Assessment of the effects of mechanical bottom sludge removal from lakes Didžiulis and Lentvaris (Trakai district) based on macrozoobenthos indicators

Abstract

Two lakes in Trakai district – Didžiulis and Lentvaris were heavily polluted in the past by discharges of municipal wastewater without proper treatment. This anthropogenic impact resulted in large amounts of bottom sludge in both lakes, high amounts of biogenic substances and deterioration of water ecosystems. In both lakes, methods of mechanical lake restoration were applied in 2008 by removing 80000 m3 of bottom sludge from the northern part of Lake Didžiulis and 60000 m3 of bottom sludge from the southern part of Lake Lentvaris. The objectives of this article are 1) to examine composition of local macrozoobenthos communities in both lakes prior and after sludge removal and 2) evaluate changes and trends of ecological status in restored parts of both lakes by using two most popular in Lithuania indices based on macrozoobenthos: Trent Biotic Index and Danish River Fauna Index.