Degraded Softwater Lakes: Possibilities for Restoration

Abstract

In the Netherlands, the characteristic flora of shallow softwater lakes has declined rapidly as a consequence of eutrophication, alkalization and acidification. The sediment of most lakes has become nutrient rich and anaerobic. We expected that, if a vital seed bank was still present, restoration of the original water quality and sediment conditions would lead to the return of softwater macrophytes. The restoration of 15 degraded, shallow, softwater lakes in the Netherlands was monitored from 1983 to 1998. In eutrophied as well as in acidified lakes, removal of accumulated organic matter from the sediment and shores was followed by rapid recolonization of softwater macrophytes present in the seedbank. After isolation from alkaline water and subsequent mud removal, this recovery was also observed in alkalized lakes. Further development of softwater vegetation correlated strongly with the water quality. When renewed eutrophication was successfully prevented, softwater macrophytes could expand. However, in acidified lakes, Juncus bulbosus and Sphagnum species became dominant after restoration. Liming of an acidified lake was followed by re‐acidification within 3 years. Recolonization by softwater macrophytes was inhibited by high turbidity of the water column and spreading of large helophytes on the shore. As an alternative, controlled inlet of alkaline, nutrient‐poor groundwater was studied in a few lakes. The pH of those lakes increased, the carbon and nitrogen availability decreased and softwater macrophytes returned. Successful restoration has contributed considerably to maintaining biodiversity in softwater lakes in the Netherlands.

Restoring macrophyte diversity in shallow temperate lakes: biotic versus abiotic constraints

“…Macrophytes have traits that affect the ecosystem services that shallow water bodies provide as they can maintain clear water and nutrient retention, while they also strongly improve aquatic biodiversity by providing a habitat and food for many aquatic organisms (Carpenter & Lodge, 1986). The ongoing eutrophication of freshwater bodies (Carpenter et al, 1998;Tilman et al, 2001) has induced a decline or disappearance of macrophytes from many shallow water ecosystems Brouwer & Roelofs, 2001;Gulati & van Donk, 2002;Lamers et al, 2002). This has been observed in many shallow lakes in densely populated areas, for instance in the Loosdrecht lakes (Best et al, 1984;Gulati & van Donk, 2002;Van de Haterd & Ter Heerdt, 2007) and Lake Veluwemeer (Van den Berg et al, 1999;Ibelings et al, 2007) in The Netherlands, Lake Fure (SandJensen et al, 2008) and Lake Arresø in Denmark and the Müggelsee in Germany (Korner, 2001).…”

Pumpkinseed sunfish (Lepomis gibbosus) invasions facilitated by introductions and nature management strongly reduce macroinvertebrate abundance in isolated water bodies

“…These changes caused characteristic plant and animal species to decline or to disappear (Roelofs 1983;Leuven et al 1986aArts and Leuven 1988;Arts et al 1990). In order to counteract the effects of acidification and eutrophication in moorland pools (Brouwer and Roelofs 2001), management practices consisting of the removal of accumulated organic matter and macrophytes and the sod cutting of littoral shores have been implemented. This exposes bare mineral soils which facilitates the return of characteristic plant species.…”

Effects of Dredging and Lanthanum-Modified Clay on Water Quality Variables in an Enclosure Study in a Hypertrophic Pond

“…Since the low oxygen levels exert adverse effects on biota, the accumulation of nutrient-rich organic materials on the sediment can be considered polluting [45]. Removal of organic and nutrient-rich sediments is a standard maintenance and restoration strategy in the Netherlands [3,46], but it is also relatively expensive [3]. Dredging could affect the benthic fauna [47], which was not studied in the present study; however, based on the observed strongly improved oxygen, a more diverse benthic community is likely to develop in a properly dredged environment with sufficient organic-rich material removed.…”