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Modeling interactions between dissolved organic carbon, phosphorus, and chlorophyll in North Temperate lakes.
Dent, Lisa1, Carpenter, Steve1, Houser, Jeff1, 1
ABSTRACT- Land use change and development can alter inputs of dissolved organic carbon (DOC) and phosphorus (P) to lakes, potentially causing eutrophication (excessive algal production). Empirical work has shown that lakes with high P and low DOC inputs have higher and more variable chlorophyll levels. However, there are important interactions between P and DOC that make the net response of lakes to development unclear. High DOC may protect against eutrophication by reducing light penetration and thus reducing algal growth. High DOC may also increase metabolism in the hypolimnion, thereby increasing anoxia and thus recycling of P from bottom sediments, exacerbating eutrophication. In addition, in small lakes, DOC affects the depth of the epilimnion. We used a mathematical model to ask how these competing mechanisms could alter lake response to changing DOC and P inputs. The model predicted that steady state areal algae would be lower in lakes with more DOC, and that higher P inputs were necessary to shift high DOC lakes to a eutrophic state. Interestingly, this effect was due to faster export from the smaller epilimnion, rather than shading. Changes in epilimnetic depth compensated for light intensity changes. In contrast, volumetric algae increased with DOC inputs, largely due to effects of epilimnion size. DOC had minimal impact on steady state chlorophyll levels via enhanced internal P recycling.
KEY WORDS: eutrophication, nutrients, carbon, model