Limnology and Oceanography Letters最新文献

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.

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.

River networks contribute disproportionately to the global carbon cycle. However, global estimates of carbon emissions from inland waters are based on perennial rivers, even though more than half of the world's river length is prone to drying. We quantified CO₂ and CH₄ emissions from flowing water and dry riverbeds across six European drying river networks (DRNs, 120 reaches) and three seasons and identified drivers of emissions using local and regional variables. Drivers of emissions from flowing water differed between perennial and non-perennial reaches, both CO₂ and CH₄ emissions were controlled partly by the annual drying severity, reflecting a drying legacy effect. Upscaled CO₂ emissions for the six DRNs at the annual scale revealed that dry riverbeds contributed up to 77% of the annual emissions, calling for an urgent need to include non-perennial rivers in global estimates of greenhouse gas emissions.

We investigated changes in physiology and mechanical properties of diatoms exposed to chemical cues released by copepods Pseudodiaptomus annandalei. Our results showed that the diatoms Phaeodactylum tricornutum, Cylindrotheca closterium, Thalassiosira weissflogii, and Amphora coffeaeformis exhibited elevated growth rates and a substantial 2- to 50-fold increase in biogenic silica (BSi) content increase when exposed to the chemical cues except for Cyclotella sp. Atomic force microscopy and X-ray photoelectron spectroscopy analyses revealed that diatom frustules exhibited a remarkable 3- to 10-fold increase in modulus and a substantial 2- to 5-fold increase in hardness when they received grazing signals. The increase in the proportion of condensed silicon in the frustules could be the major reason for the more mechanically robust cells. Our results indicate that diatoms simultaneously increase their growth rate and robustness when exposed to copepod chemical cues. This study at the nanoscale enhanced our understanding of how diatoms respond to zooplankton predation in marine ecosystems.

Although understanding nutrient limitation of primary productivity in lakes is among the oldest research priorities in limnology, there have been few broad-scale studies of the characteristics of phosphorus (P)-, nitrogen (N)-, and co-limited lakes and their environmental context. By analyzing 3342 US lakes with concurrent P, N, and chlorophyll a (Chl a) samples, we showed that US lakes are predominantly co-limited (43%) or P-limited (41%). Majorities of lakes were P-limited in the Northeast, Upper Midwest, and Southeast, and co-limitation was most prevalent in the interior and western United States. N-limitation (16%) was more prevalent than P-limitation in the Great Basin and Central Plains. Nutrient limitation was related to lake, watershed, and regional variables, including Chl a concentration, watershed soil, and wet nitrate deposition. N and P concentrations interactively affected nutrient–chlorophyll relationships, which differed by nutrient limitation. Our study demonstrates the value of considering P, N, and environmental context in nutrient limitation and nutrient–chlorophyll relationships.