Fil: Mayora, Gisela Paola. Universidad Nacional del Litoral. Facultad de Bioquimica y Ciencias Bi... more Fil: Mayora, Gisela Paola. Universidad Nacional del Litoral. Facultad de Bioquimica y Ciencias Biologicas; Argentina.
High-elevation wetlands in South America are not well described despite their high sensitivity to... more 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...
Phosphorus (P) inputs are increasing in river-floodplain systems, but the factors which influence... more 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
How diversity is structured has been a central goal of microbial ecology. In freshwater ecosystem... more 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.
Abstract The release of allelochemicals by aquatic macrophytes can inhibit or benefit other plant... more Abstract The release of allelochemicals by aquatic macrophytes can inhibit or benefit other plants. Here we studied allelopathic interactions between syntopic species native to the Neotropical region. First, we quantified the phenolic exudation in monospecies cultures of Ludwigia peploides (L) and Azolla sp. (A) and in co-cultures of both species growing together (A + L) compared to control water. Then, we studied the germination of Polygonum ferrugineum seeds exposed to the exudates and control water. Incubation water from L had a significant lower pH than the other treatments, and a lower conductivity than the control. L alone or in co-culture with A reduced the dissolved oxygen content of the incubation water. Phenolic compounds were undetectable in control water (C) and the A treatment. In water of L and A + L treatments, phenolic concentration increased during the 5-day bioassay, with significant differences from day 3 on compared to treatments C and A. On day 5, more phenolic exudates were found in the A + L than in the L treatment. The germination rate but not germination speed was significantly higher in P. ferrugineum seeds treated with A + L exudates, and correlated positively with the phenolic concentration. Our results suggest that the allelopathic potential of aquatic macrophytes such as L. peploides can be higher in multispecies patches than in monospecies ones. Furthermore, phenolic exudates of macrophytes might stimulate the germination of plants native to the same region, which may have implications in the formation of vegetation patterns in aquatic ecosystems.
Stresses imposed by insecticides and predators are possibly the most rigorous filters to which aq... more Stresses imposed by insecticides and predators are possibly the most rigorous filters to which aquatic organisms are exposed in rivers and lakes associated with agricultural lands. However, their interactive effects on zooplankton communities are still unclear. This study elucidated the zooplankton community response to fish predation, the insecticide chlorpyrifos (CLP), and a combination of both factors, using a 30-day mesocosm experiment. The zooplankton assemblage was influenced by fish presence prior to CLP toxicity. Fish predation reduced microcrustacean density leading to a community dominated by microzooplankton (i.e.: rotifers and copepod nauplii). CLP decreased the species richness in treatments with and without fish, yielding an increase in the abundance of bdelloid rotifers, in the genera Lepadella and Trichocerca. The zooplankton:phytoplankton (<20 μm) ratio decreased substantially when the two stressors, fish predation and insecticide toxicity, were combined. Although CLP dissipated relatively rapidly in the aqueous phase and accumulated in sediment and fish tissue, zooplankton richness was unable to recover. A possible explanation for this could be the inhibitory effect of CLP on resting stage hatchings in the sediment. Therefore, the combined effects of fish predation and CLP might influence zooplankton richness, leading to an assemblage dominated by rotifers that appeared to be resistant to both factors, with a limited capability to control phytoplankton growth. Thus, the effects of natural and anthropogenic stressors should be considered together when assessing community dynamics in aquatic ecosystems.
Abstract River-floodplain systems host very high biodiversity and provide a great variety of ecos... more Abstract River-floodplain systems host very high biodiversity and provide a great variety of ecosystem services due largely to their high environmental heterogeneity, which is strongly dependent on spatial and temporal scales of observation. We aimed to describe the main patterns of environmental variation of the subtropical system of the Middle Parana River at different scales of analysis using univariate and multivariate statistics. Physical, chemical and biological variables were analyzed during different hydro-sedimentological phases along four consecutive years in 31 aquatic environments. We considered four aquatic habitat types with different degrees of hydrological connectivity and water flow characteristics (major rivers, secondary channels, floodplain lakes permanently connected to the major rivers, and floodplain lakes temporarily connected to the major rivers) from two geomorphologic units with different drainage patterns: anastomosing and meandering. The environmental heterogeneity was mainly associated with the habitat types and relative contributions of lateral tributaries with different water qualities to each unit, in combination with the influence of the hydro-sedimentological regime. The heterogeneity of the system was significantly higher during low water than during high water phases. However, although the extreme flood reduced dissimilarities between habitat types within each geomorphologic unit, it increased differences between major rivers and between units. In conclusion, at different spatial scales, floods may simultaneously have a homogenization effect due to increased hydrological connectivity and a differentiation effect due to enhanced inputs of water from regions with variable geological characteristics and land uses. Finally, geomorphologic units can play a key role in maintaining the environmental heterogeneity during floods of high magnitude, even when land barriers among aquatic environments disappear.
ABSTRACTDetermining which processes take place in the spatial distribution of bacterioplankton me... more 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...
Annales de Limnologie - International Journal of Limnology, 2018
In this study we analyzed if cyanobacteria total, specific and trait abundance are regulated by t... more 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...
Abstract Hydrosedimentological conditions of floodplain rivers can affect nutrient delivery proce... more Abstract Hydrosedimentological conditions of floodplain rivers can affect nutrient delivery processes. This study evaluated the effects of sedimentological and hydrological regimes on nitrogen (N) speciation and transport in the floodplain–river system of the Middle Paraná. Relations of sedimentological and hydrological regimes, assessed through turbidity and hydrometric level, with N speciation and concentration were analyzed. Simple linear regressions were performed to assess whether N load changed within the main channel in response to hydrological and sedimentological regimes. From the main channel to the floodplain, dissolved inorganic N decreased; however, the most isolated lake had the highest N concentration, almost totally in organic form. Turbidity was negatively associated with concentrations of nitrate-N (NO3-N), nitrite-N (NO2-N), and dissolved organic N (DON), and relative contributions of these N forms to total N (TN) but was positively correlated to particulate N (PN) and ammonium-N (NH4-N). The hydrometric level was positively associated with DON concentration and its relative contribution at the main channel but negatively associated with DON, PN, and TN concentrations in the most isolated lake. Simple linear regressions showed that the sedimentological regime significantly explained all N forms but not TN load. Flooding increased TN and mainly DON load. The results show that the hydrosedimentological regime largely affects N transport and speciation. The sediment peak incorporates PN to the system and affects dissolved N speciation, probably through effects of suspended particles on redox reactions. The increase of N inputs to the fluvial system during the flood could be caused by DON exportation from the floodplain.
AbstractAlthough several studies explain the trophic cascade in water systems, we lack knowledge ... more AbstractAlthough several studies explain the trophic cascade in water systems, we lack knowledge about top-down–bottom-up effects on phytoplankton from eutrophic lakes. In this study, we tested the importance of trophic cascades on phytoplankton structure, predicting that environmental variations are the main drivers. We performed a monthly sampling during a year to measure environmental variables, phytoplankton and zooplankton, plus two samplings (winter and summer) to assess fish structure. Furthermore, we analyzed zooplanktivorous fish stomach-gut contents and completed a hatching zooplankton resting egg experiment to assess the effect of fish on dormant populations. We ran a partial redundancy analysis (pRDA) for phytoplankton using zooplankton, nutrient availability and environmental variables as predictor variables. We finally calculated several ratios of the zooplankton:phytoplankton biovolume to assess potential predation effects. Phytoplankton was correlated with variations in temperature and conductivity plus nutrients (pRDA: 63.4%, F = 4.6, P = 0.001) and was dominated alternatively by diatoms and cyanobacteria. Zooplankton was dominated by microphagous rotifers (> 45% of the total biovolume), and only the ratio of microphagous rotifer:small chlorophytes was significant during summer and autumn (F = 10.6, P = 0.005). The fish community was dominated by insectivorous-planktivorous fish (> 65% of total density), yet a negative selection of zooplankton items (Ivlev’s index < 0) was found. Nevertheless, the zooplankton resting stage analysis showed that microphagous Rotifera were dominant (29 species emerged), suggesting a structuring effect of fish on the zooplankton size. We conclude that phytoplankton was mainly controlled by environmental variations plus nutrient availability, while top-down had a less evident effect.
Urban lakes constitute important recreational areas, but often they are eutrophicated. In this st... more Urban lakes constitute important recreational areas, but often they are eutrophicated. In this study we discuss the utility of 12 ecological quality metrics to test whether they: (1) can be applied to Neotropical lakes; (2) are sensitive to environmental variations throughout the year; and (3) are affected by heterogeneous spatial distribution of phytoplankton. Phytoplankton and environmental variables (including nutrients) were sampled monthly in an urban lake (four littoral and one limnetic station) throughout 1 year (n=60 samples). Twelve ecological quality metrics were tested using total phosphorus as a proxy of eutrophication through general lineal models. The best adjusted metrics were then transformed to an ecological quality ratio (EQR) to allow comparisons. The Phytoplankton Assemblage Index (Q-index) and the Cyanobacteria Bloom Index (CBI) were the most accurate. Differences in water quality estimation occurred across the year, with an overestimation of water quality in th...
PurposeThe study was carried out in a wetland of the Middle Paraná River system, Argentina, in or... more PurposeThe study was carried out in a wetland of the Middle Paraná River system, Argentina, in order to evaluate the processes associated with the decomposition of manure, which includes changes in chemical composition, nutrient release of manure, and colonization of invertebrates. We also compared the invertebrate assemblage that colonized manure with that present in the benthos of the wetland.Materials and methodsNylon bags were filled with fresh cattle manure and anchored to the littoral zone of the wetland. Six bags were collected after 1, 2, 6, 14, 21, 28, 33, 55, and 79 days: three for invertebrate determination and the other three bags for determination of dry mass and chemical analyses. The nutrient content, cellulose, lignin, and total phenolic compounds of manure were determined. In addition, the leachate of manure was collected for nutrient analyses. Samples of the wetland benthic sediment were collected for benthic invertebrate determination and particle size analyses. Spearman rank correlation was used to evaluate the relationship between chemical compounds of manure and breakdown rate. Principal component analysis was used to explore invertebrate assemblage composition of manure and sediment during the experiment.Results and discussionLimnodrilus, Dero, and Chironomus were dominant in the manure. Gatherer-collector was the dominant group in the manure, comprising almost 95 % of the total density of invertebrates. Breakdown rate was significantly related with nutrients, cellulose and total phenolics of manure. An ordination plot showed changes in invertebrate assemblages of manure and sediment samples over time.ConclusionsThis study provides new insight on the importance of manure as a substrate for macroinvertebrate colonization. Cattle manure needs to be considered as a potential source of nutrients for aquatic systems and a substrate for invertebrate assemblages.
Macrophyte health status can influence the composition of their exudates causing different effect... more 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.
The progressive degradation of wetlands has stressed the need of developing sustainable managemen... more 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.
Chromophoric dissolved organic matter (CDOM) affects ecological processes in freshwater environme... more 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.
Fil: Mayora, Gisela Paola. Universidad Nacional del Litoral. Facultad de Bioquimica y Ciencias Bi... more Fil: Mayora, Gisela Paola. Universidad Nacional del Litoral. Facultad de Bioquimica y Ciencias Biologicas; Argentina.
High-elevation wetlands in South America are not well described despite their high sensitivity to... more 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...
Phosphorus (P) inputs are increasing in river-floodplain systems, but the factors which influence... more 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
How diversity is structured has been a central goal of microbial ecology. In freshwater ecosystem... more 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.
Abstract The release of allelochemicals by aquatic macrophytes can inhibit or benefit other plant... more Abstract The release of allelochemicals by aquatic macrophytes can inhibit or benefit other plants. Here we studied allelopathic interactions between syntopic species native to the Neotropical region. First, we quantified the phenolic exudation in monospecies cultures of Ludwigia peploides (L) and Azolla sp. (A) and in co-cultures of both species growing together (A + L) compared to control water. Then, we studied the germination of Polygonum ferrugineum seeds exposed to the exudates and control water. Incubation water from L had a significant lower pH than the other treatments, and a lower conductivity than the control. L alone or in co-culture with A reduced the dissolved oxygen content of the incubation water. Phenolic compounds were undetectable in control water (C) and the A treatment. In water of L and A + L treatments, phenolic concentration increased during the 5-day bioassay, with significant differences from day 3 on compared to treatments C and A. On day 5, more phenolic exudates were found in the A + L than in the L treatment. The germination rate but not germination speed was significantly higher in P. ferrugineum seeds treated with A + L exudates, and correlated positively with the phenolic concentration. Our results suggest that the allelopathic potential of aquatic macrophytes such as L. peploides can be higher in multispecies patches than in monospecies ones. Furthermore, phenolic exudates of macrophytes might stimulate the germination of plants native to the same region, which may have implications in the formation of vegetation patterns in aquatic ecosystems.
Stresses imposed by insecticides and predators are possibly the most rigorous filters to which aq... more Stresses imposed by insecticides and predators are possibly the most rigorous filters to which aquatic organisms are exposed in rivers and lakes associated with agricultural lands. However, their interactive effects on zooplankton communities are still unclear. This study elucidated the zooplankton community response to fish predation, the insecticide chlorpyrifos (CLP), and a combination of both factors, using a 30-day mesocosm experiment. The zooplankton assemblage was influenced by fish presence prior to CLP toxicity. Fish predation reduced microcrustacean density leading to a community dominated by microzooplankton (i.e.: rotifers and copepod nauplii). CLP decreased the species richness in treatments with and without fish, yielding an increase in the abundance of bdelloid rotifers, in the genera Lepadella and Trichocerca. The zooplankton:phytoplankton (<20 μm) ratio decreased substantially when the two stressors, fish predation and insecticide toxicity, were combined. Although CLP dissipated relatively rapidly in the aqueous phase and accumulated in sediment and fish tissue, zooplankton richness was unable to recover. A possible explanation for this could be the inhibitory effect of CLP on resting stage hatchings in the sediment. Therefore, the combined effects of fish predation and CLP might influence zooplankton richness, leading to an assemblage dominated by rotifers that appeared to be resistant to both factors, with a limited capability to control phytoplankton growth. Thus, the effects of natural and anthropogenic stressors should be considered together when assessing community dynamics in aquatic ecosystems.
Abstract River-floodplain systems host very high biodiversity and provide a great variety of ecos... more Abstract River-floodplain systems host very high biodiversity and provide a great variety of ecosystem services due largely to their high environmental heterogeneity, which is strongly dependent on spatial and temporal scales of observation. We aimed to describe the main patterns of environmental variation of the subtropical system of the Middle Parana River at different scales of analysis using univariate and multivariate statistics. Physical, chemical and biological variables were analyzed during different hydro-sedimentological phases along four consecutive years in 31 aquatic environments. We considered four aquatic habitat types with different degrees of hydrological connectivity and water flow characteristics (major rivers, secondary channels, floodplain lakes permanently connected to the major rivers, and floodplain lakes temporarily connected to the major rivers) from two geomorphologic units with different drainage patterns: anastomosing and meandering. The environmental heterogeneity was mainly associated with the habitat types and relative contributions of lateral tributaries with different water qualities to each unit, in combination with the influence of the hydro-sedimentological regime. The heterogeneity of the system was significantly higher during low water than during high water phases. However, although the extreme flood reduced dissimilarities between habitat types within each geomorphologic unit, it increased differences between major rivers and between units. In conclusion, at different spatial scales, floods may simultaneously have a homogenization effect due to increased hydrological connectivity and a differentiation effect due to enhanced inputs of water from regions with variable geological characteristics and land uses. Finally, geomorphologic units can play a key role in maintaining the environmental heterogeneity during floods of high magnitude, even when land barriers among aquatic environments disappear.
ABSTRACTDetermining which processes take place in the spatial distribution of bacterioplankton me... more 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...
Annales de Limnologie - International Journal of Limnology, 2018
In this study we analyzed if cyanobacteria total, specific and trait abundance are regulated by t... more 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...
Abstract Hydrosedimentological conditions of floodplain rivers can affect nutrient delivery proce... more Abstract Hydrosedimentological conditions of floodplain rivers can affect nutrient delivery processes. This study evaluated the effects of sedimentological and hydrological regimes on nitrogen (N) speciation and transport in the floodplain–river system of the Middle Paraná. Relations of sedimentological and hydrological regimes, assessed through turbidity and hydrometric level, with N speciation and concentration were analyzed. Simple linear regressions were performed to assess whether N load changed within the main channel in response to hydrological and sedimentological regimes. From the main channel to the floodplain, dissolved inorganic N decreased; however, the most isolated lake had the highest N concentration, almost totally in organic form. Turbidity was negatively associated with concentrations of nitrate-N (NO3-N), nitrite-N (NO2-N), and dissolved organic N (DON), and relative contributions of these N forms to total N (TN) but was positively correlated to particulate N (PN) and ammonium-N (NH4-N). The hydrometric level was positively associated with DON concentration and its relative contribution at the main channel but negatively associated with DON, PN, and TN concentrations in the most isolated lake. Simple linear regressions showed that the sedimentological regime significantly explained all N forms but not TN load. Flooding increased TN and mainly DON load. The results show that the hydrosedimentological regime largely affects N transport and speciation. The sediment peak incorporates PN to the system and affects dissolved N speciation, probably through effects of suspended particles on redox reactions. The increase of N inputs to the fluvial system during the flood could be caused by DON exportation from the floodplain.
AbstractAlthough several studies explain the trophic cascade in water systems, we lack knowledge ... more AbstractAlthough several studies explain the trophic cascade in water systems, we lack knowledge about top-down–bottom-up effects on phytoplankton from eutrophic lakes. In this study, we tested the importance of trophic cascades on phytoplankton structure, predicting that environmental variations are the main drivers. We performed a monthly sampling during a year to measure environmental variables, phytoplankton and zooplankton, plus two samplings (winter and summer) to assess fish structure. Furthermore, we analyzed zooplanktivorous fish stomach-gut contents and completed a hatching zooplankton resting egg experiment to assess the effect of fish on dormant populations. We ran a partial redundancy analysis (pRDA) for phytoplankton using zooplankton, nutrient availability and environmental variables as predictor variables. We finally calculated several ratios of the zooplankton:phytoplankton biovolume to assess potential predation effects. Phytoplankton was correlated with variations in temperature and conductivity plus nutrients (pRDA: 63.4%, F = 4.6, P = 0.001) and was dominated alternatively by diatoms and cyanobacteria. Zooplankton was dominated by microphagous rotifers (> 45% of the total biovolume), and only the ratio of microphagous rotifer:small chlorophytes was significant during summer and autumn (F = 10.6, P = 0.005). The fish community was dominated by insectivorous-planktivorous fish (> 65% of total density), yet a negative selection of zooplankton items (Ivlev’s index < 0) was found. Nevertheless, the zooplankton resting stage analysis showed that microphagous Rotifera were dominant (29 species emerged), suggesting a structuring effect of fish on the zooplankton size. We conclude that phytoplankton was mainly controlled by environmental variations plus nutrient availability, while top-down had a less evident effect.
Urban lakes constitute important recreational areas, but often they are eutrophicated. In this st... more Urban lakes constitute important recreational areas, but often they are eutrophicated. In this study we discuss the utility of 12 ecological quality metrics to test whether they: (1) can be applied to Neotropical lakes; (2) are sensitive to environmental variations throughout the year; and (3) are affected by heterogeneous spatial distribution of phytoplankton. Phytoplankton and environmental variables (including nutrients) were sampled monthly in an urban lake (four littoral and one limnetic station) throughout 1 year (n=60 samples). Twelve ecological quality metrics were tested using total phosphorus as a proxy of eutrophication through general lineal models. The best adjusted metrics were then transformed to an ecological quality ratio (EQR) to allow comparisons. The Phytoplankton Assemblage Index (Q-index) and the Cyanobacteria Bloom Index (CBI) were the most accurate. Differences in water quality estimation occurred across the year, with an overestimation of water quality in th...
PurposeThe study was carried out in a wetland of the Middle Paraná River system, Argentina, in or... more PurposeThe study was carried out in a wetland of the Middle Paraná River system, Argentina, in order to evaluate the processes associated with the decomposition of manure, which includes changes in chemical composition, nutrient release of manure, and colonization of invertebrates. We also compared the invertebrate assemblage that colonized manure with that present in the benthos of the wetland.Materials and methodsNylon bags were filled with fresh cattle manure and anchored to the littoral zone of the wetland. Six bags were collected after 1, 2, 6, 14, 21, 28, 33, 55, and 79 days: three for invertebrate determination and the other three bags for determination of dry mass and chemical analyses. The nutrient content, cellulose, lignin, and total phenolic compounds of manure were determined. In addition, the leachate of manure was collected for nutrient analyses. Samples of the wetland benthic sediment were collected for benthic invertebrate determination and particle size analyses. Spearman rank correlation was used to evaluate the relationship between chemical compounds of manure and breakdown rate. Principal component analysis was used to explore invertebrate assemblage composition of manure and sediment during the experiment.Results and discussionLimnodrilus, Dero, and Chironomus were dominant in the manure. Gatherer-collector was the dominant group in the manure, comprising almost 95 % of the total density of invertebrates. Breakdown rate was significantly related with nutrients, cellulose and total phenolics of manure. An ordination plot showed changes in invertebrate assemblages of manure and sediment samples over time.ConclusionsThis study provides new insight on the importance of manure as a substrate for macroinvertebrate colonization. Cattle manure needs to be considered as a potential source of nutrients for aquatic systems and a substrate for invertebrate assemblages.
Macrophyte health status can influence the composition of their exudates causing different effect... more 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.
The progressive degradation of wetlands has stressed the need of developing sustainable managemen... more 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.
Chromophoric dissolved organic matter (CDOM) affects ecological processes in freshwater environme... more 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.
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