The significance of ponds in maintaining biodiversity in an intensively farmed landscape

Abstract

*Background/Question/Methods*

Ponds are amongst the most diverse freshwater habitats and have been recently found to support more species, as well as more uncommon, rare, and threatened species compared to lakes, rivers, and streams. The conservation of ponds represents a cost-effective way of maintaining or enhancing biodiversity, because of the typical small size of pond catchment areas. Moreover, ponds may be effectively used as models systems because of their small size and large number compared to lakes. At present, there is an urgent need to collect data on the ecological quality of freshwater bodies to develop programmes aimed at meeting defined water quality targets by the year 2015, in fulfillment of obligations deriving from the European Water Framework Directive (Directive 2000/60/EC). In this study, we used ponds to make a rapid assessment of the ecological quality of an intensively farmed region in Ireland. Such an assessment was based on an investigation of the aquatic Coleoptera and wetland plant assemblages of 25 farmland ponds, in June and July 2008. The relationships between Coleoptera and wetland plants with 20 habitat characteristics and water chemistry variables were also investigated, in order to improve our understanding of the factors that are important in determining patterns in pond diversity. *Results/Discussion*Gamma diversity was high, with 63 aquatic Coleoptera species recorded between June and July 2008, although alpha diversity ranged widely (4-33, mean = 15). Overall, pond water quality was poor and high levels of nitrates and phosphates were recorded. However, patterns in pond diversity were complex and no single factor was determinant. PCA, MDS, BIOENV, and regression analyses showed that habitat variables such as pond size, habitat complexity, wetland plant richness (68 species, range: 1-26, mean = 13), permanency, and grazing intensity were more important than water chemistry variables in determining patterns in Coleoptera assemblages. Permanency, pond depth, conductivity, and dissolved oxygen were the variables that best explained patterns in the taxonomic composition of wetland plants. Overall, this study confirmed the importance of ponds in supporting biodiversity even within intensively farmed regions and where reference sites are not available. Aquatic Coleoptera proved to be a useful group for assessing the ecological quality of ponds. The results of this study are important to improve our understanding of the relationship between patterns of pond diversity and environmental variables, as well as to integrate existing large-scale datasets on pond diversity.