Limnology and Oceanography最新文献

Antarctica is a seasonally active region for marine organic sulfur cycling and ocean-atmospheric sulfur fluxes. Organic sulfur compounds, such as dimethylsulfoniopropionate and dimethylsulfide, produced by microbes are key chemical currencies in interspecies interactions, which in turn, underpin marine sulfur dynamics. This study examined Antarctic phytoplankton-bacteria associations and their influence on marine sulfur cycling along a coastal gradient from an inner fjord of the Sørsdal glacier to the open ocean (six sites). Phytoplankton abundance increased with distance from the glacier, corresponding with an increase in dimethylsulfoniopropionate concentrations (dissolved 13–28 nM; total 73–140 nM) and phytoplankton dimethylsulfoniopropionate lyase activity. Microbial community composition varied with glacial-influence, and overall abundance declined with distance from the glacier. We identified strong associations between dominant phytoplankton genera (Cylindrotheca, Corethron, Chaetoceros, Fragilariopsis, Leptocylindrus/Dactyliosolen, and Phaeocystis) and bacteria from the Rhodobacteraceae (i.e., Roseobacter group), highlighting the prevalence of these species' complexes in Antarctic waters. Specifically, pigment markers of Phaeocystis sp. and amplicon sequence variants (ASVs) belonging to Octadecabacter and Sulfitobacter correlated positively with dissolved dimethylsulfoniopropionate concentrations and phytoplankton dimethylsulfoniopropionate lyase activity, supporting their role in marine sulfur metabolism and extending the known geographical range of sulfur-mediated phytoplankton associations with the Roseobacter group. In broadening the reported range of these interorganism interactions to Antarctic waters, these results extend the prevalence and weight of the role of sulfur-based dependencies in structuring marine microbial communities.

Human pressures are leading to the replacement of macroalgal forests by alternative opportunistic species on shallow temperate reefs. Nonetheless, the ecological consequences of habitat reconfiguration for coastal biodiversity and ecosystem functioning remain poorly quantified. By means of a field study, we compared the metabolic functioning and biodiversity of macroalgal forests dominated by the fucoid Ericaria brachycarpa at pristine sites with that of assemblages formed by a shrub-like rhodophyte (i.e., Halopithys incurva) at urban sites. Dominant macroalgae at pristine and urban sites supported similar abundance and species richness of vagile invertebrates, but macroalgal forests supported higher invertebrate biomass. Shrub-like assemblages at urban sites sustained an autotrophic metabolism with a net diel O₂ production throughout the year, whereas macroalgal forests tended to be heterotrophic during warmer months. Diel fluxes of total dissolved inorganic carbon, as well as the contribution of production/respiration, were consistent with O₂ fluxes, with E. brachycarpa forests functioning as a heterotrophic carbon source in summer. This could be the result of reduced photosynthetic performance of the dominant brown macroalga and/or increased community respiration in warmer seawater. Our findings suggest that benthic assemblages in urban areas, formed by large and architecturally complex macroalgae, do not markedly differ from those found in pristine areas in terms of supported biodiversity and may sustain a more stable autotrophic balance under varying environmental conditions. Avoiding further degradation of these urban habitats (i.e., shift from shrub-like to mat-like turfs) could be a viable strategy for sustaining ecosystem functioning along peri-urban and urban Mediterranean coasts.

There is a global increase in the decommissioning of offshore oil and gas (O&G) infrastructure at the end of its operating lifetime. However, there is strikingly limited empirical evidence for the environmental and ecological impacts of decommissioning. Here, we employed a meta-analytical approach on an industry benthic monitoring database to investigate the benthic biodiversity and food web properties of structures sampled in the short term (< 1 yr; scenario 1), medium term (1–5 yr; scenario 2), and long term (> 5 yr; scenario 3) after decommissioning. We found reduced species richness and simplified food webs in scenario 1, followed by the first signs of recovery in scenario 2, with a slightly higher proportion of intermediate species and density of food web connections. Food webs recovered further in scenario 3, with a much greater density of interactions, but also more links and longer food chains, while a reduction in generalism and connectance indicated an increased prevalence of specialist species. Our findings demonstrate disturbance risks associated with the decommissioning process in the short term, but a positive recovery trajectory over longer timescales. We highlight the importance of industry collecting more extensive and long-term data at multiple time points and covering different decommissioning types, establishing a standardized data workflow for integrating with available monitoring efforts, and improving stakeholder participation and data accessibility to support an environmentally sound decommissioning process.

Macroalgae aquaculture ecosystems have been increasingly recognized as coastal biogeochemical hotspots of air–sea net ecosystem carbon dioxide (CO₂) exchange; however, their roles in regulating the temporal variability of net ecosystem methane (CH₄) exchange (NME) receive little attention mainly due to very limited data availability. Here, we applied the eddy covariance (EC) technique to acquire 1-yr (June 2023 to May 2024) NME measurements, over a subtropical macroalgae aquaculture ecosystem in southeast China, to examine the temporal variability of NME across time scales and its contribution to net radiative forcing. The results indicated that (a) this ecosystem acted as a CH₄ source in most months with the summer accounting for about two-thirds of annual NME of 0.40 g C m⁻² yr⁻¹; (b) the inclusion of annual NME increased the sustained-flux global warming potentials (SGWPs) by 11.0% from 219.3 (CO₂ only) to 243.4 g CO₂-eq. m⁻² yr⁻¹ for a 100-yr time horizon; (c) NME and its radiative contribution varied across seasons, farming periods, and growth stages, with the temporal fluctuations mainly controlled by temperature and tidal activities; (d) bimodal varying patterns across tidal levels were identified with larger fluxes occurring when tidal level changed most rapidly. This is the first EC study to confirm that CH₄ emission intensifies the warming effect of CO₂ efflux from macroalgae aquaculture ecosystems. The observed strong temporal variability of CH₄ and CO₂ fluxes and their asynchrony highlight the importance of high-frequency and continuous flux measurements in accurately assessing their net radiative forcing at both short- and long-term scales.

Climate change profoundly alters riverine flow regimes and community composition, affecting key ecosystem functions. We used an experimental mesocosm approach to examine how gradual flow velocity reduction (Experiment 1) and flushing events (Experiment 2) influence periphyton community composition and metabolism, with and without a macroinvertebrate assemblage. We prepared eight stream mesocosms with pre-grown periphyton, half including macroinvertebrates. Six mesocosms gradually transitioned from high (0.25 m s⁻¹) to low flow velocity (0.05 m s⁻¹), followed by three flushing events of increasing frequency (i.e., reducing time between events) and same intensity, raising from 0.05 to 0.25 m s⁻¹ for 6 h before returning to base flow. Two control mesocosms (one with and one without macroinvertebrates) remained at constant flow (0.1 m s⁻¹) throughout the experiment. We measured algal biovolume, taxonomic composition, and metabolic rates (gross primary production; ecosystem respiration; net ecosystem production) over time. Macroinvertebrates altered community composition and reduced algal biovolume, with stronger effects at low flow. Flow reduction had scale-dependent effects: at the chamber scale it lowered periphyton gross primary production and net ecosystem production, while at the whole-mesocosm scale it decreased ecosystem respiration more than production, increasing net ecosystem production. Flushing events decreased algal biovolume, but enhanced periphyton autotrophy, though this effect weakened with repeated disturbance. Macroinvertebrate assemblages, while reducing total algal biovolume, enhanced the resistance of metabolic responses to flushing. Together, these results show that hydrological variability and macroinvertebrate presence jointly regulate periphyton structure and function and provide mechanistic insight into the processes controlling carbon cycling in running waters.

Passive dispersal plays a key role in the distribution of marine benthic species that have reduced mobility and lack planktonic life stages. However, its qualitative and quantitative importance, as well as the ecological and environmental factors responsible for it, remain largely unknown. Here, we address these issues by analyzing the dispersal of benthic foraminifera using environmental DNA (eDNA) from the water column and sediment samples collected at 24 stations in the Nordic Seas. Our results show that water eDNA contains large amounts of benthic foraminiferal DNA. Approximately 41.5% of the foraminiferal Amplicon Sequence Variants (ASVs) found in the sediment were also present in the water samples, with over 22.1% shared among samples from the ocean surface, at 100 m water depth, and in the sediment. However, not all benthic foraminiferal taxa were equally represented in the water samples. The calcareous species (mainly rotaliids) are more frequently observed in surface water. Our study suggests that some benthic foraminifera are likely dispersed over long-distance transport, traversing distances of hundreds of kilometers. Dispersal patterns depend on species' habitat and water circulation patterns, with shallow-water species being preferentially transported by surface water currents and deep-sea species primarily carried by bottom-water currents. This work highlights the importance of passive dispersal in shaping the biogeography of benthic protists and underlines the value of eDNA metabarcoding for studying connectivity in marine ecosystems.

Dissolved organic carbon (DOC) in the coastal ocean originates from multiple sources that differ in composition and reactivity, influencing their fates in the ocean. The diffuse export of coastal marsh-derived DOC remains poorly quantified, creating uncertainties in ocean carbon budgets. A major challenge is identifying marsh-derived DOC within heterogeneous mixtures in coastal waters. Here, we introduce a new multivariate framework to partition terrigenous DOC (tDOC) into saltmarsh-derived and riverine fractions in nearshore and coastal waters, focusing on the northern Gulf of Mexico. The approach integrates ratios of cinnamyl (C), vanillyl (V), and p-hydroxyphenyl (P) dissolved lignin phenols (C/V and P/V) with salinity and other compositional indicators of tDOC (spectral slope coefficient, S_275–295, and carbon-normalized yield of lignin phenols carbon, TDLP₉-C) to quantify DOC contributions from riverine, marsh, and marine sources. Implementation of the source framework revealed that nearshore tDOC was dominated by riverine inputs near the Mississippi and Atchafalaya river deltas, whereas saltmarsh-derived tDOC was prevalent near the marsh-dominated Terrebonne Bay. Offshore, tDOC comprised a small but non-negligible fraction (< 20%) of the DOC pool, with ~ 90% derived from rivers, and ~ 10% from saltmarshes on average. This study provides a novel framework for quantifying the contributions of marsh-derived and riverine DOC in coastal waters, advancing understanding of their roles in coastal carbon budgets.

Seasonal stratification in freshwater lakes suppresses vertical exchange, often leading to strong biogeochemical gradients in bottom waters. This study investigates the dynamics of near-inertial internal waves and their role in driving turbulence in Lake Inawashiro, a medium-sized, seasonally stratified lake in Japan. Microstructure profiler observations in June 2023 revealed elevated turbulent kinetic energy dissipation rates (ε), reaching approximately 3 × 10⁻⁷, 2 × 10⁻⁸, and 4 × 10⁻⁹ W kg⁻¹ in the epilimnion, metalimnion and hypolimnion, respectively. Near-surface ε profiles followed Monin–Obukhov similarity scaling, consistent with contemporaneous wind speeds of 2–4 m s⁻¹, indicating a dominant influence of wind-driven mixing. Complementary acoustic Doppler current profiler measurements from June 2020 captured strong near-inertial oscillations (~ 17.9 h period) across the lake basin. Cross-power spectral density analysis revealed high coherence and smooth phase progression among the three mooring sites. Plane wave fitting indicated southwestward propagation (~ 235°) of near-inertial waves, with a horizontal wavelength of ~ 5.4 km and a phase speed of ~ 0.07 m s⁻¹ (≈ 6 km d⁻¹). The inferred spatial scale and propagation direction are likely shaped by the interplay between wind-driven Ekman transport and shoreline constraints. These findings demonstrate that Earth's rotation can exert a dynamically significant influence even in medium-sized lakes (~ 10–15 km), where the basin scale approaches the local Rossby radius. The observed enhancement of ε below the thermocline suggests that near-inertial waves can effectively transmit energy into deeper layers, contributing to vertical mixing and the redistribution of nutrients and biogeochemical tracers during the early summer stratification period.

Temperature is a critical environmental variable for ecosystem processes, since metabolic rates of organisms increase with temperature, which could potentially elevate their excretion rates. In a warming climate, it is imperative to understand how temperature influences consumers' nutrient excretion, especially nitrogen (N) and phosphorus (P). Here, we review, quantify and synthesize the effect sizes of temperature on nutrient excretion rates of freshwater fishes through a meta-analysis. Because there are too few studies measuring fish P excretion under different temperatures, we could only test the temperature effect on N excretion rates. Overall, our results show that fish N excretion increases with temperature, but there is considerable variability between studies. We investigated the nature of this heterogeneity by testing the influence of fish body size, climate (tropical, subtropical, temperate), delta temperature (difference between the lowest and highest temperature used in the experiment), acclimatization time, and feeding status (being fed or starved before excretion measurements) as moderators (predictors in meta-analysis). We found that delta temperature and feeding status significantly influenced the magnitude of the effect, with studies applying the highest delta temperatures, and studies with starved fish, showing the highest effect sizes. Our meta-analysis suggests that the magnitude of temperature increase and food availability can partly determine how global warming will affect fishes' N excretion in freshwater ecosystems.

We present the biogeochemical cycling of dissolved zinc (dZn) in marginal and open waters of the Indian Ocean using a high-resolution dataset collected during multiple GEOTRACES-India (GI) cruises. Atmospheric dust deposition is a minor source compared to continental shelf inputs for dZn in photic waters of the northern Indian Ocean. A strong linear relationship between dZn and silicate (Si) is noted across the Indian Ocean, with lower slope ratios (dZn : Si) in the Arabian Sea (0.045 ± 0.001 nM μM⁻¹) and Bay of Bengal (0.049 ± 0.001 nM μM⁻¹) relative to the southern tropical Indian Ocean (STIO, 0.062 ± 0.002 nM μM⁻¹). We investigated these regional differences using an inverse modeling approach by quantifying the fractional contribution of each water mass to the measured dZn concentrations in the water column. Our results indicate that water mass mixing and scavenging are the primary mechanisms controlling dZn distribution in the region. Scavenging of dZn in the intermediate waters is likely driving the lower dZn-Si regression slopes in the northern Indian Ocean. Intense scavenging may result from zinc sulfide formation in anoxic microenvironments of poorly ventilated waters or adsorption onto sinking particles. Dissolved Zn in excess of its preformed component is nearly twice as high in deep waters of the northern Indian Ocean compared to the STIO, suggesting desorption of previously scavenged Zn and/or presence of regional deep sources. These findings advance our understanding of regional zinc cycling in the Indian Ocean.