Groundwater-dependent ecosystems as transfer vectors of nitrogen from the aquifer to surface waters in agricultural basins: The fontanili of the Po Plain (Italy)

The most spread groundwater-dependent ecosystems in the River Po valley are semi-natural lowland springs called "fontanili". They provide specific habitats and support high biodiversity, but are often strongly impaired by agricultural pollution. In the present study we seasonally monitored the discharge and nitrogen concentration of 48 fontanili from the Adda and the Ticino river basins. We observed a wide spatial variability of both NO3-N concentrations and flows. The annual NO3-N loads ranged from <1 to 75 t y(-1) and < 1 to 29 t y(-1) in the Adda and Ticino basins respectively. In the springs characterized by variable discharge the N loads were exported mostly during the summer season when water table level was elevated mainly due to irrigation. Upscaling the mean NO3- N load to each river catchment based on the total number of springs, we obtained an aerial export of 33.2 +/- 6.0 and 12.5 +/- 3.2 kg y(-1) ha(-1). Such loads accounted for the 30.4 and 21.5% of the N surplus estimated for the Adda and Ticino basins respectively.