Simulating nutrient loads in an intensively cultivated Mediterranean watershed under current and projected climate conditions

On the global scale, agriculture constitutes the most significant non-point pollution source for surface water bodies, especially in terms of nitrogen and phosphorus. Located in northeastern Greece, Vistonis basin constitutes the area that discharges into Vistonis estuarine system, which is very significant both from the environmental and economic perspective. Divided into three sub-basins basin includes 220 km2 of agricultural land cultivated mainly with cotton, corn and wheat. The present study aims to quantify the effects of agricultural activities in nutrient loads that discharge in Vistonis. Therefore, detailed spatial distribution of crops and soil data, combined to cultivation practices were used in order to apply SWAT model and quantify discharge, nitrogen and phosphorus loads for the period 2003-2014. The results presented significant variation in nutrient loads, while their contribution on a massive fish kill event that took place on summer 2014 was found to be significant. Nutrient loads variation were further investigated using projected, bias-corrected climate data from 3 Regional Climate Models (RCMs) for the period 2021-2040 and 2061-2080. The results indicate decreasing trend in nutrient loads due to decrease in river discharge because of precipitation decrease.