Individual study: Consequences of lake drainage for macroinvertebates at De Maten nature reserve near Genk, Limburg, Belgium
van de Meutter F., Stoks R. & Meester L.C. (2006) Rapid response of macroinvertebrates to drainage management of shallow connected lakes. Journal of Applied Ecology, 43, 51-60
Lake drainage has become a tool for the restoration of shallow turbid lakes. The benefits arise from the removal of fish and nutrient rich sediment, and promotion the growth of macrophytes in order to restore clear waters. Previous studies have shown that some macrophytes and zooplankton benefit from drainage and subsequent fish removal but little was known about the consequences for macro-invertebrate communities. A study was undertaken on a nature reserve close to the city of Genk, north-east Belgium, to investigate the effects on the macro-invertebrate community of drainage of a series of inter-connected lakes.
A series of 34 shallow eutrophic lakes at De Maten nature reserve in Belgium had been traditionally drained every 4-5 years as part of the fish farming regime dating back to the Middle Ages. However, this had been abandoned during their incorporation into the nature reserve from 1956 to 1991. It was decided that drainage should be re-instated and since 1993 each lake has been drained every 3-4 years, partly to facilitate feeding opportunities for waders and wildfowl, and also to reduce the fish population especially of non-native fish species including pumpkinseed Lepomis gibbosus and brown bullhead Ameiurus nebulosus.
Six lakes were sampled over three years (2001-3). They were drained from November 2001 to March 2002. To reduce the confounding impact of year effects another six lakes were sampled that had been drained a year earlier.
Macroinvertebrate abundance did not increase but diversity increased following drainage for all macroinvertebrates (at the family level). This suggested that recolonisation was important. This was attributed to the decline in fish predation following drainage. The families and higher order taxa that benefited most from drainage were dragonflies (Anisoptera), mayflies (Baetidae), mosquitoes and gnats (Culicidae), leeches (Hirudinae), water bugs (Naucoridae) and damselflies (Zygoptera). The species that benefitted most were the larger predatory species. Chironomid (midge) larvae were less abundant after drainage, perhaps because of the increased numbers of invertebrate predators (coming about as a response of fish removal).
The authors suggest that when recolonisation is possible from adjacent, non-drained lakes (as in the case of this extensive, joined lake system) then drainage is the most cost effective restoration tool for shallow lakes but suggest it may be less suitable where recolonisation is constrained, as is the case for isolated lakes.
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