Impacts Of Hillslope And Floodplain Characteristics On Groundwater Dynamics: Implications For Riparian Denitrification

One of the beneficial roles of riparian buffers is the capacity to attenuate groundwater nitrate before it can discharge to streams. Denitrification is one of the most important processes that permanently removes nitrate from groundwater; it requires anoxic conditions, a carbon source, and a suitable residence time as the reaction is microbially mediated. As denitrification rates are highly dependent on carbon availability, there is a higher potential towards the soil surface where carbon sources are more abundant. These facts highlight the importance of hillslope-floodplain hydrology as to determine how much nitrate can be removed from the landscape. There are three crucial hydrological factors that impact denitrification. Firstly, proximity of the water table to the root zone; this determines the extent of the anoxic root zone as well as the level of activity as shallower water tables mean that the groundwater is interacting with surface soils that are richer in carbon. Secondly, residence time determines how much nitrate is transformed while it resides within the riparian buffer. Thirdly, base flow discharge determines the total nitrate mass interacting with the riparian buffer. It is postulated that the soil type (and hence hydraulic parameters) of both the hillslope and floodplain play a crucial role in determining whether or not the hydrology is favourable for denitrification processes.