POTENTIAL EFFECTS OF CLIMATE CHANGES ON AQUATIC SYSTEMS: LAURENTIAN GREAT LAKES AND PRECAMBRIAN SHIELD REGION

• Published in: Hydrological processes 1997-06, Vol.11 (8), p.825-871
• Main Authors: MAGNUSON, J. J., WEBSTER, K. E., ASSEL, R. A., BOWSER, C. J., DILLON, P. J., EATON, J. G., EVANS, H. E., FEE, E. J., HALL, R. I., MORTSCH, L. R., SCHINDLER, D. W., QUINN, F. H.
• Format: Article
• Language: English
• Subjects: aquatic systems; biogeochemistry; chemical limnology; climate change; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; fish; Freshwater; heterogeneity in response; Hydrology; Hydrology. Hydrogeology; interaction with other stresses; lake ice; Laurentian Great Lakes; north temperate glacial lakes; paleoclimates; physical limnology; phytoplankton; Pollution, environment geology; Precambrian Shield; terrestrial-aquatic linkages; water level; zooplankton
• ISSN: 0885-6087; 1099-1085
• DOI: 10.1002/(SICI)1099-1085(19970630)11:8<825::AID-HYP509>3.0.CO;2-G

The region studied includes the Laurentian Great Lakes and a diversity of smaller glacial lakes, streams and wetlands south of permanent permafrost and towards the southern extent of Wisconsin glaciation. We emphasize lakes and quantitative implications. The region is warmer and wetter than it has been over most of the last 12000 years. Since 1911 observed air temperatures have increased by about 0·11°C per decade in spring and 0·06°C in winter; annual precipitation has increased by about 2·1% per decade. Ice thaw phenologies since the 1850s indicate a late winter warming of about 2·5°C. In future scenarios for a doubled CO2 climate, air temperature increases in summer and winter and precipitation decreases (summer) in western Ontario but increases (winter) in western Ontario, northern Minnesota, Wisconsin and Michigan. Such changes in climate have altered and would further alter hydrological and other physical features of lakes. Warmer climates, i.e. 2 × CO2 climates, would lower net basin water supplies, stream flows and water levels owing to increased evaporation in excess of precipitation. Water levels have been responsive to drought and future scenarios for the Great Lakes simulate levels 0·2 to 2·5 m lower. Human adaptation to such changes is expensive. Warmer climates would decrease the spatial extent of ice cover on the Great Lakes; small lakes, especially to the south, would no longer freeze over every year. Temperature simulations for stratified lakes are 1–7°C warmer for surface waters, and 6°C cooler to 8°C warmer for deep waters. Thermocline depth would change (4 m shallower to 3·5 m deeper) with warmer climates alone; deepening owing to increases in light penetration would occur with reduced input of dissolved organic carbon (DOC) from dryer catchments. Dissolved oxygen would decrease below the thermocline. These physical changes would in turn affect the phytoplankton, zooplankton, benthos and fishes. Annual phytoplankton production may increase but many complex reactions of the phytoplankton community to altered temperatures, thermocline depths, light penetrations and nutrient inputs would be expected. Zooplankton biomass would increase, but, again, many complex interactions are expected. Generally, the thermal habitat for warm‐, cool‐ and even cold‐water fishes would increase in size in deep stratified lakes, but would decrease in shallow unstratified lakes and in streams. Less dissolved oxygen below the thermocline of lakes would further d