Analysis of Recent Nutrient Emission Pathways, Resulting Surface Water Quality and Ecological Impacts under Extreme Continental Climate: The Kharaa River Basin (Mongolia)

This paper presents primary research results on nutrient emissions, resulting water quality and ecological impacts of the Kharaa river basin (Mongolia) during a three-year water resource management study. Based on surveillance data from Mongolian environmental authorities and a complementary own monitoring scheme we calculated nutrient emissions on a sub-basin scale. Additionally, the ecological situation of fish fauna, macroinvertebrates and their habitats were investigated on selected river sections in order to link anthropogenic pressures, nutrient status and ecological impact. Although the headwaters of the Kharaa represent natural background conditions (total nitrogen (TN) 0.46 to 0.58 mg N L-1, total phosphorus (TP) 0.011 to 0.018 mg P L-1) and population densities within the catchment are very low (< 10 inhabitants km(-2)), the river basin is facing relatively high anthropogenic pressures on water quality in the middle and especially in the lower reaches (total nitrogen 1.50 to 1.52 mg N L-1, total phosphorus 0.18 to 0.26 mg P L-1). Nitrogen emissions into the Kharaa river basin were about 301 t N yr(-1) for the time period 2006-2008. For phosphorus a total emission of 56 t P yr(-1) was estimated. Main contributors are urban settlements with a high proportion of households without connection to wastewater treatment plants and, to a lesser extent, agricultural land-use. These nutrient levels have a significant eutrophication potential in the Kharaa River and we observed functional shifts of the macroinvertebrates and fish fauna, while the drinking water abstraction through bank filtration showed no significant alteration of raw water quality.