Denitrification potential in the subsurface environment in the Manawatu River catchment

Understanding the effects of hydrogeological factors on loss, transport and fate of farm nutrients is essential for predicting their impacts on ecosystem health of receiving waters. We assessed the potential of groundwater to attenuate nitrate through denitrification, and the distribution of this potential across the Tararua Groundwater Management Zone (GWMZ) in the Manawatu River catchment, NZ. We combined a number of methods in an unprecedented manner to confirm findings and obtain supporting evidence. Our results showed that denitrification characteristics of groundwater varied considerably in the Tararua GWMZ, influenced by soil texture, drainage class, and the aquifer material or rock type, and found high denitrification potential in groundwaters in the Upper Manawatu sub-catchment. Intensive farming over well-drained soils and rocks showed high nitrate concentration in groundwater. Nutrient management should target areas with low subsurface denitrification potential.