LAKE BROWNING EXACERBATES LOSS OF COLD-WATER FISH HABITAT ASSOCIATED WITH WARMING

Surface warming is reducing oxythermal habitat for cold-water organisms. Lakes in many regions are also undergoing increasing dissolved organic carbon (DOC) concentrations, a process commonly referred to as “browning”. Browning is associated with both expanded cold-water volumes and reduced bottom-water dissolved oxygen (DO) during warm seasons. Expanded cold water could benefit cold-water species, which often retreat to cooler depths during summer. Yet, to serve as thermal refugia cold water must be sufficiently oxygenated. We sought to understand whether browning mitigates or exacerbates the effects of climate warming for cold-water fishes. We outfitted 15 Adirondack region lakes in New York State with high frequency temperature and DO loggers during one open-water season. Using published temperature and oxygen tolerances for cold-water brook trout, we assessed the amount of suitable oxythermal habitat and related this to DOC concentrations. Browning compressed the depth of thermally stressful surface water while shallowing the depth of low-oxygen water. In very clear lakes, limited browning expands suitable habitat. However, beyond moderate DOC concentrations, browning constricts suitable habitat; shallowing of oxygen-depleted water outpaces compression of warm water in most cases. Applying our fitted relationships to a database of 1,476 Adirondack lakes, we find that for ~ 95% of Adirondack lakes, further browning will exacerbate the loss of cold-water habitat as warming continues, reducing the available habitat for economically and ecologically important fishes.

Primary Presenter: Stephen Jane, University of Notre Dame (coachman7777@yahoo.com)

Authors:

Stephen Jane, University of Notre Dame  (sjane@nd.edu)

Thomas Detmer, Cornell University  (td389@cornell.edu)

Siena Larrick, Cornell University  (sll238@cornell.edu)

Kevin Rose, Rensselaer Polytechnic Institute  (rosek4@rpi.edu)

Eileen Randall, Cornell University  (eab345@cornell.edu)

Kurt Jirka, Cornell University  (kjj23@cornell.edu)

Peter McIntyre, Cornell University  (pbm3@cornell.edu)