The influence of glacial meltwater on alpine and Arctic lake phytoplankton throughout the holocene

The contemporary effects of alpine and Arctic glaciers on the hydrology, physical features, and biogeochemistry of lakes is well understood. However, the influence of these factors on aquatic community, primary productivity rates, nutrient limitations patterns as well as algal communities over longer time scales, and hence algal sedimentary records, remains unclear. Understanding the role of glaciers in driving aquatic communities is critical to paleolimnological interpretation of environmental change as well as establishing a baseline understanding of the ecological disparity between glacier-fed lakes and those fed by snow-pack alone. Here I explore, by merging neo- and paleolimnolgocial techniques, the effects of glacier meltwater on ecosystem processes and phytoplankton community structure on diverse time scales in both Arctic and alpine lakes.;I compared primary productivity rates and nutrient limitation patterns in a set of lakes fed by glaciers and those fed by snow-pack alone in the alpine lakes of the central Rocky Mountains, USA. Furthermore, I related diatom species richness from 1850, the end of the Little Ice Age, to the modern time period to determine the overall change in diatom species richness. To examine the influence of glacial meltwater on a longer temporal scale, I conducted a paired study of a glacier-fed lake and a snow-fed lake where I examined species richness, algal functional groups, diatom community assemblage structure and turnover, and geochemical properties through the late Holocene (last 3000 years). In the Arctic, I surveyed diatom community structure and turnover as well as algal pigments in a lake fed by the Renland Ice Cap, East Greenland and compared these metrics to changes in glacial meltwater input. I also modeled lake-level change to identify how glaciers have altered the physical habitat of this lake over time.;Overall, I found key differences in ecological structure and processes in glacier-fed lakes and that these differences have been accentuated as the result and termination of the Little Ice Age. Alpine glacier-fed lakes were phosphorus limited and had primary productivity rates five times that of snow-fed lakes. Both Arctic and alpine glacier-fed lakes showed greater assemblage turnover and variability through time compared to their snow-fed counterparts. However, alpine glacier-fed lakes showed a decrease in species diversity throughout the last 150 years and the Arctic lake demonstrated an increase in diversity at the onset of the Little Ice Age. This study not only highlights the importance in evaluating the response of Arctic and alpine lakes through time to changing glacial ice in order to understand the future trajectory of lake ecosystems as glaciers decline, but also underscores the role that glaciers play in altering the algal sedimentary record, potentially affecting paleolimnological interpretations, and should be considered when interpreting high-elevation and high-latitude lake records.