A paleolimnological approach to reconstructing recent historical climate change in Rocky Mountain National Park, United States

Haskett, Danielle

ABSTRACT: The chironomid communities from nine alpine lakes were assessed and compared to establish which environmental variables are responsible for modern chironomid distribution. Surface water temperature and nitrate were negatively correlated, and glacial meltwater is the variable that explains the most variance. On average, lakes receiving glacial meltwater were 2.62°C colder and contained 66% more nitrate than lakes only receiving meltwater from snow. The presence of Diamesinae indicates very cold input from running water, and this taxon may be used as a qualitative indicator species for the presence of glacial meltwater within a lake catchment. Temporal diversity indices and chironomid-based inference models were applied to six short cores. Overall, species richness was higher in snow-fed lakes, and lower in lakes receiving glacial meltwater and biodiversity increased in lower elevation lakes. A regional calibration set consisting of 153 lakes from the Colorado Rocky Mountains, Uinta Mountains, and Sierra Nevada, was used to develop two inference models for mean July air temperature (MJAT, r2jack=0.32, RMSEP=1.59oC) and surface water temperature (SWT, r2jack=0.36, RMSEP=2.82oC). Predicted MJATs and SWTs deviate from one another. The overall trend for MJATs had temperatures slightly decreasing over the 20th century while SWTs increased over the early part of the century. However, SWTs varied greatly from lake to lake by the 21st century. Within-lake variability and changes in other environmental variables, such as lake depth and oxygen levels, may have overridden both air and surface water temperatures signals.