Macrophyte growth forms shift along the trophic gradient of lakes

ABSTRACT

A shift in phototrophic organisms occurs along lake trophic gradients characterized by a change from macrophyte- to phytoplankton-dominated states. Before lakes reach a turbid and phytoplankton-dominated state, shifts from meadow-forming Characeae to canopy-forming macrophyte species can occur where Characea are present, especially in oligotrophic to mesotrophic lakes with sand or gravel substrate. However, eutrophication intensity causing this shift has not previously been examined. We analysed data from 132 lakes located in Mecklenburg-Vorpommern (Germany) with a generalized linear model (GLM) and random forest (RF) models complemented with grid approximation to determine if (1) species richness of macrophytes declines along eutrophication gradients, (2) the chlorophyll a (Chl-a) concentrations above which the abundance of Characeae declines, and (3) the Chl-a concentrations above which the abundance of canopy-forming species declines. The number of macrophyte taxa declined gradually following a log-linear trend and with increasing Chl-a concentrations. Based on the RF models, the abundance of Characeae decreased abruptly at 5–13 µg L⁻¹ Chl-a, whereas canopy-forming species showed a monotonous and slight unimodal decreasing response at 35–103 µg L⁻¹ Chl-a. The results support the theory of shifts in growth forms along eutrophication gradients in lakes and provide, for the first time, estimates of Chl-a concentrations required for these shifts. Changes in growth forms are obvious indicators for eutrophication and can serve as an additional incentive to improve lake trophic status.

KEYWORDS:

• aquatic plants
• canopy-forming macrophytes
• Characeae
• chlorophyll a

Acknowledgements

We thank the Ministry of Agriculture and the Environment of the federal state of Mecklenburg-Vorpommern for kindly providing the macrophyte and water quality data of the lakes in Mecklenburg-Vorpommern.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Data are available from the respective authority upon reasonable request.

Additional information

Funding

This study was partly conducted within the AQUATAG project supported by Bundesministerium für Bildung, Wissenschaft und Forschung für Bildung, Wissenschaft und Forschung: [Grant Number 033W046C]; Deutsche Forschungsgemeinschaft: [Grant Number 426547801]. WK and DH were partly supported by the Collaborative Research Centre 1439 RESIST (Multilevel Response to Stressor Increase and Decrease in Stream Ecosystems; www.sfb-resist.de) funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation; CRC 1439/1, project number: 426547801).