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. Moreover, ponds may be effectively used as model systems in conservation biology 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 habitats to develop programmes aimed at meeting defined biodiversity and water quality objectives deriving by national and interantional obligations. 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. The relationships between Coleoptera and wetland plants with 20 habitat characteristics and water chemistry variables were investigated to improve our understanding of the factors that may be important in determining patterns in pond diversity.
Gamma diversity was high, with 63 aquatic Coleoptera species recorded between June and July 2008 (range: 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) were more important than water chemistry variables in determining patterns in Coleoptera assemblages. Grazing proved to be detrimental to Coleoptera diversity. 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. The creation of a fence or a buffer zone of woody or grassland vegetation proved to be beneficial to pond diversity. Such measures represent a cost-effective way of conserving biodiversity at the landscape level. Aquatic Coleoptera proved to be a useful group to make a rapid assessment of the ecological quality of ponds.