Over the past century, the retreat of alpine glaciers across the world has produced thousands of newly formed mountain lakes. These “newborn” lakes receive solute-rich meltwater, yet little is known about their physical (i.e., turbidity from glacial flour) and biogeochemical conditions across a range of glacial influence. We surveyed alpine lakes fed by both glacial and snowpack meltwaters and those fed by snowpack alone to compare nutrient concentrations, stoichiometry, water clarity, chlorophyll, and zooplankton communities across elevational gradients. Total phosphorus and nitrate concentrations were two and three times higher in glacial lakes than in non-glacial lakes, respectively. Despite increased nutrient concentrations, total organic carbon concentrations in glacial lakes were two times lower than in non-glacial lakes, likely due to reduced primary production caused by low water clarity from glacial flour. The carbon to phosphorus ratio and the nitrogen to phosphorus ratio of lake seston increased with water clarity in glacial lakes, suggesting that turbidity from glacial flour increases light limitation and increases stoichiometric food quality for zooplankton in newborn lakes. However, chlorophyll-a concentrations did not differ between lake types. Through piecewise structural equation modeling we found that glaciers exhibit a bidirectional control on nitrate and total phosphorus concentrations mediated through landscape NDVI and lake clarity. In addition, zooplankton communities in high-turbidity glacial lakes comprised cyclopoid copepods and rotifers (i.e., non-filter feeders), while non-glacial lakes tended to be dominated by calanoid copepods and cladocerans (i.e., filter feeders). Our results show that glacier-associated lakes have biogeochemical and ecological characteristics distinct from those in other mountain lakes.  Sustained studies are needed to assess the dynamics of these unique features as the influence of the alpine cryosphere fades under ongoing climate change.

Primary Presenter: Joseph Vanderwall, University of Montana (joseph.vanderwall@gmail.com)

Authors:

James Elser, Flathead Lake Biological Station  (jim.elser@flbs.umt.edu)

Ze Ren, Beijing Normal University  (renzeasu@gmail.com)

Tyler Tappenbeck, Flathead Lake Biological Station  (tyler.tappenbeck@flbs.umt.edu)

Clint Muhlfeld, USGS  (cmuhlfeld@usgs.gov)

Joseph Giersch, Flathead Lake Biological Station  (joe.giersch@flbs.umt.edu)

Joseph Vanderwall, University of Montana  (joseph.vanderwall@gmail.com)