Journal of Geophysical Research: Biogeosciences最新文献

{"title":"Diverse Altitudinal Patterns and Drivers of Greenhouse Gas Dynamics in Southwest China Alpine Streams and Rivers","authors":"Ying Wang,&nbsp;Yuhao Li,&nbsp;Genxu Wang,&nbsp;Yang Li,&nbsp;Xiangyang Sun,&nbsp;Wenzhi Wang,&nbsp;Chunlin Song","doi":"10.1029/2024JG008458","DOIUrl":"https://doi.org/10.1029/2024JG008458","url":null,"abstract":"<p>Streams and rivers are globally significant sources of greenhouse gases (GHGs) to the atmosphere. However, GHG evasion from mountain streams remains poorly constrained due to scarce data. In this study, we measured concentrations and estimated fluxes of riverine carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) across three alpine catchments in Southwest China. GHG concentrations in these turbulent streams and rivers are slightly oversaturated but much lower than the global average, likely due to high gas transfer velocities that rapidly deplete GHGs. Headwater streams (first-order) exhibited higher gas evasion rates than large rivers (fourth-order), despite having lower CO₂ and N₂O concentrations. The partial pressure of CO₂ and dissolved N₂O concentrations decreased linearly with elevation, likely linked to the altitudinal patterns of forest cover and groundwater table depth. Dissolved CH₄ concentrations and the three GHGs fluxes showed weak relationships with elevation. We observed significant seasonal differences in GHG fluxes, with higher evasion rates during the wet season. The seasonal and spatial heterogeneity in stream GHG concentrations and fluxes was primarily controlled by hydrology, climate, and geomorphology. Our analyses also revealed that GHG fluxes were positively correlated with stream water temperature, velocity, and channel slope. This study demonstrates that these alpine streams are underestimated net sources of GHGs, particularly CO₂ and N₂O, highlighting the importance of mountain headwater systems in regional and global GHG budgets. The diverse altitudinal patterns of GHG dynamics also suggest complex controls of GHG in alpine streams and rivers.</p>","PeriodicalId":16003,"journal":{"name":"Journal of Geophysical Research: Biogeosciences","volume":"130 2","pages":""},"PeriodicalIF":3.7,"publicationDate":"2025-02-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143380762","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Elevated Atmospheric Sulfur Deposition Affects Predominant Forms of Sulfur in Ombrotrophic Peatlands","authors":"Hongyan Wang,&nbsp;Zhi-Guo Yu,&nbsp;Tanja Broder,&nbsp;Jörg Göttlicher,&nbsp;Ralph Steininger,&nbsp;Sindy Wagner,&nbsp;Harald Biester,&nbsp;Klaus-Holger Knorr","doi":"10.1029/2024JG008563","DOIUrl":"https://doi.org/10.1029/2024JG008563","url":null,"abstract":"<p>Long-term transformations of sulfur from atmospheric deposition in ombrotrophic peatlands have rarely been studied, although the potential impact on carbon mineralization and particularly methane formation is acknowledged. To elucidate the long-term fate of sulfur in peat, we therefore applied sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy to investigate peatlands with either natural or anthropogenic atmospheric sulfur deposition. A peatland in central Europe (Germany, BBM) experienced high sulfur deposition during the Industrial Revolution, and an oceanic peatland (Chilean Patagonia, PBr) continuously exposed to aerosols from sea spray, were investigated. During early phases of site BBM, when sulfur deposition was constantly low, wet-chemical extractions indicated that 98% ± 0.7% of sulfur was present as organic sulfur. The S K-edge XANES fitting suggested that sulfur redox transformations mainly occurred near the water table, at which reduced sulfur forms (primarily organic sulfides, and thiols) increased from ∼40% to and stabilized at 65% ± 4% in anoxic peat. An increased contribution of reduced sulfur forms was observed in the polluted section of BBM and entire peat profile of PBr. While increases in reduced inorganic sulfur (TRIS) likely depended on available Fe, rises in the ratio of reduced organic sulfur to total organic sulfur from both sites were pronounced. This increase in reduced organic sulfur forms likely resulted from abiotic sulphurization of organic carbon after sulfate reduction. Our study highlights the long-term fate of elevated sulfur in ombrotrophic peatlands, being mainly transformed into reduced organic sulfur.</p>","PeriodicalId":16003,"journal":{"name":"Journal of Geophysical Research: Biogeosciences","volume":"130 2","pages":""},"PeriodicalIF":3.7,"publicationDate":"2025-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143380075","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Impact of Diagenesis on Biogenic Silica- Structural, Chemical, and Isotope Proxies","authors":"Franziska M. Stamm,&nbsp;Rebecca A. Pickering,&nbsp;Patrick J. Frings,&nbsp;Daniel A. Frick,&nbsp;Sylvain Richoz,&nbsp;Daniel J. Conley","doi":"10.1029/2024JG008160","DOIUrl":"https://doi.org/10.1029/2024JG008160","url":null,"abstract":"<p>The silicon isotope composition (δ³⁰Si) of biogenic silica is often used as an archive of past environmental conditions. For example, sponge spicule δ³⁰Si is known to be related to seawater-dissolved Si concentrations. Such a proxy application requires that the δ³⁰Si is not diagenetically altered—or at least that any alteration can be identified and accounted for. Yet the preservation of pristine isotope signals during (early) diagenesis is challenged by observations of structural changes to the amorphous silica (opal-A) of biogenic silica toward a more stable amorphous silica phase (opal-CT). This transformation is known to be associated with a resetting of oxygen isotope (δ¹⁸O) values but with unclear implications for the preservation of other geochemical signatures. This was investigated using modern and Cretaceous siliceous sponge spicules. Modern spicules collected from different ocean basins were uniformly transparent opal-A, whereas Cretaceous spicules exhibited two preservation states: visually similar to modern or clearly altered toward a milky, translucent composition. A comparison of δ³⁰Si and δ¹⁸O values of spicules from both categories within single samples reveals the milky, translucent individuals are offset from the transparent individuals and thus presumably unsuitable for palaeoenvironmental applications. A suite of geochemical and structural analyses (XRD, Raman spectroscopy, and FT-IR spectroscopy) demonstrate that even visually clear Cretaceous spicules are subtly different from their modern counterparts, implying caution is required when interpreting δ³⁰Si values or other geochemical proxies in ancient biogenic silica.</p>","PeriodicalId":16003,"journal":{"name":"Journal of Geophysical Research: Biogeosciences","volume":"130 2","pages":""},"PeriodicalIF":3.7,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024JG008160","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143186378","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Deciphering Microbially Driven Labile and Refractory Molecular Candidates in Dissolved Organic Matter","authors":"Qi Chen,&nbsp;Jiaxin Chen,&nbsp;Ruanhong Cai,&nbsp;Chen He,&nbsp;Quan Shi,&nbsp;Chuanlun Zhang,&nbsp;Nianzhi Jiao,&nbsp;Qiang Zheng","doi":"10.1029/2024JG008484","DOIUrl":"https://doi.org/10.1029/2024JG008484","url":null,"abstract":"<p>Microbial activities drive the cycling of dissolved organic matter (DOM) from labile to refractory states, thus contributing to the long-term carbon sequestration in the ocean. However, due to the intricate molecular composition of DOM, identifying indicators of microbially related DOM remains a challenge. In this study, we propose molecular candidates for bio-labile (<i>n</i> = 537) and bio-refractory (<i>n</i> = 1,025) formulas, which were discerned through incubation experiments using ultrahigh-resolution mass spectrometry. Bio-labile formulas exhibited greater hydrogenation, whereas bio-refractory formulas comprised oxidized, unsaturated and aromatic molecules with higher molecular weight. Bio-candidates, in contrast to photo- or terrestrial-related counterparts, dominated molecular composition by higher relative intensity. The application of these molecular candidates facilitated the tracing of molecular distribution and transformation patterns across large-scale aquatic environmental gradients. This molecular identification framework offers insights into resolving microbially mediated molecules and advancing our understanding of biologically related DOM at the molecular level.</p>","PeriodicalId":16003,"journal":{"name":"Journal of Geophysical Research: Biogeosciences","volume":"130 2","pages":""},"PeriodicalIF":3.7,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143186377","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Seasonal Effects of Soil Temperature and Soil Water Content on Upscaled Soil Respiration and Its Contribution to Ecosystem Respiration in Chaparral Shrublands","authors":"J. A. Montes,&nbsp;K. Lunneberg,&nbsp;M. N. Montemayor,&nbsp;B. M. Gillespie,&nbsp;W. C. Oechel","doi":"10.1029/2023JG007985","DOIUrl":"https://doi.org/10.1029/2023JG007985","url":null,"abstract":"<p>Chaparral, a semi-arid Mediterranean plant community, has the potential to act as a sink, which is an essential ecosystem to mitigate climate change. However, soil respiration (Rs) responses to meteorological variables remain uncertain in these regions, and no studies have quantified how much Rs attributes to Reco in chaparral shrublands. This study identifies the effects of soil temperature (Ts) and soil water content (SWC) on upscaled Rs and its contribution to Reco (Rs/Reco) in chaparral shrublands in Southern California between 2020 and 2021. Hourly Rs and net ecosystem exchange (NEE) were collected by automated chambers and the eddy covariance technique, respectively. Due to high daily variability and gaps in our data, 5-day averages were calculated to understand the effects of meteorological on Rs and Rs/Reco. First, we proposed that SWC was the primary driver of Rs regardless of the season, while Ts effects were prominent when SWC was sufficient. Secondly, we hypothesized Rs/Reco to vary seasonally, particularly due to Rs contributing less under dry conditions. Our results showed SWC to have a strong significant effect on Rs throughout the year, whereas Ts was only a significant control when the soil was wet and Ts was below 20°C. Monthly Rs/Reco was highest during January and February, likely due to the reduced aboveground respiration. While Rs/Reco was lowest when the soil was the driest. These findings improve our understanding of Rs response to climatic conditions and emphasize the importance of estimating Rs/Reco in chaparral shrublands.</p>","PeriodicalId":16003,"journal":{"name":"Journal of Geophysical Research: Biogeosciences","volume":"130 2","pages":""},"PeriodicalIF":3.7,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023JG007985","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143186418","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Machine Learning Reveals the Contrasting Roles of Rainfall and Canopy Structure Metrics on the Formation of Canopy Drip and Splash Throughfall","authors":"Kazuki Nanko,&nbsp;Delphis F. Levia,&nbsp;Shin'ichi Iida,&nbsp;Yoshinori Shinohara,&nbsp;Naoki Sakai","doi":"10.1029/2024JG008340","DOIUrl":"https://doi.org/10.1029/2024JG008340","url":null,"abstract":"<p>Throughfall is a significant majority of the total precipitation reaching the ground in forested areas. This study revealed biotic and abiotic factors influencing the throughfall generation process, with the throughfall partitioning into free throughfall, splash throughfall, and canopy drip created at foliar surface drip points (FSDPs) and occasional woody surface drip points (O-WSDPs), utilizing machine learning. Using a large-scale rainfall simulator, throughfall drops were simultaneously measured at 19 locations under a mix of deciduous and coniferous tree species in both foliated and unfoliated states. Random forest modeling showed that biotic factors, such as foliage amount, primarily affected the development and volume fraction of canopy drip in foliated trees. In contrast, for unfoliated trees, canopy drip volume fraction was mainly influenced by abiotic factors, including drop size and kinetic energy of open rainfall. The formation and volume fraction of splash throughfall were primarily influenced by abiotic factors for both foliated and unfoliated trees. From the comparison between the foliated and unfoliated states, the generation process of canopy drip was separately clarified between FSDPs and O-WSDPs. More and larger canopy drip was generated by more foliage with a more wetted canopy with less fluctuation at the FSDPs, whereas a less wetted canopy and/or higher drop impact energy generated more and larger canopy drip at O-WSDPs. This study underscores the importance of canopy structure and meteorological conditions in determining throughfall partitioning. The findings contribute to a nuanced understanding of rainwater redistribution in forest ecosystems.</p>","PeriodicalId":16003,"journal":{"name":"Journal of Geophysical Research: Biogeosciences","volume":"130 2","pages":""},"PeriodicalIF":3.7,"publicationDate":"2025-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143111532","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Exploring the Significance of Chlorophyll Fluorescence-Based Photosynthetic Capacity in Gross Primary Productivity Simulations Across Diverse Ecosystems in China","authors":"Muhammad Amir,&nbsp;Bin Chen,&nbsp;Jinghua Chen,&nbsp;Shaoqiang Wang,&nbsp;Kai Zhu,&nbsp;Shiliang Chen,&nbsp;Ye Xia","doi":"10.1029/2023JG007889","DOIUrl":"https://doi.org/10.1029/2023JG007889","url":null,"abstract":"<p>Accurate estimation of gross primary productivity (GPP) plays a critical role in developing effective climate change policies. In addition to climatic factors, CO₂ levels, and leaf area index (LAI), GPP is also primarily regulated by the maximum rate of carboxylation (<i>V</i>_cmax) in ecosystem models. However, significant uncertainties in <i>V</i>_cmax measurements, along with its limited availability over larger geographical areas, hinder our ability to address scientific questions in context of increasing atmospheric CO₂ concentrations. Recently, solar-induced fluorescence (SIF) signals have been used as non-invasive way to monitor plant physiological processes. In this study, we utilized eddy covariance-based GPP and the Soil-Canopy Observation of Photosynthesis and Energy (SCOPE) model to infer <i>V</i>_cmax. We aimed to establish relationships between site-scale <i>V</i>_cmax and far-red solar-induced chlorophyll fluorescence yield (SIF_yield) to estimate photosynthetic capacity across diverse ecosystems in China from 2008 to 2010. Our findings revealed a robust relationship between SIF_yield and site-level <i>V</i>_cmax retrievals, with a coefficient of determination (<i>R</i>²) ranging from 0.36 to 0.74 (<i>p</i> &lt; 0.05) at biweekly (once every two weeks) intervals across all studied sites. Incorporating SIF_yield-derived <i>V</i>_cmax into the SCOPE model resulted in a 9% improvement in GPP simulation accuracy compare to using a constant <i>V</i>_cmax. Additionally, integration SIF_yield-derived <i>V</i>_cmax into the BEPS (Boreal Ecosystem Productivity Simulator) model demonstrated strong agreement between flux-based and simulated GPP values, further validating the accuracy of the estimated <i>V</i>_cmax in capturing ecosystem photosynthetic capacity. This study highlights the importance of utilizing SIF_yield to precisely quantify GPP estimates in the context of imminent climate change challenges.</p>","PeriodicalId":16003,"journal":{"name":"Journal of Geophysical Research: Biogeosciences","volume":"130 2","pages":""},"PeriodicalIF":3.7,"publicationDate":"2025-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143110762","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Strong Effects of Increased Hydrostatic Pressure on Polysaccharide-Hydrolyzing Enzyme Activities in Coastal Seawater and Sediments","authors":"C. Chad Lloyd,&nbsp;John Paul Balmonte,&nbsp;Ronnie N. Glud,&nbsp;Carol Arnosti","doi":"10.1029/2024JG008417","DOIUrl":"https://doi.org/10.1029/2024JG008417","url":null,"abstract":"<p>Heterotrophic microorganisms are responsible for transforming and respiring a substantial fraction of the organic matter produced by phytoplankton in the surface ocean. Much of this organic matter is composed of polysaccharides, high-molecular weight (HMW) sugars. To initiate degradation of polysaccharides, microorganisms must produce extracellular enzymes of the right structural specificity to hydrolyze these complex structures. To date, most measurements of enzyme activities are made at in situ temperatures, but at atmospheric pressure. However, previous studies have shown that hydrostatic pressure can impact the functionality of enzymes. Since deep sea communities may be seeded by microbes from shallow waters, we aimed to determine if pressure affects the performance of enzymes from coastal waters. To determine the extent to which enzymatic activities of coastal microbial communities are affected by pressure, we quantified the degradation of seven polysaccharides under pressures ranging from 0.1 MPa (atmospheric) to 40 MPa (equivalent to 4,000 m). Enzyme activities of pelagic communities were inhibited with increased pressure, while enzyme activities of benthic microbial communities were more resistant to increased pressure. Addition of HMW organic matter resulted in communities with enzyme activities that were more resistant to increased pressure. However, the freely-dissolved enzymes (&lt;0.2 μm) produced by these communities were strongly inhibited by increased hydrostatic pressure, suggesting that the pressure-resistant enzymes were cell-surface attached. Because pressure inhibition of enzyme activities varied strongly by polysaccharide, we surmise that the structural complexity of a polysaccharide—and therefore the number of distinct enzymes required for hydrolysis—is likely closely associated with pressure inhibition.</p>","PeriodicalId":16003,"journal":{"name":"Journal of Geophysical Research: Biogeosciences","volume":"130 2","pages":""},"PeriodicalIF":3.7,"publicationDate":"2025-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143110735","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Leaf Spectroscopy Reveals Drought Response Variation in Fagus sylvatica Saplings From Across the Species' Range","authors":"Dave Kurath,&nbsp;Sofia J. van Moorsel,&nbsp;Jolanda Klaver,&nbsp;Tis Voortman,&nbsp;Barbara Siegfried,&nbsp;Yves-Alain Brügger,&nbsp;Aboubakr Moradi,&nbsp;Ewa A. Czyż,&nbsp;Marylaure de La Harpe,&nbsp;Guido L. Wiesenberg,&nbsp;Michael E. Schaepman,&nbsp;Meredith C. Schuman","doi":"10.1029/2024JG008404","DOIUrl":"https://doi.org/10.1029/2024JG008404","url":null,"abstract":"<p>The common European beech (<i>Fagus sylvatica</i>), sensitive to prolonged drought, is expected to shift its distribution with climate change. To persist in novel environments, young trees rely on the capacity to express diverse response phenotypes. Several methods exist to study drought effects on trees and their diverse adaptive mechanisms, but these are usually destructive and challenging for the large sample numbers needed to investigate biological variation. We conducted a common garden experiment outdoors, but under controlled watering conditions, with 180 potted 2-year-old saplings from 16 beech provenances across the species' range, representing three distinct genetic clusters. Drought stress was simulated by interrupting irrigation and stomatal conductance and soil moisture were used to assess drought severity. We measured leaf reflectance of visible to short-wave infrared electromagnetic radiation to determine drought-induced changes in biochemical and structural traits derived from spectral indices and a model of leaf optical properties. We quantified changes in pigmentation, water balance, nitrogen, lignin, epicuticular wax, and leaf mass per area in drought-treated saplings, revealing differences in likely adaptive responses to drought. <i>F. sylvatica</i> saplings from the Iberian Peninsula showed signatures of greater drought resistance, that is, the least drought-induced change in spectrally derived traits related to leaf pigments and leaf water content. We demonstrate that high-resolution leaf spectroscopy is an effective and non-destructive tool to assess individual drought responses that can characterize functional intraspecific variation among young beech trees. Next, this approach should be scaled up to canopy-level or airborne spectroscopy to support drought response assessments of forests.</p>","PeriodicalId":16003,"journal":{"name":"Journal of Geophysical Research: Biogeosciences","volume":"130 2","pages":""},"PeriodicalIF":3.7,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143110456","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Confirming the Primacy of Light Controlling Ammonium Removal in Response to Biofilm Colonization and Shade Using Experimental Streams","authors":"Anna E. S. Vincent,&nbsp;Jennifer L. Tank,&nbsp;Shannon L. Speir,&nbsp;Elise D. Snyder,&nbsp;Abagael N. Pruitt,&nbsp;Ursula H. Mahl,&nbsp;Robert O. Hall Jr.","doi":"10.1029/2024JG008259","DOIUrl":"https://doi.org/10.1029/2024JG008259","url":null,"abstract":"<p>The removal of riparian shading alters stream biogeochemical cycling by stimulating algal biofilms through the release of light limitation. Few studies have examined the combined effects of shading and biofilm growth on ammonium (NH₄⁺–N) and nitrate (NO₃⁻–N) removal in the same experiment. We quantified water column NH₄⁺–N and NO₃⁻–N removal using <i>n</i> = 176 short-term additions in four experimental streams over 2 years and assessed the influence of shading (shaded vs. open canopy) and biofilm colonization (early vs. late) on removal using a Bayesian three-level hierarchical model. First, we assessed the roles of biofilm and shade on NH₄⁺–N removal. Shading lowered NH₄⁺–N uptake velocity [<i>V</i>_<i>f</i>; slope: −0.45 (−0.69, −0.22)], while the effect of biofilm was too small to detect [0.06 (−0.18, 0.29)]. The following season, we compared NH₄⁺–N and NO₃⁻–N removal, and added night releases to estimate autotrophic and heterotrophic contributions to removal. Shading reduced NH₄⁺–N and NO₃⁻–N <i>V</i>_<i>f</i>, while the effect of biofilm often depended on shading. NH₄⁺–N <i>V</i>_<i>f</i> was higher than NO₃⁻–N <i>V</i>_<i>f</i> by 51% during the day and 38% at night, confirming preferential NH₄⁺–N removal. NO₃⁻–N <i>V</i>_<i>f</i> declined more between the Late-Open and Late-Shade phases compared to NH₄⁺–N, suggesting a stronger decline in NO₃⁻–N demand than for NH₄⁺–N with shade during late biofilm colonization. We found no strong diel shift in NH₄⁺–N or NO₃⁻–N demand. Results demonstrate the primacy of light on NH₄⁺–N and NO₃⁻–N removal in streams. Understanding how shading and biofilm colonization alter removal is critical as streams are vulnerable to the impacts of land use change.</p>","PeriodicalId":16003,"journal":{"name":"Journal of Geophysical Research: Biogeosciences","volume":"130 2","pages":""},"PeriodicalIF":3.7,"publicationDate":"2025-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024JG008259","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143121455","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}