Effects of Landuse in Lake/Reservoir Shore Area on Reduction Rate of Nitrogen and Phosphorus in Groundwater

Spatial variation of nitrogen and phosphorus concentrations in shallow groundwater in shore areas different in land use (cropland, grassland, woodland and barren bottomland) around Lake Tianmu and the Daxi Reservoir, to the west of Lake Taihu was studied, and effect of landuse reducing N and P in shallow groundwater and its affecting factors analyzed. Results show that nitrate-N was the major form of inorganic nitrogen in the shallow groundwater, varying in the range of 0.48 -6.83mg·L^-1, and comparatively, ammonia-N was quite low in concentration. Woodland and grassland showed good effects of reducing nitrate-N in groundwater, with nitrate-N reducing rate reaching to 68.3% and 63.4%, respectively, while cropland did a reverse trend, increasing the concentration of nitrate-N somewhat. The phosphorus in the groundwater was mainly in the form of dissolved phosphorus. Barren land was the highest in P reduction rate, reaching up to 32.0% and followed by grassland and woodland. On the whole, the effect of land use in the shore area was far more obvious on the reduction of N than on P. Correlation analysis indicates that soil structure, vegetation type and hydrological regime were the major factors affecting N and P reduction rates in the studied shore area.