GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 14-2
Presentation Time: 8:20 AM


MCKNIGHT, Diane M.1, SOKOL, Eric2, WILLIAMS, Mark3, HELL, Katherina2, JOHNSON, Piet2 and PRESTON, Daniel2, (1)Institute for Arctic and Alpine Research, University of Colorado, 1560 30th Street, Boulder, CO 80309, (2)Institute for Arctic and Alpine Research, Univ. of Colorado, 1560 30th Street, Boulder, CO 80309, (3)Institute for Arctic and Alpine Research, University of Colorado at Boulder, 1560 30th St, Campus Box 450, Boulder, CO 80309,

Alpine regions are vulnerable to climate change, but detailed records are limited. Analysis of data from 7 alpine and sub-alpine lakes in in the Colorado Front Range shows that spring ice-off dates have shifted 7 days earlier over the last 33 years. Further, winter/spring snowfall and spring/summer air temperatures were found to be strong predictors of ice cover duration. In turn, the physical characteristics and phytoplankton community dynamics of the most studied lake varied with ice-off timing. Summers with earlier ice-off had slower flushing rates, stronger stratification and higher conductivity, pH and inorganic nitrogen. A NMDS ordination and RDA analysis of the data revealed a strong response to climate by the phytoplankton community at the surface. A much weaker response was found at 9 m. Using composite climate variables representing “too-much-summer”, we found that these variables explained 29.1% of phytoplankton community composition at the surface, but only 9.7% at 9 m. Observed photobleaching of dissolved organic matter suggests that greater exposure to ultraviolet light at the surface may contribute to differences between the responses at the surface and 9 m. The links among hydrological, chemical and biological responses to climate highlight the integration by lakes of larger-scale ecosystem change.