Aquatic Sciences最新文献

The Baikal Rift Zone (BRZ) (Lake Baikal and the Barguzin Valley, Russia) is characterized by a large number of alkaline sulfidic springs. In zones with water temperatures below 44ºC and intensive outflow, massive bacterial fouling develops, the diversity and structure of which have not been previously studied. We investigated eight hydrotherms within the BRZ, and in seven of these we found and analyzed fouling dominated by colorless sulfur bacteria of the genus Thiothrix. The fouling communities contained members of 34 bacterial phyla, with a predominance of Pseudomonadota, Bacteroidota and Chloroflexota. Bacterial diversity differed at the genus and species level and was determined by a combination of physicochemical parameters. The morphology of Thiothrix sp. bacteria in the studied hot springs was similar: they formed rosettes with numerous filaments and deposited elemental sulfur in their cells. Based on the analysis of the tilS gene encoding tRNA-lysidine synthetase, one species, Ca. T. namsaraevi, previously detected near the hydrothermal vent in Zmeinaya Bay, represented this genus in six hot springs. Only the Goryachinsk hot spring located on the shore of Lake Baikal contained several genotypes of the genus Thiothrix homologous to Ca. T. namsaraevi in gene structure, as well as to other species. The predominance of the novel Thiothrix species in hydrotherms that are geographically distant from each other within the BRZ is probably determined by specific physical and chemical characteristics of the thermal waters due to the composition of the host rocks, as well as by harsh climate conditions: freezing of sulfur fouling development zones during the winter period and reduction of solar radiation due to significant snow cover.

Lakes and reservoirs play a key role in the global carbon cycle, representing important carbon sinks and sources within the terrestrial landscape under different environmental conditions. Changes in climate and land use have led to increased air and surface water temperatures; increased occurrence and duration of hypolimnetic anoxia; and altered hydrology and nutrient loading, which have the potential to affect how these freshwater ecosystems receive and process carbon. To assess how interacting environmental drivers influence carbon cycling in lakes and reservoirs, we used a 5-year whole-ecosystem experiment to investigate the effects of variable catchment, meteorology, and in-lake drivers on epilimnetic and hypolimnetic dissolved organic carbon in a small reservoir. Using a combination of whole-ecosystem models and time-series analyses, we found that primary production and other internal sources contributed a mean of 29% (range: 7–49%) of the dissolved organic carbon in the reservoir’s epilimnion over the 5-year period. We also found that sinking epilimnetic primary production, dissolved organic carbon from the sediments, and other factors were likely important sources of hypolimnetic dissolved organic carbon, especially during periods of anoxia. Both the epilimnion and hypolimnion were found to be intermittent sinks, yet net sources, of dissolved organic carbon. Overall, water temperature was identified as the most important environmental predictor for water-column dissolved organic carbon, with higher concentrations observed under seasonally elevated temperatures during the late summer and early fall. Our results suggest that lakes and reservoirs may become larger sources of dissolved organic carbon to downstream ecosystems in a warmer, more anoxic future.

An understanding of how functional traits correspond to environmental conditions is essential for assessing species–environment associations. In this study, we examined functional trait–environment interactions affecting ostracod abundance across 122 aquatic sites in the Manisa Province (Türkiye) and identified 62 ostracod taxa, including 42 living species, four living unclassified taxa, and 16 subfossils. Using canonical correspondence analysis, we identified manganese (Mn²⁺), electrical conductivity (EC), and potassium (K¹⁺) as the most influential factors among 13 environmental variables affecting the distribution of ostracod species. Multivariate functional trait-based analyses revealed that length of the swimming setae on the second antennae (A2), uropod development, and carapace length explained a significant portion of ostracod abundance, with a fourth-corner correlation of 60%. These functional traits were found to be strongly associated with key environmental gradients, EC, dissolved oxygen, K¹⁺⁺, Mn²⁺, sediment grain size, and habitat type. Double-constrained correspondence analysis indicated that the first axis explained 35.7% of the joint functional trait–environment variance, while both the functional traits set and environmental variables set each accounted for 23.7% of the total abundance inertia. Among all functional traits, carapace length was the most influential trait explaining the species abundance that was strongly associated with Mn²⁺, pH, habitat type, and water temperature. Lotic habitats tended to support species with reduced swimming setae, while smaller-bodied species were more associated with pH, sediment grain size, and Mn²⁺ gradients. Overall, our findings demonstrate that functional traits provide meaningful insights into how ostracod species respond to environmental variation. Functional trait-based approaches therefore offer a powerful tool for understanding community assembly processes and for improving biomonitoring of freshwater ecosystems.

Oil palm plantations in Guatemala’s northern lowlands have been expanding rapidly over the past two decades, driven by large-scale conversion of tropical forests and croplands. This extensive land use change to oil palm has placed enormous pressure on the region’s freshwater ecosystems. The extent to which various land uses impact the quality of tropical stream water remains poorly understood. In this study, we evaluated the effect of different land uses on aquatic macroinvertebrates and stream water quality in the northern lowlands of Guatemala. We assessed 19 sampling sites, including at least four replicated headwater streams for each of the four dominant land uses: tropical forest, cropland, pastureland, and oil palm plantation. In each stream, we measured and analyzed physicochemical water quality parameters in both rainy and dry seasons and sampled benthic macroinvertebrates during the dry season. Subsequently, we used the resulting data to calculate two water quality indices and assess the ecological status of the sampling sites: the Water Quality Index (WQI_simp), based on physicochemical parameters, and the Biological Monitoring Working Party for Costa Rica (BMWP-CR), based on the aquatic macroinvertebrate community. Water quality scores differed among sampling sites, with sites draining forested catchments exhibiting the highest scores and those draining pastureland and oil palm plantations exhibiting the lowest. In contrast, the WQI_simp results did not differ significantly among land uses and were largely influenced by seasonal variations. Overall, water quality scores declined as the proportion of tropical forest within the watershed decreased. Oil palm plantation sites were characterized by the lowest benthic macroinvertebrates species richness and diversity, alongside higher abundance of contamination-tolerant families. These findings reveal significant negative impacts of oil palm plantations on water quality and aquatic macroinvertebrate communities, particularly when compared with forested areas and basic grains croplands. Therefore, safeguarding primary forests and basic grains cropland from further conversion to oil palm is crucial to preserving biodiversity, maintaining ecosystem functions and services, and securing food provision.

Macrophytes, which are important components of aquatic ecosystems, release nutrients and dissolved organic matter (DOM) through their decomposition that are crucial constituents of the water body’s endogenous load. The decomposition, and transformation of substances originating from this process, of four major aquatic macrophytes—lotus, coontail, yellow floating heart, and Eurasian watermilfoil—was investigated using indoor culture methods. In parallel with water quality analysis, the sources, types, and concentrations of DOM released by the aquatic macrophytes were analyzed by a combination of ultraviolet–visible spectroscopy and three-dimensional excitation-emission matrix spectroscopy. The species composition of plant-attached microorganisms was explored using 16S ribosomal RNA sequencing. The decomposition rates were fastest on the fifth day of culture, and lotus released the highest amount of nutrients and DOM. The DOM in the overlying water was dominated by humic acid, while fulvic acid was produced relatively late during decomposition and exhibited endogenous attributes. In the early stages of decomposition, the labile DOM mainly comprised fulvic acid, humic-like and protein-tyrosine-like compounds, while in the later stages of decomposition, the recalcitrant DOM mainly comprised fulvic acid, humic-like compounds, and nutrient-enrichment tracers. The dominant phyla of the plant-attached bacteria were Proteobacteria, Bacteroidota, and Firmicutes, while the dominant genera were Acinetobacter, Hydrogenophaga, and C39, which played important roles in nutrient utilization and DOM transformation. These results provide insights into macrophyte management, pollutant control, and microbe-related ecological restoration of aquatic ecosystems.

Global warming can interact with eutrophication at regional and local scales, promoting changes in the composition of microbial communities and having distinct effects on trophic levels of freshwater ecosystems. The use of experimental strategies associated with metabarcoding techniques can help elucidate the responses of prokaryotic and eukaryotic microbiota to the individual and combined effects of these stressors. In this study, we experimentally evaluated the effects of eutrophication and water warming on planktonic microbiota in terms of taxonomic composition and trophic levels (i.e., autotrophic and heterotrophic). The study was conducted in 30 mesocosms, randomly distributed in two nutrient concentrations (oligotrophic and eutrophic) and three temperature conditions based on future scenarios of global warming. Water and planktonic microbiota were obtained from an oligotrophic lake and monitored over 30 days of exposure to include combinations of temperature and nutrients. We found a strong effect of eutrophication on the composition of prokaryotic and eukaryotic microbiota. However, no isolated effects of temperature were detected for the communities. We found no effects of these two stressors on beta diversity; in other words, community dispersion remained the same across treatments. These results underscore the predominant role of eutrophication in restructuring aquatic microbial communities as assessed by DNA metabarcoding. While warming did not have strong independent effects, its interaction with eutrophication can alter the structure and composition at different trophic levels of communities.

Environmental and spatial filtering are key drivers of metacommunity assembly in streams. Their relative importance may depend on factors such as network connectivity or species’ dispersal abilities. However, studies comparing different taxonomic groups across connectivity gradients in the same area remain rare. Here, we assessed metacommunity assembly in two groups with contrasting dispersal abilities (diatoms and macroinvertebrates) in a Mediterranean catchment where connectivity is disrupted by stream flow cessation. We combined local predictors (e.g., water and habitat quality) with drying variables at local and regional scales to evaluate the role of environmental and spatial factors using variation partitioning at annual and seasonal scales. Diatoms were mainly shaped by spatial factors, while macroinvertebrates responded more to local environmental conditions. High dispersal in diatoms and ongoing input from suboptimal habitats suggest a mass-effect archetype. In contrast, macroinvertebrates showed dispersal limitation, preventing mass effects but allowing for species-sorting. Drying effects varied seasonally, with a lower influence in spring. Considering flow direction improved the explanation of diatom distributions, shedding light on drift processes. These results underscore the importance of analyzing aquatic communities independently, accounting for taxonomic and seasonal differences, particularly in dynamic systems such as temporary rivers. Multi-taxon studies incorporating seasonal variability and river network connectivity are essential to deepen our understanding of biodiversity and ecosystem functioning. Such approaches can guide conservation and management efforts in temporary rivers worldwide, which are increasingly prevalent owing to global change.

Assessing biological biomarkers is essential for evaluating the impact of environmental pollution. In this study we examine the effects of heavy metal contamination on erythrocyte genotoxicity, oxidative stress, and body condition of Perrin’s green toads (Bufotes perrini) collected from two aquatic habitats—Golestan National Park (GNP) and its adjacent agricultural area. A total of 72 toads were analyzed for concentrations of heavy metal ions, including Pb(II), Cd(II), As(V), Zn(II), Cr(III), and Cu(II), in liver tissue. The results showed significantly elevated concentrations of heavy metals in toads collected in the agricultural area compared to those collected within GNP (P < 0.05), with Zn and Cu being the primary contributors to the observed differences. Blood cell nuclear abnormalities, including micronuclei and apoptotic cells, were more prevalent in the agricultural area (P < 0.05). Additionally, increased malondialdehyde (MDA) levels, indicative of oxidative stress (P < 0.05), and a lower residual index in toads from the agricultural area were observed (P < 0.05). A significant positive correlation was found between heavy metal concentrations, nuclear abnormalities, MDA levels, and reduced body condition, indicating that heavy metal contamination negatively affects both the genetic health and physical condition of toads. Given that amphibians are bioindicators of polluted ecosystems, this study underscores the importance of physiological biomarkers in determining the pollution status of distinct habitats with different pollution levels, offering insights for conservation strategies.

Understanding fish assemblages in lentic ecosystems and the factors influencing them is crucial for effective management and conservation. Yet, data on lentic ecosystems in the Eastern Mediterranean are scarce. To bridge this gap, we conducted a comprehensive study, gathering fish data from 16 lentic Greek water bodies, including natural lakes, reservoirs, and heavily modified water bodies. Sampling was performed once per water body between 2010 and 2023, following a standardized gillnet protocol. Our study aimed to address two key questions: (1) which genera dominate fish assemblages and (2) which environmental and anthropogenic drivers shape dominance patterns. Generally, the Leuciscidae family accounted for more than 50% of the total abundance and biomass catches, with few exceptions. At the species level, a single species often dominated catches, contributing over 50% of total abundance or biomass. Non-native species, including introduced and translocated ones, were prevalent in 6 out of 16 water bodies, especially the most modified ones. Cluster analysis revealed similarities among water bodies within the same ecoregion/ichthyoregion due to high fish fauna endemism. Canonical correspondence analysis (CCA) indicated that altitude, drainage area, total phosphorus concentrations and Lake Habitat Modification Score (LHMS) were the main environmental variables explaining variation in fish family catches. Our findings underscore the influence of regional, environmental and anthropogenic factors on Greek lentic water body fish assemblages, including species introductions and hydromorphological alterations. This study contributes essential baseline data for regional conservation planning in Mediterranean inland waters.

Members of the blue-green algal genus Microcystis are widely distributed in freshwater ecosystems and frequently dominate harmful algal blooms (HABs). They are also the most notorious producers of microcystin (MC). Numerous studies have demonstrated that nitrogen (N) and phosphorus (P) nutrients are key factors controlling Microcystis growth and proliferation, yet the mechanisms by which these two elements drive toxic Microcystis bloom formation remain incompletely understood. In this review, we examine the driving factors of Microcystis blooms, nutrient inputs in algal bloom waters, the characteristics of nutrients, and the mechanisms of internal nutrient cycling. The phenomenon of Microcystis responding to N and P speciation and concentrations, and N-limited and P-limited environments in the external environment was analyzed, and the mechanisms of N and P assimilation by Microcystis and spp. their interrelationships were summarized. Finally, future research on Microcystis is proposed. Future studies should: (1) avoid experimental N and P concentrations exceeding 4.0 mg/L and 0.4 mg/L, respectively; (2) investigate the effects of different combinations of N and P on Microcystis; (3) evaluate combined effects of N and P with common lake pollutants on Microcystis; and (4) investigate N and P speciation and thresholds conducive to the succession from Microcystis-dominated blooms to beneficial phytoplankton assemblages.