Temporal and spatial variability of redox values and its implications for nitrate reduction in a tile-drained area in Fensholt subcatchment, Denmark

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Tile-drained agricultural areas are generally considered to enhance nitrate leaching into the groundwater. However, this is an overly simplified assumption since tile drainage systems present a unique hydrology of extremely fluctuating water table levels and redox values over a relatively small area. It is then assumed that nitrate reduction may be higher than initially estimated. For this study, the particular relationship between redox dynamics and nitrate reduction were explored in the highly drained Fensholt subcatchment within the Norsminde Fjord catchment, Denmark. Piezometers and redox probes were installed on average of three depths within the tile-drainage depth, each nest at approximately 20 m apart, to account for fine scale variability of pH, temperature, redox values, and inorganic nitrogen concentrations. A total of 150 piezometers and redox probes were initially installed throughout the different parts of the subcatchment. These areas were chosen to represent variations in hydrotopographic settings. Physico-chemical measurements and water samples were obtained every ~3 weeks. As predicted, the redox values and nitrate values were highly spatially and temporally variable even within a subcatchment. Redox values were generally stratified where the redox values decreases with depth. The layer of higher redox values generally expands during the warmer months of June to July, which is probably due to greater evapotranspiration. Naturally depressed areas tend to have low redox values/ more reducing conditions even during the warmer months. Pockets of higher redox values at the deeper parts of the profiles may indicate high local, subsurface flow conditions that bring oxic waters into the deeper parts of the soil. The interplay of temperature, rainfall, soil texture, and gradient seems to ultimately dictate the redox conditions in the tile-drainage depth.
Udgivelsesårapr. 2018
Antal sider1
StatusUdgivet - apr. 2018
BegivenhedEGU2018 European Geosciences Union General Assembly 2018 - Austria Center Vienna, Vienna, Østrig
Varighed: 8 apr. 201813 apr. 2018


KonferenceEGU2018 European Geosciences Union General Assembly 2018
Lokation Austria Center Vienna

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