Controls on stream hydrochemistry dynamics in a high Arctic snow-covered watershed

Arctic streams are highly sensitive to climate change due to warmer air temperatureand increased precipitation associated with an encroaching low Arctic climatic zoneinto currently high‐Arctic coastal areas. Increases in nivation processes and perma-frost degradation will lead to potential changes in stream physicochemical habitat,although these impacts are poorly understood. To address this gap, physicochemicalhabitat characteristics in streams around Zackenberg in Northeast Greenland NationalPark were investigated during the summers of 2013 to 2016. Streams with differentsized snowpacks represented both low and high snowfall conditions leading to differ-ent nivation processes. Streams with larger snowpacks displayed lower channel stabil-ity, with higher channel mobility, suspended sediment and solute concentrations.Suspended sediment concentration was identified as a key driver of stream soluteconcentrations, and varying snowpack levels caused high interannual variability in sol-ute concentrations. Winter snowpack size was confirmed to be an important driver ofstream physicochemical habitat in an Arctic region with low glacial cover. We predictclimate change will strongly impact stream hydrochemistry in this region throughincreased nivation processes alongside active layer thickening and solifluction,thereby increasing stream suspended sediment and solute concentrations. These find-ings indicate that hydrochemistry was principally a function of erosion, with variationbeing determined by spatial and temporal patterns in erosional processes, and as such,alternative methods to fingerprint water sources should be considered in this region

Diversity and composition of macroinvertebrate assemblages in high-altitude Tibetan streams

Knowledge on the ecology of streams at extreme altitudes is relatively sparse. We conducted a preliminary survey of the macroinvertebrate fauna of Tibetan streams in June 2009 and August 2011 and compared streams with different water sources. We collected quantitative samples of macroinvertebrates and measured physicochemical variables at 16 sites (8 each sampling year) at altitudes ranging from 4315 to 5065 m a.s.l. and grouped the sites into 3 types according to origin: glacier-fed, rain-fed, and lake-outlets. We identified 38 taxa, with a mean of 8.9 taxa per site. Overall the benthic fauna was dominated by insects (71%), mainly Diptera (especially Chironomidae). Ephemeroptera, Plecoptera, and Trichoptera were found at nearly all sites but mostly in low numbers; however, the fauna was significantly different in the 2 sampling years, especially due to the proportions of Chironomidae (68% in June 2009 and 10% in August 2011) and Baetidae (6% vs. 35%, respectively). The 3 stream types had significantly different faunas. Rain-fed streams had the highest total taxon richness (γ-diversity), but glacier-fed streams had a slightly higher taxon turnover rate (β-diversity). Percent glacial cover in the catchment and water turbidity explained most of the variability in taxon richness. Although not particularly taxon rich compared to other high-altitude streams, the Tibetan stream fauna showed considerable spatial variability. The fast retreat of the glaciers and permanent snow fields in Tibet makes further studies on distribution patterns and driving forces for aquatic biodiversity urgent