Comparative biodiversity of rivers, streams, ditches and ponds in an agricultural landscape in Southern England Original Research Article

Information about the relative biodiversity value of different waterbody types is a vital pre-requisite for many strategic conservation goals. In practice, however, exceptionally few inter-waterbody comparisons have been made. The current study compared river, stream, ditch and pond biodiversity within an 80 km2 area of lowland British countryside. The results showed that although all waterbody types contributed to the diversity of macrophytes and macroinvertebrates in the region, they differed in relative value. Individual river sites were rich but relatively uniform in their species composition. Individual ponds varied considerably in species richness, with the richest sites supporting similar numbers of taxa to the best river sections, but the poorest sites amongst the most impoverished for all waterbody types. At a regional level, however, ponds contributed most to biodiversity, supporting considerably more species, more unique species and more scarce species than other waterbody types. Streams typically supported fewer species and fewer unique species at local and regional level than either ponds or rivers. Ditches (most of which were seasonal) were the least species-rich habitat, but supported uncommon species, including temporary water invertebrates not recorded in other waterbody types. Multivariate analysis indicated that permanence, depth, flow and altitude were the main environmental variables explaining invertebrate and plant assemblage composition. The findings, as a whole, suggest that ponds and other small waterbodies can contribute significantly to regional biodiversity. This contrasts markedly with their relative status in national monitoring and protection strategies, where small waterbodies are largely ignored.