Nitrogen removal by an irrigated wooded buffer area

Abstract

To demonstrate the efficiency of the wooded riparian soil in removing the exceeding nitrogen from the river water, a pilot-scale experimental system (0,8 ha) was planned and built on an area previously used to grow arable crops. It was constructed to allow the precise management of the system hydrology, because the water is electrically pumped from the adjacent Zero River into the irrigation ditches (ridges). The particular structure, characterized by ridges and furrows, facilitates sub-surface water flow through the woodland area and the creation of a suspended artificial aquifer seldom in contact with the groundwater. A grid of 36 piezometers was used to collect water samples. The results indicated that the nitrates retention capacity increased strongly from about 40 to 85% from the first to the third year. Ammonia nitrogen showed the highest annual variability, with the outputs in some cases exceeding the inputs. Organic nitrogen outputs were always higher than the inputs, but with a progressive reduction from the first to the third year. Overall, total nitrogen retention increased from 26% in the first year, to 62% in the third year. A monitoring campaign conducted after 8 year confirmed the long term efficiency of the site in nitrate removal with an increase also in organic nitrogen reduction.