A deterministic, year-round, one-dimensional water quality model, MINLAKE95,
was used to investigate climate change effects on water temperatures and dissolved
oxygen (DO) in five North Carolina lakes. The model was applied in daily timesteps over
periods of several years. Past (recorded) weather conditions and a projected climate
scenario under a doubling of atmospheric carhon dioxide were used as model inputs.
Many of the lakes in the southeastern United States are matl~made reservoirs. Three such
reservoirs atld two shallow natural lakes were modeled. The reservoirs are in the
Piedmont and Mountain regions of North Carolina and are from 20 m to 65 m deep. The
natural lakes are in the Coastal Plain and less than 4 m deep. All five lakes are major
water bodies with long hydraulic residence times and surface areas ranging from 11 to 58
km2• Standard errors of simulation relative to point measurements were 2.0DC for water
temperature and 1.4 mg L-J for dissolved oxygen. Measurements were available as
profiles against depth at a single station in each lake. Each lake was modeled under past
lxC02 climate conditions (1961- 79) and under a projected 2xC02 climate scenario. To
illustrate the climate change effect, plots of isotherms and DO-isopleths in a depth versus
time coordinate system were prepared. Mean annual and extreme year values were
- plotted. To quantify the climate change effect further, extreme values of temperature and
DO values in the surface layer and the bottom layer of each lake were tabulated, as well
as periods of anoxia, lake volumes affected by anoxia, and periods and lake volumes with
DO < 2' mg/l or DO < 3 mg/I. The .climate change effects were most apparent in
maximum surface temperature increases of 2.8 to 3 DC, maximum bottom temperature
increases of 1.6 to 2.9DC, and a 20% increase in evaporation in all five lakes. Low DO
levels in the three reservoir hypolimnia were projected to be extended by up to 48 days
in the 2xC02 climate scenario. Implications for fish habitat are that only the most
temperature tolerant of the warm~water fishes would find suitable habitat in the natural
'lakes under the 2xC02 climate scenario. Cool~water fishes might survive at the
intermediate (thermocline) depths of reservoirs where DO levels are sufficient and
maximunl temperatures tolerable. Cold-water fishes would not find suitable habitat,
except in refugia, e.g. due to groundwater inflows.
US Environmental Protection Agency, Environmental Research Laboratory; National Agricultural Water Quality Laboratory, US Department of Agriculture
Rasmussen, Anders H.; Stefan, Heinz G..
Climate Change Effects on Water Temperature and Dissolved Oxygen in Five North Carolina Lakes.
St. Anthony Falls Laboratory.
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