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

Abstract

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.

Evidence of eutrophication in Arctic lakes

“…Bird feces were noted around most lakes and ponds, with higher concentrations found in and around shallower water areas (P. Blackburn-Desbiens, unpublished data). Feces are a source of TP and TN and can trigger cyanobacterial blooms (Jensen et al 2019;Mariash et al 2019), but residence time, dictated by geomorphology would determine the likelihood of a persistent or annual recurring bloom. The area surrounding ERA5 is dominated by moderate slopes on the northern side of the lake and characterized by Dryas integrifolia -Carex rupestris plant associations that can range from 10 to 75% cover (Ponomarenko et al 2019).…”

Dominance of net autotrophy in arid landscape low relief polar lakes, Nunavut, Canada

“…Accordingly, headwater lakes showed significantly higher concentrations of DIC, DOC and TN that were likely consumed by autotrophic production, while larger downstream lakes had a lower solute to volume ratio, due to dilution in larger lake volume. Additionally, headwater lakes and surrounding wetland areas are ideal habitat for geese, and generally have abundant goose droppings (Cadieux et al., 2005) that are an important source of nutrients, especially N, for small waterbodies (Jensen et al., 2019; Mariash et al., 2019). The dominance of concurrent CO 2 supersaturation with autotrophic metabolism, plus terrestrial DIC delivery in headwater sites demonstrates that the headwater lakes surveyed here act more as chimneys that facilitate the emission of terrestrial CO 2 to the atmosphere.…”

Sentinel responses of Arctic freshwater systems to climate: linkages, evidence, and a roadmap for future research

“…For example, the arrival of certain species may add a new trophic level (e.g., the observed colonization by Red throated loons of high Arctic lakes that have lost their ice cover because of climate warming; Vincent et al 2009), or may change the trophic status of lakes. Increasing populations of geese migrating from lower latitudes have the potential to cause changes in the nutrient regime of northern lakes; for example, in a goose-breeding site in the eastern Canadian Arctic, a decadal rise in populations of Lesser snow geese (Chen caerulescens) was accompanied by a doubling of total phosphorus concentrations in lakes of the area (Mariash et al 2018) and an increase in planktonic cyanobacteria (Mariash et al 2019).…”