Global Biogeochemical Cycles最新文献

{"title":"Carbon Export in the Subantarctic Zone Revealed by Multi-Year Observations From Biogeochemical-Argo Floats and Sediment Traps","authors":"Xiang Yang,&nbsp;Cathryn A. Wynn-Edwards,&nbsp;Peter G. Strutton,&nbsp;Elizabeth H. Shadwick","doi":"10.1029/2024GB008135","DOIUrl":"10.1029/2024GB008135","url":null,"abstract":"<p>The biological gravitational pump (BGP) and particle injection pumps (PIPs) are significant export pathways for particulate organic carbon from the surface ocean to the interior. Part of this exported carbon fuels remineralization in the mesopelagic ocean and part is sequestered in the deep ocean. Using observations from Biogeochemical-Argo, we characterized the seasonality and magnitude of the BGP and two PIPs: the mixed layer pump (MLP) and eddy subduction pump (ESP), in the Australian sector of the Subantarctic Zone (SAZ sector). For the first time, float-based estimates were rigorously combined with sediment trap flux (<i>F</i>₁₀₀₀) observations from the Southern Ocean Time Series (SOTS), to investigate these pumps' relative and cumulative contributions to carbon export. The BGP exports about 28.6 g C m⁻² year⁻¹, mostly during the productive season and dominates the <i>F</i>₁₀₀₀ seasonality. The MLP exports about 7.6 g C m⁻² year⁻¹, mostly while the mixing layer seasonally shoals; the ESP sporadically exports up to 100 mg C m⁻² day⁻¹, such that these two PIPs have a short but intense impact on the <i>F</i>₁₀₀₀. The carbon transfer efficiency is 3.6% in the SOTS region. An oxygen-based annual net community production estimate (∼50 g C m⁻² year⁻¹) further strengthens this study, and suggests the BGP and MLP make the dominant contribution to the mesopelagic carbon budget. This is representative of the broader SAZ sector in terms of the magnitude and seasonality of carbon export, the consumption of organic material in the mesopelagic, and the organic carbon sequestration in the deep sea.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"38 7","pages":""},"PeriodicalIF":5.4,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GB008135","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141853684","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Trends and Drivers of Terrestrial Sources and Sinks of Carbon Dioxide: An Overview of the TRENDY Project","authors":"Stephen Sitch,&nbsp;Michael O’Sullivan,&nbsp;Eddy Robertson,&nbsp;Pierre Friedlingstein,&nbsp;Clément Albergel,&nbsp;Peter Anthoni,&nbsp;Almut Arneth,&nbsp;Vivek K. Arora,&nbsp;Ana Bastos,&nbsp;Vladislav Bastrikov,&nbsp;Nicolas Bellouin,&nbsp;Josep G. Canadell,&nbsp;Louise Chini,&nbsp;Philippe Ciais,&nbsp;Stefanie Falk,&nbsp;Ian Harris,&nbsp;George Hurtt,&nbsp;Akihiko Ito,&nbsp;Atul K. Jain,&nbsp;Matthew W. Jones,&nbsp;Fortunat Joos,&nbsp;Etsushi Kato,&nbsp;Daniel Kennedy,&nbsp;Kees Klein Goldewijk,&nbsp;Erik Kluzek,&nbsp;Jürgen Knauer,&nbsp;Peter J. Lawrence,&nbsp;Danica Lombardozzi,&nbsp;Joe R. Melton,&nbsp;Julia E. M. S. Nabel,&nbsp;Naiqing Pan,&nbsp;Philippe Peylin,&nbsp;Julia Pongratz,&nbsp;Benjamin Poulter,&nbsp;Thais M. Rosan,&nbsp;Qing Sun,&nbsp;Hanqin Tian,&nbsp;Anthony P. Walker,&nbsp;Ulrich Weber,&nbsp;Wenping Yuan,&nbsp;Xu Yue,&nbsp;Sönke Zaehle","doi":"10.1029/2024GB008102","DOIUrl":"https://doi.org/10.1029/2024GB008102","url":null,"abstract":"<p>The terrestrial biosphere plays a major role in the global carbon cycle, and there is a recognized need for regularly updated estimates of land-atmosphere exchange at regional and global scales. An international ensemble of Dynamic Global Vegetation Models (DGVMs), known as the “Trends and drivers of the regional scale terrestrial sources and sinks of carbon dioxide” (TRENDY) project, quantifies land biophysical exchange processes and biogeochemistry cycles in support of the annual Global Carbon Budget assessments and the REgional Carbon Cycle Assessment and Processes, phase 2 project. DGVMs use a common protocol and set of driving data sets. A set of factorial simulations allows attribution of spatio-temporal changes in land surface processes to three primary global change drivers: changes in atmospheric CO₂, climate change and variability, and Land Use and Land Cover Changes (LULCC). Here, we describe the TRENDY project, benchmark DGVM performance using remote-sensing and other observational data, and present results for the contemporary period. Simulation results show a large global carbon sink in natural vegetation over 2012–2021, attributed to the CO₂ fertilization effect (3.8 ± 0.8 PgC/yr) and climate (−0.58 ± 0.54 PgC/yr). Forests and semi-arid ecosystems contribute approximately equally to the mean and trend in the natural land sink, and semi-arid ecosystems continue to dominate interannual variability. The natural sink is offset by net emissions from LULCC (−1.6 ± 0.5 PgC/yr), with a net land sink of 1.7 ± 0.6 PgC/yr. Despite the largest gross fluxes being in the tropics, the largest net land-atmosphere exchange is simulated in the extratropical regions.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"38 7","pages":""},"PeriodicalIF":5.4,"publicationDate":"2024-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GB008102","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141730175","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Modeled Seasonal Cycles of Surface N2O Fluxes and Atmospheric N2O","authors":"Qing Sun,&nbsp;Fortunat Joos,&nbsp;Sebastian Lienert,&nbsp;Sarah Berthet,&nbsp;Dustin Carroll,&nbsp;Cheng Gong,&nbsp;Akihiko Ito,&nbsp;Atul K. Jain,&nbsp;Sian Kou-Giesbrecht,&nbsp;Angela Landolfi,&nbsp;Manfredi Manizza,&nbsp;Naiqing Pan,&nbsp;Michael Prather,&nbsp;Pierre Regnier,&nbsp;Laure Resplandy,&nbsp;Roland Séférian,&nbsp;Hao Shi,&nbsp;Parvadha Suntharalingam,&nbsp;Rona L. Thompson,&nbsp;Hanqin Tian,&nbsp;Nicolas Vuichard,&nbsp;Sönke Zaehle,&nbsp;Qing Zhu","doi":"10.1029/2023GB008010","DOIUrl":"https://doi.org/10.1029/2023GB008010","url":null,"abstract":"<p>Nitrous oxide (N₂O) is a greenhouse gas and stratospheric ozone-depleting substance with large and growing anthropogenic emissions. Previous studies identified the influx of N₂O-depleted air from the stratosphere to partly cause the seasonality in tropospheric N₂O (aN₂O), but other contributions remain unclear. Here, we combine surface fluxes from eight land and four ocean models from phase 2 of the Nitrogen/N₂O Model Intercomparison Project with tropospheric transport modeling to simulate aN₂O at eight remote air sampling sites for modern and pre-industrial periods. Models show general agreement on the seasonal phasing of zonal-average N₂O fluxes for most sites, but seasonal peak-to-peak amplitudes differ several-fold across models. The modeled seasonal amplitude of surface aN₂O ranges from 0.25 to 0.80 ppb (interquartile ranges 21%–52% of median) for land, 0.14–0.25 ppb (17%–68%) for ocean, and 0.28–0.77 ppb (23%–52%) for combined flux contributions. The observed seasonal amplitude ranges from 0.34 to 1.08 ppb for these sites. The stratospheric contributions to aN₂O, inferred by the difference between the surface-troposphere model and observations, show 16%–126% larger amplitudes and minima delayed by ∼1 month compared to Northern Hemisphere site observations. Land fluxes and their seasonal amplitude have increased since the pre-industrial era and are projected to grow further under anthropogenic activities. Our results demonstrate the increasing importance of land fluxes for aN₂O seasonality. Considering the large model spread, in situ aN₂O observations and atmospheric transport-chemistry models will provide opportunities for constraining terrestrial and oceanic biosphere models, critical for projecting carbon-nitrogen cycles under ongoing global warming.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"38 7","pages":""},"PeriodicalIF":5.4,"publicationDate":"2024-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GB008010","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141639631","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Physical Mechanisms Sustaining Silica Production Following the Demise of the Diatom Phase of the North Atlantic Spring Phytoplankton Bloom During EXPORTS","authors":"Mark A. Brzezinski,&nbsp;Leah Johnson,&nbsp;Margaret Estapa,&nbsp;Samantha Clevenger,&nbsp;Montserrat Roca-Martí,&nbsp;Elisa Romanelli,&nbsp;Kristen N. Buck,&nbsp;Bethany D. Jenkins,&nbsp;Janice L. Jones","doi":"10.1029/2023GB008048","DOIUrl":"https://doi.org/10.1029/2023GB008048","url":null,"abstract":"<p>Each spring, the North Atlantic experiences one of the largest open-ocean phytoplankton blooms in the global ocean. Diatoms often dominate the initial phase of the bloom with succession driven by exhaustion of silicic acid. The North Atlantic was sampled over 3.5 weeks in spring 2021 following the demise of the main diatom bloom, allowing mechanisms that sustain continued diatom contributions to be examined. Diatom biomass was initially relatively high with biogenic silica concentrations up to 2.25 μmol Si L⁻¹. A low initial silicic acid concentration of 0.1–0.3 μM imposed severe Si limitation of silica production and likely limited the diatom growth rate. Four storms over the next 3.5 weeks entrained silicic acid into the mixed layer, relieving growth limitation, but uptake limitation persisted. Silica production was modest and dominated by the &gt;5.0 μm size fraction although specific rates were highest in the 0.6–5.0 μm size fraction over most of the cruise. Silica dissolution averaged 68% of silica production. The resupply of silicic acid via storm entrainment and silica dissolution supported a cumulative post-bloom silica production that was 32% of that estimated during the main bloom event. Diatoms contributed significantly to new and to primary production after the initial bloom, possibly dominating both. Diatom contribution to organic-carbon export was also significant at 40%–70%. Thus, diatoms can significantly contribute to regional biogeochemistry following initial silicic acid depletion, but that contribution relies on physical processes that resupply the nutrient to surface waters.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"38 7","pages":""},"PeriodicalIF":5.4,"publicationDate":"2024-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GB008048","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141631230","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Size-Fractionated Primary Production Dynamics During the Decline Phase of the North Atlantic Spring Bloom","authors":"Meredith G. Meyer,&nbsp;Mark A. Brzezinski,&nbsp;Melanie R. Cohn,&nbsp;Sasha J. Kramer,&nbsp;Nicola Paul,&nbsp;Garrett Sharpe,&nbsp;Alexandria K. Niebergall,&nbsp;Scott Gifford,&nbsp;Nicolas Cassar,&nbsp;Adrian Marchetti","doi":"10.1029/2023GB008019","DOIUrl":"https://doi.org/10.1029/2023GB008019","url":null,"abstract":"<p>The North Atlantic is a region of enhanced biogeochemical and climatological importance for the global ocean as it is the site of one of the largest seasonal phytoplankton blooms on the planet. However, there is a lack of understanding of how phytoplankton size influences bloom dynamics and associated nutrient utilization rates, particularly during the decline phase when export to the deep ocean is especially pronounced. Here, we evaluate trends in size-fractionated carbon, nitrogen, and silicic acid uptake rates in conjunction with environmental parameters to assess these dynamics. In our study, the decline phase of the bloom continued to be highly productive with net primary production (NPP) ranging from 36.4 to 146.6 mmol C m⁻² d⁻¹ and approximately 54% of primary production being driven by large phytoplankton cells (≥5 μm) that were primarily utilizing nitrate (mean <i>f</i>-ratio of 0.77). Entrainment of silicic acid related to deepening of the mixed layer caused by storms increased silicic acid uptake rates to 2.0–5.7 mmol Si m⁻² d⁻¹ without concomitant increases in NPP by large cells (silicic acid to carbon uptake ratios averaged 0.12). A companion study in the North Pacific allowed for paired evaluation of these regions. Our results suggest that in highly productive regions where phytoplankton biomass and productivity is distributed across a broad range of cell sizes, such as the North Atlantic, size itself has a stronger influence on nutrient cycling and potential carbon export relative to regions with lower production and a predominance of small (&lt;5 μm) cells, such as the North Pacific.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"38 7","pages":""},"PeriodicalIF":5.4,"publicationDate":"2024-07-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141556574","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Observational and Numerical Modeling Constraints on the Global Ocean Biological Carbon Pump","authors":"Scott C. Doney,&nbsp;Kayla A. Mitchell,&nbsp;Stephanie A. Henson,&nbsp;Emma Cavan,&nbsp;Tim DeVries,&nbsp;Nicolas Gruber,&nbsp;Judith Hauck,&nbsp;Colleen B. Mouw,&nbsp;Jens D. Müller,&nbsp;Francois W. Primeau","doi":"10.1029/2024GB008156","DOIUrl":"https://doi.org/10.1029/2024GB008156","url":null,"abstract":"<p>This study characterized ocean biological carbon pump metrics in the second iteration of the REgional Carbon Cycle Assessment and Processes (RECCAP2) project. The analysis here focused on comparisons of global and biome-scale regional patterns in particulate organic carbon (POC) production and sinking flux from the RECCAP2 ocean biogeochemical model ensemble against observational products derived from satellite remote sensing, sediment traps, and geochemical methods. There was generally good model-data agreement in mean large-scale spatial patterns, but with substantial spread across the model ensemble and observational products. The global-integrated, model ensemble-mean export production, taken as the sinking POC flux at 100 m (6.08 ± 1.17 Pg C yr⁻¹), and export ratio defined as sinking flux divided by net primary production (0.154 ± 0.026) both fell at the lower end of observational estimates. Comparison with observational constraints also suggested that the model ensemble may have underestimated regional biological CO₂ drawdown and air-sea CO₂ flux in high productivity regions. Reasonable model-data agreement was found for global-integrated, ensemble-mean sinking POC flux into the deep ocean at 1,000 m (0.65 ± 0.24 Pg C yr⁻¹) and the transfer efficiency defined as flux at 1,000 m divided by flux at 100 m (0.122 ± 0.041), with both variables exhibiting considerable regional variability. The RECCAP2 analysis presents standard ocean biological carbon pump metrics for assessing biogeochemical model skill, metrics that are crucial for further modeling efforts to resolve remaining uncertainties involving system-level interactions between ocean physics and biogeochemistry.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"38 7","pages":""},"PeriodicalIF":5.4,"publicationDate":"2024-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GB008156","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141536743","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Suppression of Nitrogen Deposition on Global Forest Soil CH4 Uptake Depends on Nitrogen Status","authors":"Xiaoyu Cen,&nbsp;Nianpeng He,&nbsp;Mingxu Li,&nbsp;Li Xu,&nbsp;Xueying Yu,&nbsp;Weixiang Cai,&nbsp;Xin Li,&nbsp;Klaus Butterbach-Bahl","doi":"10.1029/2024GB008098","DOIUrl":"https://doi.org/10.1029/2024GB008098","url":null,"abstract":"<p>Methane (CH₄) is the second most important atmospheric greenhouse gas (GHG) and forest soils are a significant sink for atmospheric CH₄. Uptake of CH₄ by global forest soils is affected by nitrogen (N) deposition; clarifying the effect of N deposition helps to reduce uncertainties of the global CH₄ budget. However, it remains an unsolved puzzle why N input stimulates soil CH₄ uptake in some forests while suppressing it in others. Combining previous findings and data from N addition experiments conducted in global forests, we proposed and tested a “stimulating-suppressing-weakened effect” (“three stages”) hypothesis on the changing responses of soil CH₄ flux (<i>R</i>_<i>CH4</i>) to N input. Specifically, we calculated the response factors (<i>f</i>) of <i>R</i>_<i>CH4</i> to N input for N-limited and N-saturated forests across biomes; the phased changes in <i>f</i> values supported our hypothesis. We also estimated the global forest soil CH₄ uptake budget to be approximately 11.2 Tg yr⁻¹. CH₄ uptake hotspots were predominantly located in temperate forests. Furthermore, we quantified that the current level of N deposition reduced global forest soil CH₄ uptake by ∼3%. This suppression effect was more pronounced in temperate forests than in tropical or boreal forests, likely due to differences in N status. The proposed “three stages” hypothesis in this study generalizes the diverse effects of N input on <i>R</i>_<i>CH4</i>, which could help improve experimental design. Additionally, our findings imply that by regulating N pollution and reducing N deposition, soil CH₄ uptake can be significantly increased in the N-saturated forests in tropical and temperate biomes.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"38 7","pages":""},"PeriodicalIF":5.4,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141536865","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Role of Climate, Mineralogy and Stable Aggregates for Soil Organic Carbon Dynamics Along a Geoclimatic Gradient","authors":"Daniel Wasner,&nbsp;Rose Abramoff,&nbsp;Marco Griepentrog,&nbsp;Erick Zagal Venegas,&nbsp;Pascal Boeckx,&nbsp;Sebastian Doetterl","doi":"10.1029/2023GB007934","DOIUrl":"https://doi.org/10.1029/2023GB007934","url":null,"abstract":"<p>Organic matter accumulation in soil is understood as the result of the dynamics between mineral-associated (more decomposed, microbial derived) organic matter and free particulate (less decomposed, plant derived) organic matter. However, from regional to global scales, patterns and drivers behind main soil organic carbon (SOC) fractions are not well understood and remain poorly linked to the pedogenetic variation across soil types. Here, we separated SOC associated with silt- and clay-sized particles (S + C), stable aggregates (&gt;63 μm, SA) and particulate organic matter (POM) from a diverse range of grassland topsoils sampled along a geoclimatic gradient. The relative contribution of the two mineral-associated fractions (S + C &amp; SA) to SOC differed significantly across the gradient, while POM was never the dominant SOC fraction. Stable aggregates (&gt;63 μm) emerged as the major SOC fraction in carbon-rich soils. The degree of decomposition of carbon in stable aggregates (&gt;63 μm) was consistently between that of the S + C and POM fractions and did not change along the investigated gradient. In contrast, carbon associated with the S + C fraction was less microbially decomposed in carbon-rich soils than in carbon-poor soils. The amount of SOC in the S + C fraction was positively correlated to pedogenic oxide contents and texture, whereas the amount of SOC associated with stable aggregates (&gt;63 μm) was positively correlated to pedogenic oxide contents and negatively to temperature. We present a conceptual summary of our findings, which integrates the role of stable aggregates (&gt;63 μm) with other major SOC fractions and illustrates their changing importance across (soil-)environmental gradients.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"38 7","pages":""},"PeriodicalIF":5.4,"publicationDate":"2024-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GB007934","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141488324","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Nitrogen Cycling in Reservoir Drawdown Areas and the Impacts on Water Quality","authors":"Dongsheng Liu,&nbsp;Qiuwen Chen,&nbsp;Taylor Maavara,&nbsp;Jianyun Zhang,&nbsp;Yuchen Chen","doi":"10.1029/2024GB008136","DOIUrl":"https://doi.org/10.1029/2024GB008136","url":null,"abstract":"<p>Reservoir drawdown areas (DAs) can be both important nitrogen (N) sources to river networks and hot spots for N removal from freshwater ecosystems. The net effect of DAs on the N availability in reservoirs within a full hydrological cycle remains unclear. In this paper, the N dynamics in the DA of the Three Gorges Reservoir, Yangtze River, China, are investigated through a combination of discrete and continuous in situ observations and sampling over a span of 2 years, complemented by numerical modeling. We show that the DA is a net source of N to the water column, and that about 30% of the total annual N load released from the DA is mitigated by the sediment through denitrification and capture. The annual net load of the total N from the DA to the reservoir is ca. 0.59 kg per meter along the river, which is on the same order of magnitude as the input load from the density current of the Yangtze River to its tributaries, generally considered to be the primary driver of eutrophication in tributaries. N release in the DA mainly occurs during the drying period, whereas denitrification in the sediment mostly takes place during the flooding period when the oxido-reducing potential is low. Our findings quantify and therefore clarify the N source/sink dynamics from the DA to the reservoir, offering a new perspective on the importance of DA nutrient loading in decision-making related to integrated management of inundated lands to alleviate reservoir eutrophication by river damming.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"38 7","pages":""},"PeriodicalIF":5.4,"publicationDate":"2024-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141488844","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Constraints and Drivers of Dissolved Fluxes of Pyrogenic Carbon in Soil and Freshwater Systems: A Global Review and Meta-Analysis","authors":"R. B. Abney,&nbsp;M. E. Barnes,&nbsp;A. Moss,&nbsp;F. Santos","doi":"10.1029/2023GB008092","DOIUrl":"https://doi.org/10.1029/2023GB008092","url":null,"abstract":"<p>Pyrogenic carbon (PyC) is a significant component of the global soil carbon pool due to its longer environmental persistence than other soil organic matter components. Despite PyC's persistence in soil, recent work has indicated that it is susceptible to loss processes such as mineralization and leaching, with the significance and magnitude of these largely unknown at the hillslope and watershed scales. We present a review of the work concerning dissolved PyC transport in soil and freshwater. Our analysis found that the primary environmental controls on dissolved PyC (dPyC) transport are the formation conditions and quality of the PyC itself, with longer and higher temperature charring conditions leading to less transport of dPyC. While correlations between dPyC and dissolved organic carbon in rivers and other pools are frequently reported, the slope of these correlations was pool-dependent (i.e., soil-water, precipitation, lakes, streams, rivers), suggesting site-specific environmental controls. However, the lack of consistency in analytical techniques and sample preparation remains a major challenge to quantifying environmental controls on dPyC fluxes. We propose that future research should focus on the following: (a) consistency in methodological approaches, (b) more quantitative measures of dPyC in pools and fluxes from soils to streams, (c) turnover times of dPyC in soils and aquatic systems, and (d) improved understanding of how mechanisms controlling the fate of dPyC in dynamic post-fire landscapes interact. With more refined quantitative information about the controls on dPyC transport at the hillslope and landscape scale, we can increase the accuracy and utility of global carbon models.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"38 6","pages":""},"PeriodicalIF":5.4,"publicationDate":"2024-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GB008092","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141488252","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}