Experimental tests of water chemistry response to ornithological eutrophication: Biological implications in Arctic freshwaters

Abstract

Many populations of Arctic-breeding geese have increased in abundance in recent decades, and in the Canadian Arctic, snow geese (Chen caerulescens) and Ross's geese (Chen rossii) are formally considered overabundant by wildlife managers. The impacts of these overabundant geese on terrestrial habitats are well documented, and, more recently, studies have suggested impacts on freshwater ecosystems as well. The direct contribution of nutrients from goose faeces to water chemistry could have cascading effects on biological functioning, through changes in phytoplankton biovolumes and community composition. We demonstrated previously that goose faeces can enrich ponds with nutrients at a landscape scale. Here, we show experimentally that goose droppings rapidly released nitrogen and phosphorus when submerged in freshwater, increasing the dissolved nitrogen and phosphorus in the water. This resulted in both a decrease in the nitrogen:phosphorus ratio and an increase in cyanobacteria in the goose dropping treatment. In contrast, this pattern was not found when we submerged cut sedge (Carex sp.) leaves. These results demonstrate that geese act as bio-vectors, causing terrestrial nutrients to be bioavailable in freshwater systems. Collectively, the results demonstrate the direct ecological consequences of ornithological nutrient loading from hyper-abundant geese in Arctic freshwater ecosystems.