Aquatic Sciences最新文献

The chironomid community is a key component of lacustrine systems, with their larvae acting as a potential pathway of trace elements from benthic substrates to higher trophic levels. In Lake Moreno Oeste, a northern Patagonian lake (Argentina), arsenic (As), a nonessential and toxic metalloid, and zinc (Zn), an essential metal, were seasonally measured in several substrates (submerged leaves of riparian vegetation, macrophytes, and sediment from vegetated littoral to non-vegetated deeper zones), and in their associated chironomid assemblages, to assess metal bioavailability by examining larval bioaccumulation and excretion in relation to their functional feeding habits. The highest As concentrations were found in sediment from littoral vegetated areas and deep zones, while the highest Zn values were recorded in Myriophyllum sp. leaves. Functional feeding strategies influenced bioaccumulation patterns: collectors recorded higher As levels (suggesting sediment ingestion as the main As pathway), and predators and shredders showed elevated Zn values (associated with its environmental availability and specific larval requirements). In feces from purged larvae, both elements reached their maximum excretion factors in biological substrates (Myriophyllum sp. and submerged riparian leaves); however, As concentrations exceeded those measured in both substrates and larvae, while Zn surpassed values in substrates but remained lower than in larvae. Our findings explore chironomid assemblages as vectors of trace elements from benthic substrates to upper trophic levels in the food web, highlighting their potential as sensitive indicators of metal(loid) bioavailability, even in low-impact systems.

In recent years, the interplay between emerging human activities (extensive flood prevention, water environment management, and ecological restoration) and traditional human activities (industrialization, urbanization, and intensive agricultural practices) has posed challenges to the conventional understanding of phosphate source structures and phosphate loads in watersheds. This study focuses on the Fuyang River, a small watershed in Northern China, to investigate the current impact of complex human activities. By utilizing phosphate oxygen isotopes (δ¹⁸O_P), we delineate the contributions of various phosphate sources and loads across different seasons in the Fuyang River watershed. The results indicate that the total phosphate load at the watershed scale is higher during the rainy season (241.42 kg/day) compared with the arid season (154.93 kg/day). During the rainy season, tributary inflows contribute the most to the phosphate load (93.78 kg/day, 38.8%), followed by sediment (56.39 kg/day, 23.4%). In contrast, during the arid season, the main contributors are tributary inflows (55.62 kg/day, 35.9%) and effluents from wastewater treatment plants (39.1 kg/day, 25.2%). Significant differences in phosphate source structures and load contributions are observed across different administrative regions, reflecting the varied industrial, urbanization, and agricultural activities. Urban and suburban sections display distinct phosphate source structures and load patterns owing to differences in human activities and environmental management practices. This study advances the application of δ¹⁸O_P at the watershed scale and provides valuable insights into the multiscale phosphate source structures and loads under the influence of complex human activities.

Graphical Abstract

Warming temperatures and nutrient pollution are increasingly affecting aquatic ecosystems, making it crucial to understand their combined impacts on food webs. Despite substantial research on the individual effects of these environmental stressors, there remains a notable gap in knowledge regarding their synergistic effects, particularly those on the production of essential fatty acids in periphyton, an important trophic base of aquatic food webs.We therefore conducted a factorial microcosm experiment in which we manipulated phosphate (PO₄-P) levels and temperature to quantify their interactive effects on the content of periphyton omega-3 (ω3) long-chain polyunsaturated fatty acids (LC-PUFA), in particular eicosapentaenoic acid (EPA, 20:5ω3), and their precursors α-linolenic acid (ALA, 18:3ω3) and linoleic acid (LIN, 18:2ω6). Our results indicated that phosphorus enrichment generally increased periphyton ω3 LC-PUFA content, whereas elevated temperature offset phosphate-driven gains in EPA content. At 25 °C, EPA content was higher at the high PO₄-P enrichment level than at the low PO₄-P level; at 30 °C, EPA content at the high PO₄-P enrichment level converged to that observed at 25 °C under the low PO₄-P condition, revealing a negative temperature × phosphate interaction. Such reductions in periphyton ω3 LC-PUFA content are likely to degrade basal food quality and undermine the stability of the trophic base of aquatic food webs. The results of this study underline the complex interplay between phosphorus enrichment and environmental warming on periphyton. By showing that a high level of PO₄-P increased EPA content at 25 °C, but not at 30 °C, we have identified a thermal limit to nutrient benefits and call for joint temperature × phosphate targets to sustain basal ω3 LC-PUFA supply.

Ponds are a large source of atmospheric methane (CH₄), a potent greenhouse gas, resulting from the net balance between input from sedimentary methanogenesis and removal by CH₄ oxidation (MOX). Here, we test whether methanogenesis pathways (acetoclastic or hydrogenotrophic) and MOX might differ between clear-water (macrophyte-dominated) and turbid-water (phytoplankton-dominated) ponds. We measured the ¹³C/¹²C ratio of CH₄ (δ¹³C-CH₄) from gas trapped in bubble traps, from bubbles deliberately released by the perturbing sediments, and in dissolved CH₄ in the water column in four urban ponds in Brussels, Belgium (Leybeek, Pêcheries, Tenreuken, Silex). In summer, the δ¹³C-CH₄ values of sediment bubbles indicated that the hydrogenotrophic methanogenesis pathway appeared to be more important in clear-water (macrophyte-dominated) ponds (Leybeek and Pêcheries), whereas the acetoclastic methanogenesis pathway appeared to be more important in turbid-water (phytoplankton-dominated) ponds (Tenreuken and Silex). The δ¹³C-CH₄ values from bubble traps indicated a seasonal shift from acetoclastic methanogenesis pathway in spring–summer to hydrogenotrophic methanogenesis in fall. The δ¹³C-CH₄ of dissolved CH₄ indicated higher rates of MOX in turbid-water ponds (Leybeek and Pêcheries) compared to clear-water ponds (Tenreuken and Silex), with an overall positive relation with total suspended matter and chlorophyll-a concentrations. The presence of suspended particles likely enhanced MOX by reducing light inhibition of MOX and/or by serving as substrates in the water column for attached methanotrophic bacteria. MOX represented ~ 80% of the total dissolved CH₄ removal from the water column (MOX plus diffusive emission to the atmosphere) in the turbid-water ponds (Leybeek and Pêcheries) and < 60% in the clear-water ponds (Tenreuken and Silex). Our results suggest that shifts from clear- to turbid-water ecological states due to eutrophication may change CH₄ production pathways (with a higher contribution of acetoclastic versus hydrogenotrophic methanogenesis) and enhance dissolved CH₄ removal by MOX in the water column.

Trait-based approaches have been widely employed to advance the understanding of the relationships between species diversity and ecosystem functioning. However, limited knowledge exists regarding how shifts in nutrient levels influence functional traits dynamics during the colonization process of periphytic algae. In this study, it is hypothesized that nutrient availability drives algal colonization through functional trait assembly, and that algal functional diversity is shaped by substrate geometry. A 13-week in situ experiment was conducted to evaluate the colonization of periphytic algae on two types of artificial substrates (perforated and unperforated granite) in both eutrophic and oligotrophic lakes using a trait-based approach. The results of this study revealed that in the nutrient-rich, light-constrained lake, colonization was initially dominated by small-celled, nonattached taxa, followed by stalk-attached and subsequently filamentous taxa; taxa forming arbuscular or irregular colonies and those possessing phycocyanin predominated throughout most of the colonization period. In contrast, in the nutrient-deficient, light-sufficient lake, colonization was initiated by large-celled, adnate-attached, unicellular species, succeeded by filamentous taxa, with nitrogen-fixing taxa contributing substantially to the community. Across substrate types, significantly higher taxonomic and functional diversities of periphytic algae were observed on perforated substrates compared with unperforated substrates in the oligotrophic lake, whereas no such pattern was detected in the eutrophic lake. These findings demonstrate that incorporating functional traits into periphytic algae research can substantially enhance the understanding of how nutrients and substrate characteristics shape key ecological functions during colonization processes.

Differences in lability between allochthonous and autochthonous dissolved organic matter (DOM) can drive changes in bacterial community composition and metabolism. To assess riverine inputs versus in situ production as DOM sources, we measured optical properties in Bellingham Bay, Washington (USA) over 1 year (n = 38 measurements). Optical indices were consistent with riverine inputs as the primary source of chromophoric DOM (CDOM) throughout the year. Three components were identified by parallel factor analysis of the excitation–emission matrices (EEMs). The major terrestrial humic-like component from riverine inputs dominated all samples. A secondary component was attributed to microbial degradation of the terrestrial humic material. A minor protein-like component was present in 70% of samples. The highest absorption coefficient at 300 nm (a300; increases with increasing chromophoric DOM amount) and lowest spectral slope (S; 300 to 400 nm; higher for more photochemically and biologically processed material) occurred in the fall with increased river discharges. This increase was attributed to high levels of freshly-produced terrestrial CDOM washing in from the watershed with the first rainfall after the summer dry season. S occasionally increased with low river discharges, which was attributed to the influence of seawater. There was evidence of sporadic instances across all seasons when in situ production was significant. Variability in the optical parameters suggested monthly sampling would miss events with increased CDOM levels and indicators of different CDOM sources. Impacts of climate change on rainfall, river discharges and hydrodynamics may change the relative contributions of riverine and in situ sources, affecting the biological community.

Human activities such as peatlands drainage and global climate change have caused fluctuations in water table depth in subtropical mountainous Sphagnum peatlands of central China. However, the ecological impacts of these water table fluctuations remain unclear. This study conducted a 10-month microcosm experiment with three dominant plant communities collected from Dajiuhu peatland under eight water table treatments. The experiment aimed to investigate the effects of water table depth, and fluctuations thereof, on Sphagnum palustre growth and plant community succession, and to elucidate the underlying mechanism. A stable water table above –10 cm proved optimal for S. palustre. Both fluctuating and sustained low water tables reduced its productivity by disrupting nutrient ratios (potassium excess) and impairing photosynthesis (oxidative stress). Community responses diverged: Carex heterolepis – S. palustre communities maintained stability except under –10 cm drawdown, which increased vascular plant richness; Sanguisorba officinalis – S. palustre communities showed enhanced productivity and diversity at +10 cm water table rise but reduced richness and diversity under low (−20 cm) and fluctuating (0 to −20 cm) conditions; Polytrichum commune + S. palustre communities underwent succession reversal to Polytrichum dominance under (−10 to − 30 cm) and low (− 30 cm) water tables. Significant fluctuations in water table depth, particularly sustained drops or large-amplitude oscillations, can reduce S. palustre productivity and trigger a state shift in plant communities toward vascular plant invasion or desiccation-tolerant moss dominance, ultimately impacting plant community succession and ecological functions.

This study explores the application of strontium (Sr) isotope ratios (⁸⁷Sr/⁸⁶Sr) as geochemical tracers to understand hydrological connectivity and anthropogenic influences in a geologically diverse Alpine river catchment encompassing regions of Austria and Slovenia. Focusing on the Mur River and its tributaries, water samples were collected across 45 sites during three hydrological regimes to capture seasonal and spatial variability. In total, 28 tributaries were sampled to evaluate their influence on the isotope composition of the main river. Isotope analyses using multi-collector inductively coupled plasma mass spectrometry, supplemented by geospatial mapping and multivariate statistics, were combined with measurements of 26 elemental concentrations to investigate land–water interactions and human impacts. The results demonstrate substantial temporal and spatial variability in ⁸⁷Sr/⁸⁶Sr ratios (ranging from 0.70853 to 0.71322), reflecting both geological heterogeneity and varying tributary inputs. A preliminary aquatic isoscape was developed, enabling the monitoring of connectivity and the impacts of geological and human influences under varying flow regimes. Tributaries, such as the Mürz River, significantly modulate isotope signatures in the main channel, often overriding local geological signals. The application of isotope pattern deconvolution revealed a contribution of 17% from the Mürz River to the Mur River’s isotope signature downstream of the confluence. Correlations between ⁸⁷Sr/⁸⁶Sr and metal concentrations further suggest the utility of ⁸⁷Sr/⁸⁶Sr as a proxy for source identification and anthropogenic influence assessment. By constructing a preliminary strontium isoscape for the region, this research provides novel insights into riverine connectivity, catchment-scale processes, and ecosystem dynamics. The integration of isotope data contributes to interdisciplinary understanding across geological, chemical, and ecological boundaries, and supports the development of isotope-based tools for sustainable aquatic system monitoring and management, including potential applications in fish ecology and habitat tracking.

Graphical abstract

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.