deposits. Thus it may be argued that the new canal is desirable from an economic or flood control point of view, but not from an environmental point of view.