Grey water footprint of agricultural production: An assessment based on nitrogen surplus and high-resolution leaching runoff fractions in Turkey.

Agricultural activities are responsible for three quarter of global nitrate (NO3) pollution. Many surface and ground water resources have been detrimentally affected from high rate of nitrogen (N) deposition due to excessive fertilizer and manure application. Grey water footprint (GWF) is one of the internationally accepted indicators quantifying the environmental effects of contaminants on water bodies. The main scope of this study is to assess GWF of agricultural nitrogen utilization in Turkey using Tier-1 approach, which is proposed by Water Footprint Network considering detailed spatially continuous soil, climate and agricultural data in order to provide quantifications at both provincial and basin level. Leaching runoff fractions of diffuse N loads are very important for GWF accounts. However, the previous studies are mainly relied on assigning constant leaching runoff fractions and superficial N applications rates. Nevertheless, many studies reported remarkable variations in leaching fractions due to heterogeneities in soil and water resources. To the author's knowledge, this is the first GWF assessment of the study area employing high resolution leaching runoff fractions which is estimated using soil texture, natural drainage and climate data maps. Nitrogen emissions and GWF accounts of 81 administrative provinces and 25 hydrological basins were quantified using provincial N application and surplus amounts. Accordingly, GWF of anthropogenic N accumulation is estimated to be 24.7 Gm3/y corresponding to an average water height of 114 mm per agricultural land area and 340 m3 per capita for the time period of five years (2007-2011). The water pollution level (WPL) is found to be critical (>0.75) at several river basins while the national average WPL is around 0.13. This study is expected to contribute to the national and international water and agricultural management and planning studies in order to decrease the water pollution levels by providing suitable information to policy-makers.