Hydrology

One of the characteristics of hydroclimatic variables is its variability, understanding this as a measure of the dispersion of the samples. The most universally measures used to analyze the variability of hydroclimatic variables are the variance, standard de- viation, range and, with certain limitations, the coefficient of vari- ability (undefined when the average is close to zero). The aim of this paper is to attempt to exploit the entropy (as has been defined by Shannon in 1948 as a measure of disorder) of the probability distribution as a measure of variability, associating with other measures of the distribution characteristics of variables (such as skewness) and various indicators of non-stationary. Using Monte Carlo methods discrete time series have been gen- erated, both stationary and with different types of non-stationary (white noise with hidden fluctuations and trends), drawn from nor - mal and non-normal populations. The variations of the entropy of all samples were anal...

In the paper Entropy Analysis of Synthetic Time Series (Silber, M. & Vanlesberg, S.) properties of the entropy of the in- formation provided by synthetic series with different characteris- tics were demonstrated. In this opportunity, observed time series of precipitation on Mesopotamian and central region of Argentina were analyzed, with the following objectives: to verify the proper- ties shown in the cases described in the theoretical work mentioned above, the entropy of geographically related information with its variability and, in some way, to relate the empirical entropy (inde- pendent of the parameters of the theoretical probability distribution of the variable) with some of the variables included in the water bal- ance.

Chlorophyll-a (Chl-a) and abiotic variables were measured in the main channel and floodplain waterbodies of the Middle Paraná River to analyse the system dynamics and to assess their spatial variability during different hydrological phases, including an extreme flood. We wanted to test that the flood does not always have a homogenising effect in a river-floodplain system. An explanatory model for Chl-a was performed according to Akaike's Information Criterion (AIC), and the relation of water level with the coefficient of variation (CV) among sites for each variable was explored. The model explained 64% of Chl-a variability. Water level, depth:euphotic zone ratio (Z d :Z eu) (inverse correlation) and conductivity (direct correlation) were the significant explicative variables. The CV of Chla decreased with flood from the main channel to the floodplain, but for turbidity, Z d :Z eu , pH, dissolved oxygen, soluble reactive phosphorus and Chl-a:pheophytin-a ratio, it increased. However, within the floodplain, CV of turbidity, Z d :Z eu and pH decreased during flood. These suggest that the homogenising effect frequently observed during inundation cannot be generalised and that the floodplain may maintain its identity even during flood. The extreme flood and its overlap with the warm season and sedimentological pulse probably contributed to the heterogeneity in the spatial gradient.

Bottom-up and top-down control of phytoplankton is one of the most important hypothesis that explains and predicts the structure of aquatic community. Our aim was to elucidate whether predation and resource limitation can control phytoplankton composition and abundance in a subtropical shallow lake with groundwater connection to the river system. During 12 months, the lake was sampled at three points. Physico-chemical parameters, phytoplankton and zooplankton were sampled fortnightly, whereas fish were sampled every 3 months. The results showed that Euglenophyta dominated the total biovolume, followed by Dinophyta and Cryptophyta. As for the species composition, Chlorophyta was the dominant group (80 species recorded), followed by phylum Cyanobacteria (26 species recorded). Redundancy analysis (RDA) indicated that temperature and nitrate + nitrite concentration mainly explained biovolume changes, with zooplankton predation not having any measurable effect on phytoplankton during the...

Chromophoric dissolved organic matter (CDOM) affects ecological processes in freshwater environments. Few studies assessed its spatial variability and relations with phytoplankton in floodplain rivers. Therefore, these topics were examined in a hydrological connectivity gradient in the Middle Paraná system. Absorption coefficients at 250 and 365 nm were measured to estimate CDOM concentration and molecular weight (MW), to find their explanatory limnological variables (Redundancy Analysis, RDA), and to assess their contribution to the explanation of phytoplankton structure (Canonical Correspondence Analysis, CCA). Conductivity and turbidity explained CDOM significantly. Increased conductivity from the main channel to floodplain lakes was associated with increased CDOM concentration. The lake indirectly connected to the river showed the highest turbidity associated with high-MW-CDOM, while the isolated lake showed the highest conductivity associated with low-MW-CDOM. Phytoplankton structure was significantly explained by conductivity, turbidity, and high-MW-CDOM (CCA). Environments directly connected to the river (with the lowest conductivity) were associated with diatoms. Phytoflagellates were associated with turbidity and high-MW-CDOM in the lake indirectly connected to the river, whereas Cyanobacteria were associated with conductivity and low-MW-CDOM in the isolated lake. The combined effect of physical factors and CDOM explained the highest fraction of species variation (partial CCA). As a conclusion: (1) CDOM increases as hydrological connectivity with the river decreases; (2) lake sediment resuspension is linked to an increase of high-MW-CDOM; (3) lake isolation from the river corresponds to an increase in low-MW-CDOM; and (4) CDOM explains phytoplankton structure significantly and should be considered as an important variable in studies of microalgal assembly.

The progressive degradation of wetlands has stressed the need of developing sustainable management strategies for maintaining their ecological character within the context of sustainable development. Rotational cattle grazing is a common grazing strategy in aquatic systems but its effect on nutrient dynamics in lakes is scarcely known. The objectives of this study were to evaluate if cattle produces a significant increase of TN and TP in wetlands, and if the value of these nutrients decrease after cattle are removed. Samples of water, sediment and macrophytes were collected for nutrient, organic matter and other chemical analyses. Results showed a significant increase in water nutrients during the presence of cattle, decreasing during their absence. These changes occurred surprisingly rapid, suggesting a high resilience of these systems to this impact. The presence of submerged vegetation in lakes ameliorated the effect of cattle on water nutrients, suggesting an important role of these plants in ecosystem management. Rotational management would minimize the increase of nutrients in water, maintaining the ecological integrity of wetlands.

Macrophyte health status can influence the composition of their exudates causing different effects on zooplankton behavior and distribution in nature. We hypothesize that: (1) the release of phenolic compounds and chromophoric dissolved organic matter (CDOM) depends on macrophyte species and its health status (broken macrophytes: BM, or healthy macrophytes: HM); (2) the repellency effect depends on zooplankton species, macrophyte species and its health status; and (3) higher concentrations of phenolic compounds and CDOM produce a stronger repellency effect. Phenolic compounds and CDOM were analyzed in exudates of BM and HM of Salvinia sp., Eichhornia crassipes, Pistia stratiotes, Azolla sp. and Ludwigia peploides. Through a flow-through experiment, the repellency produced by these exudates was assessed in two copepods (Notodiaptomus conifer and Argyrodiaptomus falcifer) and one cladoceran (Ceriodaphnia dubia). Our hypotheses were partially validated. The quantity of exudated phenolic compounds and CDOM depended on macrophyte species and, to a lesser extent, on the plant health status. The repellency effect was affected by macrophyte and zooplankton species but not by the health status of plants. Only C. dubia and A. falcifer increased their evasion behavior when phenolic compound and CDOM concentrations increased. In brief, the structuring effect of repellent substances depends on different factors. Under a certain threshold concentration, zooplankton behavior might depend on the information associated with the plant odor (e.g., predation risk, structural complexity) more than on the quantity of the released chemical compounds. Above this threshold, evasion would be the only possible option to avoid damaging effects.

In this study we analyzed if cyanobacteria total, specific and trait abundance are regulated by the same environmental variables in a Neotropical urban lake that recurrently suffers harmful cyanobacteria blooms. To assess the predictor variables for cyanobacteria total and species density we performed a multiple regression (GLM) and a redundancy analysis (RDA), respectively. Temperature and oxygen were the main predictor variables for both total and species abundance. Conductivity was an exclusive predictor for cyanobacteria total density (GLM) and light availability (Zd:Zeu) for species abundance (RDA). Nutrients were unnoticeable predictor variables for both. Cyanobacteria blooms showed high recurrence (8 blooms in 12 months) and occurred within 17–28 °C. Blooms were mostly dominated by one species, and less frequently co-dominated by two species. These blooms were more recurrently dominated by dispersive non-fixing filamentous species (mainly Raphidiopsis curvata) linked to lower...

ABSTRACTDetermining which processes take place in the spatial distribution of bacterioplankton metacommunities has been a central goal of microbial ecology. In freshwater ecosystems, selection has been spotted as the main driver shaping bacterial community. However, its relative importance compared with others processes (dispersal, drift, diversification) may depend on spatial heterogeneity and dispersal rates within a metacommunity. Still, a decrease in the role of selection is expected with increasing dispersal homogenization. Here, we investigate the main ecological processes modulating the bacterial assembly in contrasting scenarios of environmental heterogeneity. We carried out a spatiotemporal survey in the floodplain system of Paraná River. The bacterioplankton metacommunity was studied by a step-forward analysis combining different statistical inferences based on the phylogenetic and taxa turnover as well as co-occurrence networks. We found that selection was the main proces...

How diversity is structured has been a central goal of microbial ecology. In freshwater ecosystems, selection has been found to be the main driver shaping bacterial communities. However, its relative importance compared with other processes (dispersal, drift, diversification) may depend on spatial heterogeneity and the dispersal rates within a metacommunity. Still, a decrease in the role of selection is expected with increasing dispersal homogenization. Here, we investigate the main ecological processes modulating bacterial assembly in contrasting scenarios of environmental heterogeneity. We carried out a spatiotemporal survey in the floodplain system of the Paraná River. The bacterioplankton metacommunity was studied using both statistical inferences based on phylogenetic and taxa turnover as well as co-occurrence networks. We found that selection was the main process determining community assembly even at both extremes of environmental heterogeneity and homogeneity, challenging the general view that the strength of selection is weakened due to dispersal homogenization. The ecological processes acting on the community also determined the connectedness of bacterial networks associations. Heterogeneous selection promoted more interconnected networks increasing β-diversity. Finally, spatiotemporal heterogeneity was an important factor determining the number and identity of the most highly connected taxa in the system. Integrating all these empirical evidences, we propose a new conceptual model that elucidates how the environmental heterogeneity determines the action of the ecological processes shaping the bacterial metacommunity.

Phosphorus (P) inputs are increasing in river-floodplain systems, but the factors which influence the dynamics of this nutrient are not clear. To assess P dynamics in this kind of river, the main channel of the Middle Paraná River, 3 anabranches, 9 secondary channels, and 20 lakes (7 permanently connected and 13 temporarily connected to the fluvial system) were sampled. Multiple linear regressions were applied to explain spatio-temporal patterns of P through commonly measured limnological variables. Particulate P increased during the sediment peak (evaluated through turbidity). Soluble reactive P (SRP) was positively associated with dissolved organic matter (DOM, mainly the chromophoric fraction), which increased during high waters in the fluvial system but was highly variable in each kind of aquatic environment. In temporarily connected lakes, vegetated zones dominated by emergent macrophytes displayed the highest SRP and chromophoric DOM concentrations. The flood and sediment peak positively affected P load in the river due to the increase in dissolved and particulate fractions, respectively. In addition, particle-bound alkaline phosphatase activity was positively associated with SRP concentration and load. These results suggest that the sediment peak incorporates particulate P in the system while the floodplain is a P source during floods through exportation of the dissolved fraction. Dissolved P could be largely exported associated with DOM, which stimulates phosphatase biosynthesis by decreasing P bioavailability. The effect of aquatic macrophytes on P dynamics seems to be influenced by DOM exudation. According to these considerations, DOM should be taken into account to analyse P dynamics in river-floodplain systems. KEYWORDS aquatic macrophytes, chromophoric dissolved organic matter, hydrosedimentological regime, Middle Paraná River system, particle-bound alkaline phosphatase activity, spatio-temporal patterns of phosphorus 1 | INTRODUCTION Phosphorus (P) is a key element of eutrophication processes in freshwater systems (Vollenweider, 1990). The increase in its bioavailability has negative implications for overall water quality, including increased turbidity and occurrence of anoxic events (Vollenweider, op. cit.). In river-floodplain systems, temporal dynamics of P is largely affected by the hydrosedimentological regime. During high waters, the increasing exchange of materials among environments increases the deposition of particle-bound P carried by the river in floodplain lakes (Kiedrzyńska, Kiedrzyński, & Zalewski, 2008). Several authors have pointed out that floodplains reduce the downstream transport

High-elevation wetlands in South America are not well described despite their high sensitivity to human impact and unique biodiversity. We describe the hydroclimatological and limnological characteristics of 21 wetlands on the High Andean Plateau of Argentina, synthesizing information gathered over ten years (2010–2020). We collected physical-chemical, phytoplankton, and zooplankton data and counted flamingos in each wetland. We also conducted an extensive analysis of climatic patterns and hydrological responses since 1985. These wetlands are shallow, with a wide range of salinity (from fresh to brine), mostly alkaline, and are dominated by carbonate and gypsum deposits and sodium-chloride waters. They tend to have high nutrient concentrations. Plankton shows a low species richness and moderate to high dominance of taxa. Flamingos are highly dependent on the presence of Bacillariophyta, which appears to be positively linked to silica and soluble reactive phosphorus availability. Cli...