Mowing Submerged Macrophytes in Shallow Lakes with Alternative Stable States: Battling the Good Guys?

Jan J Kuiper,Elisabeth S Bakker,Michiel J J M Verhofstad,Evelien L M Louwers,Luuk P A Van Gerven,Robert J Brederveld,Jeroen J M De Klein,Wolf M Mooij,Annette B G Janssen

doi:10.1007/s00267-016-0811-2

Abstract

Submerged macrophytes play an important role in maintaining good water quality in shallow lakes. Yet extensive stands easily interfere with various services provided by these lakes, and harvesting is increasingly applied as a management measure. Because shallow lakes may possess alternative stable states over a wide range of environmental conditions, designing a successful mowing strategy is challenging, given the important role of macrophytes in stabilizing the clear water state. In this study, the integrated ecosystem model PCLake is used to explore the consequences of mowing, in terms of reducing nuisance and ecosystem stability, for a wide range of external nutrient loadings, mowing intensities and timings. Elodea is used as a model species. Additionally, we use PCLake to estimate how much phosphorus is removed with the harvested biomass, and evaluate the long-term effect of harvesting. Our model indicates that mowing can temporarily reduce nuisance caused by submerged plants in the first weeks after cutting, particularly when external nutrient loading is fairly low. The risk of instigating a regime shift can be tempered by mowing halfway the growing season when the resilience of the system is highest, as our model showed. Up to half of the phosphorus entering the system can potentially be removed along with the harvested biomass. As a result, prolonged mowing can prevent an oligo—to mesotrophic lake from becoming eutrophic to a certain extent, as our model shows that the critical nutrient loading, where the lake shifts to the turbid phytoplankton-dominated state, can be slightly increased.

Highlights

Shallow lake ecosystems depend on the presence of submerged aquatic plants for good water quality and high biodiversity (Heimans and Thijsse 1895; Carpenter and Lodge 1986; Jeppesen et al 1998)
Such self-stabilizing mechanism causes a tendency of the system to resist changes in external environmental conditions, i.e. it promotes a clear water state within the context of alternative stable states in lakes (Scheffer 2004)
Lakes in the turbid state may be resilient to changes in external environmental conditions (Hosper 1998), reduction of external nutrient loading is effective in the long run (Jeppesen et al 2005), and many of the impacted lakes have recovered or are recovering to a clear-water state with submerged macrophytes (Sondergaard and Moss 1998; Gulati and Van Donk 2002)

Summary

Introduction

Shallow lake ecosystems depend on the presence of submerged aquatic plants (macrophytes) for good water quality and high biodiversity (Heimans and Thijsse 1895; Carpenter and Lodge 1986; Jeppesen et al 1998). There is a positive feedback between aquatic plants and water clarity, through which the plants enhance their own growing conditions (Van Donk and Van de Bund 2002; Scheffer 2004) Such self-stabilizing mechanism causes a tendency of the system to resist changes in external environmental conditions, i.e. it promotes a clear water state within the context of alternative stable states in lakes (Scheffer 2004). Lakes in the turbid state may be resilient to changes in external environmental conditions (Hosper 1998), reduction of external nutrient loading is effective in the long run (Jeppesen et al 2005), and many of the impacted lakes have recovered or are recovering to a clear-water state with submerged macrophytes (Sondergaard and Moss 1998; Gulati and Van Donk 2002)

Methods

Results

Discussion

Conclusion