Hydrobiologia最新文献

Freshwater ecosystems have been severely disturbed in recent years. However, our understanding of the ecosystem-level changes within freshwater food webs under complex disturbances is still limited. To address this knowledge gap, we took Dongting Lake as a case study, which has undergone significant environmental changes. We established Ecopath models for Dongting Lake in 1997, 2013, and 2021, and validated them using stable isotope-determined trophic levels. Our focus was on describing the structure and maturity of the ecosystem, identifying key species, and quantifying energy flows. The verification result showed that the models were acceptable. The model outputs revealed a significant decline in the average energy transfer efficiency of Dongting Lake. The food web maturity of Dongting Lake decreased and subsequently increased in these three representative periods. Simultaneously, the food web structure was successively simplified over time. Moreover, the identification of keystone species revealed the significance of Zooplankton, Other fish, Silurus asotus, and Molluscs within the ecosystem. Overall, our results offer a scientific underpinning for the effective management and conservation of freshwater ecosystems.

To evaluate the effect of glyphosate, 2,4-D, and their combination on daily dissolved oxygen saturation percentage (DO%) in freshwater, two separate outdoor mesocosm experiments were performed. The experiments were conducted under contrasting conditions: one in clear mesotrophic status lasting 23 days, and the other in organic turbid eutrophic conditions lasting 21 days. Single concentrations were applied as commercial formulations at two levels. Samples of phytoplankton (micro + nano, picoeukaryotes, picocyanobacteria), mixotrophic algae, and heterotrophic bacteria were analyzed at four sampling dates. Increases in DO levels were consistently observed in both clear and turbid systems treated with glyphosate, either alone or in combination with 2,4-D, suggesting that DO is a sensitive indicator. DO increased in all glyphosate treatments. DO increases reflected different changes in phytoplankton communities, increasing with micro + nano phytoplankton abundance in the clear experiment but with increased picocyanobacteria in the turbid. In contrast, 2,4-D reduced DO levels, but only in the turbid system, where micro + nano phytoplankton abundance decreased. The clear system showed greater resilience by restoring DO levels before the turbid one. Mainly additive effects of the herbicide mixture were observed on dissolved oxygen levels (DO%), but a distinct synergistic decrease was detected within turbid systems, underscoring the importance of considering turbidity as a contributing factor in the freshwater impacts of herbicides.

Aquatic invasive species can affect food web structure, native fish growth, and production, depending on the traits of the invasive species and the pre-invasion conditions of the ecosystem. Thermal tolerances and behavioral traits can further influence differential exploitation of resources shared between native and invasive species. An unauthorized introduction of redside shiner (Richardsonius balteatus) into reservoirs in the Upper Skagit River, Washington, USA caused concern of potential competition, decreased production, and recruitment of rainbow trout (Oncorhynchus mykiss). We combined bioenergetics modeling and stable isotope analysis with field data to quantify consumption demand of native and invasive fishes and related consumption to the availability of key zooplankton prey. Per capita consumption on Daphnia by redside shiner was low; however, their high abundance imposed considerable demand on prey resources in Ross Lake. Although monthly consumption demand by the fish community was less than 50% of the monthly production and biomass of Daphnia in Ross Lake, the current Daphnia densities and growth of rainbow trout were considerably lower than before the invasion. These reductions correspond to lower annual consumption of Daphnia. Our study provides insight on mechanisms that influence food web impacts of an invasive omnivore in cold-water reservoirs.

Temporary rivers are aquatic ecosystems that alternate periods of water flow with dry periods. Diatoms are a group of unicellular microalgae with a high colonizing ability, but little is known about their responses to drying. We carried out different resistance and resilience experiments to evaluate temporal and spatial dispersal capacity of diatoms during the dry period. The resistance was tested experimentally by rehydrating dried biofilms and sediments from temporary rivers, whereas resilience was tested by installing artificial mesocosms along a dry river section. Disconnected pools were also sampled to evaluate their propagule emission capacity. In turn, dogs from the area were sampled to test potential zoochory dispersal capacity. In the resistance experiment, we found living diatoms in all the rehydrated sediments but not in biofilms. Diatoms with mobility traits, high ecological plasticity, and resistance spores presented high, along with typical soil diatoms. In the resilience experiment, all mesocosms hosted living diatoms, which were low-profile, pioneering, and small species. Diatoms found in the mesocosms were also common in the disconnected pools, underscoring the potential role of the latter as a propagule emission zone. Dogs' paws also had living diatoms, which evidences that wild fauna could potentially act as passive diatom vectors.

In previous studies, cyanobacteria have been associated with embryonic toxicity, including teratogenic effects, though the underlying mechanism remains unclear. Here, we explored differential responses to Microcystis aeruginosa by endangered Sinocyclocheilus grahami and introduced Pseudorasbora parva from Lake Dianchi, China. We conducted fish embryo test under Microcystis aeruginosa exudates (MaE) exposure, and developmental responses, cell structure and metabolism were measured. We observed increased malformation, mortality rate and decreased fertilization, hatching rate and heartbeats in both fish species when exposed to MaE. Transmission electron microscopy revealed damage to brain cells of both species. Transcriptomics revealed that mitochondria were a MaE target in both species, with impairment occurring to respiratory enzyme complexes and oxidative stress enzymes. Oxidative stress induced by MaE was mainly associated with hydrogen peroxide, though the underlying mechanism differed: In Sinocyclocheilus grahami, hydrogen peroxide increased owing to its decreased degradation, whereas in Pseudorasbora parva, it increased owing to increased synthesis. All results were consistent in that the Sinocyclocheilus grahami was more vulnerable than Pseudorasbora parva to MaE exposure. Our work highlights that MaE may harm fish in species-specific ways and contribute to replacement of native by invasive species in Lake Dianchi.

The Host-Habitat Continuum Concept (HHCC) predicts changes in the proportions of freshwater mussels with different life-history strategies (i.e., equilibrium, periodic, opportunistic) along stream gradients and between habitat types. We analyzed mussel assemblages from a large, diverse geographic area to test predictions of the HHCC and to assess if species richness, abundance, and host strategy patterns change predictably among different habitats (lakes, reservoirs, and streams) and stream sizes. Species richness and abundance were low in lakes, reservoirs, and small streams and increased with stream size. Mussels use various strategies to attract fish hosts and the proportion of mussels that release conglutinates (i.e., packets of glochida) increased with stream size and the proportion that use lures decreased. Our results supported predictions of the HHCC: greater proportions of opportunistic or periodic strategists in lakes, reservoirs, and small streams and a shift to equilibrium strategists in larger streams. Patterns differed slightly in lakes and reservoirs with a higher proportion of periodic strategists than expected. Not all watersheds followed predictions of the HHCC likely due to the effects of biogeography and anthropogenic impacts. These life history strategy patterns can be used to test the expected composition of mussel communities and to detect possible anthropogenic impacts.

Strong ecological and economic impacts of zebra and quagga mussels (Dreissena polymorpha and D. rostriformis bugensis) on the invaded waterbodies require timely and reliable estimates of their population densities. However, samples collected with conventional methods take years for processing. In this study, we analyzed video recorded using a Benthic Imaging System to assess quagga mussels distribution and density in near-real time (during a typical 2 week cruise aboard EPA research vessel Lake Guardian) in Lake Michigan in 2021 and in Lake Huron in 2022 and compared that data with the Ponar grab samples collected at the same sites. We found that videography could be a reliable and useful addition for dreissenid monitoring, especially on hard substrates where bottom grabs are not efficient. Analysis of dreissenid dynamics since the late 1990s revealed a strong increase in mussel density in the shallowest polymictic zones of both lakes, suggesting local boom and bust dynamics. In the deepest zone of Lake Michigan there was a further increase in quagga mussel density coincided with the ninefold decline in Diporeia density. Declines in Diporeia were also recorded in the main basin and in Georgian Bay of Lake Huron.

Owing to increased awareness of the value of long-term ecological studies, there have been numerous calls for long-term data. Natural lakes and reservoirs provide ecosystem services and serve as sentinels of change but differ in origin, water movement, and location. We conducted a meta-analysis of study duration for lake and reservoir studies from 1975 to 2015 (6362 studies were initially identified, and 801 met study criteria). Study duration increased among longer studies (> 0.5 quantile) with increases of 20 years for the highest (0.9) quantile, and there were no changes among short-term studies. Increased study duration was inversely related to number of focal areas or metrics (e.g., phytoplankton, zooplankton, vertebrates) with few focal areas or metrics (< 2 metrics) indicating few focal areas for long-term studies. Surprisingly, despite continued construction of reservoirs, the ratio of studies of lakes to reservoirs was 5 to 1 with no change over time, with the dearth of data on reservoirs making it difficult to characterize long-term trends. Increased duration in high quantiles concurrent with static duration of short-term studies suggests limnologists have fundamentally altered the way they approach questions that are influenced by study duration, but also that gaps remain in multifaceted studies and in reservoir studies.

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.

Lake restoration by biomanipulation or phosphorus fixation has been commonly applied methods to improve the ecological status of lakes. However, the effects of lake restoration on food-web dynamics are still poorly understood, especially when biomanipulation and nutrient fixation are used simultaneously. This study investigated the combined effects of a 70% fish removal (mainly roach (Rutilus rutilus Linnaeus, 1758) and bream (Abramis brama Linnaeus, 1758) and Phoslock® treatment on fish trophic ecology in Lyngsø (area: 9.6 ha, mean depth: 2.6 m), Denmark. The lake restoration resulted in decreased nutrient levels, increased water clarity, and increased coverage of more structurally complex submerged macrophytes. Following lake restoration, significant changes in diets of the dominant fish species were observed. Stomach content analyses of roach and perch (Perca fluviatilis Linnaeus, 1758) revealed significantly reduced detritus utilization and increased foraging on macrophytes and macrophyte living invertebrates. Results from stable isotope mixing models indicated a shift from littoral benthic to more pelagic food resources by the dominant fish species. Our findings provide further evidence that lake restorations can lead to substantial changes in lake food webs and fish communities, thereby potentially facilitating a shift toward an ecological state resembling the pristine reference state, less influenced by anthropogenic factors.