14-6. Biogeochemical Cycling and Transport of Carbon in Fluvial Aquatic Ecosystems
Streams and rivers are dynamic biogeochemical reactors that receive, transform, store, and export inorganic and organic carbon. The perception of the importance of streams and rivers in the global carbon cycle has shifted in recent years from one of passive receivers and exporters of terrestrial dissolved and particulate carbon (C) to dynamic processors of C, with important roles in C gas emission to the atmosphere and C sequestration, in addition to exporting C and nutrients to coastal areas (Cole et al., 2007; Aufdenkampe et al. 2011). These systems are important in global (Cole et al., 2007) and national (Zhu et al., 2010; Butman and Raymond, 2011) C budgets, and consequently they need to be quantitatively accounted for in strategies to manage and mitigate climate (Battin et al., 2009) and land use change effects on natural resources. In addition, C processing and transport in streams and rivers is central to issues impacting the quality of water for sustainable ecological health and human use, such as food web dynamics, eutrophication, and contaminant transport.
Carbon cycling and transport in fluvial aquatic ecosystems is highly complex; components include dissolved and particulate organic and inorganic C, dissolved C gases (carbon dioxide, methane), land-water-atmosphere transfers of C, and within-river transformations of inorganic and organic C by biological and geochemical processes. While progress has been made on many fronts, there remains a need for improved quantification and an integrated ecosystem-level understanding of stream and river C sources and sinks, C processing, C fluxes, and the important drivers of these components across multiple scales. This is especially true with regards to understanding the relative importance of terrestrial and in-stream C sources, and the relations between organic C metabolism and subsequent generation of dissolved and gaseous inorganic C.
Recent studies of fluvial aquatic systems have focused on distinct aspects of river C budgets, including characterization and transport of aqueous C (Striegl et al., 2007; Spencer, et al., 2008; Humborg et al., 2010; Lauerwald et al., 2012; Spencer et al., 2012), within-river photo- and bio-degradation of dissolved organic C (Obernosterer and Benner, 2004; Wickland et al., 2012), exchange of carbon dioxide (CO2) and/or methane (CH4) across water surfaces (Butman and Raymond, 2011; Striegl et al., 2012), and exports of C species to the oceans (Holmes et al., 2011; Stets and Striegl, 2012). These studies have greatly improved our understanding of aquatic fluvial C cycling and transport. However, there is a crucial need for studies that accurately quantify interactions among organic and inorganic C speciation and transformation, hydrology, and gas exchange, in order to assess the impacts of changes in land use, nutrient inputs, and climate on the fluvial mass balance of C. Integrated studies of organic and inorganic C dynamics will also help inform and improve models of fluvial C exports, such as Global NEWS (Seitzinger et al, 2010) and SPARROW (Shih et al., 2010), which currently do not explicitly link organic and inorganic C.
The overarching objectives of this Mendenhall Research Opportunity are to: 1) identify and quantify drivers associated with the cycling and transport of riverine organic and inorganic C, including dissolved gases, and 2) present an integrated assessment of major C inputs and losses in one or more stream or river ecosystems. Within the broad objective of assessing links between organic and inorganic C dynamics during transport in fluvial systems, the postdoctoral researcher will have wide latitude to pose specific research questions, define approaches, and adapt or develop new methodologies. We are seeking research that incorporates the investigation of controls and rates of aquatic inorganic and organic C production, oxidation of aquatic and/or terrestrially-derived OC to CO2 (and/or reduction to CH4), and fluvial and gaseous C transport. Applicants may explore questions focused on topics such as the relative importance of terrestrially-derived versus aquatic sources of organic and inorganic C, the generation of inorganic C from in-stream processing of organic C during transport, and the influence of factors such as nutrients and organic C quality on stream C metabolism. Possible approaches include field-based studies of headwater streams to large rivers, laboratory experiments, evaluation of existing models, development of new models, analysis of historical data, or any combination of these. Results of the Mendenhall Fellow’s research are expected to provide a more robust understanding of transformations of C during transport and of the mass balance of fluvial C in aquatic ecosystems.
Aufdenkampe, A.K., E. Mayorga, P.A. Raymond, J.M. Melack, S.C. Doney, S.R. Alin, R.. Aalto, and K. Yoo, 2011, Riverine coupling of biogeochemical cycles between land, oceans, and atmosphere, Front. Ecol. Environ. 9(1): 53-60, doi:10.1890/100014.
Battin, T.J., S. Luyssaert, L.A. Kaplan, et al., 2009, The boundless carbon cycle, Nature Geosci..2: 598-600.
Butman, D. and P.A. Raymond, 2011, Significant efflux of carbon dioxide from streams and rivers in the United States, Nature Geosci. 4: 839-842.
Cole, J.J., Y.T. Prairie, N.F. Caraco, W.H. McDowell, L.J. Tranvik, R.G. Striegl, C.M. Duarte, P. Kortelainen, J.A. Downing, J.J. Middelburg, and J. Melack, 2007, Plumbing the global carbon cycle: integrating inland waters into the terrestrial carbon budget, Ecosystems 10:171-184, doi:10.1007/s10021-006-9013-8.
Holmes, R.M., J.W. McClelland, B.J. Peterson, S.E. Tank, E. Bulygina, T.I. Eglinton, V.V. Gordeev, T.Y. Gurtovaya, P.A. Raymond, D.J. Repeta, R. Staples, R.G. Striegl, A.V. Zhulidov, and S.A. Zimov, 2011, Seasonal and annual fluxes of nutrients and organic matter from large rivers to the Arctic Ocean and surrounding seas, Estuaries and Coasts, doi:10.1007/s12237-011-9386-6.
Humborg, C., C.-M. Mörth, M. Sundbom, H. Borg, T. Blencker, R. Giesler, V. Ittekkot, 2010, CO2 supersaturation along the aquatic conduit in Swedish watersheds as constrained by terrestrial respiration, aquatic respiration and weathering, Glob. Change Biol. 16:1966-1978.
Lauerwald, R. J. Hartmann, W. Ludwig, N. Moosdorf, 2012, Assessing the nonconservative fluvial fluxes of dissolved organic carbon in North America, J. Geophys. Res. 117, G01027, doi:10.1029/2011JG001820.
Obernosterer, I. and R. Benner, 2004, Competition between biological and photochemical processes in the mineralization of dissolved organic carbon, Limnol. Oceanogr., 49(1): 117-124.
Seitzinger, S.P., E. Mayorga, A.F. Bouwman, C. Kroeze, A.H.W. Beusen, G. Billen, G.Van Drecht, E. Dumont, B.M. Fekete, J. Garnier, and J.A. Harrison, 2010, Global river nutrient export: a scenario analysis of past and future trends, Global Biogeochem. Cycles, 24, GB0A08, doi:10.1029/2009GB003587.
Shih, J.-S., R.B. Alexander, R.A. Smith, E.W. Boyer, G.E. Schwarz, and S. Chung, 2010, An initial SPARROW model of land use and in-stream controls on total organic carbon in streams of the conterminous United States, U.S. Geological Survey Open-File Report 2010-1276, 22 p., available at http://pubs.usgs.gov/of/2010/1276.
Spencer, R.G.M., G.R. Aiken, K.P. Wickland, R.G. Striegl, and P.J. Hernes, 2008, Seasonal and spatial variability in dissolved organic matter quantity and composition from the Yukon River basin, Alaska, Global Biogeochem. Cycles, 22, GB4002, doi:10.1029/2008GB003231.
Spencer, R.G.M., K.D. Butler, and G.R. Aiken, 2012, Dissolved organic carbon and chromophoric dissolved organic matter properties of rivers in the USA, J. Geophys. Res., 117, G03001, doi:10.1029/2011JG001928.
Stets, E.G. and R.G. Striegl, 2012, Carbon export by rivers draining the conterminous United States, Inland Waters 2: 177-184, doi:10.5268/IW-2.4.510.
Striegl, R.G., M.M. Dornblaser, G.R. Aiken, K.P. Wickland, P.A. Raymond, 2007, Carbon export and cycling by the Yukon, Tanana, and Porcupine Rivers, Alaska, 2001-2005, Water Resour. Res., 43, W02411, doi:10.1029/2006WR005206.
Striegl, R.G., M.M. Dornblaser, C.P. McDonald, J.R. Rover, and E.G. Stets, 2012, Carbon dioxide and methane emissions from the Yukon River system, Global Biogeochem. Cycles, 26, GB0E05, doi:10.1029/2012GB004306.
Wickland, K.P., G.R. Aiken, K. Butler, M.M. Dornblaser, R.G.M. Spencer, and R.G. Striegl, 2012, Biodegradability of dissolved organic carbon in the Yukon River and its tributaries: seasonality and importance of inorganic nitrogen, Global Biogeochem. Cycles, 26, GB0E03, doi:10.1029/2012GB004342.
Zhu, Zhiliang, ed., 2010, A method for assessing carbon stocks, carbon sequestration, and greenhouse-gas fluxes in ecosystems of the United States under present conditions and future scenarios, U.S. Geological Survey Scientific Investigations Report 2010 - 5233, 188 p. (Available at pubs.usgs.gov/sir/2010/5233/).
Proposed Duty Station: Boulder, CO
Areas of Ph.D.: Biogeochemistry, hydrology, ecology, biology, chemistry, geography, physics, or related fields (candidates holding a Ph.D. in other disciplines, but with extensive knowledge and skills relevant to the Research Opportunity may be considered).
Qualifications: Applicants must meet one of the following qualifications - Research Hydrologist, Research Ecologist, Research Physical Scientist, Research Chemist, Research Geographer.
(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant’s background, education, and research proposal. The final classification of theposition will be made by the Human Resources specialist).
Research Advisor(s): Kimberly Wickland, (303) 541-3072, firstname.lastname@example.org.; Edward Stets, (303) 541-3048, email@example.com.; Robert Striegl, (303) 541-3091, firstname.lastname@example.org.; George Aiken, (303) 541-3036, email@example.com.
Human Resources Office Contact: Jennifer Daberkow, (303) 236-9566, firstname.lastname@example.org.
|Summary of Opportunities|