Biogeosciences discussions : (BGD)最新文献

{"title":"Growth rate rather than temperature affects the B / Ca ratio in the\u0000calcareous red alga Lithothamnion corallioides","authors":"Giulia Piazza, V. Bracchi, A. Langone, A. Meroni, D. Basso","doi":"10.5194/BG-2021-21","DOIUrl":"https://doi.org/10.5194/BG-2021-21","url":null,"abstract":"Abstract. The B / Ca ratio in calcareous marine species is informative of past seawater CO32− concentrations, but scarce data exist on B / Ca in coralline algae (CA). Recent studies suggest influences of temperature and growth rates on B / Ca, the effect of which could be critical for the reconstructions of surface ocean pH and atmospheric pCO2. In this paper, we present the first LA-ICP-MS analyses of Mg, Sr, Li and B in the CA Lithothamnion corallioides collected from different geographic settings and depths across the Mediterranean Sea and in the Atlantic Ocean. We produced the first data on temperature proxies (Mg, Li and Sr / Ca) and B / Ca in a CA species grown in different Basins (the Mediterranean Sea and the Atlantic Ocean), from shallow to deep waters (12 m, 40 m, 45 m and 66 m depth). We tested the B / Ca correlation with temperature proxies and growth rates, in order to evaluate their possible effect on B incorporation. Our results showed a growth rate influence on B / Ca, especially in the deepest sample (Pontian Isl., Italy; 66 m) and in the shallowest sample (Morlaix, Atlantic coast of France; 12 m), where the growth rates were respectively 0.11 mm/yr and 0.13 mm/yr and the B / Ca was respectively 462.8 ± 49.2 μmol/mol and 726.9 ± 102.8 μmol/mol. A positive correlation between B / Ca and the temperature proxies was found only in Morlaix, where the seasonal temperature variation (ΔT) was the highest (8.90 °C). These pieces of evidence suggest that growth rates, triggered by the different ΔT and light availability across depth, affect the B incorporation in L. corallioides.\u0000","PeriodicalId":89897,"journal":{"name":"Biogeosciences discussions : (BGD)","volume":" ","pages":"1-27"},"PeriodicalIF":0.0,"publicationDate":"2021-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49120636","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"CO2 emissions from peat-draining rivers regulated by water pH","authors":"Alexandra Klemme, T. Rixen, Denise Müller-Dum, Moritz Müller, J. Notholt, T. Warneke","doi":"10.5194/BG-2021-13","DOIUrl":"https://doi.org/10.5194/BG-2021-13","url":null,"abstract":"Abstract. Southeast Asian peatlands represent a globally significant carbon store that is destabilized by deforestation and the transformation into plantations, causing high carbon dioxide (CO2) emissions from peat soils and increased leaching rates of peat carbon into rivers. While global model studies assumed that CO2 emissions from peat-draining rivers would be high, estimates based on field data suggest they are only moderate. In this study we offer an explanation for this phenomenon and show that carbon decomposition is hampered by the low pH in peat-draining rivers, which limits CO2 production in and emissions from these rivers. We find an exponential pH limitation that shows good agreement with laboratory measurements from high latitude peat soils. Additionally, our results suggest that enhanced input of carbonate minerals increase CO2 emissions from peat-draining rivers by counteracting the pH limitation. As such inputs of carbonate minerals occur due to human activities like deforestation of river catchments, liming in plantations and enhanced weathering projects, our study points out an important feedback mechanism of those practices.\u0000","PeriodicalId":89897,"journal":{"name":"Biogeosciences discussions : (BGD)","volume":" ","pages":"1-20"},"PeriodicalIF":0.0,"publicationDate":"2021-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44584401","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Assessing MODIS Vegetation Continuous Fields tree cover product\u0000(collection 6): performance and applicability in tropical forests and \u0000savannas","authors":"Rahayu Adzhar, D. Kelley, N. Dong, Mireia Torello Raventos, E. Veenendaal, T. Feldpausch, O. Philips, S. Lewis, B. Sonké, H. Taedoumg, Beatriz Schwantes Marimon, T. Domingues, L. Arroyo, G. Djagbletey, G. Saiz, F. Gerard","doi":"10.5194/BG-2020-460","DOIUrl":"https://doi.org/10.5194/BG-2020-460","url":null,"abstract":"Abstract. The Moderate Resolution Imaging Spectroradiometer vegetation continuous fields (MODIS VCF) Earth observation product is widely used to estimate forest cover changes, parameterise vegetation and Earth System models, and as a reference for validation or calibration where field data is limited. However, although limited independent validations of MODIS VCF have shown that MODIS VCF's accuracy decreases when estimating tree cover in sparsely-vegetated areas, such as in tropical savannas, no study has yet assessed the impact this may have on the VCF based tree cover distributions used by many in their research. Using tropical forest and savanna inventory data collected by the TROpical Biomes In Transition (TROBIT) project, we produce a series of corrections that take into account (i) the spatial disparity between the in-situ plot size and the MODIS VCF pixel, and (ii) the trees' spatial distribution within in-situ plots. We then applied our corrections to areas identified as forest or savanna in the International Geosphere-Biosphere Programme (IGBP) land cover mapping product. All IGBP classes identified as savanna show substantial increases in cover after correction, indicating that the most recent version of MODIS VCF consistently underestimates woody cover in tropical savannas. We estimate that MODIS VCF could be underestimating tropical tree cover by between 9–15 %. Models that use VCF as their benchmark could be underestimating the carbon uptake in forest-savanna areas and misrepresenting forest-savanna dynamics. While more detailed in-situ field data is necessary to produce more accurate and reliable corrections, we recommend caution when using MODIS VCF in tropical savannas.","PeriodicalId":89897,"journal":{"name":"Biogeosciences discussions : (BGD)","volume":"1 1","pages":"1-20"},"PeriodicalIF":0.0,"publicationDate":"2021-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41987748","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Experimental production of charcoal morphologies to discriminate fuel source and fire type in the Siberian taiga","authors":"A. Feurdean","doi":"10.5194/BG-2021-1","DOIUrl":"https://doi.org/10.5194/BG-2021-1","url":null,"abstract":"Abstract. The analysis of charcoal fragments in peat and lake sediments is the most widely used approach to reconstruct past biomass burning. With a few exceptions, this method typically relies on the quantification of the total charcoal content of the sediment. To enhance charcoal analyses for the reconstruction of past fire regimes, and to make the method more relevant to studies of both plant evolution and fire management, more information must be extracted from charcoal particles. Here, I burned in the laboratory seven fuel types comprising 17 species from boreal Siberia, and build on published schemes to develop morphometric and finer diagnostic classifications of the experimentally charred particles. As most of the species used in this study are common to Northern Hemisphere forests and peatlands, these results can be directly applicable over a broad geographical scale. Results show that the effect of temperature on charcoal production is fuel dependent. Graminoids and Sphagnum, and wood (trunk) lose the most mass at low burn temperatures, whereas heathland shrub leaves, brown moss, and ferns retain the most mass at high burn temperatures. In contrast to the wood of trunk, the wood of twigs retained their mass at intermediate temperature. This suggests that species with low mass retention at hotter burning temperatures might be underrepresented in the fossil charcoal record. Charred particle aspect ratio (L / W) appeared to be the strongest indicator of the fuel type burnt. Graminoid charcoals are more elongate than those of all other fuel types, leaf charcoals are the shortest and bulkiest, and twig and wood charcoals are intermediate. Finer diagnostic features were the most useful in distinguishing between wood, graminoid, and leaf particles, but further distinctions within these fuel types are difficult. High-aspect-ratio particles dominated by graminoid and Sphagnum morphologies are robust indicators of cooler surface fires. Contrastingly, abundant wood and leaf morphologies and low-aspect-ratio particles likely indicate higher-temperature fires. However, the overlapping morphologies of leaves and wood from trees and shrubs make it hard to distinguish between high-intensity surface fires combusting living shrubs and dead wood and leaves or high-intensity crown fires combusting living trees. Despite these limitations, the combined use of charred-particle aspect ratios and fuel morphotypes can aid in more robustly interpreting changes in fuel source and fire type, thereby substantially refining histories of past wildfires. Further fields of investigation to improve the interpretation of the fossil charcoal records will require: i) More in-depth knowledge of plant anatomy for a better determination of fuel sources; ii) Relate the proportion of particular charcoal morphotypes to the quantity of biomass; iii) Link the chemical composition of fuels, combustion temperature, and charcoal production. The advanced use of image-recognition softwar","PeriodicalId":89897,"journal":{"name":"Biogeosciences discussions : (BGD)","volume":" ","pages":"1-26"},"PeriodicalIF":0.0,"publicationDate":"2021-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47804140","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Reviews and syntheses: Trends in primary production in the Bay of Bengal – is it at a tipping\u0000point?","authors":"C. Löscher","doi":"10.5194/BG-2020-494","DOIUrl":"https://doi.org/10.5194/BG-2020-494","url":null,"abstract":"Abstract. Ocean primary production is the basis of the marine food web, sustaining life in the ocean via photosynthesis, and removing carbon dioxide from the atmosphere. Recently, a small but significant decrease of global marine primary production has been reported based on ocean color data, which was mostly ascribed to decreases in primary production in the northern Indian Ocean, particularly in the Bay of Bengal. Available reports on primary production from the Bay of Bengal (BoB) are limited, and due their spatial and temporal variability difficult to interpret. Primary production in the BoB has historically been described to be driven by diatom and chlorophyte clades, while only more recent datasets also show an abundance of smaller, visually difficult to detect cyanobacterial primary producers. The different character of the available datasets, i.e. direct counts, metagenomic and biogeochemical data, and satellite-based ocean color observations, make it difficult to derive a consistent pattern. However, making use of the most highly resolved dataset based on satellite imaging a shift in community composition of primary producers is visible in the BoB over the last two decades. This shift is driven by a decrease in chlorophyte abundance, and a coinciding increase in cyanobacterial abundance, despite stable concentrations of total chlorophyll. A similar but somewhat weaker trend is visible in the Arabian Sea, where satellite imaging points towards decreasing abundances of chlorophytes in the North and increasing abundances of cyanobacteria in the eastern parts. Statistical analysis indicated a correlation of this community change in the BoB to decreasing nitrate concentrations, which may provide an explanation for both, the decrease of eukaryotic nitrate-dependent primary producers and the increase of small unicellular cyanobacteria related to Prochlorococcus, which have a comparably higher affinity to nitrate. Changes in community composition of primary producers and an overall decrease of system productivity would strongly impact oxygen concentrations of the BoB's low oxygen intermediate waters. Assuming decreasing nitrate concentrations and concurrent decreasing biomass production, export and respiration, oxygen concentrations within the oxygen minimum zone would not be expected to further decrease, an effect which would be enhanced by stronger stratification as a result of future warming. Therefore, given a decrease in primary production, the BoB may not be at a tipping point for becoming anoxic, unless external nutrient inputs increase.\u0000","PeriodicalId":89897,"journal":{"name":"Biogeosciences discussions : (BGD)","volume":" ","pages":"1-15"},"PeriodicalIF":0.0,"publicationDate":"2021-01-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42653245","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Defining BGC-Argo-based metrics of ocean health and biogeochemical \u0000functioning for the evaluation of global ocean models","authors":"A. Mignot, H. Claustre, G. Cossarini, F. D’Ortenzio, E. Gutknecht, J. Lamouroux, P. Lazzari, C. Perruche, S. Salon, R. Sauzède, V. Taillandier, A. Terruzzi","doi":"10.5194/BG-2021-2","DOIUrl":"https://doi.org/10.5194/BG-2021-2","url":null,"abstract":"Abstract. Numerical models of ocean biogeochemistry are becoming a major tool to detect and predict the impact of climate change on marine resources and ocean health. Classically, validation of such models relies on comparison with surface quantities from satellite (such as chlorophyll-a concentrations), climatologies, or sparse in situ data (such as cruises observations, and permanent fixed oceanic stations). However, these datasets are not fully suitable to assess how models represent many climate-relevant biogeochemical processes.  These limitations now begin to be overcome with the availability of a large number of vertical profiles of light, pH, oxygen, nitrate, chlorophyll-a concentrations and particulate backscattering acquired by the Biogeochemical-Argo (BGC-Argo) floats network. Additionally, other key biogeochemical variables such as dissolved inorganic carbon and alkalinity, not measured by floats, can be predicted by machine learning-based methods applied to float oxygen concentrations. Here, we demonstrate the use of the global array of BGC-Argo floats for the validation of biogeochemical models at the global scale. We first present 18 key metrics of ocean health and biogeochemical functioning to quantify the success of BGC model simulations. These metrics are associated with the air-sea CO2 flux, the biological carbon pump, oceanic pH, oxygen levels and Oxygen Minimum Zones (OMZs). The metrics are either a depth-averaged quantity or correspond to the depth of a particular feature. We also suggest four diagnostic plots for displaying such metrics.\u0000","PeriodicalId":89897,"journal":{"name":"Biogeosciences discussions : (BGD)","volume":"1 1","pages":"1-66"},"PeriodicalIF":0.0,"publicationDate":"2021-01-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44788818","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Variability of the surface energy balance in permafrost-underlain boreal forest","authors":"S. M. Stuenzi, J. Boike, W. Cable, U. Herzschuh, S. Kruse, L. Pestryakova, T. Schneider von Deimling, S. Westermann, Evgenii S. Zakharov, M. Langer","doi":"10.5194/BG-18-343-2021","DOIUrl":"https://doi.org/10.5194/BG-18-343-2021","url":null,"abstract":"Abstract. Boreal forests in permafrost regions make up around one-third of the global forest cover and are an essential component of regional and global climate patterns. Further, climatic change can trigger extensive ecosystem shifts such as the partial disappearance of near surface permafrost or changes to the vegetation structure and composition. Therefore, our aim is to understand how the interactions between the vegetation, permafrost, and the atmosphere stabilize the forests and the underlying permafrost. Existing model set-ups are often static or are not able to capture important processes such as the vertical structure or the leaf physiological properties. There is a need for a physically based model with a robust radiative transfer scheme through the canopy. A one-dimensional land surface model (CryoGrid) is adapted for the application in vegetated areas by coupling a multilayer canopy model (CLM-ml v0) and is used to reproduce the energy transfer and thermal regime at a study site (N 63.18946, E 118.19596) in mixed boreal forest in Eastern Siberia. We have in-situ soil temperature and radiation measurements, to evaluate the model and demonstrate the capabilities of a coupled multilayer forest-permafrost model to investigate the vertical exchange of radiation, heat, and water. We find that the forests exert a strong control on the thermal state of permafrost through changing the radiation balance and snow cover phenology. The forest cover alters the surface energy balance by inhibiting over 90 % of the solar radiation and suppressing turbulent heat fluxes. Additionally, our simulations reveal a surplus in longwave radiation trapped below the canopy, similar to a greenhouse, which leads to a comparable magnitude in storage heat flux to that simulated at the grassland site. Further, the end of season snow cover is three times greater at the forest site and the onset of the snow melting processes are delayed.","PeriodicalId":89897,"journal":{"name":"Biogeosciences discussions : (BGD)","volume":"18 1","pages":"1-35"},"PeriodicalIF":0.0,"publicationDate":"2021-01-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49526707","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"New constraints on biological production and mixing processes in the\u0000South China Sea from triple isotope composition of dissolved oxygen","authors":"Hana Jurikova, O. Abe, F. Shiah, M. Liang","doi":"10.5194/BG-2020-448","DOIUrl":"https://doi.org/10.5194/BG-2020-448","url":null,"abstract":"Abstract. South China Sea (SCS), world’s largest marginal sea, plays an important role in the global as well as regional biogeochemical cycling of carbon and oxygen. However, its overall metabolic balance, primary production rates, and their link to East Asian Monsoon forcing still remain poorly constrained. Here, we report seasonal trends in triple oxygen isotope composition (17Δ) of dissolved O2, a tracer for biological O2, gross primary production (GP; inferred from δ17O and δ18O values), and net community production (NP; evaluated from oxygen–argon ratios) from the SouthEast Asian Time-series Study (SEATS) in SCS. Our results suggest stable mixed-layer GP rates of 1.8 g C m−2 d−1 and NP of −0.02 g C m−2 d−1 during the summer southwest monsoon, indicating the prevalence of net heterotrophy. During winter months characterised by stronger northeast monsoon forcing, the system is more dynamic with variable production rates, which may shift the metabolism from net heterotrophy to net autotrophy (NP up to ~0.15 g C  m−2 d−1). These findings underscore the importance of monsoon intensity on tilting the carbon balance from source to sink in a warm oligotrophic sea, and on driving the regional circulation pattern. Finally, our data from the deeper regions show that SCS circulation is strongly affected by monsoon wind forcing, with a larger part of the water column down to at least 400 m depth fully exchanged during a winter, suggesting the 17Δ of deep O2 as a valuable novel conservative tracer for probing mixing processes from a new perspective.\u0000","PeriodicalId":89897,"journal":{"name":"Biogeosciences discussions : (BGD)","volume":" ","pages":"1-25"},"PeriodicalIF":0.0,"publicationDate":"2021-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48392552","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Radiative transfer modeling with BGC-Argo float data in the\u0000Mediterranean Sea","authors":"Elena Terzić, Arnau Miró, P. Lazzari, E. Organelli, F. D’Ortenzio","doi":"10.5194/BG-2020-473","DOIUrl":"https://doi.org/10.5194/BG-2020-473","url":null,"abstract":"Abstract. A radiative transfer model was parameterized and validated using Biogeochemical Argo float data acquired between 2012 and 2017 across the Mediterranean Sea. Fluorescence-derived chlorophyll a concentration, particle backscattering at 700 nm and fluorescence of colored dissolved organic matter were used to parametrize the light absorption and scattering coefficients of the optically significant water constituents (pure water, non-algal particles, colored dissolved organic matter and phytoplankton). The model was validated with in-situ downwelling irradiance profiles and irradiance-derived apparent optical properties from satellite data, such as the diffuse attenuation coefficients and remote sensing reflectance. To the authors' knowledge, this is the first time that a three-platform comparison of such kind is performed between model, floats and satellites. Results showed that by using regional parameterizations that are not only related to chlorophyll concentration and vertical distribution, the model was able to capture a more accurate spectral response in the examined wavelength range compared to chlorophyll-related (or Case 1) optical models. When using alternative models that incorporated also measurements of colored dissolved organic matter fluorescence or particulate optical backscattering, the model skill increased at all examined wavelengths. A series of upgrades, such as the inclusion of temperature and salinity data for the modification of the pure water absorption spectra, a refined pure water absorption model, as well as the correction of regional algorithms that had overestimated the pure water contribution in the blue, all contributed to improve the model performance. Finally, using a multi-spectral optical configuration enabled to estimate also the relative contribution of separate water constituents in the examined spectral range. Simulations including non-algal particles and colored dissolved organic matter performed up to 60 % and 76 % better than when considering the optical properties of pure seawater alone. Moreover, a simulation including phytoplankton absorption resulted in an error reduction of up to 43 %, especially at 412 nm and with a more uniform response at the wavelengths considered. Such studies can therefore also tackle the bio-optically anomalous nature of the Mediterranean Sea, and show that non-chlorophyll-related constituents (i.e. non-algal particles and colored dissolved organic matter) can substantially modulate the underwater light field in the blue.","PeriodicalId":89897,"journal":{"name":"Biogeosciences discussions : (BGD)","volume":"1 1","pages":"1-30"},"PeriodicalIF":0.0,"publicationDate":"2021-01-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42228229","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Spatial and temporal variability of pCO2 and CO2 emissions from the Dongjiang River in South China","authors":"Boyi Liu, M. Tian, K. Shih, C. Chan, Xiankun Yang, L. Ran","doi":"10.5194/BG-2020-477","DOIUrl":"https://doi.org/10.5194/BG-2020-477","url":null,"abstract":"Abstract. CO2 efflux at the water–air interface is an essential component of the riverine carbon cycle. However, the lack of spatially resolved CO2 emission measurement still hinges the accuracy of estimates on global riverine CO2 emissions. By deploying floating chambers, seasonal changes in river water CO2 partial pressure (pCO2) and CO2 evasion from the Dongjiang River in South China were investigated. Lateral soil CO2 input and dilution effect caused by precipitation played critical roles in controlling riverine pCO2 in small rivers, while the decomposition of allochthonous organic carbon is responsible for pCO2 variability in large rivers. Temperature-normalized gas transfer velocity (k600) in small rivers were 8.29 ± 11.29 m d−1 and 4.90 ± 3.82 m d−1 for the wet season and dry season, respectively, which were nearly 70 % higher than that of large rivers (3.90 ± 5.55 m d−1 during the wet season and 2.25 ± 1.61 m d−1 during the dry season). A significant correlation was observed between k600 and flow velocity but not wind speed regardless of river size. Majority of the surveyed rivers were net CO2 source, exhibiting substantial seasonal variations. The mean CO2 flux was 300.1 and 264.2 mmol m−2 d−1 during wet season for large and small rivers, respectively, 2-fold larger than that during dry season. The absence of commonly observed higher CO2 fluxes in small rivers could be associated with the depletion effect caused by abundant and consistent precipitation in this subtropical monsoon catchment.\u0000","PeriodicalId":89897,"journal":{"name":"Biogeosciences discussions : (BGD)","volume":"1 1","pages":"1-24"},"PeriodicalIF":0.0,"publicationDate":"2021-01-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46185869","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}