Effects of liming on the Coleoptera, Hemiptera, Araneae and Opiliones of catchment wetlands in Wales

The liming of hydrological source areas in stream catchments has been increasingly proposed for treating the symptoms of surface water acidification. Here, we assess the effects on terrestrial invertebrates in upland mires in Wales by comparing assemblages at three limed sites with 10 unlimed reference sites. The Veliidae (Heteroptera) and Hydrophilidae (Coleoptera) were significantly more abundant, while the Carabidae were significantly less abundant at limed sites. Over 50% of 113 beetle species occurred at single sites. Among spiders, the Lycosidae were significantly less abundant at limed sites whereas the Linyphiidae and Tetragnathidae were less abundant at unlimed sites. None of these significant effects could be ascribed to differences in other measured attributes of the sites other than liming. At the community level, there were no gross differences between limed and unlimed sites shown by rank-abundance curves or diversity indices. However, assemblages at limed and unlimed sites were clearly differentiated by ordinations on spider families, carabid species and all beetle species. Qualitative differences of this type were more closely related to liming than to any other factor. Further studies are required to assess whether these correlations between lime additions and invertebrate assemblages are causal. In the meantime we advocate caution over lime additions to upland mires, particularly when important invertebrate assemblages are known to occur.