Original paper

Phytoplankton photosynthesis-irradiance relationships in a large, managed, eutrophic, subtropical lake: The influence of lake stage on ecological homogeneity

Maki, R.P. Sharfstein


Phytoplankton photosynthesis-irradiance curves are routinely generated as part of the long-term plankton monitoring program of a large, eutrophic, subtropical lake (Lake Okeechobee, Florida). Because previous water chemistry and phytoplankton research found the lake to be more heterogeneous under lower lake stage than under higher lake stage conditions, these photosynthesis data were used to investigate whether phytoplankton from four geographically distinct stations exhibited similar photosynthetic behavior during a period of high lake stage as opposed to spatially heterogeneous photosynthetic behavior after a managed recession and drought reduced water depths. Integrated samples were collected February 1997– October 2001 from the four stations. Photosynthesis-irradiance curves (14 C-bicarbonate method) were generated, leading to mean lake-wide values (± SD) of photosynthetic parameters, α B, PmB, and Ek, of 0.049 ± 0.046 mg C (mg Chl-a)–1 h–1 (μ mol photons m– 2 s–1)–1, 7.71 ± 5.81 mg C (mg Chl-a)–1 h–1, and 189 ± 101μ mol photons m– 2 s–1, respectively. The parameters did not differ between stations under high lake stage conditions (with one exception), but αB and PmB differed significantly between stations after the reduction in lake stage, suggesting a shift toward ecological heterogeneity. Variation in photosyn- thetic parameters was predicted by a different suite of environmental variables for low and high lake stage conditions. These results point to the importance of lake stage to the ecological function of this shallow, subtropical system.


p-i curveslake okeechobeelong-term monitoringdroughtspatial heterogeneity