Plant community structure determines primary productivity in shallow, eutrophic lakes
Correspondence: Soren M. Brothers, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Berlin 12587, Germany. E-mail: email@example.com
- Regime shifts are commonly associated with the loss of submerged macrophytes in shallow lakes; yet, the effects of this on whole-lake primary productivity remain poorly understood. This study compares the annual gross primary production (GPP) of two shallow, eutrophic lakes with different plant community structures but similar nutrient concentrations.
- Daily GPP rates were substantially higher in the lake containing submerged macrophytes (586 ± 23 g C m−2 year−1) than in the lake featuring only phytoplankton and periphyton (408 ± 23 g C m−2 year−1; P < 0.0001). Comparing lake-centre diel oxygen curves to compartmental estimates of GPP confirmed that single-site oxygen curves may provide unreliable estimates of whole-lake GPP. The discrepancy between approaches was greatest in the macrophyte-dominated lake during the summer, with a high proportion of GPP occurring in the littoral zone.
- Our empirical results were used to construct a simple conceptual model relating GPP to nutrient availability for these alternative ecological regimes. This model predicted that lakes featuring submerged macrophytes may commonly support higher rates of GPP than phytoplankton-dominated lakes, but only within a moderate range of nutrient availability (total phosphorus ranging from 30 to 100 μg L−1) and with mean lake depths shallower than 3 or 4 m.
- We conclude that shallow lakes with a submerged macrophyte–epiphyton complex may frequently support a higher annual primary production than comparable lakes that contain only phytoplankton and periphyton. We thus suggest that a regime shift involving the loss of submerged macrophytes may decrease the primary productivity of many lakes, with potential consequences for the entire food webs of these ecosystems.