Aquatic carbon cycling in the conterminous United States and implications for terrestrial carbon accounting

Significance Inland waters provide habitat for aquatic organisms; are sources of human drinking water; and integrate, transport, and process carbon across continents. Estimates of the accumulation of carbon in terrestrial environments suggest that agricultural and forest ecosystems have annual net gains in carbon storage. These ecosystems are considered sinks of atmospheric carbon dioxide. None of these estimates have considered the loss of carbon to and also through aquatic environments at the national or continental scale. We show that aquatic ecosystems in the conterminous United States export over 100 teragrams of carbon (TgC) per year, highlighting the need to attribute the sources of aquatic carbon more accurately, and assert that inland waters play an important role in carbon accounting. Inland water ecosystems dynamically process, transport, and sequester carbon. However, the transport of carbon through aquatic environments has not been quantitatively integrated in the context of terrestrial ecosystems. Here, we present the first integrated assessment, to our knowledge, of freshwater carbon fluxes for the conterminous United States, where 106 (range: 71–149) teragrams of carbon per year (TgC⋅y−1) is exported downstream or emitted to the atmosphere and sedimentation stores 21 (range: 9–65) TgC⋅y−1 in lakes and reservoirs. We show that there is significant regional variation in aquatic carbon flux, but verify that emission across stream and river surfaces represents the dominant flux at 69 (range: 36–110) TgC⋅y−1 or 65% of the total aquatic carbon flux for the conterminous United States. Comparing our results with the output of a suite of terrestrial biosphere models (TBMs), we suggest that within the current modeling framework, calculations of net ecosystem production (NEP) defined as terrestrial only may be overestimated by as much as 27%. However, the internal production and mineralization of carbon in freshwaters remain to be quantified and would reduce the effect of including aquatic carbon fluxes within calculations of terrestrial NEP. Reconciliation of carbon mass–flux interactions between terrestrial and aquatic carbon sources and sinks will require significant additional research and modeling capacity.

[1]  G. P. Zimmerman,et al.  The first state of the carbon cycle report (SOCCR): The North American carbon budget and implications for the global carbon cycle. , 2007 .

[2]  Robert B. Cook,et al.  The North American Carbon Program Multi-scale Synthesis and Terrestrial Model Intercomparison Project – Part 2: Environmental driver data , 2013 .

[3]  P. Raymond,et al.  Relationships between Δ14C and the molecular quality of dissolved organic carbon in rivers draining to the coast from the conterminous United States , 2012 .

[4]  T. C. Winter,et al.  Hydrologic support of carbon dioxide flux revealed by whole‐lake carbon budgets , 2009 .

[5]  C. Wirth,et al.  Reconciling Carbon-cycle Concepts, Terminology, and Methods , 2006, Ecosystems.

[6]  C. Duarte,et al.  Prevalence of Heterotrophy and Atmospheric CO2 Emissions from Aquatic Ecosystems , 2005, Ecosystems.

[7]  J. Hartmann,et al.  Atmospheric CO2 consumption by chemical weathering in North America , 2011 .

[8]  T. Filley,et al.  Temporal variability in sources of dissolved organic carbon in the lower Mississippi river , 2004 .

[9]  Chris C. Park.  World-wide variations in hydraulic geometry exponents of stream channels: An analysis and some observations , 1977 .

[10]  R. B. Jackson,et al.  A Large and Persistent Carbon Sink in the World’s Forests , 2011, Science.

[11]  C. Schubert,et al.  Aquatic Ecosystems: Interactivity of dissolved organic matter , 2003 .

[12]  T. Blenckner,et al.  CO2 supersaturation along the aquatic conduit in Swedish watersheds as constrained by terrestrial respiration, aquatic respiration and weathering , 2010 .

[13]  P. Raymond,et al.  Event controlled DOC export from forested watersheds , 2010 .

[14]  P. Ciais,et al.  Global carbon dioxide emissions from inland waters , 2013, Nature.

[15]  M. Billett,et al.  Supersaturation and evasion of CO2 and CH4 in surface waters at Mer Bleue peatland, Canada , 2008 .

[16]  J. Miesel,et al.  Paradigm shifts in soil organic matter research affect interpretations of aquatic carbon cycling: transcending disciplinary and ecosystem boundaries , 2014, Biogeochemistry.

[17]  Richard Bernknopf,et al.  A method for assessing carbon stocks, carbon sequestration, and greenhouse-gas fluxes in ecosystems of the United States under present conditions and future scenarios , 2010 .

[18]  D. L. Parkhurst,et al.  User's guide to PHREEQC (Version 2)-a computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations , 1999 .

[19]  S. Miller,et al.  Similarity scaling of turbulence in a temperate lake during fall cooling , 2014 .

[20]  M. Pace,et al.  Is Net Ecosystem Production Equal to Ecosystem Carbon Accumulation? , 2006, Ecosystems.

[21]  L. Hess,et al.  Outgassing from Amazonian rivers and wetlands as a large tropical source of atmospheric CO2 , 2002, Nature.

[22]  P. Ciais,et al.  The impact of lateral carbon fluxes on the European carbon balance , 2006 .

[23]  Hari Seshan,et al.  Phytoplankton, not allochthonous carbon, sustains herbivorous zooplankton production , 2009, Proceedings of the National Academy of Sciences.

[24]  M. A. Arain,et al.  Analysis of nitrogen controls on carbon and water exchanges in a conifer forest using the CLASS-CTEMN+ model , 2011 .

[25]  P. Yager,et al.  Degradation of terrestrially derived macromolecules in the Amazon River , 2013 .

[26]  C. W. Hunt,et al.  Contribution of non-carbonate anions to total alkalinity and overestimation of p CO 2 in New England and New Brunswick rivers , 2011 .

[27]  D. W. Stewart,et al.  RESIS-II: An Updated Version of the Original Reservoir Sedimentation Survey Information System (RESIS) Database , 2009 .

[28]  Jonathan J. Cole,et al.  Atmospheric exchange of carbon dioxide in a low‐wind oligotrophic lake measured by the addition of SF6 , 1998 .

[29]  I. Strachan,et al.  The net carbon footprint of a newly created boreal hydroelectric reservoir , 2012 .

[30]  A. McGuire,et al.  Insights and issues with simulating terrestrial DOC loading of Arctic river networks. , 2013, Ecological applications : a publication of the Ecological Society of America.

[31]  James P. M. Syvitski,et al.  Geolocation of man-made reservoirs across terrains of varying complexity using GIS , 2008, Comput. Geosci..

[32]  R. Sinsabaugh,et al.  Aquatic ecosystems: interactivity of dissolved organic matter , 2004, Journal of the North American Benthological Society.

[33]  B. Reed,et al.  Baseline and projected future carbon storage and greenhouse-gas fluxes in ecosystems of the Western United States , 2012 .

[34]  W. Cai,et al.  The role of marsh‐dominated heterotrophic continental margins in transport of CO2 between the atmosphere, the land‐sea interface and the ocean , 2003 .

[35]  Timothy A. Cohn,et al.  Load Estimator (LOADEST): A FORTRAN Program for Estimating Constituent Loads in Streams and Rivers , 2004 .

[36]  Atul K. Jain,et al.  North American Carbon Program (NACP) regional interim synthesis: Terrestrial biospheric model intercomparison , 2012 .

[37]  W. M. Post,et al.  Soil carbon sequestration and land‐use change: processes and potential , 2000 .

[38]  Patrick M. Crill,et al.  Freshwater Methane Emissions Offset the Continental Carbon Sink , 2011, Science.

[39]  P. Raymond,et al.  Significant efflux of carbon dioxide from streams and rivers in the United States , 2011 .

[40]  Peter E. Thornton,et al.  Modeling and measuring the effects of disturbance history and climate on carbon and water budgets in evergreen needleleaf forests , 2002 .

[41]  R. Wanninkhof.  Relationship between wind speed and gas exchange over the ocean , 1992 .

[42]  W. McDowell,et al.  Scaling the gas transfer velocity and hydraulic geometry in streams and small rivers , 2012 .

[43]  Edward G. Stets,et al.  The regional abundance and size distribution of lakes and reservoirs in the United States and implications for estimates of global lake extent , 2012 .

[44]  Andreas Richter,et al.  The boundless carbon cycle , 2009 .

[45]  H. Laudon,et al.  Sources of and processes controlling CO2 emissions change with the size of streams and rivers , 2015 .

[46]  N. Oh,et al.  Contribution of agricultural liming to riverine bicarbonate export and CO2 sequestration in the Ohio River basin , 2006 .

[47]  Edward G. Stets,et al.  Inorganic carbon loading as a primary driver of dissolved carbon dioxide concentrations in the lakes and reservoirs of the contiguous United States , 2013 .

[48]  Peter E. Thornton,et al.  Remote Sensing Evaluation of CLM4 GPP for the Period 2000–09* , 2012 .

[49]  J. Rover,et al.  Carbon dioxide and methane emissions from the Yukon River system , 2012 .

[50]  J. Downing,et al.  Plumbing the Global Carbon Cycle: Integrating Inland Waters into the Terrestrial Carbon Budget , 2007, Ecosystems.

[51]  N. Caraco,et al.  Carbon in catchments: connecting terrestrial carbon losses with aquatic metabolism , 2001 .

[52]  B. Wehrli,et al.  Extreme methane emissions from a Swiss hydropower reservoir: contribution from bubbling sediments. , 2010, Environmental science & technology.

[53]  Philippe Ciais,et al.  Anthropogenic perturbation of the carbon fluxes from land to ocean , 2013 .

[54]  P. Raymond,et al.  Increased mobilization of aged carbon to rivers by human disturbance , 2015 .

[55]  K. Verdin,et al.  Organic Carbon Burial in Lakes and Reservoirs of the Conterminous United States. , 2015, Environmental science & technology.

[56]  Changhui Peng,et al.  Modelling methane emissions from natural wetlands by development and application of the TRIPLEX-GHG model , 2014 .

[57]  R. Sinsabaugh,et al.  20 – Dissolved Organic Matter: Out of the Black Box into the Mainstream , 2003 .

[58]  R. Houghton.  The emissions of carbon from deforestation and degradation in the tropics: past trends and future potential , 2013 .

[59]  Gregg Marland,et al.  The North American Carbon Budget and Implications for the Global Carbon Cycle , 2007 .

[60]  Jung-Hyun Kim,et al.  Amazon River carbon dioxide outgassing fuelled by wetlands , 2013, Nature.

[61]  W. Post,et al.  The North American Carbon Program Multi-Scale Synthesis and Terrestrial Model Intercomparison Project – Part 1: Overview and experimental design , 2013 .

[62]  K. Paustian,et al.  The North American carbon budget past and present , 2007 .

[63]  H. Laudon,et al.  Evasion of CO2 from streams – The dominant component of the carbon export through the aquatic conduit in a boreal landscape , 2013, Global change biology.

[64]  H. Tian,et al.  China's terrestrial carbon balance: Contributions from multiple global change factors , 2011 .

[65]  R. Striegl,et al.  Carbon export by rivers draining the conterminous United States , 2012 .

[66]  C. Melching,et al.  Reaeration equations derived from U.S. geological survey database , 1999 .

[67]  C. Driscoll,et al.  The role of organic acids in the acidification of surface waters in the Eastern U.S. , 1989 .

[68]  L. B. Leopold,et al.  The hydraulic geometry of stream channels and some physiographic implications , 1953 .

[69]  U. S. Geological.  Magnitude and Significance of Carbon Burial in Lakes , Reservoirs , and Peatlands , 2017 .

[70]  Aaron I. Packman,et al.  Biophysical controls on organic carbon fluxes in fluvial networks , 2008 .

[71]  Yinghai Ke,et al.  Evaluating runoff simulations from the Community Land Model 4.0 using observations from flux towers and a mountainous watershed , 2011 .

[72]  P. Lozovik.  Contribution of Organic Acid Anions to the Alkalinity of Natural Humic Water , 2005 .

[73]  P. Raymond,et al.  Carbon export and cycling by the Yukon, Tanana, and Porcupine rivers, Alaska, 2001–2005 , 2007 .

[74]  Robert F. Stallard,et al.  Terrestrial sedimentation and the carbon cycle: Coupling weathering and erosion to carbon burial , 1998 .

[75]  L. N. Plummer,et al.  The solubilities of calcite, aragonite and vaterite in CO2-H2O solutions between 0 and 90°C, and an evaluation of the aqueous model for the system CaCO3-CO2-H2O , 1982 .