Limnology of shallow lakes of the semi-arid Central Pampa of Argentina

Abstract

Aim The Central Pampa of Argentina has three recognized phytogeographic regions that arise due to the decrease in rainfall towards the west. The area has numerous lakes that are mainly temporary, with hydroperiods that relate to climatic cycles, although some of them have changed due to anthropogenic influence. Some of these lakes have been studied with special reference to zooplankton, but information on their physical and chemical aspects is scarce. Consequently, managing and evaluating the anthropogenic effects on these ecosystems is challenging. The objective of this study was to explore the limnological characteristics of lakes in different regions in the Central Pampa that experience different anthropic influences. Methods Ten lakes were sampled seasonally (January, April, July, and October) during 2007. In situ measurements included transparency, pH, temperature, and dissolved oxygen concentration, and 2-L water samples were collected to determine salinity, ion composition, suspended solids, nutrient concentration, and phytoplankton chlorophyll- a concentration. Results Salinity ranged from 0.32-136.72 g L-1, with Na+ being the dominant ion in nine lakes and Cl- and HCO3- predominating in the higher- and lower-salinity lakes respectively. Nutrient concentrations were high (total Kjeldahl nitrogen: 7.97-34.69 mg L-1; total phosphorous: 4.07-14.82 mg L-1), and all lakes were hypertrophic. We determined three lake classes: i) lakes transformed from low-salinity lakes into hypersaline ones through human inactivation of the fluvial system that fed it; ii) mesosaline temporary lakes lacking fish, with low concentrations of chlorophyll-a and influenced by agricultural activities, and iii) subsaline and hyposaline lakes, highly modified by urban sewage, converted in permanent lakes (which allowed fish fauna development) and with reduced water transparency (due to high concentrations of phytoplankton chlorophyll-a). Conclusions The chemical diversity of the studied lakes is low, and their predominance of Na+ and Cl- indicated that evaporation and crystallization control the water chemistry. Additionally, this study showed the consequences of the anthropic impact, which alter water chemical composition, trophic structure and, thus, the ecological characteristics of lakes.

Associations of ostracods in shallow lakes in the northeast of La Pampa province (Argentina)

“…On the other hand, EBe, DMo, and LTE are subsaline lakes (Hammer, 1986) with a predominance of bicarbonate, but the first differs slightly because it is more extensive and its transparency is much lower. The greater transparency that characterizes DMo and LTE is related to a greater vegetation cover that inhibits the growth of phytoplankton and decreases the removal of sediments by the wind (Echaniz & Vignatti, 2019).…”

“…This means that different ecoregions are represented in its territory from the fertile Pampa Plains in the wetter northeast to the arid Patagonian steppe in the southwest (Morello et al, 2012). These conditions affect the characteristics of their wa-ter bodies, which show considerable heterogeneity, sometimes in small geographic areas (Echaniz & Vignatti, 2019), such as those included in this study.…”

Análise de atributos limnológicos em reservatórios do semiárido nordestino

“…Além disso, os resultados mais baixos do pH durante os meses de dezembro e março, é condizente com o resultado obtido por Grieco et al (2017). De modo geral, observou-se que esse parâmetro não apresentou variação sazonal, assim como na pesquisa realizada por (Chaves et al, 2019;Echaniz;Vignatti, 2019).…”