Limnology and Oceanography最新文献

Nutrient availability drives community structure and ecosystem processes, especially in tropical lagoons that are typically oligotrophic but often receive allochthonous inputs from land. Terrestrially derived nutrients are introduced to tropical lagoons by surface runoff and submarine groundwater discharge, which are influenced by seasonal precipitation. However, terrigenous inputs presumably diminish along the onshore–offshore gradients within lagoons. We characterized nutrient availability in the lagoons of a tropical high island, Moorea, French Polynesia, using spatially distributed measurements of nitrogen content in the tissues of a widespread macroalga during the rainy season over 4 yr. We used synoptic water column sampling to identify associations among macroalgal nutrient content and the composition of inorganic macronutrients, dissolved organic matter, and microbial communities. We paired these data with quantifications of land use in nearby watersheds to uncover links between terrestrial factors, aquatic chemistry, and microbial communities. Algal N content was highest near shore and near large, human-impacted watersheds, and lower at offshore sites. Sites with high algal N had water columns with high nitrite + nitrate, silicate, and increased humic organic matter (based on a fluorescence Humification Index), especially following rain. Microbial communities were differentiated among nearshore habitats and covaried with algal N and water chemistry, supporting the hypothesis that terrigenous nutrient enrichment shapes microbial dynamics in otherwise oligotrophic tropical lagoons. This study reveals that land–sea connections create nutrient subsidies that are important for lagoon biogeochemistry and microbiology, indicating that future changes in land use or precipitation will modify ecosystem processes in tropical lagoons.

Coastal marshes and their carbon sequestration capacity are threatened by development and accelerated sea level rise, yet we lack an understanding of how carbon dynamics vary among dominant zones due to confounding feedbacks between environmental gradients and vegetation. We implemented a three-year mesocosm experiment (48 379-L tanks) manipulating plant species (Spartina alterniflora, Phragmites australis, unvegetated tidal flat) under controlled hydroperiod and brackish salinity conditions to limit confounding physiochemical gradients. We quantified all biomass pools, net ecosystem exchange (NEE), and soil respiration (CO₂) during the 2021 and 2022 growing seasons, and soil microbial communities in 2021. We measured field-based soil respiration (CO₂) rates in P. australis and S. alterniflora zones at one site in Stonington, Connecticut, USA, to compare with experimental fluxes. We observed greater biomass in vegetated than in tidal flat treatments, but no differences between vegetated P. australis and S. alterniflora treatments. Spartina alterniflora had the highest rates of NEE yet also had the highest soil respiration rates; both patterns were likely due to differential physiology between S. alterniflora and P. australis. Field-based fluxes were comparable in magnitude to our experimental fluxes and similar across vegetation zones. Soil microbial community diversity was higher in vegetated treatments compared to unvegetated, whereas community composition moderately differed between vegetated treatments. Overall, growing two dominant coastal marsh grasses under similar physiochemical conditions neutralized many species differences typically observed in situ, suggesting strong environmental control on carbon cycling in coastal marshes.

The contribution of organic alkalinity (A_DOM), derived from dissolved organic matter, to coastal acid–base chemistry remains poorly understood, particularly regarding its spatial, seasonal, and compositional variability. This study examines A_DOM dynamics across distinct Korean coastal environments, focusing on regional distributions in lagoons, estuaries, and salt marshes with tidal flats, and on year-round temporal variability in a macroalgal-dominated habitat. A_DOM concentrations ranged from < 5 to 29 μmol kg⁻¹, accounting for less than 2% of total alkalinity (A_T), while DOC ranged from 51 to 359 μM. The A_DOM–DOC correlation was strong in lagoons and river-influenced systems (r > 0.8), but weaker in bays, salt marshes, and macroalgal habitat (r ~ 0.5–0.7), likely reflecting variability in DOM sources and composition. Back-titration analysis further revealed consistent acid dissociation constants across regions and seasons, primarily associated with carboxyl (pKa₁ ~ 4.6) and phenolic or amine (pKa₂ ~ 7.0) groups. These two functional groups contributed nearly equally to DOM acid–base behavior across all habitats and seasons, suggesting a shared chemical foundation underlying A_DOM despite diverse environmental settings in Korea. These findings provide a mechanistic understanding of how DOM functional group composition governs A_DOM across diverse coastal environments.

Bi, S., and M. Hieronymi. 2024. “Holistic Optical Water Type Classification for Ocean, Coastal, and Inland Waters.” Limnology and Oceanography 69: 1547–1561. https://doi.org.10.1002/lno.12606.

In the original publication, there was an error in Equation (4) on page 1551. The equation for calculating the trapezoidal area at RGB bands was incorrectly written with a minus sign between the reflectance.

This was a typo that only appeared in the text document. All calculations, analyses, results, and conclusions presented in the paper were based on the correct formula. The scientific findings of the study are therefore unaffected by this error. The authors apologize for this error.

Microbial communities in Arctic coastal lagoons mediate nitrogen and carbon cycling at the terrestrial–marine interface of these rapidly changing ecosystems. To investigate these microbial processes, we measured gene expression, nitrification, and inorganic carbon assimilation in waters of Elson Lagoon on the Beaufort Sea coast under ice cover (April), during spring break-up (July), and in open water (August). Quantitative metatranscriptomics with internal controls quantified per-liter transcript abundances alongside in situ light and dark ¹⁵N-ammonium, ¹⁵N-urea, and ¹³C-bicarbonate stable isotope tracer incubations. Nitrification was only detectable during ice cover, showing high rates for Arctic coastal systems and evidence of light inhibition. Although carbon assimilation was relatively low during ice cover, dark carbon assimilation accounted for nearly half of total uptake, matching estimates of chemoautotrophic potential based on nitrification. Microbial gene expression also shifted seasonally in abundance and function. Transcripts for nitrification peaked during ice cover when genes for ammonia oxidation and 3-HP/4-HB carbon fixation were primarily expressed by archaeal genus Nitrosopumilus, while those for nitrite oxidation and reverse TCA carbon fixation were expressed by bacterial phylum Nitrospinota. During break-up and open water, expression shifted toward urea metabolism, nitrogen assimilation, Calvin Cycle carbon fixation, and anaplerotic pathways. These shifts highlight the seasonality of microbial metabolic strategies and reveal distinct functional shifts across the Arctic lagoon seasonal cycle. The findings suggest that ongoing warming and declining ice cover may reduce chemoautotrophic activity and alter nitrogen and carbon cycling under future conditions, with implications for nutrient dynamics and primary production in Arctic coastal ecosystems.

Horizontal/Vertical nutrient supply in the upper ocean of the North Pacific Subtropical Gyre (NPSG) plays a pivotal role in biogeochemical cycling and CO₂ uptake. However, research quantifying water/nutrient transport based on direct chemical observations and measurements is limited. Based on observations made during three GEOTRACES cruises in spring, summer, and winter, we identified horizontal and vertical water sources and quantified the water and nutrient supply, applying modified Optimum Multiparameter (OMP) analysis based on iterative calculation, in which rare earth elements (REEs) were used as quasi-conservative chemical tracers. The mean quantification results with a depth of ≤ 200 m show that Equator-derived water (Nutrient fraction: 51% ± 37%) and vertical supply (31% ± 33%) are the dominant nutrient sources; northern NPSG-derived water (0% ± 1%) has little influence; North Equatorial Current-derived water shows a higher contribution at 200–300 m (38% ± 26%) than the shallow layers (10% ± 19%); coast-derived water (7% ± 15%) contributes to NPSG in an inconsistent way. In addition, the enhanced vertical nutrient supply during the sampling period, which is more significant in spring, is likely to be attributed to the influence of what are considered different types of eddies based on the sea surface height. The vertical fluxes of dissolved inorganic nitrogen in the bottom euphotic layer at stations near warm, cold, and no eddies were estimated to be 0.10–0.76, 0.21–2.13, and 0.066–0.53 mmol m⁻² d⁻¹, respectively, which are 1–100 times the supply from nitrogen fixation. These nutrient fluxes could explain 5–169 mg C m⁻² d⁻¹ of the carbon fixation in the euphotic zone.

Silicic acid controls the production of diatoms, a predominant phytoplankton in the Southern Ocean. Diatoms are major contributors to the biological carbon pump, which is particularly active in the Southern Ocean as well as in areas naturally enriched in iron, such as around the Kerguelen Plateau. This study evaluates the factors controlling the biogeochemical cycle of Si and its dynamics in this area and how it is impacted by the island mass effect using the Si isotopic signatures of both dissolved and biogenic Si. While subsurface winter waters have similar δ³⁰Si signatures and dissolved Si concentrations, surface δ³⁰Si and dissolved Si values are different between stations. We show that this results from both (i) a different degree of dissolved Si utilization by silicifiers from winter water as the main Si source and (ii) an additional significant Si source to dissolved Si in the mixed layer from lithogenic Si dissolution for areas under the influence of the shelf. Indeed, the δ³⁰Si_DSi signatures near the islands are homogeneous and lighter by −0.33‰ ± 0.07‰ in the mixed layer compared to the outside plateau station. We estimate such lithogenic Si contribution to dissolved Si at 2.9 ± 1.8 μmol L⁻¹ for a corresponding specific flux of 3.7 ± 2.3 × 10⁶ mol km⁻² yr⁻¹ in shallow areas around Heard and McDonald Islands (< 100 m). This Si dissolution flux per surface area is among the highest in the ocean and has a traceable biogeochemical impact over the Northern Kerguelen Plateau. It is likely due to the active volcanic nature of these islands combined with subglacial erosion on Heard.

Sargassum species play a critical role in tropical and temperate coastal ecosystems by contributing to primary production and providing habitat to different species, while causing ecological disruptions and social challenges in some localities. As global warming intensifies, understanding how Sargassum species respond to rising seawater temperatures becomes increasingly important, and synthesizing evidence across diverse research approaches is critical to this goal. This study combines a comprehensive review and meta-analysis to evaluate the effects of warming on native and invasive Sargassum species in tropical and temperate regions. A total of 1471 studies were screened, of which 175 met the inclusion criteria and addressed Sargassum responses across tropical, warm-temperate, and cold-temperate regions. Our findings revealed that benthic native species are particularly vulnerable, with reduced growth rates and photosynthetic efficiency under projected warming scenarios in tropical and warm-temperate regions. In contrast, invasive species showed positive or neutral outcomes. Long-term monitoring and species distribution modeling studies supported these results, predicting significant habitat contractions and population declines for native species, while the invasive Sargassum muticum exhibited expanded ranges under future warming scenarios. These shifts could exacerbate ecological and social challenges, with cascading effects that compromise the functioning of ecosystems. Our study underscores the urgent need for monitoring programs and management strategies targeting Sargassum populations.

The littoral zone of lakes is recognized as hotspots of biogeochemical cycles. While the coupling of Fe(III) reduction and ammonium oxidation is acknowledged as an important nitrogen loss pathway, the role of anaerobic ammonium oxidation mediated by Mn oxides (Mnammox) remains uncertain. In this study, we conducted a ¹⁵NH₄⁺ isotopic incubation experiment and applied Mn oxides amended treatment to investigate the role of Mnammox in the lake littoral zone with respect to the N biogeochemical cycle. Our findings confirmed the widespread presence of Mnammox in the littoral zone of Baiyangdian Lake, the largest freshwater lake in the North China Plain. The sediment exhibited an average ³⁰N₂ production rate of 19.91 μg kg⁻¹ d⁻¹, accounting for approximately 2.0% of total nitrogen loss in situ. Significant nitrate production was also observed with a rate of 0.26 mg N kg⁻¹ d⁻¹, highlighting the role of Mnammox as a potential source of nitrate under anaerobic conditions. Furthermore, we identified a key threshold of 3.15 g kg⁻¹ dry weight sediment MnO₂ amendment, roughly 20 times the in situ MnO₂ content, which most significantly enhanced the Mnammox process. Sediment Mn oxides content, moisture content, and pH were the main stimulators for the Mnammox process, with unique microbial groups. This work underscores the importance of Mnammox in the lake littoral zone, illuminating the Mn–N coupling that drives multi-element cycles in this critical environment.

The Yellow Sea has experienced the world's largest green tide of Ulva prolifera in each of the last 18 yr. Limited understanding of the mechanisms controlling U. prolifera growth and death complicates mitigation efforts. Focusing on the crucial factors and processes affecting U. prolifera blooms, we constructed a nutrient–microalgae–U. prolifera–detritus (NmiAUD) model based on the results of field microcosm experiments. The NmiAUD model characterized the growth and death processes of U. prolifera and the nitrogen and phosphorus biogeochemical processes in the Yellow Sea with good reliability. Parameter sensitivity, process correlation analysis, and numerical experiments were used to identify the most critical factors and processes. Nutrient concentrations were the most important factors controlling the growth and death of U. prolifera, followed by seawater temperature, initial biomass, and photosynthetically active radiation, with contribution rates of 55.1%, 23.9%, 16.0%, and 5.0%, respectively. Nitrogen was more important than phosphorus, with nitrate-nitrogen accounting for 29.9%, followed by ammonium-nitrogen (26.3%), dissolved organic nitrogen (19.9%), phosphate-phosphorus (17.1%), and dissolved organic phosphorus (6.8%). The key processes comprised nutrient absorption, nutrient assimilation, degradation, detritus generation, dissolved organic matter mineralization, and detritus decomposition. Microalgae, which show high rates of growth, mortality, and nutrient uptake, are indicated to have a competitive advantage in the higher nutrient conditions in the South Yellow Sea, whereas U. prolifera is better adapted to the lower nutrient conditions in the North Yellow Sea. This study provides a scientific basis for the prevention and control of green tides.