INFLUENCE OF FRESHWATER INPUTS ON FORAMINIFERAL DISTRIBUTIONS IN COASTAL ENVIRONMENTS FROM SOUTHEASTERN NORTH CAROLINA

This study focused on the changing distribution of foraminifers across three salt marshes from Onslow Bay, North Carolina, to assess the relationship between the microfauna and salinity, freshwater input, and elevation. The results indicate that foraminifers have potential as a tool for determining environmental alteration and prehistoric changes in freshwater input for the marshes and estuaries of southeastern North Carolina, but their inconsistent distribution between geographic regions limits their utility.

Three locations along Onslow Bay were selected for study: The marginal-marine environments surrounding Fort Fisher (southern Onslow Bay), Alligator Bay (mid-latitude Onslow Bay) and Tar Landing Bay (northern Onslow Bay). Rainfall data was regularly monitored during the 370-day study for each of these marshes and compared to historical surface precipitation data (from the previous 30 years) to determine the ideal time for foraminiferal sampling: after a seven-day period of no precipitation during the dry season and after a seven-day period of excessive precipitation when totals exceeded the 95^th percentile of the historical data. The marginal-marine subenvironments that were studied at each location included the high and low marsh, high-marsh fringe (high marsh/mainland contact), low marsh/estuary fringe (“extreme low marsh”), and shallow estuary (< 2 m water depth).

Foraminifers, and especially agglutinated foraminifers, appear to prefer increases in precipitation (and thus lower surface salinities) in marsh subenvironments and decreases in precipitation (and thus higher salinities) in estuarine subenvironments. This trend was consistent for the majority of the subenvironments in the three marsh systems and could be used as an indicator of previous and even prehistoric changes in precipitation. However, other factors, including changing subenvironments via transgression, differential preservation of foraminifers, and bioturbation could provide misleading interpretations regarding paleo-precipitation.