Ecological effects of glacial dust deposition on remote Arctic lakes

由于气候变暖和其他全球环境变化进程，北极正在迅速变化。北极热量收支变化最明显的影响之一是格陵兰冰盖变薄，出口冰川消退。然而，来自冰川的河流-冰川产量的增加也充满了泥沙，越来越多的证据表明，随着季节性融化的加剧，格陵兰冰盖的这种产量正在增加。这种从冰川中提取的物质中，有一些会流失到海洋系统中，但很大一部分会沉积在冰川冲刷平原上，从那里释放出更细的颗粒，并将其输送到附近的陆地和水生生态系统。重要的是，这些淤泥和泄气的尘埃并不是惰性的。由于其高营养含量(碳、磷、氮、二氧化硅和微量营养素)，这种淤泥/灰尘可能具有重要的生态意义，因为邻近的水生和陆地生态系统的营养状况较低。现在有相当多的证据表明，尘埃刺激了冰川上的微生物活动和冰面上的冷水洞(由粒子沉积引起的融水洞，增加了热量吸收)。然而，尽管知道湖泊是碳处理的热点，但还没有关于冰川尘埃如何影响邻近冰缘陆地地区的湖泊的类似研究。绝大多数与格陵兰冰盖相邻的湖泊在水文上没有通过融化的水通道与其相连，因此航空尘埃可能是一个重要的甚至是主要的湖泊营养来源。通过与灰尘相关的营养物质给湖泊施肥，可以刺激初级生产力，从而促进碳动态。已知低纬度湖泊的尘埃输入对湖泊生物地球化学循环有重大影响。然而，在北极，对这些过程的考虑有限，因为湖泊对区域碳循环很重要，尽管它们没有很好地纳入区域和全球碳预算。北极湖泊众多(其丰度最高在北纬65-75度之间)，通常营养非常贫乏，如果沙尘作为气候变化的间接影响增加湖泊生产力，这将是一个积极的结果。这是由于碳埋藏量增加的不成比例效应，碳埋藏量从陆地碳循环中移除碳，因此可以抵消变暖。相反，增加对水生生态系统的有机质输入可能会促进湖泊中的微生物分解，并刺激湖泊二氧化碳的排放。在这项研究中，我们将沿着沙尘沉积速率的梯度比较格陵兰西南部湖泊中冰川沙尘的生态效应，并在时间(每年到百年)和空间尺度(湖泊到区域景观)的范围内评估其在区域碳和水生群落动态中的作用。

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).