Spatial and Temporal Distribution of Chlorophyll a and Pheopigments in Surface Waters of Lake Erie
Chlorophyll a analyses including pheopigments were made on water samples taken on 10 cruises on Lake Erie between April and December, 1970. The highest mean chlorophyll a values of approximately 11 μg/liter occurred in the mid-Western Basin, with a second maximum of 6 μg/liter off Erie, Pennsylvania. The southern shore is also characterized by high values of chlorophyll to the east of Cleveland, Ohio. The lowest yearly means were found in the eastern portion of the Central Basin and most of the Eastern Basin (approximately 3 μg/liter.) Ratios of chlorophyll a between the Eastern, Central, and Western basins have a yearly mean of 1:1.4:2.8, respectively; with maximum differences in the summer, i.e. late August, the ratio was 1:1.5:7.2.Pheopigment concentration in the surface waters reached a maximum in late October corresponding to the fall overturn of the lake and subsequent resuspension of organic matter containing degradation products from the bottom of the lake. No significant correlation was found between zooplankton abundance and pheopigment concentration as in other water bodies studied. This may indicate that zooplankton food chains are primarily detrital in Lake Erie, with grazing of living phytoplankton playing a lesser role compared with more oligotrophic water bodies.