Journal of Geophysical Research: Biogeosciences最新文献

Metagenomics provides insights into the potential of microorganisms to mediate key biogeochemical processes encoded in ecosystem models. Efforts have been made to model gene abundance changes, but it is unclear how much gene abundance variation can be explained by modeled biogeochemical rates alone. We compare the relative abundance of 32 genes having the potential for photosynthesis, nitrification, denitrification, and sulfur cycling with rates predicted by a model in the Chesapeake Bay. Modeled rates explained a significant amount of gene abundance variation for half of the genes examined and at least one gene involved in four of five processes examined. An average of 21.3% of gene abundance variability is explained by the modeled rates, which increases to 31.8% when considering the 16 genes with significant relationships. For photosynthesis and denitrification, rates represent the behavior of some taxonomic groups (cyanobacteria and gammaproteobacteria) better than others (eukaryotic algae and Bacteroidetes). Significant correlations between sulfur cycling rates and genes appear for oxidative but not reductive forms of the relevant genes. The marker genes amoAB were not significantly correlated with nitrification rates. However, another gene involved in nitrification but not considered a marker gene (hao) was significantly correlated. This work demonstrates modeled rates often but not always and capture a significant amount variation of genes encoding enzymes involved in the modeled processes. Other factors, like temperature-dependent rates or cell transport, may need to be incorporated into models to explain more variation in gene abundance. Doing so could be a useful quality control for microbial processes encoded in ecosystem-level biogeochemical models.

Streams transport carbon (C) and nutrients across the terrestrial-aquatic interface and are significant sources of methane (CH₄) and carbon dioxide (CO₂) to the atmosphere. Climate-induced changes in vegetation and hydrology increase the export of dissolved organic carbon (DOC) from terrestrial to aquatic ecosystems, but the impact of these alterations on freshwater C gas emissions remains uncertain. We investigated the influence of landcover and hydrology on stream CH₄ and CO₂ fluxes in two subarctic catchments differing in vegetation and soil type by floating chamber measurements, stable isotope analyses of emitted CH₄ and CO₂, and microbial analyses of CH₄-related microbial communities. Monthly flux measurements and water and microbial sampling were performed from spring to fall during two growing seasons. The results reveal higher CH₄ and CO₂ fluxes from a brown-water stream surrounded by peatlands compared with a clear-water stream located in an upland mineral soil catchment. While CO₂ fluxes peaked during spring freshet in both streams, CH₄ dynamics showed distinct seasonal patterns between the streams. In the brown-water stream, the maximum CH₄ fluxes coincided with the spring peak in discharge and DOC, suggesting that the CH₄ fluxes were controlled by surface flow and DOC load from peatlands. In the clear-water stream, the maximum CH₄ fluxes detected during late summer were likely connected to rain events and shifting hydrological pathways during base flow. Furthermore, submerged vegetation and sediment surfaces contributed to CH₄ dynamics by providing important habitats for methanotrophic microbes. We highlight that landcover and hydrology regulate C gas fluxes from subarctic streams.

Fjord sediments are important reservoirs and conduits of potentially bioavailable iron (Fe) and manganese (Mn). Both elements are critical to life, serving as key reactants in metabolic pathways, and play an important role in the reactivity and burial of organic carbon. Once deposited in marine sediments, these micronutrients undergo cycling through abiotic and microbially driven redox reactions. Here, we investigate the primary controls on the distribution, partitioning, and cycling of extractable Fe and Mn within fjord sediments from Chilean Patagonia. Sequential chemical extractions of samples from sediment cores covering a range of environmental variables reveal that active redox cycling in Patagonian fjord sediments leads to Fe and Mn enrichment in surface sediments comparable to or exceeding those in Arctic fjords. The main factors controlling Fe and Mn distributions were: grain size; sedimentation rate; bedrock lithology; local oceanography. Mobility indices reveal a decoupling in the behavior of Mn and Fe. Mn shows greater mobility, particularly in the most labile phase, which is attributed to faster reaction kinetics and much slower oxidation compared to Fe. While diagenesis is thought to obscure paleo-signatures, we identify the preservation of seemingly intact Fe and Mn phases beneath instantaneous deposits. Our findings suggest that integrating sedimentological analyses offers new insights into benthic fjord sediment diagenesis and may help infer past redox conditions. Ultimately, by connecting biogeochemical patterns to glacially-driven controls on sedimentation in marine systems, our work provides a framework to better predict how benthic micronutrient cycling and carbon burial will respond to future climate change.

Picophytoplankton are drivers of biogeochemical cycling and serve as key indicators of seafood productivity, ocean health, and climate change. The Arabian Sea and the Bay of Bengal—two basins of the northern Indian Ocean that support the livelihoods of over a billion people—share similar climatic conditions but differ in their hydrographic and ecological characteristics. However, the environmental factors governing picophytoplankton abundance and their implications on carbon biomass in these regions remain poorly understood. This study investigated the abundance, carbon biomass, and environmental relationships of three groups of picophytoplankton: Prochlorococcus, Synechococcus, and picoeukaryotes. We observed Synechococcus dominating the surface waters (47% in the Arabian Sea and 63% in the Bay of Bengal), while Prochlorococcus showed the highest abundance and variability in the water column between basins. Picoeukaryotes contributed more to the total picophytoplankton carbon biomass in both basins. In particular, picophytoplankton carbon biomass contribution to particulate organic carbon were not substantially distinct between the two basins. The estimated picophytoplankton carbon stock was 1.05 Tg C in the Arabian Sea and 0.5 Tg C in the Bay of Bengal. Furthermore, we determined key environmental factors—temperature, salinity, light, dissolved inorganic phosphorus (DIP), and dissolved inorganic silicate (DSi)—that shape picophytoplankton dynamics in the region. Temperature and salinity primarily influenced picophytoplankton distribution in the Arabian Sea, while nutrients were critical in the Bay of Bengal. Overall, we underscore the role of physicochemical dynamics in carbon cycling by presenting the contribution of picophytoplankton carbon biomass to the region's particulate organic carbon pool.

Sediment cores recovered from the deep sea often cannot be sampled for microbiological analysis immediately due to the need for core splitting and processing for subsequent onboard measurements and core storage. Consequently, sections are often stored at 4°C under anaerobic conditions for extended periods. However, the impact of the temporal storage on microbiological analysis remains uncertain. In this study, using paired sediment samples from the Japan Trench collected during International Ocean Discovery Program (IODP) Expedition 386, we performed comparative analysis of microbial community composition between samples immediately frozen after core recovery onboard and samples stored anaerobically for 9–11 months onshore. Although the overall community structure was broadly preserved, we observed substantial increases in some opportunistic taxa (e.g., Shewanella, Psychrobacter, and Firmicutes) and a marked decrease in archaeal abundance and diversity. Nevertheless, more than 95% of amplicon sequence variants (ASVs) were retained, and key subseafloor bacterial lineages such as Atribacterota and Chloroflexi showed no significant change in abundance. These results indicate that although long-term cold storage can introduce identifiable preservation-related biases, DNA-based analyses of archived cores can still provide meaningful insights into subseafloor microbial communities when interpreted with appropriate caution.

Complex coastal ecosystems require management that addresses interacting stressors affecting ecosystem size and persistence. In natural systems, lateral erosion of salt-marsh edges and mudflats is thought to enhance vertical resilience to sea-level rise (SLR) by augmenting sediment delivery to the marsh platform. Using the Coastal Landscape Transect model, we test how two common restoration practices, shoreline stabilizations and thin-layer placements, affect vertical and lateral resilience of marshes under accelerating SLR. We find that shoreline stabilization provides optimum restoration at low rates of SLR, but in later years, as SLR accelerates and losses from drowning supersede those associated with edge erosion, thin-layer placement imparts a higher degree of marsh resilience. Furthermore, stabilizing the marsh edge eventually facilitates threshold responses to SLR with sudden and extensive narrowing of the marsh due to interior drowning. However, contrary to expectations, results suggest that vertical-lateral couplings fail to meaningfully counteract drowning with a 1 m yr⁻¹ increase in edge erosion delaying initiation of interior drowning by <3 years. Finally, we propose “volumetric elevation capital” as a metric that allows for the assessment of marsh health across multiple dimensions, thereby avoiding drawbacks otherwise associated with threshold responses to management interventions.

Despite the widely recognized importance of wetland CH₄ emissions as a climate change feedback, simultaneous measurements of CH₄ transport pathways and oxidation in a wetland are rare. Thus, these critical components of many CH₄ models are poorly parameterized because of the lack of appropriate data. We measured plant CH₄ transport and diffusion on two sampling dates in a Minnesota, USA, bog where a whole-ecosystem manipulation experiment of temperature and atmospheric CO₂ (SPRUCE) is occurring. We also used stable-isotope methods to estimate CH₄ oxidation rates. Plant CH₄ transport was high in graminoids and, especially, the forb Maianthemum trifolium early in the growing season, while CH₄ emissions from the trees Picea mariana and Larix laricina were minimal. Diffusive transport and CH₄ oxidation rates were uniformly low. A prior study found low rates of episodic, large bubble CH₄ ebullition in this bog. Despite large variation in plant and whole-plot CH₄ emissions, a substantial fraction of whole-plot CH₄ emissions could not be accounted for using a mass balance approach, which may be attributable to microbubble release from peat, although this requires further investigation. We compare our measured rates to two CH₄ models that have been developed and tested at SPRUCE, both of which overestimate plant and diffusive CH₄ transport in S1 Bog relative to our results. We emphasize the importance of enabling CH₄ models to incorporate plant-mediated CH₄ transport that is species-dependent and allowing plant species to dynamically change in response to climate change.

Inland waters are a major global source of greenhouse gas emissions. Quantifying aquatic emissions at high spatiotemporal resolution is critical for understanding their biophysical drivers, constraining the global carbon budget, and improving climate projections. Current floating chamber techniques rely on labor-intensive manual sampling or expensive infrared greenhouse gas analyzers, which limit the spatial and temporal sampling frequency. Here, we present an improved, inexpensive autonomous floating chamber design: AQUA-Flux (autochamber for quantifying and understanding aquatic fluxes), which can capture diffusive and ebullitive methane (CH₄) and carbon dioxide (CO₂) fluxes on small freshwater bodies at high frequency. A solar-power system enables long-term deployment. We have successfully tested 12 AQUA-Flux systems for up to six months in two environmental extremes—the Arctic tundra and Brazilian Amazon. Low-cost sensors measure CH₄ and CO₂ concentrations within a closed chamber, and a linear actuator extends and retracts to vent the chamber headspace between flux measurements. Field-based calibrations using an infrared gas analyzer indicate that these low-cost sensors perform well, with average resolutions of 2–3 ppm for both CH₄ and CO₂. We also show that sensors can be field-calibrated using discrete samples collected manually for laboratory analysis (gas chromatography), providing a lower-cost calibration method. The AQUA-Flux is well-suited for water bodies with high fluxes. We include detailed assembly instructions to enable others to create and improve the design. By developing inexpensive open-source tools, we aim to democratize greenhouse gas flux measurements and ultimately improve global estimates of fluxes from aquatic environments.

We present a high-resolution, multi-proxy record from Mustjärve bog, northwest Estonia, covering the past ∼2,500 years. By integrating paleoecological, historical, and climate data, we evaluate how climate and land use shaped peatland hydrology, vegetation, and carbon dynamics. The record reflects regional land-use history, confirming the usefulness of peatbogs as archives of land-use changes. Our profile identifies raised bog hydrology as a part of the surrounding catchment, and we discuss the susceptibility of these ecosystems to climate change. From the start of the record until ca. 700 CE, local agricultural activity was limited. After 700 CE, population growth and deforestation drove ecological instability, marked by reduced carbon accumulation, hydrological change, and increased fire activity. Since ∼1960 CE, drainage has caused a long-term water table decline and arboreal encroachment. Our results suggest that past land-use changes have greatly affected the peatland ecosystem at Mustjärve. Despite this, Mustjärve appears to have been very resilient. Although there is no evidence for past critical transitions/thresholds, the current state of the Mustjärve peatland suggests high vulnerability, highlighting the importance of contemporary management practices to prevent further disturbances.