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Effects of polyphenols on plankton assemblages and bacterial abundance representative of a pampean shallow lake: an experimental study

M. Fernanda Alvarez*, Hernán H. Benítez, Lía C. Solari, J. Camilo Villegas Cortés, Néstor A. Gabellone, M. Cristina Claps

*Corresponding author:

ABSTRACT: Shallow lakes are complex environments playing an essential ecologic role. The relationship with the surrounding areas makes these lentic water bodies susceptible to alterations in response to human activity. For example the input of polyphenols could be critical altering species interactions. The shallow lakes located in the pampean plain of Argentina are major reservoirs of diversity, with the environmental habitats of the Salado-River basin in particular having become impacted by human activities. The aim of this work was thus to evaluate the effects of different polyphenol concentrations (i. e., tannins) on changes in the plankton assemblages and on the abundance of bacteria of the San Miguel del Monte Lake. In factorial experiments under laboratory conditions at four tannin-concentration levels and four response times, the results obtained revealed that high tannin concentrations affected neither the phyto- and zooplankton assemblages nor the bacterial abundances. The major changes in both assemblages and in the bacterioplankton abundances were dependent on exposure time. The initial foodweb of grazers was found to have shifted to a detritivorous feeding, thus producing a simplification of the community toward an early succession. Although no effects of polyphenols were registered here, what proved striking was the resilience of the system and the capability to support high tannin concentrations throughout the experiment. Therefore, future investigations are necessary to elucidate the key role of such humic substances in the structuring of plankton assemblages of the shallow lakes from areas strongly impacted, such as those found in the pampean region.