Biomass Production with Willow and Poplar Short Rotation Coppices on Sensitive Areas-the Impact on Nitrate Leaching and Groundwater Recharge in a Drinking Water Catchment near Hanover, Germany

In a lowland drinking water catchment area, nitrate leaching as well as groundwater recharge (GWR) was investigated in willow and poplar short rotation coppice (SRC) plantations of different ages, soil preparation measures prior to planting and harvesting intervals. Significantly increased nitrate concentrations of 16.6 +/- 1.6 mg NO3-N L-1 were measured in winter/spring 2010 on a poplar site, established in 2009 after deep plowing (90 cm) but then, subsequently decreased strongly to below 2 mg NO3-N L-1 in spring 2011. The fallow ground reference plot showed nitrate concentrations consistently below 1 mg L-1 and estimated annual seepage output loss was only 1.36 +/- 1.1 kg ha(-1) a(-1). Leaching loss from a neighboring willow plot from 2005 was 14.3 +/- 6.6 kg NO3-N ha(-1) during spring 2010 but decreased to 2.0 +/- 1.5 kg NO3-N ha(-1) during the subsequent drainage period. A second willow plot, not harvested since its establishment in 1994, showed continuously higher nitrate concentrations (10.2 +/- 1.7 NO3-N L-1), while a neighboring poplar plot, twice harvested since 1994 showed significantly reduced nitrate concentrations. Water balance simulations, referenced by soil water tension and throughfall measurements, showed that at 655 mm annual rainfall, GWR from the reference plot (300 mm a(-1)) was reduced by 40 % (to 180 mm a(-1)) on the 2005 willow stand, mainly due to doubled rainfall interception losses. However, transpiration was limited by low soil water storage capacities, which in turn led to a moderate impact on GWR. We conclude that well-managed SRC on sensitive areas can prevent nitrate leaching, while impacts on GWR may be mitigated by management options.