Restoration of degraded raised bogs: do aquatic invertebrates tell a different story?

Vegetation development and time elapsed after rewetting are generally regarded as important factors in the progress of fauna restoration. We compared invertebrate species assemblages between water bodies created by rewetting measures in raised bog areas in the Netherlands, differing in vegetation development and time elapsed after rewetting. Next to that, we sampled water bodies which have not been subject to restoration measures, but are remnants of the former use of the bogs, like peat cutting pits. Macroinvertebrates as well as microinvertebrates (Rotifera, Copepoda and Cladocera) were studied. As a reference macroinvertebrates were sampled in an intact raised bog system in Estonia. The number of characteristic invertebrate species was not clearly related to the presence of a characteristic raised bog vegetation. The microinvertebrate fauna seems to recover quickly after rewetting, but this is not the case for macroinvertebrates. Until now rewetting measures, having attained different success regarding the vegetation, resulted in a fairly similar macroinvertebrate species assemblage, including only a part of the species spectrum of an intact raised bog. Remnant water bodies, like former peat cutting pits, that are not influenced by rewetting measures were inhabited by relatively high numbers of characteristic macroinvertebrate species, even when no characteristic vegetation is present. Safeguarding habitat diversity during the restoration process and restoring habitat diversity of complete raised bog systems will help to conserve and restore the characteristic fauna diversity more successfully. Introduction Restoration measures are taken in many cutover peatlands to rehabilitate the characteristic raised bog flora and fauna. As Sphagnum species are key species in raised bogs, restoration measures are generally focussed on creating suitable hydrological conditions for re-colonization and growth of Sphagnum by means of blocking drainage ditches or building dams to retain rain water (Lamers et al. 1999, Rochefort et al. 2003, Vasander et al. 2003). Although the main part of species diversity concern fauna species, especially invertebrates, only little attention has been paid to effects of restoration measures on fauna (Kiel & Matzke 2002, Van Duinen et al. 2003). Since most restoration projects do not include a fauna monitoring programme, it is generally unknown whether they have had any effects on the fauna, whether positive or negative. Also, little attention is being paid to fauna diversity in the planning of management measures. Restoration of characteristic fauna is generally expected to follow restoration of the abiotic conditions and characteristic vegetation in course of time. A stable water table close to the peat surface generally offers the best chance for successful restoration of a Sphagnum dominated vegetation (Wheeler & Shaw 1995). Apart from the water table and its fluctuations, quality of water and the remaining peat are important aspects in the restoration of raised bog vegetation. In cases of deeper inundation presence of floating peat or light penetration and CO2-availability in the surface water are key-factors in Sphagnum-growth (Lamers et al. 1999; Smolders et al. 2001 and 2002). High levels of atmospheric nitrogen deposition may hamper restoration of ombrotrophic bog vegetation (Lamers et al. 2000; Limpens et al. 2003; Tomassen et al. 2003). To assess the effects of restoration measures on fauna and identify the key factors in successful conservation and restoration of fauna we started a comparative study on aquatic macroinvertebrates in an intact raised bog system (Nigula in Southwestern Estonia) and several raised bog areas in the Netherlands in which either or not rewetting measures have been taken. This study showed that the total number of characteristic species per site tend to increase with the time elapsed after rewetting, but this increase is slow. The number of characteristic species appeared to be not clearly related to the presence of a characteristic raised bog vegetation. Until now rewetting measures, taken in different starting conditions and having attained different success regarding the vegetation, have resulted in a fairly similar species assemblage, including only a part of the species spectrum of an intact raised bog. Remnant water bodies -remnants of the former use of raised bogs, like peat cutting pits, and not influenced by restoration measureswere inhabited by relatively high numbers of characteristic macroinvertebrate species, even when the vegetation is not very characteristic (Van Duinen et al. 2002 and 2003). Thus, the environmental key-factors in the restoration of the aquatic macroinvertebrate fauna seem to be different from those for the vegetation. Contrary to our results on aquatic macroinvertebrates Buttler et al. (1996) showed that the testate amoebae fauna of raised bogs can recover rapidly and fully, regardless of the initial condition of the cutover surface. The testate amoebae species assemblage is mainly structured by wetness, pH and nutrient availability. Probably different fauna groups respond to rewetting and Sphagnum-recovery in a different way as they make different demands to their environment. Microinvertebrates may respond more rapid to restoration of the abiotic environment and vegetation than macroinvertebrates. Next to the study on macroinvertebrates, we started a comparative study on aquatic zooplankton (Rotifera, Copepoda and Cladocera) in several raised bog areas in the Netherlands. The present paper addresses the questions whether the numbers of characteristic species differ between remnant water bodies and water bodies created by restoration measures and whether these numbers are related to 1) the presence of a characteristic vegetation and 2) the time that had elapsed since restoration measures were taken. Do these microinvertebrates react in the same way as vegetation or as macroinvertebrates to the restoration measures? Material and Methods Aquatic microinvertebrates were sampled at 21 sites in 7 raised bog areas in the Netherlands. Sampling sites were chosen to include most of the various types of water body present. The water bodies sampled differed in age, size, water and substrate quality, vegetation composition and structure. Ten of the water bodies sampled were created by rewetting measures, 11 were remnants of former peat cutting pits, which had been in existence for more than 50 years and had not been subject to bog restoration measures. These sites were in different stages of secondary succession. All samples were taken between April 1 and May 6, 2002, using two plankton nets with different mesh size. Rotifers were captured with a 35μm mesh net and Cladocera and Copepoda with a 115μm mesh net. Macroinvertebrates were sampled in 20 remnant sites and 27 restoration sites both in spring 1999 and autumn 1998 or 1999. For more details on the sampling of macroinvertebrates see Van Duinen et al. (2003). Invertebrate species were considered to be characteristic of natural raised bogs if they were listed in literature as acidophilous, acidobiontic, tyrphophilous, tyrphobiontic or typical of raised bogs. For each sampling site a Vegetation Quality Score (VQS) was calculated as described by Van Duinen et al. (2003), based on rareness, trend and desirability from the point of view of raised bog restoration. Thus, a site with a high score had a vegetation dominated by Sphagnum spp. , preferably hummock-building species, accompanied by other plants charactersitic to natural raised bogs. Table 1. Total numbers of species and characteristic species found at all sampling sites together, remnant sites and restoration sites. n= number of