Contribution of agricultural land in the Po Valley to coastal eutrophication of the Adriatic Sea

Abstract

The objective of this study was to determine the extent to which agricultural land is responsible for the eutrophication of the Adriatic Sea. Considering soil as a non-point source of nutrients in drainage water, the problem was approached by studying the nutrient loading and seasonal patterns in drainage water from cultivated soils. For the last seven years, we have systematically monitored the nutrient contents and volumes of drainage water from underground drainage systems installed in typical cultivated soils in the Emilia-Romagna Region. The resulting data has provided quantitative information concerning the actual amounts of N and P as well as other essential plant nutrients being removed from the soil. According to our data, phosphorus loadings from cultivated soils to the surface waters in the Po Valley have been largely overestimated. The concentration of P in water drained from agricultural land is at least an order of magnitude lower than that found in rivers flowing to the Adriatic Sea. Nitrate-nitrogen concentration and loadings are high during late winter and early spring when field capacity usually has been reached, evapotranspiration is low, and precipitation is high. In conclusion, these results clearly show that when normal agricultural practices are followed, the contribution of agricultural land (cultivated soils) in the Emilia-Romagna Region to marine coastal eutrophication is of some concern with regard to nitrogen and very low in regard to phosphorus.