Journal of Geophysical Research: Biogeosciences最新文献

Surface water is a significant source of carbon dioxide (CO₂) emissions to the atmosphere, yet knowledge gaps remain, particularly in high-altitude plateau mountain river systems. This study investigates the spatio-temporal variability of CO₂ partial pressure (pCO₂) and CO₂ efflux across the Yarlung Zangbo River (YZR) basin to better understand the primary drivers of CO₂ emissions in high-altitude river systems. Specifically, we assess pCO₂ levels, CO₂ efflux at the water-air interface, and the factors influencing pCO₂ distribution in the river, with an emphasis on the river's role in the regional carbon cycle. Our findings reveal that the average pCO₂ was 813 μatm during the low-flow season and 690 μatm in the high-flow season. The CO₂ flux range averaged 3,323 mg C (m² d)⁻¹. Correlation analysis suggests a limited role of aerobic respiration in controlling pCO₂ while a strong correlation underscores the influence of altitude on CO₂ distribution. We estimate that CO₂ emissions from the YZR mainstream are 2.18 (±0.76) teragrams of carbon per year (Tg C yr⁻¹), accounting for 18.63 (±6.49)% inland water CO₂ emissions of Tibetan Plateau rivers, and comparable to the estimated dissolved inorganic carbon flux of the YZR (1.74 Tg C yr⁻¹). These emissions are notably higher than carbon uptake from chemical weathering and about six times the CO₂ absorption by local lakes. This finding positions the YZR basin as a “weak source” of CO₂ in the regional carbon cycle, contributing valuable insights for refining global CO₂ emission estimates.

Anthropogenic impacts such as land use change are increasing dissolved nitrogen (N) loading to streams and rivers, degrading downstream water quality. Denitrification, where nitrate (NO₃⁻-N) is converted to dinitrogen gas (N₂), serves as a permanent N sink. While stream denitrification is well studied, its role in larger rivers remains understudied, despite rivers playing a key role in reach-scale N retention. Moreover, it remains uncertain how denitrification rates differ throughout the year. We compared stream and river denitrification rates across seasons using an open-channel N₂-exchange method in the Tippecanoe River and its tributary, Shatto Ditch. Areal denitrification rates were higher in the stream than the river in spring (stream = 148.0, river = 5.8 mg N m⁻² h⁻¹), summer (76.2 vs. 0.95), and fall (65.5 vs. 18.6). Rates were strongly influenced by NO₃⁻-N concentrations (R² = 0.93), which were higher in the stream. When scaled per km of channel length, river N removal was comparable or higher to the stream: summer (stream = 167.8, river = 56.7 g N km⁻¹ h⁻¹), spring (325.6 vs. 348.0), and fall (144.0 vs. 1116.5). These results confirm that streams have high biogeochemical reactivity, but they also reveal that when we account for size discrepancies, rivers can contribute a similar or greater amount of N removal because of their relatively larger size and volume. This work expands our knowledge of denitrification in fluvial ecosystems and demonstrates that both rivers and streams in agriculturally impacted areas can mitigate excess N loading to downstream ecosystems, which is needed to improve water quality.

The El Niño (EN) event of 2023 exhibited a unique evolution, starting with an extremely warm coastal episode off Peru followed by a moderate basin-scale event. We addressed the associated oceanographic and biological conditions (chlorophyll and zooplankton biomass) in the Humboldt Archipelago. It is part of the Coquimbo upwelling system (29°–30°S), within the Humboldt Current System. Eight (8) campaigns between November 2022 and December 2023, over a deep canyon surrounding the archipelago, provided hydrographic profiles and samples for determinations of chlorophyll (Chl) and particulate organic carbon (POC) concentrations and large- and small-sized mesozooplankton biomass. Oceanographic variability over the period was analyzed through reanalysis products and satellite observations, including data of sea level, surface wind, sea surface temperature (SST) and sea surface chlorophyll, geostrophic currents, and mixed layer depth (MLD). Upwelling was promoted by high-frequency variability in winds and deeper MLD associated with the basin-scale EN. The EN also fosters the arrival of a Kelvin wave in June and July, leading to positive anomalies in SST and sea level, elevated oxygen levels, and increased pH in the upper 100 m. The lowest Chl concentration was recorded after the warming event, while POC concentration and mesozooplankton biomass exhibited temporal and vertical stability. However, a significant surface increase for both size fractions was observed during the spring. Zooplankton biomass was correlated to food resources and transport, suggesting stronger regulation by local drivers. Current findings are discussed in the context of recent studies that have documented the local circulation patterns in this region.

The formation of Ca-sulfate minerals on Mars is believed to have been driven by hydrothermal alteration processes during the late Noachian. On Earth, microbial involvement in the crystallization of Ca-sulfate minerals could contribute to the development of distinctive biosignatures. However, understanding potential biosignatures in Martian hydrothermal alteration zones remains limited. In this study, we investigate anhydrite crystal formation in hydrothermally altered rocks colonized by endoliths. It is worth noting that anhydrite crystals within endolith-colonized zones exhibited diverse morphologies, including prismatic, tubular, pseudo-hexagonal, lenticular, and twinned shapes. These morphologies were randomly distributed on or around microbial cells, contrasting sharply with the uniform tabular and prismatic morphologies typically observed in abiotic processes on non-colonized rock surfaces. The coexistence of varied crystal morphologies and iterative formation-dissolution patterns indicates microbial involvement, making these features potential biosignatures. Our findings highlight the significance of microbial interactions in shaping Ca-sulfate mineral morphology, offering critical insights for biosignature exploration on Mars.

Anthropogenic warming in the Arctic has caused accelerated permafrost thaw, leading to the export of relict organic carbon (OC) to the atmosphere and surrounding depositional environments. Past episodes of warmth exceeding pre-industrial temperatures, such as the Holocene Thermal Maximum (HTM; 11–8 ka at our study site), may serve as an analog for how the Arctic carbon cycle responds to ongoing warming. Here, we reconstructed accumulation rates of three OC endmembers (aquatic biomass, postglacial soil, and MIS 5 soil) in downcore sediments from Lake CF8, northeastern Baffin Island, during the 12.4 kyr since local deglaciation. We characterized endmembers and sediment mixtures using Ramped Pyrolysis/Oxidation (RPO), radiocarbon (¹⁴C) age offsets between bulk sediment and macrofossils, and stable carbon isotope ratios (δ¹³C). We then modeled endmember contributions to the lake sediments using MixSIAR. RPO revealed similar patterns between OC volatilization and pyrolysis temperature indicating minimal OC degradation between endmembers and mixtures. MixSIAR-derived endmember accumulation rates showed that mean soil-derived OC inputs to Lake CF8 were proportionally greatest between 11.9 and 9.0 ka (5.2 ± 1.9 g OC/m²/yr), 1.5 times greater than the rest of the record (3.4 ± 1.5 g OC/m²/yr). This period coincided with regional rapid warming and peak Holocene summer temperatures. Since modern Arctic temperatures have already warmed by 2–3°C, similar to the HTM, modern regional permafrost OC may be mobilized at the same rates that we estimate for that period.

Vegetation phenology serves as a highly sensitive indicator of climate change with the effects of warming on vegetation phenological dynamics extensively documented. However, the role of precipitation variability in shaping vegetation phenology remains relatively under-explored, particularly in grassland ecosystems where precipitation is often a critical driver of seasonal vegetation dynamics. The Great Plains (GP), one of the largest grassland-dominated regions globally, provides an ideal setting to investigate the climatic determinants of spatiotemporal variations in vegetation phenophases and their potential changes. Here, we used contiguous solar-induced chlorophyll fluorescence data sets to derive the timing of three key phenophases—the start of the growing season (SOS), the peak of the growing season (POS), and the end of the growing season (EOS)—across GP grasslands from 2000 to 2021. Our findings indicate that temperature predominantly determined SOS and POS in the northern and central GP, whereas precipitation played a more dominant role in EOS. Notably, from 2000–2010 to 2011–2021, the influence of precipitation on all three phenological events increased while the influence of temperature decreased. These results were further corroborated using MODIS normalized difference vegetation index time series. Furthermore, projections suggest that temperature limitation on vegetation phenology will be alleviated with warming, while water limitation will intensify in the southern GP, potentially constraining warming-induced advance of spring phenology.

Understanding long-term carbon storage in temperate seagrass habitats is crucial for assessing their role as a “nature-based” climate solution. However, many studies often use shallow cores, low-resolution analyses, and inconsistent methodologies, limiting the ability to infer large-scale carbon storage potential. This study presents the first high-resolution carbon analysis of temperate seagrass sediments to 3 m depth and provides first estimates of sediment and carbon accumulation rates for UK subtidal meadows. Three sediment vibrocores were collected from a subtidal Zostera marina meadow at Drakes Island, Plymouth Sound, UK. High-resolution sampling at 1 cm intervals in the upper meter, and every 5 cm thereafter, enabled detailed analysis of organic carbon (%OC), calcium carbonate, and particle size, with microscope observations recorded. Several methods for %OC analysis were compared, and ²¹⁰Pb dating was used to determine accumulation rates. OC content varied widely (0.24%–27.55%), yielding variable mean OC stocks of 302.34 ± 197.44 Mg C ha⁻¹ over the upper meter. Exceptionally high OC peaks were attributed to coal layers in the sediment. Estimated sediment and carbon accumulation rates ranged from 0.19 to 0.27 g cm⁻² yr⁻¹ and 0.32 to 0.45 Mg C ha⁻¹ yr⁻¹, indicating potential core ages up to 1,300 years. Findings highlight the importance of high-resolution, multi-proxy analysis to assess long-term carbon storage and provided valuable historical insights. This study shows how methodological inconsistencies can lead to inaccurate stock estimates, emphasizing the need for standardization. Addressing these issues aids the advancement of accurate carbon storage quantification, provides valuable storage rate data for management, and strengthens future seagrass carbon research.

Salt marshes remove nitrogen (N) from tidal water via denitrification (DNF) but simultaneously retain N in sediments via dissimilatory nitrate reduction to ammonium (DNRA). The rate of N removal may be governed by NO₃⁻ supply through nitrification and tidal exchange and the relative partitioning of NO₃⁻ to DNF or DNRA. Although both DNF and nitrification are inhibited by sulfide (H₂S), DNRA may be favored by high H₂S and dissolved organic carbon to nitrate (DOC:NO₃⁻) ratios, conditions often found in pore water of low-elevation interior marshes. We compared seasonal rates of DNF and DNRA in control and fertilized plots across three locations with varying geochemical characteristics. Fertilization stimulated DNF regardless of location, whereas DNRA responses to fertilization were variable. DNRA rates ranged 0%–90% and averaged 21.6% of total nitrate reduction but varied by season, location, and N enrichment status. Structural equation modeling suggested that DNF rates were directly influenced by fertilization, DOC:NO₃⁻ ratio, and temperature, but DNRA rates were promoted primarily by temperature and sulfide. This indicates that high sulfide concentrations may promote DNRA as an important pathway for NO₃⁻ reduction. This study highlights how nitrogen removal (via DNF) and nitrogen retention (via DNRA) are regulated by distinct biogeochemical factors. This indicates that salt marshes do not universally act as nitrogen sinks; their function may be location-specific and influenced by environmental conditions such as temperature, sulfide concentrations, and DOC:NO₃⁻ ratios.

Interconnected landscape features such as terrestrial-aquatic interfaces play an outsized role in biogeochemical cycles as ecosystem control points, but it is notoriously challenging to characterize these. Here, we document a synoptic sensor network design that is (a) flexible to accommodate diverse ecosystem interfaces and gradients, (b) adaptable to monitoring and modeling needs of small and large projects alike, (c) standardized for intercomparability across sites and field experiments, and (d) adequately replicated to capture heterogeneity of each parameter monitored. This real-time monitoring of surface water, groundwater, soil, and vegetation supports configuration and evaluation of models that span upland, wetland, open water strata, and transitions between them. We established the network at seven sites along the Chesapeake Bay and Lake Erie coastlines, including large-scale flood manipulation experiments in both regions. A central design element is “one data logger program to rule them all”—a collection of sensor-specific modules deployed on 40 loggers controlling ∼2,000 sensors, with the goal of streamlining maintenance, debugging, and reproducible data processing. The network generates ∼6 M observations per month, capturing system dynamics at the broad spatial and fine temporal scales needed to initialize and benchmark models; measurement frequency can be modified remotely to capture events. This network design has also revealed behaviors not represented in Earth system models, such as transient groundwater oxygen pulses. Completely documented and open source, this standardized, flexible, and efficient sensor network design can reduce barriers to understanding environmental changes and ecosystem responses across systems and scales.

The effects of multiple global change factors on soil carbon (C) stocks are difficult to capture in short-term experiments, but urbanization and other localized characteristics impose long-term, gradual increases in temperature, carbon dioxide and ozone with observable in situ effects. We conducted an observational study in 62 golf courses at varying distances from urbanized areas in the temperate, mesic, mid-Atlantic U.S., measuring soil carbon stocks in minimally managed areas where cool-season turfgrasses had grown without disturbance for at least 25 years. In 2009–2010, soils were sampled to 30 cm depth and site and management variables were recorded. Total and permanganate oxidizable soil carbon were quantified and potential explanatory factors were explored using multiple regression analysis. Extractable soil lead (Pb) was strongly and positively correlated with total soil C (Pb incremental R² = 30.3%) above a threshold of ca. 4 mg/kg soil extracted. Increasing minimum daily temperature in February and cation exchange capacity were also positively correlated with total soil carbon (incremental R² = 2.8% for each factor). These findings suggest that atmospherically deposited Pb atoms chemically associated with and stabilized soil carbon in these soils. Large quantities of Pb were deposited atmospherically over the last century. If the effects observed here are widespread (i.e., in other regions and ecosystems), legacy Pb may impact soil carbon at a scale relevant to global carbon cycle modeling and uncertainty. Further exploration of Pb effects on soil C mineralization is urgently needed to improve quantitative models and our understanding of soil C dynamics.