New insights into the fate of Nitrate at the Soil – Groundwater interface of riparian corridors by using a novel high resolution monitoring system

Niklas Gassen1, Nico Trauth2, Christian Griebler1, Christine Stumpp1
1 Institut für Grundwasserökologie, Helmholtz Zentrum München
2 Helmholtz Zentrum für Umweltforschung, Department für Hydrogeologie, Leipzig

O 9.3 in Nitrate in groundwater - input, degradation and prognosis

14.04.2016, 10:45-11:00, Plank Hörsaal, Geb. 40.32


Nitrate monitoring systems commonly focus on depth integrated samples of aquifers. In order to better resolve nitrate attenuation processes and redox zonations, depth-specific sampling is required. We herewith present data from a novel high resolution sampling system, installed in a shallow alluvial aquifer of a riparian corridor. The field site is part of the TERENO network and situated next to the Selke river in the northern Harz foreland. Riparian zones are important buffer zones for non-point groundwater contaminants like nitrate. Shallow water tables favour denitrification, as nitrate rich groundwater comes into contact with anoxic, organic rich layers in hydric soils. To date, riparian research has focused on influences of groundwater-surface water interactions on nitrate removal mechanisms, but little is known about processes occurring at the interface between the saturated and the unsaturated zone during groundwater table fluctuations. With the newly developed sampling well, we are able to obtain water samples both from the saturated and the unsaturated zone with a vertical resolution of 5 cm. For the first time, this enables a determination of governing small scale processes at the soil-groundwater interface and helps to identify spatial zones with high potential for denitrification processes, so called hot spots. First data of our monitoring system show high Nitrate concentrations in the soil water, a zone of lower Nitrate concentrations in the vicinity of the fluctuating water table, and a steep gradient with increasing concentrations 1 m below the water table. We conclude that in the fluctuation zone of the water table, hot spots are created where both nitrification and denitrification processes can occur spatially close to each other and therefore remove nitrogen more effectively from the system. Furthermore, the fluctuating water table enhances the exchange of solutes and triggers hot moments of solute turnover. With these new insights, we are able to improve our understanding of spatial scaling of denitrification processes. This leads to a better prediction and improved management strategies for buffer mechanisms in riparian zones

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