Ecological status of the River Nysa Łużycka (Lausitzer Neisse) assessed by epilithic diatoms

The River Nysa Łuzycka (Lausitzer Neisse) is a left-side tributary of the River Odra with springs located in Iser Mountains (Czech Republic). Its sub-basin has been selected as one of 15 Pilot River Basins to test CIS Guidance Documents of the EU Water Framework Directive/60/2000 EC (the WFD). The total length of the river is 246.1 km; the first section of 49.6 km belongs to the Czech Republic, while the remaining stretch of 196.5 km constitutes the Polish–German boundary. The whole sub-basin covers 4426.6 km (58 % Poland, 33 % Germany and 9 % Czech Republic). In the upper part, the sub-basin is composed of magmametamorphic (Iser Mts.) and crystalline (Lausitzer Mts.) geological formations, in the middle part of Tertiary deposits with brown coal, and in the lower part of Quaternary deposits. The river is strongly impacted by various anthropogenic pressures. The main point sources of pollution are six municipal wastewater treatment plants (Liberec, Sieniawka–Zittau, Bogatynia, Zgorzelec–Goerlitz, Łeknica–Bad Muskau and Gubin–Guben) and one industrial wastewater treatment plant (Bogatynia). The main diffuse sources of pollution, particularly of nutrients are agricultural activities and atmospheric precipitation. The river is also affected by water abstraction for industrial purposes and for flooding brown coal mine workings. The river’s morphology is significantly transformed due to bank regulation, numerous hydroelectric power plants and barriers (dams and weirs) (Blachuta et al. 2004). The aim of the study was to assess an ecological status of the river during the four years period by diatom phytobenthos using the Polish diatom multimetric index IO (Indeks Okrzemkowy).