PHYTOPLANKTON ECOLOGY AND TROPHIC STATE ANALYSIS OF RADNOR LAKE, RADNOR LAKE NATURAL AREA, NASHVILLE, TENNESSEE

The trophic state and the ecology of the phytoplankton in Radnor Lake were examined. The methods of Zafar, Carlson, and Uttormark and Wall used in characterizing the trophic state indicated that Radnor was eutrophic to hypereutrophic. Carlson's Trophic State Index was used to compare the current eutrophic state of Radnor Lake with the eutrophic state in the 1950's when Wiser completed his studies. It was ascertained that the Lake had become more eutrophic. The recent purchase of the Hall tract and the subsequent removal of the cattle from that area should decrease the rate of eutrophication of the Lake.; An algal bloom, consisting primarily of Anacystis cyanea and other blue-greens, was present from May through August, at which time the collapse of the bloom and subsequent decomposition resulted in a fish-kill on August 31, 1978. The collapse was probably due to the reduction of sunlight associated with heavy overcast skies during the month of August.; No correlation was observed between total phosphate and plankton biomass because Radnor Lake is not phosphorus limited; however, several positive correlations were observed between the phytoplankton dry weight and the following environmental variables: turbidity, total Kjeldahl nitrogen, total organic carbon, pH, phenolphthalein alkalinity. Total alkalinity was negatively correlated with dry weight.; Biogenic decalcification was shown to occur during the spring and summer of the study as a result of the high pH levels, although no marl deposits were seen.; The percent saturation of dissolved oxygen ranged from 270 percent to 107 percent before the fish-kill on August 31, and from about 17 percent to 80 percent after that date. The dissolved oxygen did not reach 100 percent saturation from the fish-kill until the end of the study in February because of the continual decomposition of organic detritus resulting from the collapse of the bloom.; Twenty-eight species of algae were identified during the study. The paucity of species probably resulted from: (1) collecting for only ten months; (2) not sampling the littoral zone with its epiphytic algae; (3) sampling a small volume of the water column; (4) destruction of fragile species by preservation techniques; and (5) the inhibition of species by the dense blue-green algal bloom which persisted from the spring throughout the summer.