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Journal of Geophysical Research
American Geophysical Union
Journal of Geophysical Research

American Geophysical Union

2169-8953

Journal of Geophysical Research/Journal Journal of Geophysical Research
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    Was Dissolved Nitrogen Regime Driving Diatom to Dinoflagellate Shift in the Bohai Sea? Evidences From Microcosm Experiment and Modeling Reproduction

    Gao, PeiyiWang, PingHang, XiurongChen, Yanan...
    23页
    查看更多>>摘要：The shift of diatom dominance to combination of diatom and dinoflagellate dominance in the Bohai Sea (BS), China might be associated with the change of dissolved nitrogen (DN). This study combines field investigation, ship-based microcosm experiments, a nitrogen biogeochemical model, and statistical analysis to reveal the impact of DN loading on the dominance of diatoms and dinoflagellates in the BS, considering the quantitative relationship between the algal growth/death and nitrogen migration/transformation processes. The diatom to diatom-dinoflagellate shift was significantly associated with the DN regime shift of oxidized nitrogen (NO3-N) to reduced nitrogen (NH4-N and dissolved organic nitrogen [DON]) since the mid-1990s. This phenomenon was supported by microcosm and numerical experiments: (a) Gonyaulax verior as a dominant dinoflagellate in the BS efficiently absorbed/assimilated NH4-N, and it can also utilize DON derived from centric diatoms; Chaetoceros densus as dominant centric diatoms in the BS was able to absorb/assimilate NO3-N, and it can also utilize DON derived from the Xiaoqing River; (b) The change in dinoflagellates/diatoms ratios was reproduced with the change in DN regime from the 1980s to the 2010s by the proposed nitrogen biogeochemical model based on localized parameters in the BS. Moreover, mixotrophism and stronger survival stability, associated with the faster NH4-N and DONalgal uptake and slower decomposition of G. verior, also supported the shift from diatoms to diatoms-dinoflagellates during high variations in nutrient supply. This study infers the phytoplankton regime shift mechanism associated with the DN structure in coastal waters, providing a credible scientific basis for the shift from water quality-based to ecosystem-based environmental management.
      原文链接:
    • NSTL
    • Amer Geophysical Union

    Sulfur Biogeochemical Cycling and Redox Dynamics in a Shale-Dominated Mountainous Watershed

    Fox, Patricia M.Carrero, SergioAnderson, CamDewey, Christian...
    18页
    查看更多>>摘要：Sulfur (S) is an essential macronutrient and important component of the earth's crust, and its cycling has critical impacts on trace metal mobility, water quality, and human health. Pyrite weathering is the primary pathway by which sulfur enters surface waters. However, biogeochemical cycling of sulfur in soils and the river corridor mediates sulfate exports. In this study, we identified the major forms of sulfur across multiple compartments and scales in a pristine mountainous watershed, including shale bedrock weathering profiles, hillslope soils, and alluvial floodplain sediments, in order to provide insight into biogeochemical sulfur cycling in a hydrologically variable alpine system. X-ray absorption near-edge spectroscopy (XANES) analysis of shale weathering profiles showed clear evidence of pyrite oxidation to sulfate, with large accumulations of intermediate S(0) (20%-53%). Micro-scale XANES showed evidence of reprecipitation of pyrite at fracture surfaces within the permanently saturated zone. Organic sulfur dominated S speciation in shallow hillslope soil and floodplain sediment, with little evidence of reduced inorganic S. However, mackinawite formation, representing active sulfate reduction, was observed in saturated oxbow sediments and saturated weathered shale underlying floodplain sediments. Further evidence of sulfate reduction from aqueous sulfur isotopic analysis was observed in shallow groundwater transects across an Fe-reducing meander, whereas increases in pore water sulfate concentrations implied sulfur oxidation at other locations. The data present an integrated picture of sulfur cycling in a shale-dominated watershed, where riverine sulfate exports are mediated by biological cycling, particularly in redox-stratified and temporally dynamic hyporheic zone sediments.
      原文链接:
    • NSTL
    • Amer Geophysical Union

    Leveraging the Historical Landsat Catalog for a Remote Sensing Model of Wetland Accretion in Coastal Louisiana

    Jensen, D. J.Cavanaugh, K. C.Thompson, D. R.Fagherazzi, S....
    14页
    查看更多>>摘要：A wetland's ability to vertically accrete-capturing sediment and biological matter for soil accumulation-is key for maintaining elevation to counter soil subsidence and sea level rise. Wetland soil accretion is comprised of organic and inorganic components largely governed by net primary productivity and sedimentation. Sea level, land elevation, primary productivity, and sediment accretion are all changing across Louisiana's coastline, destabilizing much of its wetland ecosystems. In coastal Louisiana, analysis from 1984 to 2020 shows an estimated 1940.858 km(2) of total loss at an average rate of 53.913 km(2)/year. Here we hypothesize that remote sensing timeseries data can provide suitable proxies for organic and inorganic accretionary components to estimate local accretion rates. The Landsat catalog offers decades of imagery applicable to tracking land extent changes across coastal Louisiana. This dataset's expansiveness allows it to be combined with the Coastwide Reference Monitoring System's point-based accretion data. We exported normalized difference vegetation index (NDVI) and red-band surface reflectance data for every available Landsat 4-8 scene across the coast using Google Earth Engine. Water pixels from the red-band were transformed into estimates of total suspended solids to represent sediment deposition-the inorganic accretionary component. NDVI values over land pixels were used to estimate bioproductivity-representing accretion's organic component. We then developed a Random Forest regression model that predicts wetland accretion rates (R-2 = 0.586, MAE = 0.333 cm/year). This model can inform wetland vulnerability assessments and loss predictions, and is to our knowledge the first remote sensing-based model that directly estimates accretion rates in coastal wetlands.
      原文链接:
    • NSTL
    • Amer Geophysical Union

    Turbidity Currents Can Dictate Organic Carbon Fluxes Across River-Fed Fjords: An Example From Bute Inlet (BC, Canada)

    Hage, S.Galy, V. V.Cartigny, M. J. B.Heerema, C....
    16页
    查看更多>>摘要：The delivery and burial of terrestrial particulate organic carbon (OC) in marine sediments is important to quantify, because this OC is a food resource for benthic communities, and if buried it may lower the concentrations of atmospheric CO2 over geologic timescales. Analysis of sediment cores has previously shown that fjords are hotspots for OC burial. Fjords can contain complex networks of submarine channels formed by seafloor sediment flows, called turbidity currents. However, the burial efficiency and distribution of OC by turbidity currents in river-fed fjords had not been investigated previously. Here, we determine OC distribution and burial efficiency across a turbidity current system within Bute Inlet, a fjord in western Canada. We show that 62% +/- 10% of the OC supplied by the two river sources is buried across the fjord surficial (30-200 cm) sediment. The sandy subenvironments (channel and lobe) contain 63% +/- 14% of the annual terrestrial OC burial in the fjord. In contrast, the muddy subenvironments (overbank and distal basin) contain the remaining 37% +/- 14%. OC in the channel, lobe, and overbank exclusively comprises terrestrial OC sourced from rivers. When normalized by the fjord's surface area, at least 3 times more terrestrial OC is buried in Bute Inlet, compared to the muddy parts of other fjords previously studied. Although the long-term (>100 years) preservation of this OC is still to be fully understood, turbidity currents in fjords appear to be efficient at storing OC supplied by rivers in their near-surface deposits.
      原文链接:
    • NSTL
    • Amer Geophysical Union

    Source Identification and Estimation of Organic Carbon in the Intertidal Wetlands of the Eastern Coast of China

    Wang, DongqiChen, ShuDeng, HuanguangYu, Zhongjie...
    17页
    查看更多>>摘要：Intertidal wetlands are important carbon reservoirs that play a significant role in climate change mitigation. However, the lack of large-scale quantification and source identification of sediment organic carbon (SOC) in different discharge estuaries hampers the assessment of the carbon storage potential in these systems. In this study, based on the elemental ratios and stable carbon isotopes of the core sediment from the intertidal wetlands along the east coast of China, we quantified the contribution of organic carbon (OC) derived from terrestrial/estuarine particulate organic matter (POM), marine phytoplankton, and local plants, such as mangrove and salt marsh plants in the study area. We explored the hydrological and plant drivers controlling the variation in the contribution of OC sources among different coastal environmental settings. We found that SOC in high discharge estuaries (river runoff more than 50 billion m(3)/a) originated predominantly from terrestrial/estuarine POM (45 +/- 6%), whereas the primary source for low discharge estuaries was marine phytoplankton OC (51 +/- 14%). Moreover, our estimates revealed a sharp increase in the contribution of OC from mangroves to deep sediments compared with surface sediments, owing to the infiltration of mangrove roots at greater depths and the slow degradation of roots contributing to the substantial refractory OC buried in the deep sediments. These findings indicate that carbon storage in the intertidal wetlands varies among contrasting coastal environmental conditions, which provides implications for intertidal wetlands as a critical carbon sink in the global carbon budget.
      原文链接:
    • NSTL
    • Amer Geophysical Union

    Reconstruction of the Eukaryotic Communities in Beppu Bay Over the Past 50 Years Based on Sedimentary DNA Barcoding

    Segawa, YudaiYamamoto, MasanobuKuwae, MichinobuMoriya, Kazuyoshi...
    13页
    查看更多>>摘要：Comprehensive reconstruction of changes in eukaryotic communities in the recent past is useful for determining the response of the local ecosystems to global changes during the Anthropocene. We used DNA barcoding technology to reconstruct the marine eukaryotic communities of Beppu Bay, the Seto Inland Sea, Japan, over the past 50 years based on a short sediment core. Highly vulnerable DNA fragments were preserved in the sediments, possibly due to seasonally euxinic conditions. Analysis of the 18S rRNA V9 gene region indicated the temporal variability in eukaryotic communities, which consisted mainly of dinoflagellates and diatoms, in response to changes in the nutrient regime. The dominant species in the dinoflagellate genus Alexandrium changed as the water temperature increased. In addition, enhanced contributions by terrestrial plants and mosses were detected in flood sediments. Our results suggest that DNA fragments can be used as a proxy for the paleoenvironmental and paleoecological conditions in Beppu Bay.
      原文链接:
    • NSTL
    • Amer Geophysical Union

    A Modeling Approach for Addressing Sensitivity and Uncertainty of Estuarine Greenhouse Gas (CO2 and CH4) Dynamics

    Huang, PeishengDe Sousa, Eduardo R.Wells, Naomi S.Eyre, Bradley D....
    25页
    查看更多>>摘要：Estuaries make an important contribution to the global greenhouse gas budget. Yet modeling predictions of carbon dioxide (CO2) and methane (CH4) emissions from estuaries remain highly uncertain due to both simplified assumptions about the underpinning hydrologic and biologic processes and inadequate data availability to uniquely define parameters related to CO2 and CH4 processes. This study presents a modeling framework to quantify the sensitivity and uncertainty of predicted CO2 and CH4 concentrations and emissions, which is demonstrated through application to a subtropical urban estuary (Brisbane River, Australia). A 3D hydrodynamic-biogeochemical model was constructed, and calibrated using the model-independent Parameter ESTimation software (PEST) with field data sets that captured strong gradients of CO2 and CH4 concentrations and emissions along the estuary. The approach refined uncertainty in the estimation of whole-estuary annual emissions, and enabled us to assess the sensitivity and uncertainty of CO2 and CH4 dynamics. Estuarine CO2 concentrations were most sensitive to uncertainty in riverine inputs, whereas estuarine CH4 concentrations were most sensitive to sediment production and pelagic oxidation. Over the modeled year, variance in the daily fluctuations in carbon emissions from this case-study spanned the full range of emission rates reported for estuaries around the world, highlighting that spatially or temporally limited sampling regimes could significantly bias estuarine greenhouse gas emission estimates. The combination of targeted field campaigns with the modeling approach presented in this study can help to improve carbon budgeting in estuaries, reduce uncertainty in emission estimates, and support management strategies to reduce or offset estuary greenhouse gas emissions.
      原文链接:
    • NSTL
    • Amer Geophysical Union

    Soil Amended With Organic Matter Increases Fluvial Erosion Resistance of Cohesive Streambank Soil

    Smith, D. J.Snead, M.Thompson, T. M.
    14页
    查看更多>>摘要：Fluvial erosion of cohesive soil is mediated by interactions between soil physical, biological, and chemical characteristics such as soil aggregate stability and extracellular polymeric substances (EPS). While labile organic matter (OM) stimulates microbial EPS production and significantly improves soil aggregate stability in agricultural soils, these interactions remain unexplored in streambank soils. The study goal was to quantify the impact of OM on aggregate stability, EPS, and fluvial erosion rates of cohesive streambank soil. Increasing amounts of 1-mm sieved dry grass were incorporated at rates of 0, 1, and 4 g per 100 g of 2-mm sieved silt-loam soil (treatments T0, T1, and T4, respectively). Samples (eight replicates per treatment) were matured in a greenhouse for 50 days prior to flume erosion testing. EPS carbohydrates were significantly (p < 0.05) lower in T1 (324 +/- 63 mu g/g) compared to T0 (388 +/- 37 mu g/g) and T4 (376 +/- 44 mu g/g). EPS proteins were significantly higher in T1 (194 +/- 15 mu g/g) and T4 (223 +/- 61 mu g/g) compared to T0 (101 +/- 20 mu g/g) and positively correlated with mean weight diameter (MWD), a measure of soil stability against slaking. MWD was 16% and over 100% higher for T1 and T4, respectively, than for T0. Similarly, the average soil erodibility coefficient of T1 and T4 was 25% and 61% lower than the erodibility of T0; however, only the reduction for T4 was significant. The data presented here underscore the important role labile OM plays in improving soil physical stability and increasing the resistance of cohesive soil to fluvial erosion of streambanks.
      原文链接:
    • NSTL
    • Amer Geophysical Union

    Changing Hydrographic, Biogeochemical, and Acidification Properties in the Gulf of Maine as Measured by the Gulf of Maine North Atlantic Time Series, GNATS, Between 1998 and 2018

    Balch, William M.Drapeau, David T.Bowler, Bruce C.Record, Nicholas R....
    35页
    查看更多>>摘要：The Gulf of Maine North Atlantic Time Series (GNATS) has been run since 1998, across the Gulf of Maine (GoM), between Maine and Nova Scotia. GNATS goals are to provide ocean color satellite validation and to examine change in this coastal ecosystem. We have sampled hydrographical, biological, chemical, biogeochemical, and bio-optical variables. After 2008, warm water intrusions (likely North Atlantic Slope Water [NASW]) were observed in the eastern GoM at 50-180 m depths. Shallow waters (<50 m) significantly warmed in winter, summer, and fall but cooled during spring. Surface salinity and density of the GoM also significantly increased over the 20 years. Phytoplankton standing stock and primary production showed highly-significant decreases during the period. Concentrations of phosphate increased, silicate decreased, residual nitrate [N*; nitrate-silicate] increased, and the ratio of dissolved inorganic nitrogen:phosphate decreased, suggesting increasing nitrogen limitation. Dissolved organic carbon (DOC) and its optical indices generally increased over two decades, suggesting changes to the DOC cycle. Surface seawater carbonate chemistry showed winter periods where the aragonite saturation (omega(ar)) dropped below 1.6 gulf-wide due to upward winter mixing of cool, corrosive water. However, associated with increased average GoM temperatures, omega(ar) has significantly increased. These results reinforce the hypothesis that the observed decrease in surface GoM primary production resulted from a switch from Labrador Sea Water to NASW entering the GoM. A multifactor analysis shows that decreasing GoM primary production is most significantly correlated to decreases in chlorophyll and particulate organic carbon plus increases in N* and temperature.
      原文链接:
    • NSTL
    • Amer Geophysical Union

    Past to Present: An Update to the Aims and Scope of JGR: Biogeosciences

    Xenopoulos, Marguerite A.Desai, Ankur R.Huntzinger, Deborah
    4页
    查看更多>>摘要：Plain Language Summary The Journal of Geophysical Research-Biogeosciences focuses on the interactions between biology, hydrology, geology, chemistry, and physics within the Earth system. Here, we are presenting a brief early history of the journal and evolution of the topics and papers published over the past 20 years. We present an updated aims and scope which now explicitly considers method and data articles.
      原文链接:
    • NSTL
    • Amer Geophysical Union