Langzeitdaten von neun deutschen Vorsperren mit insgesamt 124 Abflussjahren wurden ausgewertet, um die Zulauf- bzw. Ablauffrachten und entsprechenden Eliminationseffizienzen für die Nährstoffe gelöstes Phosphat, Gesamt-Phosphor, Nitrat, und Silikat zu quantifizieren. Hohe Eliminationseffizienzen wurden für gelöstes Phosphat (43,6 %) und Gesamt-Phosphor (39,9 %) realisiert, vergleichsweise geringere für Nitrat (15,3 %) und Silikat (15,9 %). In der warmen Jahreshälfte ist die Nährstoffelimination deutlich höher als in der kalten Jahreszeit.

The reduction of external nutrient loading is a key target in water quality management of reservoirs in order to mitigate eutrophication. This is particularly relevant in reservoirs used for drinking water supply. The operation of pre-dams, i.e. small impoundments of inflows located directly upstream the main reservoir, can be an efficient instrument in nutrient management as they can even limit loads from non-point sources, e.g. from agriculture. We analysed long-term data from nine German pre-dams (in total 124 discharge years) in order to quantify inflow and outflow loads as well as nutrient retention in these pre-dams for the following nutrients: dissolved phosphate (PO₄), total phosphorus (TP), nitrate (NO₃), and silicate (Si). For load estimation, four different statistical methods were employed that delivered similar results for nutrient retention efficiency though inflow and outflow loads showed larger variability. Our analysis (mean values) indicated that pre-dams have a high potential to retain PO₄ (43.6%) and TP (39.9%) while retention of NO₃ (15.3%) and Si (15.9%) was lower. Variability among pre-dams was high. We found intra-annual variability in nutrient retention to be higher than inter-annual variability with higher retention in the warm season due to higher biological activity when compared to winter conditions.