Variability in hydrogeochemical conditions in shallow groundwater in the Manawatu River catchment and implications for denitrification potential

Abstract

Aims Favourable hydrogeochemical conditions in soil-water systems can attenuate nitrate (NO3-) leached from agricultural lands before it has impact on receiving surface waters. Denitrification has been identified as an important NO3- attenuation process in groundwater systems. However, the denitrification characteristics of groundwater systems vary in space and time depending on the properties of the surface and subsurface environments. The magnitude of, and variability in, attenuation capacity has implications for both the policy related to, and management of, NO3- losses from farm systems. Therefore it is important to investigate denitrification. However, in-situ measurements of denitrification are costly and time consuming. On the other hand, some water quality parameters that are commonly measured in groundwater monitoring programmes, such as redox conditions, may be used as indicators of denitrification capacity. The aims of this study were (a) to monitor hydrological and redox related water quality parameters at four selected sites in the Manawatu River catchment, (b) to determine the spatial and temporal variability in redox processes in the shallow groundwater, and (c) to identify the implications of hydrological and redox processes for denitrification at selected sites.