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Thorsten Dittmar - One of the best experts on this subject based on the ideXlab platform.
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response to comment on dilution limits Dissolved Organic Carbon utilization in the deep ocean
Science, 2015Co-Authors: Jesús M. Arrieta, Eva Mayol, Roberta L. Hansman, Gerhard J. Herndl, Thorsten Dittmar, Carlos M. DuarteAbstract:Our recent finding that dilution limits Dissolved Organic Carbon (DOC) utilization in the deep ocean has been criticized based on the common misconception that lability equates to rapid and complete utilization. Even when considering the redefinition of recalcitrant DOC recently proposed by Jiao et al., the dilution hypothesis best explains our experimental observations.
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extraordinary slow degradation of Dissolved Organic Carbon doc in a cold marginal sea
Scientific Reports, 2015Co-Authors: Taehoon Kim, Guebuem Kim, Shinah Lee, Thorsten DittmarAbstract:Dissolved Organic Carbon (DOC) is the largest Organic Carbon reservoir in the ocean, and the amount of Carbon in this reservoir rivals that in atmospheric CO2. In general, DOC introduced into the deep ocean undergoes a significant degradation over a centennial time scale (i.e., ~50 μM to ~34 μM in the North Atlantic and Mediterranean Sea). However, we here show that high concentrations of DOC (58 ± 4 μM) are maintained almost constantly over 100 years in the entire deep East/Japan Sea (EJS). The degradation rate in this sea is estimated to be 0.04 μmol C kg(-1) yr(-1), which is 2-3 times lower than that in the North Atlantic and Mediterranean Sea. Since the source of DOC in the deep EJS is found to be of marine origin on the basis of δ(13)C-DOC signatures, this slow degradation rate seems to be due to low temperature (<1 °C) in the entire deep water column. This observational result suggests that the storage capacity of DOC in the world ocean is very sensitive to global warming and slowdown of global deep-water overturning.
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Dilution limits Dissolved Organic Carbon utilization in the deep ocean
Science (New York N.Y.), 2015Co-Authors: Jesús M. Arrieta, Eva Mayol, Roberta L. Hansman, Gerhard J. Herndl, Thorsten Dittmar, Carlos M. DuarteAbstract:Oceanic Dissolved Organic Carbon (DOC) is the second largest reservoir of Organic Carbon in the biosphere. About 72% of the global DOC inventory is stored in deep oceanic layers for years to centuries, supporting the current view that it consists of materials resistant to microbial degradation. An alternative hypothesis is that deep-water DOC consists of many different, intrinsically labile compounds at concentrations too low to compensate for the metabolic costs associated to their utilization. Here, we present experimental evidence showing that low concentrations rather than recalcitrance preclude consumption of a substantial fraction of DOC, leading to slow microbial growth in the deep ocean. These findings demonstrate an alternative mechanism for the long-term storage of labile DOC in the deep ocean, which has been hitherto largely ignored.
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low volume quantification of Dissolved Organic Carbon and Dissolved nitrogen
Limnology and Oceanography-methods, 2012Co-Authors: Aron Stubbins, Thorsten DittmarAbstract:A method for the quantification of Dissolved Organic Carbon (DOC) and total Dissolved nitrogen (TDN) in aqueous samples of less than 600 µL is described. Analysis of low volumes is achieved through modification of a Shimadzu HTC TOC analyzer, which in its conventional configuration requires at least 7 mL sample. The modification allows manual injection of sample directly into the high temperature combustion column, bypassing much of the instrument's dead volume. Instrument performance (blank, precision, and response factor) in the low volume configuration was equal to that of the instrument in its native larger volume, auto-analyzer configuration. The low volume modification is simple, low cost (less than €25) and reversible, taking a matter of minutes to install or remove. It allows routine high precision and accuracy measurement of DOC and TDN in cases where sample volume is limiting. When sample volumes are not limiting, the standard configuration of the Shimadzu is recommended due to the ability to use the auto-analyzer and reduce the labor required per sample run.
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low volume quantification of Dissolved Organic Carbon and Dissolved nitrogen
Limnology and Oceanography, 2012Co-Authors: Aron Stubbins, Thorsten DittmarAbstract:A method for the quantification of Dissolved Organic Carbon (DOC) and total Dissolved nitrogen (TDN) in aqueous samples of less than 600 μL is described. Analysis of low volumes is achieved through modification of a Shimadzu HTC TOC analyzer, which in its conventional configuration requires at least 7 mL sample. The modification allows manual injection of sample directly into the high temperature combustion column, bypassing much of the instrument’s dead volume. Instrument performance (blank, precision, and response factor) in the low volume configuration was equal to that of the instrument in its native larger volume, auto-analyzer configuration. The low volume modification is simple, low cost (less than €25) and reversible, taking a matter of minutes to install or remove. It allows routine high precision and accuracy measurement of DOC and TDN in cases where sample volume is limiting. When sample volumes are not limiting, the standard configuration of the Shimadzu is recommended due to the ability to use the auto-analyzer and reduce the labor required per sample run. *Corresponding author: E-mail: aron.stubbins@skio.usg.edu Acknowledgments This work was supported by a Fellowship from the Hanse Institute for Advanced Studies (HWK, Delmenhorst, Germany) granted to Stubbins. Matthias Friebe provided Dissolved Organic Carbon and total Dissolved nitrogen standard curves acquired in the conventional, auto-analyzer configuration of the Shimadzu TOC analyzer. DOI 10.4319/lom.2012.10.347 Limnol. Oceanogr.: Methods 10, 2012, 347–352 © 2012, by the American Society of Limnology and Oceanography, Inc. LIMNOLOGY and OCEANOGRAPHY: METHODS of the instrument, which routinely come into contact with the sample. The main components requiring rinsing are the instrument tubing and the “multi-function sample pretreatment/injection system” (2.1.7 Flow Diagram, TOC-VCPH/CPN user’s manual for TOC-Control V ver.2, Shimadzu). Shimadzu offers both automatic and manual injection options. However, the instrument’s internal machinations are rinsed in both modes, such that the sample volume requirement remains at approximately 7 mL. It is possible to purchase a manual injection kit directly from Shimadzu that reduces sample volume requirements to 100 μL. This unit costs approximately €360, and to the authors’ knowledge, no protocol or appraisal for the analysis of marine samples with this setup exists in the peer reviewed literature. Here we present a low cost (< €25) adaptation to a Shimadzu TOC analyzer (TOC-VCPH). The adaptation allows for the routine analysis of small sample volumes (tens of microliters depending upon sample OM concentrations). Analytical performance in this modified setup is equivalent to that acquired by using the Shimadzu TOC-VCPH in its native, automated, larger volume configuration.
C D Evans - One of the best experts on this subject based on the ideXlab platform.
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boreal forest riparian zones regulate stream sulfate and Dissolved Organic Carbon
Science of The Total Environment, 2016Co-Authors: Jose L J Ledesma, Martyn N Futter, C D Evans, Hjalmar Laudon, Stephan KohlerAbstract:In boreal forest catchments, solute transfer to streams is controlled by hydrological and biogeochemical processes occurring in the riparian zone (RZ). However, RZs are spatially heterogeneous and information about solute chemistry is typically limited. This is problematic when making inferences about stream chemistry. Hypothetically, the strength of links between riparian and stream chemistry is time-scale dependent. Using a ten-year (2003 − 2012) dataset from a northern Swedish catchment, we evaluated the suitability of RZ data to infer stream dynamics at different time scales. We focus on the role of the RZ versus upslope soils in controlling sulfate (SO42−) and Dissolved Organic Carbon (DOC). A priori, declines in acid deposition and redox-mediated SO42− pulses control sulfur (S) fluxes and pool dynamics, which in turn affect Dissolved Organic Carbon (DOC). We found that the catchment is currently a net source of S, presumably due to release of the S pool accumulated during the acidification period. In both, RZ and stream, SO42 − concentrations are declining over time, whereas DOC is increasing. No temporal trends in SO42 − and DOC were observed in upslope mineral soils. SO42 − explained the variation of DOC in stream and RZ, but not in upslope mineral soil. Moreover, as SO42 − decreased with time, temporal variability of DOC increased. These observations indicate that: (1) SO42 − is still an important driver of DOC trends in boreal catchments and (2) RZ processes control stream SO42 − and subsequently DOC independently of upslope soils. These phenomena are likely occurring in many regions recovering from acidification. Because water flows through a heterogeneous mosaic of RZs before entering the stream, upscaling information from limited RZ data to the catchment level is problematic at short-time scales. However, for long-term trends and annual dynamics, the same data can provide reasonable representations of riparian processes and support meaningful inferences about stream chemistry.
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acidity controls on Dissolved Organic Carbon mobility in Organic soils
Global Change Biology, 2012Co-Authors: C D Evans, Nick Ostle, Timothy G Jones, Annette Burden, Piotr Zielinski, Mark D A Cooper, Mike Peacock, Joanna M Clark, Filip OulehleAbstract:Dissolved Organic Carbon (DOC) concentrations in surface waters have increased across much of Europe and North America, with implications for the terrestrial Carbon balance, aquatic ecosystem functioning, water treatment costs and human health. Over the past decade, many hypotheses have been put forward to explain this phenomenon, from changing climate and land management to eutrophication and acid deposition. Resolution of this debate has been hindered by a reliance on correlative analyses of time series data, and a lack of robust experimental testing of proposed mechanisms. In a 4 year, four-site replicated field experiment involving both acidifying and deacidifying treatments, we tested the hypothesis that DOC leaching was previously suppressed by high levels of soil acidity in peat and organo-mineral soils, and therefore that observed DOC increases a consequence of decreasing soil acidity. We observed a consistent, positive relationship between DOC and acidity change at all sites. Responses were described by similar hyperbolic relationships between standardized changes in DOC and hydrogen ion concentrations at all sites, suggesting potentially general applicability. These relationships explained a substantial proportion of observed changes in peak DOC concentrations in nearby monitoring streams, and application to a UK-wide upland soil pH dataset suggests that recovery from acidification alone could have led to soil solution DOC increases in the range 46–126% by habitat type since 1978. Our findings raise the possibility that changing soil acidity may have wider impacts on ecosystem Carbon balances. Decreasing sulphur deposition may be accelerating terrestrial Carbon loss, and returning surface waters to a natural, high-DOC condition.
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Dissolved Organic Carbon trends resulting from changes in atmospheric deposition chemistry
Nature, 2007Co-Authors: D T Monteith, John L Stoddard, C D Evans, Martin Forsius, Tore Hogasen, Anders Wilander, B L Skjelkvale, D S Jeffries, Jussi Vuorenmaa, Bill KellerAbstract:There have been widespread reports of surface waters in many remote glaciated regions of North America and Northern Europe becoming browner as levels of Dissolved Organic Carbon have increased. Several hypotheses have been proposed to explain the effect, including recent climate change, but the question remains controversial. A new survey of time series data from more than 500 remote lakes and streams, combined with a simple model, now shows that Dissolved Organic Carbon concentrations are in fact closely related to the decline in the sulphate and seasalt content of atmospheric deposition. Dissolved Organic Carbon concentrations may therefore be returning towards levels that would have been typical prior to the first onset of acid rain during the nineteenth century. The use of time series data from 522 remote lakes and streams in North America and northern Europe and a simple model shows that Dissolved Organic Carbon concentrations between 1990– 2004 have increased in proportion to the rates at which atmospherically deposited anthropogenic sulphur and sea salt have declined. It is suggested that acid deposition to these ecosystems has been partially buffered by changes in Organic acidity and that the rise in Dissolved Organic Carbon is integral to recovery from acidification. Several hypotheses have been proposed to explain recent, widespread increases in concentrations of Dissolved Organic Carbon (DOC) in the surface waters of glaciated landscapes across eastern North America and northern and central Europe1,2,3. Some invoke anthropogenic forcing through mechanisms related to climate change3,4,5, nitrogen deposition6 or changes in land use7, and by implication suggest that current concentrations and fluxes are without precedent. All of these hypotheses imply that DOC levels will continue to rise, with unpredictable consequences for the global Carbon cycle. Alternatively, it has been proposed that DOC concentrations are returning toward pre-industrial levels as a result of a gradual decline in the sulphate content of atmospheric deposition8,9,10. Here we show, through the assessment of time series data from 522 remote lakes and streams in North America and northern Europe, that rising trends in DOC between 1990 and 2004 can be concisely explained by a simple model based solely on changes in deposition chemistry and catchment acid-sensitivity. We demonstrate that DOC concentrations have increased in proportion to the rates at which atmospherically deposited anthropogenic sulphur and sea salt have declined. We conclude that acid deposition to these ecosystems has been partially buffered by changes in Organic acidity and that the rise in DOC is integral to recovery from acidification. Over recent decades, deposition-driven increases in Organic matter solubility may have increased the export of DOC to the oceans, a potentially important component of regional Carbon balances11. The increase in DOC concentrations in these regions appears unrelated to other climatic factors.
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Dissolved Organic Carbon trends resulting from changes in atmospheric deposition chemistry
Nature, 2007Co-Authors: D T Monteith, John L Stoddard, C D Evans, Martin Forsius, Tore Hogasen, Anders Wilander, B L Skjelkvale, D S Jeffries, Heleen A De Wit, Jussi VuorenmaaAbstract:Several hypotheses have been proposed to explain recent, widespread increases in concentrations of Dissolved Organic Carbon (DOC) in the surface waters of glaciated landscapes across eastern North America and northern and central Europe. Some invoke anthropogenic forcing through mechanisms related to climate change, nitrogen deposition or changes in land use, and by implication suggest that current concentrations and fluxes are without precedent. All of these hypotheses imply that DOC levels will continue to rise, with unpredictable consequences for the global Carbon cycle. Alternatively, it has been proposed that DOC concentrations are returning toward pre-industrial levels as a result of a gradual decline in the sulphate content of atmospheric deposition. Here we show, through the assessment of time series data from 522 remote lakes and streams in North America and northern Europe, that rising trends in DOC between 1990 and 2004 can be concisely explained by a simple model based solely on changes in deposition chemistry and catchment acid-sensitivity. We demonstrate that DOC concentrations have increased in proportion to the rates at which atmospherically deposited anthropogenic sulphur and sea salt have declined. We conclude that acid deposition to these ecosystems has been partially buffered by changes in Organic acidity and that the rise in DOC is integral to recovery from acidification. Over recent decades, deposition-driven increases in Organic matter solubility may have increased the export of DOC to the oceans, a potentially important component of regional Carbon balances. The increase in DOC concentrations in these regions appears unrelated to other climatic factors.
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long term increases in surface water Dissolved Organic Carbon observations possible causes and environmental impacts
Environmental Pollution, 2005Co-Authors: C D Evans, D T Monteith, David CooperAbstract:Abstract Dissolved Organic Carbon (DOC) concentrations in 22 UK upland waters have increased by an average of 91% during the last 15 years. Increases have also occurred elsewhere in the UK, northern Europe and North America. A range of potential drivers of these trends are considered, including temperature, rainfall, acid deposition, land-use, nitrogen and CO 2 enrichment. From examination of recent environmental changes, spatial patterns in observed trends, and analysis of time series, it is suggested that DOC may be increasing in response to a combination of declining acid deposition and rising temperatures; however it is difficult to isolate mechanisms based on monitoring data alone. Long-term DOC increases may have wide-ranging impacts on freshwater biota, drinking water quality, coastal marine ecosystems and upland Carbon balances. Full understanding of the significance of these increases requires further knowledge of the extent of natural long-term variability, and of the natural “reference” state of these systems.
D T Monteith - One of the best experts on this subject based on the ideXlab platform.
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Dissolved Organic Carbon trends resulting from changes in atmospheric deposition chemistry
Nature, 2007Co-Authors: D T Monteith, John L Stoddard, C D Evans, Martin Forsius, Tore Hogasen, Anders Wilander, B L Skjelkvale, D S Jeffries, Jussi Vuorenmaa, Bill KellerAbstract:There have been widespread reports of surface waters in many remote glaciated regions of North America and Northern Europe becoming browner as levels of Dissolved Organic Carbon have increased. Several hypotheses have been proposed to explain the effect, including recent climate change, but the question remains controversial. A new survey of time series data from more than 500 remote lakes and streams, combined with a simple model, now shows that Dissolved Organic Carbon concentrations are in fact closely related to the decline in the sulphate and seasalt content of atmospheric deposition. Dissolved Organic Carbon concentrations may therefore be returning towards levels that would have been typical prior to the first onset of acid rain during the nineteenth century. The use of time series data from 522 remote lakes and streams in North America and northern Europe and a simple model shows that Dissolved Organic Carbon concentrations between 1990– 2004 have increased in proportion to the rates at which atmospherically deposited anthropogenic sulphur and sea salt have declined. It is suggested that acid deposition to these ecosystems has been partially buffered by changes in Organic acidity and that the rise in Dissolved Organic Carbon is integral to recovery from acidification. Several hypotheses have been proposed to explain recent, widespread increases in concentrations of Dissolved Organic Carbon (DOC) in the surface waters of glaciated landscapes across eastern North America and northern and central Europe1,2,3. Some invoke anthropogenic forcing through mechanisms related to climate change3,4,5, nitrogen deposition6 or changes in land use7, and by implication suggest that current concentrations and fluxes are without precedent. All of these hypotheses imply that DOC levels will continue to rise, with unpredictable consequences for the global Carbon cycle. Alternatively, it has been proposed that DOC concentrations are returning toward pre-industrial levels as a result of a gradual decline in the sulphate content of atmospheric deposition8,9,10. Here we show, through the assessment of time series data from 522 remote lakes and streams in North America and northern Europe, that rising trends in DOC between 1990 and 2004 can be concisely explained by a simple model based solely on changes in deposition chemistry and catchment acid-sensitivity. We demonstrate that DOC concentrations have increased in proportion to the rates at which atmospherically deposited anthropogenic sulphur and sea salt have declined. We conclude that acid deposition to these ecosystems has been partially buffered by changes in Organic acidity and that the rise in DOC is integral to recovery from acidification. Over recent decades, deposition-driven increases in Organic matter solubility may have increased the export of DOC to the oceans, a potentially important component of regional Carbon balances11. The increase in DOC concentrations in these regions appears unrelated to other climatic factors.
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Dissolved Organic Carbon trends resulting from changes in atmospheric deposition chemistry
Nature, 2007Co-Authors: D T Monteith, John L Stoddard, C D Evans, Martin Forsius, Tore Hogasen, Anders Wilander, B L Skjelkvale, D S Jeffries, Heleen A De Wit, Jussi VuorenmaaAbstract:Several hypotheses have been proposed to explain recent, widespread increases in concentrations of Dissolved Organic Carbon (DOC) in the surface waters of glaciated landscapes across eastern North America and northern and central Europe. Some invoke anthropogenic forcing through mechanisms related to climate change, nitrogen deposition or changes in land use, and by implication suggest that current concentrations and fluxes are without precedent. All of these hypotheses imply that DOC levels will continue to rise, with unpredictable consequences for the global Carbon cycle. Alternatively, it has been proposed that DOC concentrations are returning toward pre-industrial levels as a result of a gradual decline in the sulphate content of atmospheric deposition. Here we show, through the assessment of time series data from 522 remote lakes and streams in North America and northern Europe, that rising trends in DOC between 1990 and 2004 can be concisely explained by a simple model based solely on changes in deposition chemistry and catchment acid-sensitivity. We demonstrate that DOC concentrations have increased in proportion to the rates at which atmospherically deposited anthropogenic sulphur and sea salt have declined. We conclude that acid deposition to these ecosystems has been partially buffered by changes in Organic acidity and that the rise in DOC is integral to recovery from acidification. Over recent decades, deposition-driven increases in Organic matter solubility may have increased the export of DOC to the oceans, a potentially important component of regional Carbon balances. The increase in DOC concentrations in these regions appears unrelated to other climatic factors.
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long term increases in surface water Dissolved Organic Carbon observations possible causes and environmental impacts
Environmental Pollution, 2005Co-Authors: C D Evans, D T Monteith, David CooperAbstract:Abstract Dissolved Organic Carbon (DOC) concentrations in 22 UK upland waters have increased by an average of 91% during the last 15 years. Increases have also occurred elsewhere in the UK, northern Europe and North America. A range of potential drivers of these trends are considered, including temperature, rainfall, acid deposition, land-use, nitrogen and CO 2 enrichment. From examination of recent environmental changes, spatial patterns in observed trends, and analysis of time series, it is suggested that DOC may be increasing in response to a combination of declining acid deposition and rising temperatures; however it is difficult to isolate mechanisms based on monitoring data alone. Long-term DOC increases may have wide-ranging impacts on freshwater biota, drinking water quality, coastal marine ecosystems and upland Carbon balances. Full understanding of the significance of these increases requires further knowledge of the extent of natural long-term variability, and of the natural “reference” state of these systems.
Hjalmar Laudon - One of the best experts on this subject based on the ideXlab platform.
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boreal forest riparian zones regulate stream sulfate and Dissolved Organic Carbon
Science of The Total Environment, 2016Co-Authors: Jose L J Ledesma, Martyn N Futter, C D Evans, Hjalmar Laudon, Stephan KohlerAbstract:In boreal forest catchments, solute transfer to streams is controlled by hydrological and biogeochemical processes occurring in the riparian zone (RZ). However, RZs are spatially heterogeneous and information about solute chemistry is typically limited. This is problematic when making inferences about stream chemistry. Hypothetically, the strength of links between riparian and stream chemistry is time-scale dependent. Using a ten-year (2003 − 2012) dataset from a northern Swedish catchment, we evaluated the suitability of RZ data to infer stream dynamics at different time scales. We focus on the role of the RZ versus upslope soils in controlling sulfate (SO42−) and Dissolved Organic Carbon (DOC). A priori, declines in acid deposition and redox-mediated SO42− pulses control sulfur (S) fluxes and pool dynamics, which in turn affect Dissolved Organic Carbon (DOC). We found that the catchment is currently a net source of S, presumably due to release of the S pool accumulated during the acidification period. In both, RZ and stream, SO42 − concentrations are declining over time, whereas DOC is increasing. No temporal trends in SO42 − and DOC were observed in upslope mineral soils. SO42 − explained the variation of DOC in stream and RZ, but not in upslope mineral soil. Moreover, as SO42 − decreased with time, temporal variability of DOC increased. These observations indicate that: (1) SO42 − is still an important driver of DOC trends in boreal catchments and (2) RZ processes control stream SO42 − and subsequently DOC independently of upslope soils. These phenomena are likely occurring in many regions recovering from acidification. Because water flows through a heterogeneous mosaic of RZs before entering the stream, upscaling information from limited RZ data to the catchment level is problematic at short-time scales. However, for long-term trends and annual dynamics, the same data can provide reasonable representations of riparian processes and support meaningful inferences about stream chemistry.
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regulation of stream water Dissolved Organic Carbon doc concentrations during snowmelt the role of discharge winter climate and memory effects
Biogeosciences, 2010Co-Authors: Anneli Agren, Mahsa Haei, Kevin Bishop, Stephan J Kohler, Hjalmar LaudonAbstract:Using a 15 year stream record from a northern boreal catchment, we demonstrate that the inter-annual variation in Dissolved Organic Carbon (DOC) concentrations during snowmelt was related to discha ...
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cold winter soils enhance Dissolved Organic Carbon concentrations in soil and stream water
Geophysical Research Letters, 2010Co-Authors: Mahsa Haei, Mats G Oquist, Ishi Buffam, Anneli Agren, Peder Blomkvist, Kevin Bishop, Mikaell Ottosson Lofvenius, Hjalmar LaudonAbstract:Concentrations of Dissolved Organic Carbon ([DOC]) have increased in lakes, streams and rivers across a large part of the northern hemisphere and raised an animated scientific debate about the unde ...
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importance of seasonality and small streams for the landscape regulation of Dissolved Organic Carbon export
Journal of Geophysical Research, 2007Co-Authors: Annelie Agren, Ishi Buffam, Mats Jansson, Hjalmar LaudonAbstract:The regulation of the spatial and seasonal variation in terrestrial Dissolved Organic Carbon (DOC) exports was studied in a 68 km2 boreal stream system in northern Sweden. A total of 1213 DOC sampl ...
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is a universal model of Organic acidity possible comparison of the acid base properties of Dissolved Organic Carbon in the boreal and temperate zones
Environmental Science & Technology, 2003Co-Authors: Jakub Hruska, Stephan Kohler, Hjalmar Laudon, Kevin BishopAbstract:The acid/base properties of Dissolved Organic Carbon (DOC) are an important feature of soil and surface waters. Large differences in the acid/base properties of DOC found by different studies might...
Carlos M. Duarte - One of the best experts on this subject based on the ideXlab platform.
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response to comment on dilution limits Dissolved Organic Carbon utilization in the deep ocean
Science, 2015Co-Authors: Jesús M. Arrieta, Eva Mayol, Roberta L. Hansman, Gerhard J. Herndl, Thorsten Dittmar, Carlos M. DuarteAbstract:Our recent finding that dilution limits Dissolved Organic Carbon (DOC) utilization in the deep ocean has been criticized based on the common misconception that lability equates to rapid and complete utilization. Even when considering the redefinition of recalcitrant DOC recently proposed by Jiao et al., the dilution hypothesis best explains our experimental observations.
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Dilution limits Dissolved Organic Carbon utilization in the deep ocean
Science (New York N.Y.), 2015Co-Authors: Jesús M. Arrieta, Eva Mayol, Roberta L. Hansman, Gerhard J. Herndl, Thorsten Dittmar, Carlos M. DuarteAbstract:Oceanic Dissolved Organic Carbon (DOC) is the second largest reservoir of Organic Carbon in the biosphere. About 72% of the global DOC inventory is stored in deep oceanic layers for years to centuries, supporting the current view that it consists of materials resistant to microbial degradation. An alternative hypothesis is that deep-water DOC consists of many different, intrinsically labile compounds at concentrations too low to compensate for the metabolic costs associated to their utilization. Here, we present experimental evidence showing that low concentrations rather than recalcitrance preclude consumption of a substantial fraction of DOC, leading to slow microbial growth in the deep ocean. These findings demonstrate an alternative mechanism for the long-term storage of labile DOC in the deep ocean, which has been hitherto largely ignored.
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Dissolved Organic Carbon fluxes by seagrass meadows and macroalgal beds
Frontiers in Marine Science, 2014Co-Authors: Cristina Barron, Carlos M. Duarte, Eugenia T ApostolakiAbstract:Estimates of Dissolved Organic Carbon (DOC) release by marine macrophyte communities (seagrass meadows and macroalgal beds) based on in situ benthic chambers from published and unpublished are compiled in this study. The effect of temperature and light availability on DOC release by macrophyte communities was examined. Almost 85 % of the seagrass communities and all of macroalgal communities examined acted as net sources of DOC. Net DOC fluxes in seagrass communities increase positively with water temperature. In macroalgal communities net DOC fluxes under light exceeded those under dark condition, however, this trend was weaker in seagrass communities. Shading of a mixed seagrass meadow in The Philippines led to a significant reduction on the net DOC release when shading was maintained for 6 days compared to only 2 days of shading. Net DOC fluxes increased with increasing community respiration, but were independent of primary production or net community production. The estimated global net DOC flux, and hence export, from marine macrophytes is about 0.158 ± 0.055 Pg C yr-1 or 0.175 ± 0.056 Pg C yr-1 depending on the global extent of seagrass meadows considered.