Limnology and Oceanography最新文献

Turbulence plays a key role in sediment mobilization in intertidal zones. Prior laboratory studies have explored turbulent kinetic energy (TKE) under the influence of waves and currents, but the extent to which an idealized laboratory setting translates to natural environments remains unclear. Key questions persist in application to field conditions, including the relative contributions of waves and currents to TKE, and the impact of vegetation flexibility. To address these gaps, this study made field observations of waves, currents, and TKE across the intertidal zone of Chongming Dongtan Wetland in the Yangtze Estuary. Hydrodynamic conditions differed between the mudflat and salt marsh, with the magnitude of current velocity exceeding wave velocity on the mud flat, but the reverse being true within the marsh. As a result of this shift, on the mudflat, TKE was mainly generated by currents, and in the marsh, TKE was mainly generated by waves. Additionally, TKE on the mudflat was associated with bed shear production, but within the salt marsh was mainly produced through the interaction between waves and vegetation. Finally, the influence of vegetation flexibility on vegetation-generated TKE was described by a new model that incorporated the plant Cauchy number ($��\mathrm{Ca}�$) and vegetation-to-wave-excursion length ratio ($��L�$) as descriptors for vegetation motion. The inclusion of vegetation motion significantly improved the prediction of TKE within the salt marsh canopy, which can contribute to more accurate coastal modeling, improving coastal zone management and research.

Marine mass mortality events (MMEs) are a growing source of concern globally. Affecting diverse marine ecosystems, they frequently cause significant ecological disruptions, often leading to large-scale ecological shifts. However, in contrast to terrestrial MMEs, most marine mortalities likely occur undetected, particularly in cryptic and infaunal taxa. Here, we present the first documented reports of irregular echinoid mass mortalities from the Eastern Mediterranean Sea—a region at the forefront of ocean warming and anthropogenic pressure. Compiling ecological, morphometric, molecular, and remote-sensed environmental data, we reconstruct a 14-yr history (2011–2024) of MMEs involving the key infaunal bioturbating echinoids of the genus Echinocardium. We analyzed environmental parameters, namely sea surface temperatures, chlorophyll a concentrations, river discharge, and wave intensity, in the weeks preceding five MMEs and analyzed skeletal remains to explore the potential drivers of mortalities. We show that these events are neither rare nor stochastic but rather recurring and spatially structured—spanning hundreds of meters and positioned at the outlet of major rivers, likely driven by cumulative environmental and human stressors. By revealing patterns in taxa often overlooked in marine monitoring, this work highlights the urgency of assessing ecological stability in sedimentary ecosystems. We highlight the need for implementing long-term monitoring and improved environmental assessments, at both national and regional scales, to include benthic infaunal communities—particularly in rapidly warming regions like the Eastern Mediterranean.

To elucidate the impact of changing water column hypoxia (WCH), defined as dissolved oxygen concentration < 63 μM, on sediment biogeochemical processes, we conducted a fine-scale investigation on the partitioning of major organic carbon (C_org) mineralization processes, the reduction of manganese (MnR), iron (FeR) and sulfate (SR), and the resulting Mn–Fe–S–P dynamics at two geochemically contrasting coastal sites with different manganese content. At the manganese-rich site with moderate WCH conditions, MnR and FeR dominated C_org mineralization in surface sediments, comprising up to 87% (0–1 cm depth) and 88% (1–2 cm depth) of C_org mineralization, respectively. In particular, the reoxidation of Fe²⁺ to Fe-oxides coupled to abiotic MnR in the surface sediments induced P adsorption to Fe(Mn)-oxides, thereby suppressing benthic P release. In contrast, at the relatively organic-rich and sulfidic site with severe WCH, SR comprised up to 87% of the C_org mineralization, and enhanced HS⁻ production stimulated benthic P release. Moreover, the impact of WCH on the anoxic sediment condition persisted longer even after the termination of WCH, implying that the spatial–temporal expansion of WCH ultimately grants sulfidic sediments a role as a chronic source of P in most coastal ecosystems. Our results, combining fine-scale C_org mineralization rate measurements with comprehensive geochemical inventory analysis, provide crucial information to elucidate cause-effect relationships behind observed phenomena on the distributions and flux of elements in coastal environments where WCH is expanding due to climate change and excessive human activities.

Urban ecosystems are structured by multiple anthropogenic stressors, yet despite the increasing extent and rate of urbanization worldwide, the ecological consequences of excessive road salt application and other urban phenomena remain poorly resolved. To advance understanding of these drivers and their effects on aquatic ecosystems, we collected zooplankton and associated environmental data from 50 permanent stormwater management ponds in Brampton, Canada. Generalized linear regression analysis revealed that zooplankton richness and diversity were strongly influenced by chloride and nitrate, with chloride having a strong negative effect. Community uniqueness was greatest in ponds with elevated calcium, while the presence of fish and higher pH levels promoted community homogeneity. Redundancy analysis showed that zooplankton beta-diversity was mainly impacted by water chemistry, which explained the most variation in zooplankton composition (9.2%), whereas watershed impervious cover explained none (0%). Surprisingly, despite strong negative impacts of chloride from road salts on multiple dimensions of zooplankton diversity, structural equation models failed to detect any direct or indirect effects of impervious land cover on zooplankton diversity mediated by its influence of water quality on other biotic factors (e.g., fish presence). These findings highlight the limitations of using impervious surfaces as a proxy for the impacts of urbanization on aquatic ecosystem condition but also suggest that reducing salinization may offer meaningful benefits to biodiversity even in densely populated areas.

Volatile sulfur compounds (VSCs)—carbonyl sulfide (COS), dimethyl sulfide (DMS), and carbon disulfide (CS₂)—play critical roles in atmospheric chemistry. Nevertheless, quantitative understanding of VSC exchange dynamics in coastal wetland ecosystems remains limited. Here, we quantified the sediment-air fluxes of these VSCs across vegetated (Spartina alterniflora and Suaeda glauca) and unvegetated mudflat habitats via year-round field observations in a temperate intertidal wetland. We found that S. alterniflora sediments exhibited net emissions of COS (4.61 ± 9.19 nmol m⁻² s⁻¹), DMS (10.25 ± 12.35 nmol m⁻² s⁻¹), and CS₂ (5.77 ± 7.29 nmol m⁻² s⁻¹), while S. glauca and mudflats exhibited variable sink–source dynamics. VSC fluxes from S. alterniflora habitats significantly exceeded those from other zones due to high root sulfate and total sulfur contents, as well as microbial organisms and temperature-dependent microbial activity related to sulfur metabolism. The DMS flux in S. alterniflora zones decreased by 33–224% after ebb tide compared to before flooding, with principal component analysis identifying phase-specific controls: pre-flood fluxes were associated with porewater chemistry (pH, redox potential) and atmosphere (water content, pressure) coupling, while post-ebb fluxes were governed by ionic gradients (conductivity) and residual moisture (water content). Tidal simulation experiments revealed the joint influences of illumination, water content, and anaerobic processes on VSC production, where anaerobic conditions suppressed DMS and CS₂ formation but enhanced COS emission in the dark. These findings establish that coastal VSC fluxes are regulated by the interplay between macrophyte-mediated sediment biogeochemistry and tidal pumping. This provides mechanistic insights into wetland sulfur cycle modeling.

Zooplankton communities in ponds and lakes control phytoplankton growth and serve as a food source for higher trophic levels such as fish. Recent experiments have shown that several freshwater zooplankton species as well as the phytoplankton communities on which they feed can be variably affected by rising temperatures, reduced pH and higher dissolved pCO₂ associated with global environmental change. However, to understand how freshwater ecosystems may respond to the combination of these stressors, more realistic multi-stressor tests are needed that document community-level responses. In this study, we investigated the responses of a natural zooplankton community to combinations of elevated pCO₂ (~ 300 ppm vs. 12,500 ppm) and warming (20°C vs. 24°C) in indoor microcosms over a period of 6 weeks. Overall, both treatments resulted in strong shifts in zooplankton communities. Elevated pCO₂ promoted zooplankton abundance and biomass, while warming mainly resulted in changes in community composition and body size. Elevated pCO₂ favored the small water flea Chydorus sphaericus which dramatically increased in abundance. One species (Eurycercus lamellatus) became smaller under warming. The combination of warming and elevated pCO₂ reduced body size in Simocephalus vetulus, which replaced Daphnia as the dominant zooplankter. Changes in zooplankton abundance appear to be driven by changes in phytoplankton and periphyton biomass rather than changes in stoichiometry. This experiment suggests that the combination of warming and elevated pCO₂ can result in less effective phytoplankton control by zooplankton and might negatively affect higher trophic levels that rely on large zooplankton as a food source.

Understanding how phytoplankton communities respond to environmental changes is critical for mitigating the impact of changing oceans. To identify the main drivers of changes in phytoplankton community composition and species richness, hierarchical modeling of species communities (HMSC) was used to model the summer phytoplankton communities from 29 sites, sampled between 1972 and 2017, in the Helsinki Archipelago, Finland. Models were fitted to both occurrence and abundance data. Spatial–temporal random effects accounted for most of the variance explained, followed by sea surface temperature (SST) and total phosphorus for both models. Statistically supported relationships between SST and occurrence emerged for most species. Two statistically supported trait–environment relationships were detected; however, species responses to environmental variables were strongly linked to taxonomic relatedness. A negative relationship between species richness and temperature was found. The results indicated that, independent of seasonal succession, the abundance of cyanobacteria was predicted to increase with increasing temperature, while the abundance of diatoms was predicted to decrease. This trend was most notable in the hurdle model, suggesting that even if species are not completely lost, there is still a shift in dominance from diatoms to cyanobacteria with increasing temperature. Additionally, higher total phosphorus levels also resulted in increased abundance of cyanobacteria. The primary environmental drivers of changes in the community composition of phytoplankton in the Helsinki Archipelago were SST and total phosphorus; however, the community is not temporally stable. The Baltic Sea is becoming warmer; therefore, summer phytoplankton communities are expected to be increasingly dominated by cyanobacteria.

Extreme wildfires have increased in frequency and intensity globally, particularly in the Western United States. Here we examine how the 2020 Lightning Complex Fires in California influenced coastal phytoplankton communities using monitoring network data products in the Monterey Bay, the ocean region closest to this large fire. We observed no clear response in ocean chlorophyll a, often considered a proxy for total phytoplankton biomass, during and after the fires. However, using phytoplankton community composition observations we detected a shift in phytoplankton size and taxonomic structure that coincided with the timing of the fires. Small centric diatoms initially dominated, followed by a proliferation of chain-forming diatoms, including Asterionellopsis, Skeletonema, Hemiaulus, Leptocylindrus, Thalassionema, and Thalassiosira. Cross-correlation analysis and generalized additive models identified wildfire aerosols (PM2.5) as a significant predictor of these diatom blooms, though the precise mechanisms remain uncertain. We speculate that a combination of nutrient deposition, light limitation from smoke shading, interactions with oceanographic conditions, and differential mortality due to grazing or toxicity drove the observed phytoplankton shifts. This study provides rare observational evidence linking extreme wildfires to changes in coastal phytoplankton communities and underscores the need for sustained ocean monitoring, rapid-response sampling, and mechanistic studies to unravel these complex wildfire–ocean interactions.

Surface fronts are common features across the world's oceans, particularly in estuarine and coastal regions where the merging of freshwater and saltwater creates strong density gradients. It has long been documented that fronts in these regions can trap and concentrate various properties such as floating debris, nutrients, larvae, and other buoyant materials. The prediction of such fronts has important implications for environmental protection, search and rescue operations, and scientific research. However, the realistic simulation of such features remains a challenge. In this study, we apply a high-resolution, numerical circulation model of Tampa Bay and the adjacent West Florida Shelf to predict surface fronts by computing surface convergence. The accuracy of the simulation is evaluated using drone and satellite imagery. The simulated convergence fields are then analyzed by a Self-Organizing Map, an unsupervised machine learning method. Our findings show that convergence patterns vary with tidal phases (ebb and flood) as well as the spring–neap tidal cycle. This study provides a new framework for improving monitoring strategies and reducing observational bias. Although every estuary is unique, the physical mechanisms of frontogenesis are universal. Therefore, the method we propose can be applied to other estuarine systems and serve as a valuable tool for interdisciplinary research in estuarine and coastal environments.

Ponds influence global carbon (C) cycling due to high rates of organic C (OC) burial and carbon dioxide (CO₂) and methane (CH₄) emissions. Here, we quantified OC burial rates and CO₂ and CH₄ concentrations and fluxes in two ponds that were similar in size and gross primary production, but differed in depth and dominant primary producers. The deeper (3.9 m) Texas Hollow Pond was phytoplankton dominated with stronger and longer (143 d) stratification compared to the shallower (2.7 m) macrophyte-dominated Mud Pond (85 d). Both ponds exhibited high CO₂ and CH₄ emissions and high OC burial, yet C pathways differed. Strong stratification in Texas Hollow Pond led to anoxic bottom waters, benthic CO₂ and CH₄ accumulation, and limited OC decomposition, whereas Mud Pond remained oxygenated with similar gas concentrations across the water column. Texas Hollow Pond had 2.6 times higher CO₂ emissions than Mud Pond, perhaps related to greater wetland C inputs in Texas Hollow. Despite similar diffusive CH₄ emissions between ponds, the weakly stratified Mud Pond had twice as much CH₄ ebullition, likely due to warmer waters and macrophyte-derived OC fueling methanogenesis. In summary, slight differences in depth and light attenuation can regulate stratification, plant communities, oxygen availability, and C processing in ponds. Given that ponds are hotspots for C cycling and are sensitive to climate-driven changes in stratification, understanding the mechanisms behind C processing is critical for local management and predicting global C budgets.