Authors: Gustavo D Baffico
Publish Date: 2010/01/28
Volume: 59, Issue: 3, Pages: 533-545
Abstract
The epilithic algae distribution along a pH gradient and the relationship between the chemical gradient and biomass development were studied in Río Agrio a naturally acidic river located in Patagonia Argentina The epilithic community was monitored during the summer of three consecutive years in sites located above and below the entrance of tributaries The epilithic community showed differences between sites based on the chemical composition of the water and the precipitates that appear on the streambed of the river The lowest biomass diversity and number of species were found at the most extreme part of the river in terms of pH ca 2 and element concentrations Euglena mutabilis was the dominant species in this section of the river As pH increased ca 3 the community changed to be dominated by filamentous green algae Ulothrix spp Mougeotia sp Klebsormidium sp showing luxuriant growths in terms of biomass With the inflow of a neutral tributary the pH of Río Agrio increased above 3 and the precipitates of orangered iron hydroxides appeared The algal community was not affected by these precipitates or the low P concentrations along the next 30 km of river downstream from this site The apparent physical stress that the precipitates impose on algae is in fact a dynamic reservoir of P because diel cycle of Fe could be promoting precipitation and redissolution processes that binds and releases P from these precipitates Where the pH increased above 6 precipitates of aluminum hydroxides appeared At this site the epilithic biomass and density decreased some algae species changed but the diversity and the number of species in general remained consistent with the upstream values The physical stress of the Al precipitates on the algae is added to the chemical stress that represents the sequestering of P in these precipitates that are not redissolved resulting P a limiting nutrient for algae growthThe author wish to thank Margarete Mages UFZ Germany for performing the chemical determinations in water Pedro Temporetti and Guadalupe Beamud for help in field sampling Rachel Paterson for improving the English and two anonymous reviewers for helpful suggestions This study was funded by grants from Agencia Nacional de Promoción Científica y Tecnológica PICT0108186 Universidad Nacional del Comahue Prog B940 and Volkswagen Foundation RA 1661/03
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