Ecological effects of glacial dust deposition on remote Arctic lakes

点击翻译按钮获取中文摘要

The Arctic is changing rapidly as a result of climate warming and other global environmental change processes. One of the most obvious effects of altered Arctic heat budgets is the thinning of the Greenland ice sheet and the retreat of outlet glaciers. However, the increased fluvio-glacial output from glaciers is also laden with silt and there is growing evidence that such output from the Greenland ice sheet is increasing with enhanced seasonal melting. Some of this glacially-derived material is lost to the marine system but a significant part is deposited on glacial outwash plains from where the finer particles are deflated and transported to nearby terrestrial and aquatic ecosystems. Importantly this silt and the deflated dust is not inert. Because of its high nutrient content (carbon, phosphorus, nitrogen, silica and micronutrients), this silt/dust may be ecologically important because of the low nutrient status of adjacent aquatic and terrestrial ecosystems. There is now considerable evidence that dust stimulates microbiological activity on glacial ice and in cryoconite holes (meltwater holes caused by particle deposition which increases heat uptake) on the ice surface. However, there are no comparable studies on how glacially-derived dust influences lakes within terrestrial areas adjacent to the ice margin, despite the knowledge that lakes are hotspots of carbon processing.The vast majority of lakes adjacent to the Greenland ice sheet are not hydrologically connected to it by meltwater channels, and so aerially-delivered dust might be an important or even predominant lake nutrient source. Fertilization of lakes by nutrients associated with dust stimulates primary production and hence carbon dynamics. Dust inputs to lakes at lower latitudes is known to have major impacts on lake biogeochemical cycling. There has, however, been limited consideration of these processes in the Arctic where lakes are important for regional carbon cycling although they are not well integrated into regional and global carbon budgets. Arctic lakes are numerous (their abundance is highest between 65-75 degrees N) and generally very nutrient poor and if dust increases lake productivity as an indirect effect of changing climate, this will be a positive result. This is due to the disproportional effect on increased carbon burial which removes carbon from the terrestrial carbon cycle and hence can offset warming. Conversely, increasing organic matter input to aquatic ecosystems may enhance microbial decomposition in lakes and stimulate lake CO2 emissions. In this study we will compare the ecological effects of glacially-derived dust on lakes along a gradient of dust deposition rates in SW Greenland and assess its role in regional carbon and aquatic community dynamics at a range of temporal (annual to centennial) and spatial scales (lake to regional landscape).