Loss of environmental heterogeneity and aquatic macroinvertebrate diversity following large-scale restoration management

Published source details Verberk W.C.E.P., Leuven R.S.E.W., van Duinen G.A. & Esselink H. (2010) Loss of environmental heterogeneity and aquatic macroinvertebrate diversity following large-scale restoration management. Basic and Applied Ecology, 11, 440-449.
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Summary

Desiccation is a barrier to Sphagnum growth and hence recovery of drained bog ecosystems, where these mosses dominate. Blocking drainage channels and constructing small dams to retain rainwater thus reinstating a high water table is a common restoration practice in Western Europe. However, large scale re-wetting may homogenize environmental conditions and therefore not lead to desired end results as intact bog landscapes are heterogeneous in nature. This study investigated the role of environmental heterogeneity in a restoration context and the response of aquatic macroinvertebrates to rewetting efforts of a degraded acid bog at Korenburgerveen nature reserve, eastern Netherlands.

Drainage ditches were filled in and dams constructed, thereby reducing drainage and retaining rainwater. By means of these dams the peatland was divided into several hydrological compartments. Water tables were significantly increased in some compartments but not in others. Water quality and macroinvertebrates were sampled at 45 locations (waterbodies). Samples were taken before re-wetting (2000-2002) and 2-4 years after re-wetting (2004) in spring (April-May) and autumn (October-November), in places where water tables were raised and where they were not, conforming to a replicated 'before-after-control-impact' design. Macroinvertebrate species were grouped into functional groups (life-history strategies) to facilitate interpretation of responses.

Total species numbers declined in the re-wetted parts and invertebrate assemblages became more similar both in terms of species and life-history strategies. These results indicate that large-scale re-wetting caused a functional homogenization.

Changes in environmental conditions following re-wetting could be consistently related to changes in life-history strategy composition. Retention of rainwater decreased the influence of groundwater. Here species adapted to physiological stress (as well as those employing risk spreading) increased, indicating that environmental conditions had become harsher and less predictable. In contrast, reduced drainage locally increased groundwater influence, with life-history strategies indicating enhanced predictability of environmental conditions. Importantly, such conditions characterise lagg zones (bog margins) and transitional mires in pristine raised bog landscapes (hotspots for biodiversity).

Thus, large-scale re-wetting decreased environmental heterogeneity and homogenized the aquatic macroinvertebrate assemblages. In contrast, increasing the supply of groundwater by means of reducing drainage seems a more promising restoration strategy for degraded peatlands where such possibilities exist.

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