Physical-chemical influences on vernal zooplankton community structure in small lakes and wetlands of Wisconsin, USA

We sampled zooplankton communities from 54 small water bodies distributed t hroughout Wisconsin to evaluate whether a 'snap-shot' of zooplankton commun ity structure during early spring could be used for the purpose of differen tiating lakes from wetlands. We collected a single set of zooplankton and w ater chemistry data during a one-month time window (synchronized from south to north across the state) from an open water site in each basin as a mean s to minimize and standardize sampling effort and to minimize cascading eff ects arising from predator-prey interactions with resident and immigrant aq uatic insect communities. We identified 53 taxa of zooplankton from 54 site s sampled across Wisconsin. There was an average of 6.83 taxa per site. The zooplankton species were distributed with a great deal of independence. We did not detect significant correlations between number of taxa and geograp hic region or waterbody size. There was a significant inverse correlation b etween number of taxa and the concentration of calcium ion, alkalinity and conductivity. One pair of taxa, Lynceus brachyurus and Chaoborus americanus , showed a significant difference in average duration of sites of their res pective occurrence. All other pairs of taxa had no significant difference i n average latitude, waterbody surface area, total phosphorus, total Kjeldah l nitrogen, alkalinity, conductivity, calcium ion, sulfate, nitrate, silica te or chloride. Taxa were distributed at random among the sites - there wer e no statistically significant pairs of taxa occurring together or avoiding each other. Multivariate analysis of zooplankton associations showed no ev idence of distinct associations that could be used to distinguish lakes fro m wetlands. Zooplankton community structure appears to be a poor tool for d istinguishing between lakes and wetlands, especially at the relatively larg e scale of Wisconsin (dimension of about 500 km). The data suggest that a s mall body of water in Wisconsin could be classified as a wetland if it pers ists in the spring and summer for only about 4 months, and if it is inhabit ed by Lynceus brachyurus, Eubranchipus bundyi, and if Chaoborus americanus and Chydorus brevilabris are absent.