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Benthic–planktonic coupling, regime shifts, and whole‐lake primary production in shallow lakes

Genkai-Kato, Motomi, Vadeboncoeur, Yvonne, Liboriussen, Lone, Jeppesen, Erik
Ecology 2012 v.93 no.3 pp. 619-631
algae, ecosystems, eutrophication, fish, lakes, macrophytes, models, morphometry, periphyton, phosphorus, phytoplankton, primary productivity, sediments
Alternative stable states in shallow lakes are typically characterized by submerged macrophyte (clear‐water state) or phytoplankton (turbid state) dominance. However, a clear‐water state may occur in eutrophic lakes even when macrophytes are absent. To test whether sediment algae could cause a regime shift in the absence of macrophytes, we developed a model of benthic (periphyton) and planktonic (phytoplankton) primary production using parameters derived from a shallow macrophyte‐free lake that shifted from a turbid to a clear‐water state following fish removal (biomanipulation). The model includes a negative feedback effect of periphyton on phosphorus (P) release from sediments. This in turn induces a positive feedback between phytoplankton production and P release. Scenarios incorporating a gradient of external P loading rates revealed that (1) periphyton and phytoplankton both contributed substantially to whole‐lake production over a broad range of external P loading in a clear‐water state; (2) during the clear‐water state, the loss of benthic production was gradually replaced by phytoplankton production, leaving whole‐lake production largely unchanged; (3) the responses of lakes to biomanipulation and increased external P loading were both dependent on lake morphometry; and (4) the capacity of periphyton to buffer the effects of increased external P loading and maintain a clear‐water state was highly sensitive to relationships between light availability at the sediment surface and the of P release. Our model suggests a mechanism for the persistence of alternative states in shallow macrophyte‐free lakes and demonstrates that regime shifts may trigger profound changes in ecosystem structure and function.