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This work aims to study the spatio-temporal variability of turbidity in Lake Chascomús using 34 years (1987–2020) of Landsat (TM, ETM + , and OLI) and Sentinel-2-MSI optical data and to understand this variability in terms of environmental variables. A semi-analytical algorithm, using reflectance in the red and near-infrared bands, was calibrated for Landsat and Sentinel-2 bands and tested using in situ turbidity measurements. The best performance was found using only the near-infrared band with 12.84% median accuracy and -12.84% bias when comparing in situ radiometric measurements and field data. When satellite-derived turbidity was compared to in situ values, the median accuracy was 31.8% and the bias 13.22%. Monthly climatological turbidity maps revealed spatial heterogeneity in Lake Chascomús, with differences observed between the north-west and south-east regions, particularly in summer and winter. Turbidity showed marked seasonal dynamics, with a minimum in autumn and a maximum in spring. Annual climatological turbidity maps showed significant inter-annual variability. Generalized linear models showed turbidity was positively associated with wind speed and photosynthetic active radiation (26.2% of the variability explained). Remote sensing was found to be a fundamental complement to traditional field-based methods for monitoring water quality parameters and allowing a better description of their spatio-temporal variability. [ABSTRACT FROM AUTHOR]

We analysed the changes in phytoplankton and in the main limnological features in a shallow lake during its transition from a clear-vegetated regime to a turbid one from 2005 to 2013. As samplings were discontinuous, data were analysed considering three different sampling periods. At the beginning of the first period, the lake was in a clear-vegetated regime, showing low values of chlorophyll a, Kd, total suspended solids and nutrients, and high Secchi depth. Phytoplankton was dominated by nano-phytoplanktonic species. During the second period, some evidences of the shift to a turbid regime were observed (mainly in Kd and total suspended solids). Towards the end of our study, submerged macrophytes sharply declined; in this period Kd and total suspended solids noticeably increased, whereas a significant reduction in Secchi depth occurred. Concomitantly, phytoplankton abundance augmented in two orders of magnitude, changing to a community with a higher proportion of micro-phytoplankton. Although the causes of the regimen shift could not be unequivocally assessed, the drastic reduction in the hydrometric level of the lake probably provoked a declination in macrophytes, with the consequent increase of nutrients in the water column and the increment in phytoplankton densities, carrying the system towards a turbid regime. [ABSTRACT FROM AUTHOR]

The effects of external physical forcing variables (solar radiation and winds) on short-term dynamics of total suspended solids (TSS), Chlorophyll- a (Chl- a), turbidity levels, and water transparency were studied during 15 days in a highly turbid, shallow lake (Laguna Chascomús, Argentina). Water samples were taken three times per day (8, 14 and 20 h.). Solar radiation and wind velocity showed a repeatedly bell-shaped diurnal pattern, with significant higher values during morning and afternoon, respectively. TSS and turbidity displayed a general decreasing trend during the sampling period, while water transparency showed the opposite trend. Also Chl- a displayed a decreasing trend and was closely correlated to TSS levels. We assayed a first-order kinetics model to detrend the series, obtaining the rate of change during the night, morning, and afternoon. We observed higher values on afternoon compared to morning for TSS, Chl- a, and turbidity levels and the opposite pattern for water transparency. We conclude that this pattern may result from a combination of biological activity, as it took place after a period of intense photosynthetic activity, together with resuspension by winds during the afternoon, (windiest time of the day). [ABSTRACT FROM AUTHOR]

We investigated nine Pampean shallow lakes (Argentina) across a moisture gradient (mean annual precipitation 1,000-500 mm), under the framework of a network project of lake monitoring whose main objective was to analyse the responses of ecosystems to different stressors associated with human activities. We postulate that species bloom in different shallow lakes will be determined mainly by local optical features, nutrients and salinity. We analysed the phytoplankton structure during the warm season 2012-2013, identifying those species and functional groups that proliferate in the lakes. Most lakes showed high phytoplankton biomass, except a saline lake located in the driest part of the gradient and an inorganic turbid lake. In some lakes, cyanobacteria blooms occurred in summer, persisting until autumn. Small colonial cyanobacteria and small fast-growing chlorophytes were abundant in most turbid enriched and anthropogenically impacted systems. Lowest species and functional diversity occurred in the saline lake. Multivariate analysis indicated that the phytoplankton structure was mainly defined by conductivity, transparency and variables associated with the trophic state, also reflecting the importance of the geographical location. Our results evidenced the vulnerability of most shallow lakes in the region to water level fluctuations, eutrophication and canalization. [ABSTRACT FROM AUTHOR]

The aim of this work was to study the components of the microbial food web and the degree of coupling between heterotrophic bacteria (HB) and heterotrophic flagellates (HF) in different shallow lakes of the Pampa Plain over a wide range of water transparency and nutrient levels. We hypothesized that not all microorganisms (i.e., HB, HF) equally increase with nutrient levels, thus, resulting in a weaker degree of coupling between HB and HF in more eutrophic waters. During the spring-summer 2009-2011, we sampled 40 Pampean lakes situated in different watershed of Buenos Aires Province. Abundances of most microbial components were very high, even higher than those reported in the literature. HB as well as picocyanobacteria (Pcy) increases with trophic state, while no clear relationship was found between protist (HF or ciliates) and Chl- a concentrations or nutrient levels. Photosynthetic picoplankton was generally dominated by phycocyanin-rich Pcy. Lakes with high HB and low HF were abundant, which suggest these components were weakly coupled. Based on the abundance of microorganisms, we do not accumulate enough evidence to segregate Pampean lakes into two discrete groups (clear vs turbid). [ABSTRACT FROM AUTHOR]

Shallow lakes of temperate areas experience seasonal and inter-annual variability in weather conditions, impacting on their biological communities. Here, we studied the temporal fluctuation of the zooplankton community in a highly eutrophic shallow lake, Laguna Chascomús. Rotifers and the cyclopoid copepod Acanthocyclops robustus dominated the community. The most important rotifers were Brachionus caudatus, B. havanaensis, and Keratella tropica. The abundance of the two Brachionus species reached maximum values in late summer/early autumn. In contrast, K. tropica and A. robustus did not display seasonal patterns. A prolonged period of low water temperature resulted in a massive fish winterkill event (in 2007), which seemingly allowed the development of unusually dense populations of cladocerans. We used vector autoregressive models to analyze the rotifer time series. The model accounted for 76% of the variance in rotifer abundance and provided evidence of their dependence on temperature and chlorophyll a. In addition, the impact of the fish winterkill on rotifer abundance could be assessed through intervention analysis. The evidence collected here suggests that the zooplankton community structure is controlled by fish planktivory, while rotifers population dynamics are mostly driven by temperature and available food. Both processes seem highly responsive to forcing weather variables. [ABSTRACT FROM AUTHOR]

A correction to the article "Which environmental factors trigger the dominance of phytoplankton species across a moisture gradient of shallow lakes?" that was published in the previous issue is presented.