Pond macrophyte assemblages, biodisparity and spatial distribution of ponds in the Northumberland coastal plain, UK

1. Macrophyte assemblages from 50 ponds throughout the Northumberland coastal plain were surveyed together with adjacent landscape, pond morphology and physical and chemical variables. 2. TWINSPAN classification and CANOCO ordinations suggested that, whilst distinct macrophyte assemblages recurred, relationships of assemblages to environmental variables were weak. Geographical variables (northing, easting and altitude) plus extent of drying out were the most important variables in the CANOCO ordination linking pond types and environmental factors. Most assemblages could be found across a wide range of conditions. Classifications using only aquatic or emergent taxa gave different results. 3. Regression analyses suggested that total species richness of aquatic taxa increased with greater area of deeper water and pH. Emergent taxa richness increased with pond area, areas of deeper water and drying down, and decreased with altitude. The level of prediction was weak. 4. Pond types, defined by their macrophytes, were dispersed throughout the region and interspersed so that adjacent ponds often supported different assemblages. No habitat or locale supported unique types or unusual variety. 5. Local, anecdotal classifications of pond types in Northumberland, e.g. 'subsidence ponds', proved unreliable. Classification of ponds using macrophytes suggested greater biodisparity than such simplistic categories. The two main approaches to pond assessment (spatial surveys and ecological classification) need to be combined for sound assessment of the local status of ponds. This would benefit regional selection of pond types for conservation.