| Summary: | During the winters in recent years Laholmsbuktens VA's treatment plant in Halmstad has recorded unexcepted levels of phosphorus from the polishing pond. Only between 8 and 20 January 2016 samples indicates a realese of net 75 kg. In winter the pond temperature never goes below about 8oC, which attracts wintering waterfowl. In February 19, 2016 the largest number of birds in the inventory for this thesis was noted, 325 individuals, of which 208 were tufted ducks. Even if the number of waterfowl at peak levels was to be about 1000 individuals, their combined contribution of phosphorus through droppings into the pond could not be more than 500 g per day. This study proposes that a significant factor is the foraging activity of tufted ducks, which are diving ducks. In search of food at daytime they disturb the sediment at the bottom of the pond, i.e bioturbation. The higher proportion of particle-bound phosphorus in samples with high phosphorus content also fits well with this hypothesis. A scientific investigation in which the bottom of this part of the pond was stirred up mechanically gave similar proportions between phosphorus and water-soluble phosphorus.
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