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Technical Report

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Trace metals, algae


The present investigation examines seasonal variations of algal assemblages in a south-central reservoir, Lake Fayetteville, Arkansas, in an attempt to evaluate the role of various trace metals in relation to these seasonal variations. Iron, manganese, cobalt, copper, lead and zinc concentrations were evaluated for the period of one year from March, 1976 to March, 1977 with concomitant examination of alga] assemblages. In addition to collection of this material, correlations between specific taxa and metals in the water fraction have been evaluated. A detailed literature review dealing with the role of micronutrients in various algal groups has been discussed by Rice (1978) with further evaluation and amplification of the data contained in this report and additional physicochemical parameters. Seasonal variations of phytoplankton assemblages were observed in a mesotrophic ake in northwestern Arkansas for a period of one year. Simul aneous determinations of iron, manganese, cobalt, lead, copper and zi nc were made using atomic absorption soectroscopy. All algae were identified to species where possible. Relations between variations of seasonal phytoplankton assemblage succession and micronutrient variations were examined. Distinct patterns of a ll metal concentrations are described to occur in a cyclic pattern as a result of biological, physical and chemical factors. Four major assemblages were observed: a spring Coelosphaerium nagelianum-Aphanizomenon flos-aquae dominated assemblage, a summer serially dominated assemblage consisting of Oscillatoria spp., Merismopedia trolleri and Microcystis aeruginosa, an autumnal cyanophycean assemblage dominated by Anabaena circinalis and a winter bacillariophycean-chrysophyte assemblage characterized by Melosira granulata, Navi cula spp. , Fragillaria crotonensis, Asterionella formosa and Uroglena sp. Particulate manganese concentrations were highly correlated with distrioutions of cyanophytes in the spring (r=0.66), summer (r=0.96) and autumn (r=0.79). Particulate cobalt also was related to cyanonhycean distributions during the spring and fa ll blooms with correlation coefficients of 0.5 and 0.65, respectively. Differences in levels of correlations for the spring and autumn blooms were attributed to species composition and possibly related to the nitrogen fixation a b ility of the species present. Cobalt is believed to be secreted by Navicula with subsequent incorporation by A. formosa and 7. crotonensis as confirmed by a correlation of 0.67 with cobalt. A suggested successional relationship exists between Naviula and A. formosa and crotonensis. Particulate lead was highly correlated with populations of Navicula and Stephanodi cus nigarae; correlation coefficients of 0.57 and 0.61, respectiv ely, were recorded. Uroglena sp. also were observed to interact with the element (r=0.64). Possible lethal effects of lead on the bacillariophytes were noted while no such events were found in the case of the chrysophytes. Micronutrients at no t ime were observed to be limiting. Two metals, copper and zinc, could not be correlated with any obvious algal succession. Iron may be associated with distributions of certain euglenoid species but this was not confirmed conclusively.

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