Integrated water resources management in central Asia: nutrient and heavy metal emissions and their relevance for the Kharaa River Basin, Mongolia J. Hofmann, M. Venohr, H. Behrendt and D. Opitz ABSTRACT J. Hofmann (corresponding author) M. Venohr H. Behrendt D. Opitz Department of Lowland Rivers and Shallow Lakes, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Mu ¨ ggelseedamm 310, D-12587 Berlin, Germany E-mail: j.hofmann@igbberlin.de Within the framework of Integrated Water Resources Management (IWRM) the nutrient and heavy metal levels within the Kharaa river basin were investigated. By the application of the MONERIS model, which quantifies nutrient emissions into river basins, various point and diffuse pathways, as well as nutrient load in rivers, could be analysed. Despite seasonal variations and inputs of point sources (e.g. Wastewater Treatment Plant Darkhan) the nutrient concentrations in most of the subbasins are on a moderate level. This shows evidence for a nutrient limited ecosystem as well as dilution effects. However, in the middle and lower reaches heavy metal concentrations of arsenic and mercury, which are linked to mining activities in many cases, are a point of concern. Thus measures are necessary to protect the valuable chemical and ecological status of the Kharaa River and its tributaries. As a result of the growing economic pressure Mongolia will enhance the agricultural production by irrigation. Until 2015 about 60% of the agricultural land shall be irrigated. In addition the gold mining activities shall increase by 20% a year. Both sectors have a high demand for water quantity and quality. The model MONERIS allows the assessment of measures which are inevitable to protect the water quality under shrinking water availability. Key words | heavy metals, integrated water resources management (IWRM), Kharaa river basin, modelling of nutrient emissions INTRODUCTION Under the framework of the FONA-program of the German Ministry of Education and Research (BMBF), Mongolia was selected as a model region for the development, solution and implementation of an appropriate and transferable Integrated Water Resources Management (IWRM) in Central Asia. The problems of the Kharaa developed since the late 1950s and early 1960s when the communist government decided to found the industrial city of Darkhan and to change the traditional pasture system into an agro- industrial farming complex with an extensive cultivation of cereals (wheat) and fertiliser application. Discharge of poorly treated municipal and industrial waste water as well as land use alterations (extensive tillage for cereal production, deforestation, forest fires, overgrazing etc.) have reduced the naturalness in the lower and middle reaches. Following the economic and political collapse after 1990, agricultural productivity was much lower than before and the out-dated wastewater technology led to higher inputs of poorly treated waste water. In addition, activities of gold mining industry led to several hazardous situations with the release of mercury and cyanide compounds (e.g. Khongor incident in April 2007, Hofmann 2008). Since the most productive gold mining sites of Mongolia (esp. Boroo gold mine) are located in the Kharaa river basin and the water quality in the lower reaches has deteriorated due to insufficient waste water treatment, it is necessary to consider uses and protection of freshwater doi: 10.2166/wst.2010.262 353 Q IWA Publishing 2010 Water Science & Technology—WST | 62.2 | 2010