Floodplain Coleoptera distributions: River Trent, UK
Greenwood, M. T.; Bickerton, M. A.; Petts, G. E.
The ecological role of floodplains along large rivers in sustaining biodiversity at the landscape scale has been clearly demonstrated for vegetation, fish and large animals (Naiman & Decamps 1990, La Chavanne 1994). Micro-topographic variations combine with sedimentological differences to produce a patchwork of habitats having contrasting 'wetness' characteristics, defined by frequency and duration of inundation, and permeability. More than 200 years of human interference has controlled the fluvial processes responsible for rejuvenating and sustaining floodplain systems in most parts of Europe (Petts et al. 1989). The Trent Floodplain Project, initiated in 1989 to develop an approach to assess the functional role and conservation value of floodplain patches, seeks to contribute to the rehabilitation of floodplain environments. In a preliminary investigation, based upon one sampling period of 14 days in early May 1990, Greenwood et al. (1991) characterised the floodplain units of the River Trent by assemblages from two families of beetles (Coleoptera: Carabidae and Staphylinidae). It was shown that beetles are excellent describers of floodplain patches as functional units (sensu Amoros et al. 1987). The preliminary data also suggested that stronger contrasts in faunal diversity between patches in regulated sectors, when compared with non-regulated sectors, may reflect enhanced environmental gradients; patches within regulated sectors experiencing shorter and less frequent inundation, extended periods of desiccation, and a greater rate of drying, because of lower river levels. Such contrasts may be most intense in early summer and, especially, early autumn. Furthermore, floodplain wetlands and ponds may be more dominated by rainfall and groundwater seepage characteristics than non-regulated sectors dominated by river flows, as exemplified by Bornette & Heiler (1994) for one sector of the River Rhône. This paper examines six collections of the Family Carabidae between May and July to investigate the pattern of differences between the two sectors during early summer.