Limnology and Oceanography Letters最新文献

Coastal lagoons are important nutrient filters and carbon sinks but may release large amounts of methane (CH₄) to the atmosphere. Here, we hypothesize that eutrophication and population density will turn coastal lagoons into stronger methane emitters. We report benthic fluxes from 187 sediment cores incubated from three of the largest European lagoons suffering persistent eutrophication. Methane fluxes were mainly driven by sediment porosity, organic matter, and dissolved inorganic carbon (DIC) fluxes. Methane was always supersaturated (250–49,000%) in lagoon waters leading to large, variable emissions of 0.04–26 mg CH₄ m⁻² d⁻¹. Combining our new dataset with earlier estimates revealed a global coastal lagoon emission of 7.9 (1.4–34.7) Tg CH₄ yr⁻¹ with median values of 5.4 mg CH₄ m⁻² d⁻¹. Lagoons with very highly populated catchments released much more methane (223 mg CH₄ m⁻² d⁻¹). Overall, projected increases in eutrophication, organic loading and population densities will enhance methane fluxes from lagoons worldwide.

Marine microbes are strongly interrelated to trace metals in the ocean. How the availability of trace metals selects for prokaryotic taxa and the potential feedback of microbial processes on the trace metal distribution in the ocean remain poorly understood. We investigate here the potential reciprocal links between diverse prokaryotic taxa and iron (Fe), manganese (Mn), copper (Cu), and nickel (Ni) as well as apparent oxygen utilization (AOU) across 12 well-defined water masses in the Southern Indian Ocean (SWINGS—South West Indian Ocean GEOTRACES GS02 Section cruise). Applying partial least square regression (PLSR) analysis, we show that the water masses are associated with particular latent vectors that are a combination of the spatial distribution of prokaryotic taxa, trace elements, and AOU. This approach provides novel insights on the potential interactions between prokaryotic taxa and trace metals in relation to organic matter remineralization in distinct water masses of the ocean.

Modeling and sensor innovations in the last decade have enabled routine and continuous estimation of daily gross primary productivity (GPP) for rivers. Here, we generate and evaluate within and across year variability for 59 US rivers for which we have compiled a 14-yr time series of daily GPP estimates. River productivity varied widely across (median annual GPP 462 g C m⁻² yr⁻¹, range 19–3445 g C m⁻² yr⁻¹) and within rivers (CV_GPP-Inter 5.7–37.3%). Within this dataset, we found that five rivers have become consistently more productive over time, while 11 rivers have become consistently less productive. Furthermore, trends in ecosystem phenology were identified, where cumulative annual GPP was reached earlier (n = 3) and later (n = 13) in the year across the 25^th, 50^th, 75^th, and 95^th percentiles. Understanding the drivers of productivity trends in rivers will elucidate patterns in river food webs and the functional role of river biogeochemistry.

Oxygen isotopes in stream water can serve as natural tracers of watershed dynamics. Freshwater pearl mussels provide δ¹⁸O_water estimates that overcome temporal and spatial limitations of instrumental records. The reliability of shell-based δ¹⁸O_water reconstructions depends on understanding which shell layer biomineralizes closer to oxygen isotopic equilibrium with ambient water. To determine this, both the (outer) prismatic and (inner) nacreous sublayers of the outer shell layer were sampled. Over 2500 isotope values were obtained from shells collected from the Our River (Luxembourg) and from mussels cultured in tanks at constant temperature and monitored δ¹⁸O_water. Calculated δ¹⁸O_water from the prismatic portion was in excellent agreement with monitored δ¹⁸O_water, while δ¹⁸O_shell of the nacreous portion was systematically offset by +0.43‰, overestimating δ¹⁸O_water by +0.53‰. Although shell portions were formed simultaneously from the same extrapallial fluid, they underwent different fractionation mechanisms, presumably due to differences in carbonic anhydrase activity catalyzing mineralization processes.

The frequency of news reporting about scientific topics is positively related to public interest as well as to public support for science funding and public policy change. This correlation can also have positive impacts on individual scientific careers depending on the chosen subject area of research. Analysis of a public news database shows the frequency and trends in news reporting of several popular research areas in the aquatic sciences. The frequency of appearance of topics in the news varies over more than three orders of magnitude. Temporal trends in reporting vary from steeply increasing (+25% per year) to declining (−4% per year). Suggestions are offered concerning the framing of research topics and overall better communication of research findings to journalists and the general public. This understanding may increase news prominence, public interest, science funding, and policy change in aquatic research areas.

Understanding the patterns of marine microbial diversity (Bacteria + Archaea) is essential, as variations in their alpha- and beta-diversities can affect ecological processes. Investigations of microbial diversity from global oceanographic expeditions and basin-wide transects show positive correlations between microbial diversity and either temperature or productivity, but these studies rarely captured seasonality, especially in polar regions. Here, using multiannual alpha-diversity data from eight time series in the northern and southern hemispheres, we show that marine microbial community richness and evenness generally correlate more strongly with daylength than with temperature or chlorophyll a (a proxy for photosynthetic biomass). This pattern is observable across time series found in the northern and southern hemispheres regardless of collection method, DNA extraction protocols, targeted 16S rRNA hypervariable region, sequencing technology, or bioinformatics pipeline.

In recent years, blooms of the neurotoxic dinoflagellate Alexandrium catenella have been documented in Pacific Arctic waters, and the paralytic shellfish toxins (PSTs) that this species produces have been detected throughout the food web. These observations have raised significant concerns about the role that harmful algal blooms (HABs) will play in a rapidly changing Arctic. During a research cruise in summer 2022, a massive bloom of A. catenella was detected in real time as it was advected through the Bering Strait region. The bloom was exceptional in both spatial scale and density, extending > 600 km latitudinally, reaching concentrations > 174,000 cells L⁻¹, and producing high-potency PST congeners. Throughout the event, coastal stakeholders in the region were engaged and a multi-faceted community response was mobilized. This unprecedented bloom highlighted the urgent need for response capabilities to ensure safe utilization of critical marine resources in a region that has little experience with HABs.

Bacteria and macroalgae share an inseparable relationship, jointly influencing coastal ecosystems. Within macroalgae habitats, Planctomycetota, a group of bacteria notoriously challenging to cultivate, often dominate. However, the mechanisms facilitating their persistence in this environment remain unclear. Here, we successfully isolated a novel Planctomycetota bacterium, Stieleria sp. HD01, from the surface of kelp. We demonstrated that HD01 possesses a robust ability to metabolize fucoidan, which constitutes half of the kelp-derived organic carbon and exhibits resistance to attack by most microorganisms. Moreover, HD01 can utilize a broad spectrum of other organics, indicating its metabolic versatility and competitive prowess within algal environments. Additionally, HD01 can secrete antagonistic substances against other bacteria, form biofilms, and employ superoxide dismutase and catalase to resist oxidative stress, further consolidating its ecological fitness. Comparative metagenomics analysis suggested that Planctomycetota may have a mutually beneficial relationship with kelp.

Leaf litter dominates particulate organic carbon inputs to forest streams. Using data-informed simulations, we explored how litter type (slow- vs. fast-decomposing species), pulsed autumn litter inputs, groundwater-mediated temperature regimes, and climate warming affect litter breakdown in a 3^rd-order stream network. We found that the time-dependent interactions of these variables govern network-scale litter breakdown phenology, with greater thermal sensitivity of slow-decomposing litter for both current and future scenarios. Groundwater thermal inputs modified litter breakdown phenology by reducing spring and summer and elevating winter litter breakdown fluxes. Under future warming scenarios, the source depth of contributing groundwater influenced summer detrital resources; shallow groundwater-fed streams had reduced summer resources compared to deep groundwater-fed streams. Our results demonstrate that predicting in-stream carbon cycling requires explicit consideration of the phenology of resource inputs and the seasonal timing of environmental factors, notably stream thermal regimes.