Transport and potential attenuation of nitrogen in shallow groundwaters in the lower Rangitikei catchment

Intensive agricultural activities are generally associated with nitrogen leaching from agricultural soils with potential to contaminate groundwater and surface waters. We studied nitrogen losses and its transport and attenuation in shallow groundwater in the lower Rangitikei River catchment (832 km2), NZ. We combined regional surveys, nitrogen budget modelling, and hydraulic and geochemical methods. River flow gauging combined with a groundwater survey revealed groundwater-river interactions. A groundwater chemistry survey suggests a widespread occurrence of redox conditions in the study area. Push-pull tests confirmed occurrence of denitrification in shallow groundwaters in the study area. This highlights the importance of a sound understanding of the sources, transport and fate of nutrients leached from farms, to mitigate the likely impacts of land use on water quality and ecosystem health.