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When faced with disturbances such as increased salinity, aquatic communities inhabiting inland coastal systems change and may or may not be resilient after salinity decreases. The purpose of this study was to assess the potential role of the resting egg bank for zooplankton community resilience. We predicted that (1) hatching of resting eggs is inhibited by increased salinities and (2) resting eggs remain viable when exposed to salinity and hatch when returned to freshwater. At the community level, we evaluated the hatching responses and the short-term viability of resting eggs exposed to a salinity gradient. The hatching of resting eggs was inhibited at higher salinities (16.0 and 32.0 g l −1 ). However, some resting eggs remained viable and hatched when returned to freshwater. Additionally, combining our experimental results to previously published field data, we observed that the pattern of hatching during exposure to salinity matches the temporal succession observed in the zooplankton community at our model system, after increased salinity. The recovery of zooplankton communities after disturbances involving increased salinity is likely facilitated by the presence of an egg bank. This finding has important implications for the recovery of zooplankton communities and the management of aquatic systems vulnerable to salinization worldwide.

The main goal of this research was to evaluate whether the mixture of fresh labile dissolved organic matter (DOM) and accumulated refractory DOM influences bacterial production, respiration, and growth efficiency (BGE) in aquatic ecosystems. Bacterial batch cultures were set up using DOM leached from aquatic macrophytes as the fresh DOM pool and DOM accumulated from a tropical humic lagoon. Two sets of experiments were performed and bacterial growth was followed in cultures composed of each carbon substrate (first experiment) and by carbon substrates combined (second experiment), with and without the addition of nitrogen and phosphorus. In both experiments, bacterial production, respiration, and BGE were always higher in cultures with N and P additions, indicating a consistent inorganic nutrient limitation. Bacterial production, respiration, and BGE were higher in cultures set up with leachate DOM than in cultures set up with humic DOM, indicating that the quality of the organic matter pool influenced the bacterial growth. Bacterial production and respiration were higher in the mixture of substrates (second experiment) than expected by bacterial production and respiration in single substrate cultures (first experiment). We suggest that the differences in the concentration of some compounds between DOM sources, the co-metabolism on carbon compound decomposition, and the higher diversity of molecules possibly support a greater bacterial diversity which might explain the higher bacterial growth observed. Finally, our results indicate that the mixture of fresh labile and accumulated refractory DOM that naturally occurs in aquatic ecosystems could accelerate the bacterial growth and bacterial DOM removal.

The purpose of this research was to assess the effects of dredging performed in a marginal wetland colonized by aquatic macrophytes on eutrophication of the adjacent shallow tropical lake (Imboassica Lake, Brazil). The river mouth of the Imboassica River that drains into Imboassica Lake had been densely colonized by aquatic vegetation dominated by Typha domingensis (Pers.) when it was dredged. Total and dissolved nitrogen and phosphorus concentrations were measured monthly over 13 years at four stations in the Imboassica river-lake system. Dredging activities reduced phosphorus and nitrogen retention at the river mouth and subsequently increased these nutrient stocks in the lake waters. Nutrient retention by non-dredged wetland was estimated to be ca. 1,200 kg year⁻¹ (87.3 g m⁻² year⁻¹) for nitrogen and 60 kg year⁻¹ (4.5 g m⁻² year⁻¹) for phosphorus. Our whole-lake approach suggested that dredging might intensify rather than mitigate eutrophication in shallow tropical lakes when the removal of aquatic macrophytes is coupled to the persistence of anthropogenic nutrient inputs from the watershed.

Abstract Dissolved organic carbon (DOC) photochemical reactions establish important links between DOC and planktonic bacteria. We hypothesize that seasonal changes in DOC quality, related to the flood pulse, drive the effects of light–DOC interactions on uptake by planktonic bacteria uptake in clear-water Amazonian ecosystems. Water samples from two ecosystems (one lake and one stream) were incubated in sunlight during different hydrological periods and were then exposed to bacterial degradation. Photochemical and bacterial degradation were driven by seasonal DOC inputs. Bacterial mineralization was the main degradation pathway of autochthonous DOC in the lake, while allochthonous DOC was more available for photochemical oxidation. We suggest that sunlight enhances the bacterial uptake of refractory DOC but does not alter uptake of labile forms. We also observed a positive relationship between sunlight and bacterial degradation of DOC, instead of competition. We conclude that photochemical reactions and bacteria complementarily degrade the different sources of DOC during the flood pulse in Amazonian clear-water aquatic ecosystems.

The influence of bauxite tailings on the growth and development of Oryza glumaepatula was studied in Lake Batata, a clear water lake of the Amazon. Lake Batata is an unusual lake because 30% of its total area was covered by bauxite tailings as the result of aluminum mining, influencing many communities and ecological processes. Changes in length, growth rates, total biomass production, density, culm diameter, net primary production and percentage of different plant organs of Oryza glumaepatula were studied for two consecutive flood pulses in natural and impacted areas of Lake Batata. The aim of this research was to test the hypothesis that the growth and development of this aquatic macrophyte is negatively affected in the areas impacted by bauxite tailings. This hypothesis was rejected because most studied parameters were higher in the impacted area, indicating that the growth and development of O. glumaepatula was not negatively affected by the presence of the bauxite tailings. The better development of O. glumaepatula in the impacted area was attributed to the less available space for germination than in the natural area. The lower density of individuals at the impacted area prevented future density dependent mortality that was observed in the natural areas and did not seem to occur in the impacted area.

The Amazon endemic quillwort Isoëtes cangae is a critically endangered submerged plant found exclusively at the Lake Amendoim, at iron rock fields in Serra dos Carajás, Eastern Brazilian Amazon. Lake Amendoim is an oligotrophic lake with high iron content and rocky to organic-clay sediment. Another aquatic ecosystem in the vicinity, Lake Três Irmãs-3, was evaluated for its limnological characteristics and the ecophysiological markers to assess whether this ecosystem is suitable for the translocation and conservation of I. cangae. Over the course of 2 years, underwater light spectra and water physicochemical characteristics were determined at both sites during dry and rainy periods. In addition, the chlorophyll a fluorescence of I. cangae was measured using Pulse-Amplitude Modulated fluorometry. Our findings reveal that the limnological dynamics of both lakes are very similar, and differences in limnological conditions between time periods were restricted to a few variables associated with climatic regime shifts (such as temperature, turbidity and total solids). We also identified that I. cangae can maintain its photosynthetic performance and reproduced in the Lake Três Irmãs-3. Our findings suggest that Lake Três Irmãs-3 is a suitable candidate ecosystem for I. cangae conservation due to the high limnological similarity between the studied lakes and the ecophysiological results.

Environmental deterioration resulting from the impact of bauxite tailings on the distribution of benthic macrofauna was studied in the Igarapé Água Fria, a side channel semi-isolated from the Rio Trombetas, near Porto Trombetas, Oriximiná, Pará, Brazil. The objective of this study was to relate the occurrence and seasonal distribution of the benthic macrofauna, especially larvae of Chironomidae (Insecta: Diptera) to the activities of a bauxite mine during the rainy season (May-June) and the dry season (October-November) in 1994 and 1995, at three sampling stations (comparing a reference site to polluted sites). Over the four collecting periods, we found low generic richness and low densities of Chironomidae. The chironomids Chironomus, Goeldichironomus, and Polypedilum predominated in the study area. The fine-grained bauxite tailings, dispersed by local currents, have covered much of the river bottom with drastic consequences for the benthic macrofauna.

Methane (CH 4 ) emissions from lakes are the largest of the emissions from freshwater ecosystems. We compile open water CH 4 emission estimates from individual lakes from all over the world and consider the three main emission pathways: diffusive; ebullitive; and storage. The relationships between emissions, environmental variables, lake characteristics and methodological approaches are investigated for the measurements from 297 lakes. We show that environmental factors, such as temperature and precipitation, act as important driving factors for CH 4 emissions, with higher emissions occurring where air temperature and precipitation are high. The diffusive flux of CH 4 was found to be positively related to dissolved organic carbon concentration. Diffusive flux is the most frequently estimated component of the total flux, while the other emission pathways are often neglected. Based on the cases where all three components of the total flux were measured (30 lakes), we estimate that measuring the diffusive emission only, and then assuming that the value obtained is a good surrogate for the total emission, would have led to a 277% underestimation of the real total flux. In addition we show that the estimation of fluxes is method-dependent with substantial differences revealed between the flux estimates obtained from different measurement techniques. Some of this uncertainty is due to technical constraints which should not be neglected, and lake CH 4 flux measurement techniques require thorough re-evaluation.

Sediment denitrification rates seem to be lower in tropical environments than in temperate environments. Using the isotope pairing technique, we measured actual denitrification rates in the sediment of tropical coastal lagoons. To explain the low denitrification rates observed at all study sites (<5 μmol N2 m-2 h-1), we also evaluated potential oxygen (O2) consumption, potential nitrification, potential denitrification, potential anammox, and estimated dissimilatory nitrate (NO3-) reduction to ammonium (NH4+; DNRA) in the sediment. 15NO3- and 15NH4+ conversion was measured in oxic and anoxic slurries from the sediment surface. Sediment potential O2 consumption was used as a proxy for overall mineralization activity. Actual denitrification rates and different potential nitrogen (N) oxidation and reduction processes were significantly correlated with potential O2 consumption. The contribution of potential nitrification to total O2 consumption decreased from contributing 9% at sites with the lowest sediment mineralization rates to less than 0.1% at sites with the highest rates. NO3- reduction switched completely from potential denitrification to estimated DNRA. Ammonium oxidation and nitrite (NO2-) reduction by potential anammox contributed up to 3% in sediments with the lowest sediment mineralization rates. The majority of these patterns could be explained by variations in the microbial environments from stable and largely oxic conditions at low sediment mineralization sites to more variable conditions and the prevalences of anaerobic microorganisms at high sediment mineralization sites. Furthermore, the presence of algal and microbial mats on the sediment had a significant effect on all studied processes. We propose a theoretical model based on low and high sediment mineralization rates to explain the growth, activity, and distribution of microorganisms carrying out denitrification and DNRA in sediments that can explain the dominance or coexistence of DNRA and denitrification processes. The results presented here show that the potential activity of anaerobic nitrate-reducing organisms is not dependent on the availability of environmental NO3-.