Practical estimation and distribution of diffuse pollutants arising from a watershed in Turkey

This study presents the diffuse pollution profile of a coastal watershed with respect to the dominating sector of agriculture including forestry. A rough estimation of the diffuse loads expressed by two major nutrients of nitrogen and phosphorous is realized by calculations based on unit loads obtained from the literature for each land-use activity. The key concern is to rank the different diffuse loads arising from the watershed. The major diffuse nitrogen loads are estimated to arise from agricultural activities with 54 %, followed by livestock breeding that contribute to the nitrogen budget by 11 %. Almost 7 % of the nitrogen loads come from meadows and pasture, and 5 % from forests. In the distribution of diffuse phosphorus loads, it is estimated that 48 % of the loads arise from agricultural activities, and 18 % from livestock breeding. Almost 14 % of the phosphorous loads come from septic tank effluents; however, 13 % of the loads are due to rural run-off. The future loads for 2028 and 2039 are also estimated; 30–40 % decrease is foreseen in the agricultural pollutants and animal manure through the stepwise application of ecological agriculture and livestock breeding. The basic aim of this study is to put forth a practical methodology for estimating diffuse loads in a watershed for the decision-makers and local administrative authorities with especially limited available data. Through such, distribution of various diffuse loads becomes available among the administrative units composing the watershed.