Patterns of Dissolved Oxygen, Productivity and Respiration in Old Woman Creek Estuary, Erie County, Ohio during Low and High Water Conditions

Old Woman Creek wetland is composed of a stream and freshwater estuary and may act as a sink or transformer of nutrients entering Lake Erie. Primary productivity and respiration are indicators of ecosystem level trophic conditions and may be linked to the estuary's effectiveness as a nutrient sink or transformer. Old Woman Creek National Estuarine Research Reserve has been collecting water chemistry data at 15 minute intervals using data loggers since 1995. Both diel and seasonal trends in water temperature, dissolved oxygen and water depth at selected sites in the creek and estuary were related to physical and biological processes. Daily primary productivity and respiration were estimated from diurnal changes in dissolved oxygen under both high and low water conditions. Mean water depth was higher in 1997 and 1998 (0.94-1.2 m) than in 2003 and 2004 (0.5-0.66 m). Water temperature was generally 1-2 degrees C higher in the open lower estuary and mouth than in the creek and upper estuary which is more shaded. Typical diurnal fluctuations in dissolved oxygen ranged from less than 20% to greater than 150% saturation. Primary productivity rates in the creek and upper estuary were lower (0.5-3-5 gO(2)/m(2)/day) than in the lower estuary sites (2.0-10.1 gO(2)/m(2)/day). Through both periods of high water and low water, the GPP/R ratio was less than one, thus negating our hypothesis that the ratio would be greater than 1 during high water years when the estuary was primarily an open water system.