Zooplankton communities of restored depressional wetlands in Wisconsin, USA

Wisconsin has lost approximately 2 million hectares of wetland since stateh ood (1848). Through the combined efforts of state and federal agencies and private groups focused primarily on wetland restoration for waterfowl habit at management or compensatory mitigation, a fairly substantial gain in wetl and area has been achieved. Much of the wetland restoration effort in Wisco nsin has occurred on Formerly agricultural lands. However, due to the natur e of the past disturbance and possible residual effects not corrected by si mply returning surface waters to these lands, there is some question regard ing the resultant wetland quality or biological integrity. In an effort aim ed at developing tools to measure wetland gains in terms of quality or ecol ogical integrity, the Wisconsin Department of Natural Resources (WDNR) init iated a study of biological communities on restored wetlands in Wisconsin. In this paper, we report on the community of microcrustaceans and arthropod s that can be collected with a plankton net in open water in wetlands. We e xamined zooplankton community structure in restored wetlands in terms of ri chness, taxonomic representation, and Daphnia sexual reproduction and relat ed these metrics to attributes on wetlands representing least-disturbed con ditions and agriculturally impacted wetlands. We sampled 56 palustrine wetl ands distributed across Wisconsin. These wetland sites were categorized as agricultural, least-impacted, and restored (recently withdrawn from agricul tural usage). The wetlands were reasonably homogeneous in many ways, so tha t taxon richness was not correlated with basin origin, presence of adjacent roads, presence or absence of fish, water chemistry, or the size of the op en water. We identified a total of 40 taxa. Taxon richness was significantl y lower in agricultural sites (average of 3.88 taxa per site) compared to t hat of least-impacted sites (7.29 taxa) and restored sites (7.21 taxa). Tax on richness of restored sites was significantly correlated with time since restoration. The data indicate that taxon richness changes from a value typ ical of agricultural sites to the average richness of least-impacted sites in about 6.4 years. The total taxon list for 8 agricultural sites (14 taxa) was significantly smaller than the average value for randomly chosen sets of 8 least-impacted sites (20.4 taxa). Agricultural and least-impacted site s tended to have the same common taxa. Many taxa of chydorid cladocerans an d cyclopoid copepods that were rare in least-impacted sites did not occur i n the agricultural sites, nor did fairy shrimp occur in agricultural sites. Daphnia populations only produced males in least-impacted and restored sit es. Further research is needed to identify the mechanism(s) responsible for the reduced species richness and lack of sexual reproduction in agricultur al wetland sites. Likely factors include eutrophication, turbidity, or chem ical contamination. We conclude that restoration of wetland watersheds work s. Withdrawal of the watershed from agricultural usage is followed by an in crease in taxon richness, and the sites resembled least-impacted sites in a bout 6-7 years.