Pond or lake: does it make any difference?

To investigate the importance of lake size, we analysed the chemical andbiological characteristics of nearly 800 Danish lakes ranging from 0.01 to 4200ha.Most of the lakes were shallow (median depth = 1.5m) and eutrophic (lake water meantotal phosphorus = 0.26mg P l –1 and mean chlorophyll-a = 60 µ gl –1 ). Phosphorus andnitrogen concentrations were unaffected by lake size, but positively related to agricul-tural exploitation. Lakes 1ha. The absence of fish did, however, not result in higher abun-dance of Daphnia , suggesting a higher impact by invertebrate predators in small lakes.Taxon richness of both zoo- and phytoplankton was weakly related to lake size,whereas the number of submerged macrophyte and fish species increased steadily withlake size. Also species richness of macrophytes increased with increasing alkalinity.The low impact of lake size on the species richness of several taxonomic groups sug-gests that ponds and small lakes are important biodiversity components in the agricul-tural landscape.