Comparación de los parámetros limnológicos y el zooplancton de un lago somero salino de La Pampa (Argentina) durante dos ciclos anuales con condiciones ambientales diferentes

Abstract

In central Argentina the alternation of cycles of rainfall above or below the historic mean is frequent; so, many saline lakes can dry or fill in a short time. As in La Pampa most of the studies on these lakes were limited to annual cycles, the information about variations under different climatic conditions is scarce. The aims of this study were to determine the limnological and zooplankton parameters of a semi-permanent Pampean saline lake during 2013 posterior to its filling after a drought, to compare the information with that obtained in 2007, because the two annual cycles had relatively different environmental characteristics and to test the hypotheses i) in 2013, after filling, scarce tolerant zooplankton species were recorded, replaced by more tolerant ones as salinity increased and ii) species richness in 2013 was greater than that recorded during higher hydrologic stability. Samples were taken between January and December of both years. In 2007 depth was stable and in 2013 it fluctuated markedly. The mean salinity was similar, close to 26 g/L. In 2007 it was stable, but in 2013 rose from 14.3 g/L (January) to 40.4 g/L (December). Transparency was the highest in 2007 (0.76 m ± 0.26) and the lowest in 2013 (0.17 m ± 0.05). The concentration of chlorophyll a in 2007 was lower ( (1.73 mg/ m3 ± 1.25) than in 2013 (38.16 mg/m3 ± 42.33). Species richness showed six species in 2007 and seven species in 2013. In 2007 crustaceans predominated, especially Boeckella poopoensis, but in 2013 rotifers dominated. Among them, Brachionus plicatilis and B. dimidiatus presented a maximum in autumn (1702 and 2062 ind/L, respectively). Daphnia menucoensis was absent during 2013 and the inverse correlation between the density of this cladoceran and chlorophyll a concentration could show its influence on water transparency because of its grazing on phytoplankton. The differences in limnological parameters allow us to know the variability of environmental conditions of a Pampean saline lake and to expand our knowledge about tolerance ranges of some endemic species as B. poopoensis and Moina eugeniae.