OSTRACODES, MICROENVIRONMENTS, AND CHANGING HYDROLOGY IN A FEN WETLAND IN NORTHEAST OHIO

Herrick Fen Nature Preserve in Portage County, Ohio is part of the headwaters of Tinker's Creek, the largest tributary to the Cuyahoga River. Herrick Fen is an ideal place for ostracode research in interstitial and wetland ecosystems because of the diversity of ostracode assemblages. Ground water – surface water interactions vary in space and time in this preserve, which formed in the glacial till following the Wisconsinan glaciation. The preserve is owned and managed by The Nature Conservancy and Kent State University. Spring seepage from unconfined groundwater as well as deeper aquifers occur in the complex headwater area.

Preliminary assessment of the microhabitats is underway by mapping species distributions observed seasonally since 2002 and including samples taken this year. The ostracode microhabitats shift throughout time and this movement can be tracked by measuring the distribution and abundances of ostracode species over time, subsurface temperature, and specific conductance. Major ion hydrochemistry of the sites within this wetland are identical, with significant changes occurring primarily in temperature and in specific conductance. The appearance and disappearance of species appears to correlate with the establishment and collapse of groundwater discharge seeps, and the rise and fall of the unconfined ground water table. Interstitial species include three species of the Darwinulidae family, two of which have not yet been reported from the U.S. (Microdarwinula zimmeri and Penthesilenula sp.) Semi-terrestrial species such as Scottia pseudobrowniana are present, as are many well known wetland and stream taxa, including Physocypria globula and Physocypria pustulosa, Cypridopsis vidua and Cypridopsis okeechobei, Candona elliptica, and Candona compressa. The changing pattern of species distribution indicates the complexity of ground water – surface water interactions within a single small wetland.