ENVIRONMENTAL CONSTRAINTS ON OSTRACODE HABITATS IN SPRINGS, WETLANDS, AND STREAMS OF THE UNITED STATES

Multivariate statistical analyses of a large database of aquatic sites in the United States (NANODe, Forester et al., in review) indicate that ostracode assemblages inhabiting springs, wetlands, and streams show distinct habitat associations and patterns of species richness. A total of 157 sites of a total 611 sites in the NANODe database are springs, wetlands, and streams. Each of those sites is represented in the database by hydrochemical, climatic, and ostracode presence-absence species data. Only 11% of the springs sampled contain 7 or more different ostracodes species with a maximum of 12 species found in any one spring. Cavernocypris wardi is one of the most abundant species found in spring environments. C. wardi lives only in very dilute water, and is not found in any of the sampled wetlands or streams. Of the 29 sites populated by C. wardi, the average total dissolved solids (TDS) is 260 mg/l, whereas the remaining 65 sites have an average TDS concentration of 890 mg/l. This species is a good indicator of very dilute spring waters and may prove to be a useful biomarker in environmental assessment studies or modern analog analysis. Wetland sites comprised 8.5% of the entire NANODe database. Of those 50 wetland sites, 26% contained 7 or more species with 13 being the maximum in any wetland sample. Fabaeformiscandona rawsoni is a common wetland inhabitant and is found in 24% of the wetlands, 1.1% of the springs, and 0% of the streams. F. rawsoni lives in fresh to oligohaline water, enriched in HCO₃. Average spring and stream values in the database of TDS and HCO₃ appear to be too low for F. rawsoni to become established. Ostracode assemblages from lacustrine environments have proven to be excellent hydrogeochemical and paleoclimateological indicators. Multivariate statistical analyses show that ostracodes can be used to describe environmental constraints on spring and wetland habitats, as well.