Classification of chemical status of rivers for water management planning in Lake Vortsjarv catchment area, Estonia

摘要

The EU Water Framework Directive devotes close attention to the ecological assessment of surface waters and the measure of achievement of implementation programmes. Based on long-time monitoring data that consisted in gathering water quality information from rivers in the Lake Vortsjarv catchment area in Estonia, classes of rivers with regard to water quality were devised. Secondly, a priority map at a river basin level for integrated water management planning was developed. The purpose of this study was to analyse trends in the water quality of medium-sized (from 108 to 1270 km~2), predominantly rural river basins in southern Estonia. Chemical monitoring data from 1980-2000 were used in this study. The total current ecological value of river water quality in the Lake Vortsjaerv catchment area assessed by chemical parameters as a whole is relatively low (quality class III). In order to analyse the temporal changes in the studied trends, the whole research period was divided into 2 equal parts: (1) 1981-1990 and (2) 1991-2000. The results from this study showed that the Summary Index for the water quality of the whole Lake Vortsjarv catchment area, calculated by the saturation of dissolved oxygen, BOD_7, NH_(4-)N~+, N_(tot) and P_(tot), decreased from 3.5 in the 1980s to 2.6 in the 1990s. The most remarkable trend is found for NH_(4-)N~+ and total N concentrations: the water quality improved by index values of 44 and 40% respectively. For water protection and river restoration programmes, catchments areas with higher priority for water management planning can be selected. The water quality index is preferred for this purpose.