International Review of Hydrobiology最新文献

During floods, sediments suspended in river water deposit on floodplains. Thus, floodplains are a key to improving river water quality. Yet, the factors that determine the amount of fine sediment that deposits on floodplains are largely unknown. Plant diversity typically increases structural diversity, whereas the vegetation structure and the structural characteristics of individual species are known to influence sedimentation. We hypothesised that species diversity, in addition to species identity, may promote sediment retention. Our study aimed to disentangle the effects of species richness and species identity, via differences in vegetation structure, on sediment retention within herbaceous vegetation patches. In a flume experiment, we investigated sedimentation on 30 vegetation patches (40 × 60 cm²). We created patches with five different species-richness levels (3, 4, 6, 8, and 11 species), each replicated six times. Species were randomly selected from 14 common floodplain species. We inundated the patches with silt- and clay-rich water and measured the amount of accumulated sediment on the vegetation and on the ground underneath it. Species richness significantly increased sedimentation underneath the vegetation (R² = 0.17). However, including species identity effects in a structural equation model, we showed that individual species' presence largely drove these effects. Alopecurus pratensis had a direct negative effect on sedimentation on the vegetation, whereas Bromus inermis and Elymus repens had indirect positive effects through an increase in total biomass (R² = 0.42). Elymus repens had a direct negative, and Urtica dioica a direct positive effect on sedimentation underneath the vegetation (R² = 0.38). Our results indicate that selecting the most effective species, rather than as many species as possible, may have the greatest benefits for promoting sedimentation. Overall, we conclude that floodplain management that aims to increase sediment retention should alter the vegetation structure of meadows by increasing vegetation biomass.

The giant European catfish, Silurus glanis (total length = 200 cm; total weight ≈ 80 kg) was caught downstream of Iron Gate II hydropower dam (Danube River, 863 rkm) and tagged with an ultrasonic transmitter (V16TP; Vemco Ltd.) equipped with depth and temperature sensors. Changes in catfish diving behavior and temperature exposure were monitored over a period of roughly 2 years. Transmitter detections were recorded by nine autonomous receivers (VR2W, installed in 2015 between Serbia and Romania, as well as near Romanian shiplock and upstream Romanian turbines). The first signals were recorded on April 28, 2015 and the last on February 13, 2017. Altogether 59,355 and 59,175 detections of the catfish depth and water temperature were recorded, respectively. The greatest number of signals were recorded by the two receivers closest to the location where the catfish was caught, 72.3% and 27.1%, while only 0.6% of signals were recorded by other receivers. The mean catfish depth was 8.4 m, while minimum and maximum depths were 1.2 and 16.2 m. Results obtained showed that this catfish exhibited high site fidelity, while changes in depth at certain periods are possibly related to its search for prey and upstream migration during the spawning period. Hydropower dam and shiplock were obstacles on its migration upstream and telemetry studies could ensure habitat requirements and meet the development of restoration and conservation strategies for the fish resources in the future.

Morphological alteration of shorelines and eutrophication both affect the biological integrity of European lakes. These pressures, often acting simultaneously, are difficult to tease apart. In this study, we related the number of taxa with specific habitat preference to habitat complexity across lakes of varying nutrient state. Habitat complexity at morphologically altered shorelines was significantly lower than at unaltered sites across trophic categories. A generalised linear mixed-effects model showed decreased number of taxa with specific mesohabitat preference at morphologically simplified sites in oligotrophic and mesotrophic, but not eutrophic lakes. These results suggest: (1) an antagonistic interaction between the effect of nutrient enrichment and morphological alterations on lake littoral communities and (2) the number of macroinvertebrate habitat specialists could potentially be used to assess the effects of structural simplifications of shorelines in lakes of low to medium nutrient status. We conclude that the use of functional traits approach in aquatic ecology should foster better understanding of stressor–response relationships for combined effect of multiple stressors.

Anthropogenically-induced stressors such as eutrophication and pollution cause fundamental changes of environmental factors in many coastal ecosystems worldwide and may subsequently alter the sex structure of bivalve populations. Such a change of sex structure was observed in the mussel Mytilus galloprovincialis at the Black Sea coast of Crimea, where the sex ratio shifted toward male mussels. This pattern may be caused by the sex inversion in females, higher female mortality, and their falling off to the bottom. Experiments with cultivated mussels M. galloprovincialis were conducted in natural and laboratory conditions to identify the reasons for this phenomenon. The inversion of the mussel sex proceeds in one direction: from females to males. The change of sex occurs under the influence of environmental factors during the post-spawning restructuring of gonads. Such factors can be adverse hydrological and hydrochemical conditions; environmental pollution; food availability; age and size of mollusks. The sex inversion of mussels in the polluted water area was 20% higher than in the relatively clean water of the mussel farm. The higher mortality of mussel females (69%) in the polluted area as compared to the clean one (19%) was also observed. In a laboratory experiment, the mortality level of females was 34% higher than that of males. The sex ratio on the farm, 1:2.9 (♀:♂), and on the bottom under the farm, 2.6:1 (♀:♂), was found, and the predominance of females at the bottom under the farm was noted. A bias in the sex structure in one direction—from females to males—can have economic implications in aquaculture as well as ecological significance. The increasing anthropogenic impacts on natural mussel populations can cause abnormal bias of sex ratio.

Biological invasions are one of the major threats to the integrity of aquatic ecosystems worldwide. We examined the influence of reservoirs, availability of food resources, abiotic resistance, and biotic resistance on the distribution of Daphnia lumholtzi, a non-native cladoceran that is spreading through habitats in the upper Paraná River basin, Brazil. We sampled 48 sites distributed in four habitat types: reservoirs, lakes, tributaries, and the main river. D. lumholtzi densities were higher in reservoirs than in other habitat types (lentic and lotic). We found a significant correlation between a higher density of D. lumholtzi and the distance from reservoirs to the other sampling points. Additionally, a relationship between D. lumholtzi and types of environments was noted. It is known that cladocerans, including D. lumholtzi, have a reduced swimming ability, which makes it difficult for them to overcome currents and consequently establish or maintain large populations in lotic environments. Further research is needed to identify other factors responsible for the species' occurrence in this system and to determine the possible effects this species may have on the native community.

Due to Daphnia's cosmopolitan distribution and the co-occurrence with various predators, it has developed highly diverse antipredator defenses. In response to chemical cues of Chaoborus larvae, a major predator, neckteeth are induced in vulnerable juvenile instars of Daphnia pulex. As only early juvenile instars of D. pulex are vulnerable to predation by Chaoborus sp., increased developmental time extends the time span that D. pulex is in the vulnerable size, and thus increases the risk of being preyed upon. Here, we hypothesize that increased time spent in vulnerable instars leads to a higher degree of neckteeth formation in vulnerable D. pulex instars. To test this, we created a gradient of growth conditions for Daphnia that would cause an increase in developmental time by means of decreasing the temperature or increasing the proportion of dietary cyanobacteria in separate experiments. We determined the body size during the juvenile instars and calculated the time spent in vulnerable instars. Correlations of neckteeth induction to times spent in vulnerable instars were significant for the data set of the temperature experiment and the combined data set, but not for the data set of the cyanobacteria experiment. However, we cannot exclude that an increased bacterial degradation of the kairomone at elevated temperatures has contributed to this relationship, and dose–response curves revealed that neither the sensitivity to the kairomone nor maximum neckteeth induction in D. pulex was reduced at the elevated temperature. Our results suggest that neckteeth induction is affected by the time spent in vulnerable instars, based on the factors temperature and dietary toxic cyanobacteria, but its universal validity needs to be tested further by including other factors.

Apocorophium lacustre (Vanhoffen, 1911), which is a native brackish amphipod species of the North Atlantic and Baltic coasts, was recorded in the upper Oder River for the first time in 2017. Before that, only alien amphipod species had been found in this area. The aims of the study were to describe the distribution pattern of A. lacustre in the upper Oder River catchment, to investigate the composition and structure of the amphipod assemblages against the background of the habitat conditions and to provide a genetic identification of the species using DNA barcodes. In total, 16 sites were studied. A. lacustre was recorded in 14 of them. It was not found at one site in the Oder River and at one location in the lower Klodnica River. A. lacustre outnumbered the other amphipods in the Oder, in the mouth section of the Klodnica and at one site in the Gliwice Canal. The alien species Gammarus tigrinus (Sexton, 1939) was dominant in the amphipod communities at the southernmost site in the Oder River, in the Klodnica Canal, and at most sites along the Gliwice Canal. In the Klodnica River, another alien species, Dikerogammarus villosus (Sovinsky, 1894), was dominant in the amphipod fauna at two sites. Though the density of A. lacustre was high in the Oder River, it was much lower in both the canals and the Klodnica River. In our study, the depth and river velocity both contributed to the distribution of this species.

Hydrodynamic processes can lead to the accumulation and/or dispersal of water column constituents, including sediment, phytoplankton, and particulate detritus. Using a combination of field observations and stable isotope tracing tools, we identified how hydrodynamic processes influenced physical habitat, pelagic communities, and food web structure in a freshwater tidal system. The pelagic habitat of a terminal channel differed spatially, likely aligning with differences in hydrodynamics. Three zones that we classified by exchange with downstream habitat had distinct water quality characteristics, supported different densities of zooplankton and nekton, and exhibited disparate support from benthic and pelagic trophic pathways to pelagic consumers. Hydrodynamically driven zones and their emergent characteristics appeared sensitive to hydrology, as elevated runoff was correlated with a shift in hydrodynamic habitat and organismal distributions. The results of our study highlight the relationship between hydrodynamic processes, biological responses, and climate, and suggest that understanding the physical process can improve understanding of pelagic habitats and communities.

In theory, the phytoplankton community of freshwater ecosystems with low concentrations of dissolved inorganic nitrogen (DIN) can obtain this element by atmospheric nitrogen (N₂) fixation. This process could explain the dominance of cyanobacteria in tropical reservoirs, yet is rarely quantified in these systems. Assessing the factors related to N₂ fixation can assist in the management of cyanobacterial blooms. Our study characterized environmental factors related to N₂ fixation in Brazilian tropical reservoirs with contrasting trophic states, and defined quantitative thresholds for water chemistry and physical characteristics that stimulated N₂ fixation. We used field assays with ¹⁵N for estimating N₂ fixation rates by phytoplankton. The highest rates normalized by chlorophyll-a (maximum of 143 × 10⁻⁴ μg-N μg-Chl-a⁻¹ h⁻¹) coincided with eutrophic conditions and presence of diazotrophs. Receiver operating characteristic (ROC) analysis provided significant thresholds for water temperature (≥22°C), soluble reactive phosphorus (SRP) (≥3.0 μg-P L⁻¹), total phosphorus (TP) (≥20.5 μg-P L⁻¹), DIN:SRP (≤487) and DIN:TP (≤82) molar ratios, chlorophyll-a (≥12 μg L⁻¹), and total suspended solids (≥4 mg L⁻¹). Censored regressions confirmed that temperature, chlorophyll-a, and phosphorus were important predictors of N₂ fixation rates. In general, the N₂ fixation rates determined in this study were lower than those found for temperate reservoirs. However, the temperature threshold of 22°C or above, identified in our analysis, suggests that phytoplankton have the potential to fix N₂ throughout the year in tropical reservoirs. Our results suggested that phosphorus is the main nutrient controlling the rates of N₂ fixation when N₂-fixing cyanobacteria were present. Phosphorus abatement is, thus, crucial for managing the trophic state and controlling N₂-fixing cyanobacteria in these ecosystems.