TEMPORAL AND SPATIAL VARIATION OF CHLOROPHYLL A IN OLD WOMAN CREEK ESTUARY, LAKE ERIE MEASURED FROM FIELD AND LABORATORY REFLECTANCE MEASUREMENTS

Old Woman Creek (OWC) is a tributary that runs into Lake Erie near Huron, Ohio. Seasonal formation of a mouth bar controls the draining of Old Woman Creek into Lake Erie. The mouth bar was closed during the time of sample collection in late summer 2016. Daily measurements of surface reflectance were collected at four different locations for two-weeks using an ASD FieldSpec HH1 Spectroradiometer. The spectral character of the visible light reflected up through the water surface is proportional to the amount of phytoplankton and other light absorbing material in the water. This data was used to determine the amount of chlorophyll a in the water by calculating the area of the trough below the reflectance curve between 650 nm and 700 nm, where chlorophyll a dominates the signal. The area calculations were performed following the methods explained by Wolfe et al., (2006). These calculations were used to analyze the daily and spatial variation in the amount of chlorophyll a over the two-week period. The results were compared to reflectance measurements made using a Konica/Minolta CM2600d spectrophotometer on dried GF/F filters after filtering 250 ml of water from each collection site. The data collected from the CM2600d was on average 7.9 times larger than the ASD FieldSpec Spectrophotometer data. This difference was caused by the concentration of particles on the dried GF/F filter and the absorption and scattering of light when making reflectance measurements directly from the water surface using the ASD FieldSpec Spectroradiometer. Out of the four collection sites in the estuary, the site located in stagnant water near the mouth bar showed the lowest productivity while the site located near the bridge where currents are strong showed the highest productivity. The trough area calculations were compared to water quality data for OWC obtained from the NOAA National Estuarine Research Reserve System. The variations in chlorophyll a correlate most closely to variations in daily temperature and dissolved oxygen.