Phosphorus input by nordic geese to the eutrophic Lake Arendsee, Germany

Abstract

Phosphorus import by nordic geese (Anser fabalis and Anser albifrons) was investigated in Lake Arendsee, located in the Saxony-Anhalt region, Altmark, Germany during the period 1996 to 1997. Phosphorus contained in geese excrement on the ice was measured in the winters 1996 and 1997.In February 1996 (after 9 days of frozen lake surface) two excrement fields amounted to 80 ha and 30 ha in area and in January 1997, 10 days after ice closure, the excrement field was 106 ha large. The weight of excrement was estimated to be 148 to 266 g m−2 fresh weight (mean 201 g m−2) in 1996 and 83 g m−2 to 408 g m−2 (mean of 243 g m−2) in 1997. The average of phosphorus content was 8.5 mg g−1 dry weight in 1997 and 9.2 mg g−1 in 1996. Based on these values the phosphorus input attributed to nordic geese was calculated. Our results demonstrated a phosphorus import in 1996 after 9 days of frozen lake surface of 251 kg and in 1997 after 10 days of freezing of 173 kg. During 100 days of wintering, the nordic geese on Lake Arendsee produced a phosphorus load of 2.8 t in 1996 and 1.7 t in 1997. Compared with the annual phosphorus import from different sources, the contribution by nordic geese was 88 % in 1996 and 92 % in 1997. Its yearly phosphorus load during the winter months appears as a significant eutrophication factor for the trophic level of Lake Arendsee. However, the annual external load is approximately 10 % of the phosphorus poolsize in the lake water, and even less when considering the amount lodged in the bottom sediments.