Structuring features of lake districts: landscape controls on lake chemical responses to drought

• Published in: Freshwater biology 2000-03, Vol.43 (3), p.499-515
• Main Authors: Webster, Katherine E., Soranno, Patricia A., Baines, Stephen B., Kratz, Timothy K., Bowser, Carl J., Dillon, Peter J., Campbell, PauL, FeE, Everett J., Hecky, Robert E.
• Format: Article
• Language: English
• Subjects: calcium; Canada, Ontario; climate; Freshwater; groundwater; hydrology; lake-groundwater interactions; lakes; landscape position; long term research; Ontario; regionalisation; seepage; USA, Wisconsin; water chemistry; Wisconsin
• ISSN: 0046-5070; 1365-2427
• DOI: 10.1046/j.1365-2427.2000.00571.x

1. Within a lake district of relatively homogeneous geomorphology, the responses of lakes to climate are influenced by the complexity of the hydrogeologic setting, position in the landscape, and lake‐specific biological and physical features. We examined lake chemical responses to drought in surface water‐ and groundwater‐dominated districts to address two general questions. (1) Are spatial patterns in chemical dynamics among lakes uniform and synchronous within a lake district, suggesting broad geomorphic controls; variable in a spatially explicit pattern, with synchrony related to landscape position, suggesting hydrologic flowpath controls; or spatially unstructured and asynchronous, suggesting overriding control by lake‐specific factors? (2) Are lake responses to drought a simple function of precipitation quantity or are they dictated by more complex interactions among climate, unique lake features, and hydrologic setting? 2. Annual open‐water means for epilimnetic concentrations of chloride, calcium, sulfate, ANC, DOC, total nitrogen, silica, total phosphorus, and chlorophyll a measured between 1982 and 1995 were assembled for lakes in the Red Lake and ELA districts of north‐western Ontario, the Muskoka – Dorset district in south‐central Ontario, and the Northern Highland district of Wisconsin. Within each district, we compared responses of lakes classified by landscape position into highland or lowland, depending on relative location within the local to regional hydrologic flow system. Synchrony, defined as a measure of the similarity in inter‐annual dynamics among lakes within a district, was quantified as the Pearson product‐moment correlation (r) between two lakes with observations paired by year. To determine if solute concentrations were directly related to interannual variations in precipitation quantity, we used regression analysis to fit district‐wide slopes describing the relationship between each chemical variable and annual (June to May) and October to May (Oct–May) precipitation. 3. Among lakes in each of the three Ontario districts, the pattern of chemical response to interannual shifts in precipitation was spatially uniform. In these surface water‐ dominated districts, solute concentrations were generally a simple function of precipitation. Conservative solutes, like calcium and chloride, tended to be more synchronous and were negatively related to precipitation. Solutes such as silica, total phosphorus, and chlorophyll a, which are infl