Investigating land use effects on water and nutrient balances of the Rote Main
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Estimating the impact of groundwater inflow on water and nutrient balances of a river is an important tool to evaluate effects of land use on surface water ecosystems. The aim of this study was to determine the fraction of groundwater in total discharge of the Rote Main and the nutrient fluxes in groundwater and Rote Main during different seasons. Radon-222 activities and nutrient concentrations (phosphate, nitrate, etc.) were measured at 16 sampling locations along the Rote Main between Bayreuth and Melkendorf every month. Groundwater inflow rates were calculated using an Radon-222 mass balance approach and compared to discharge data provided by the Hochwassernachrichtendienst Bayern. Nutrient fluxes in groundwater and river water were estimated. The fraction of groundwater in total discharge ranged between 20 and 78 %. A correlation between groundwater input and phosphate concentrations was frequently observed. Nutrient concentrations were highest in drier months during baseflow conditions. In spite of the complexity of characterisizing groundwater - surface water interactions this study was a first step in assessing land use effects on the Rote Main.