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Dissolved Organic Carbon (DOC) dynamics in the headwaters of the Amazon, Peru

Prof Pippa Chapman (SoG), Dr Palmer (SOG), Dr Baker (SoG)

Project partner(s): Instituto de Investigaciones de la Amazonia Peruana (IIAP), Iquitos, Peru (http://www.iiap.org.pe/)

Contact email: p.j.chapman@leeds.ac.uk

River systems connect the terrestrial biosphere, the atmosphere and the ocean in the global carbon cycle. They play a major role in transporting and transforming organic carbon fixed by primary productivity. However, compared to other components of the carbon cycle, such as net primary productivity (NPP) in the terrestrial biosphere, the factors controlling the magnitude of carbon transported by fluvial systems is poorly understood and requires further study if we are to improve our understanding of how strongly major rivers act as a sink or source of carbon, and the sensitivity to human and climate perturbations.

With a drainage area of more than 6 million km2, the River Amazon represents ~20% of the global freshwater discharge to the ocean and exports between 22 (Richey et al., 1990) and 27 Tg of dissolved organic carbon (DOC) annually to the Ocean (Ward et al., 2015), representing 10% of the DOC reaching the oceans globally (Maybeck, 1982). This DOC is sourced from organic matter in soils and decaying vegetation, and is primarily of recent origin (Mayorga et al., 2005).  However, the majority of research into the dynamics of DOC along the Amazon has occurred in its lower reaches and nearly all in Brazil (e.g. Seidel et al., 2015). Very little is known about the sources and sinks of DOC in the headwaters of the Amazon (Figure 1; Aufdenkampe et al., 2007) where significant peat deposits have recently been reported (Draper et al., 2014), such as in the subsiding Pastaza-Marañón Foreland Basin (PMFB) in the Datum de Marañón Province of Peru.

Figure 1. Amazon near Iquitos, Peru.

Concentrations of DOC in the lower reaches of the Amazon are 3.9 and 4.2 mg/L at Obidos and the mouth of the Amazon, respectively (Ward et al., 2015). However, given that much higher concentrations of DOC are usually associated with tropical peat and wetlands (e.g. Muller et al., 2015 reported DOC concentrations in the range 38.6 to 74.6 mg/L in an undisturbed peatland river system in Malaysia), we anticipate that concentrations are similarly high in the lakes and rivers of the upper Amazon. The relatively low concentrations of DOC in the lower reaches of the Amazon may indicate that the DOC soured from the peatland and wetlands in its headwaters is removed from the water column during transport via a number of potential mechanisms such as biodegradation to CO2 (and subsequent loss to the atmosphere) and loss to bottom sediments via adsorption to mineral particles or flocculation. A large potential loss of DOC between peatland source and the ocean could indicate a significant and currently unmeasured climate feedback mechanism, hence there is a need to improve our understanding of aquatic DOC dynamics in this area of the Amazon basin (Figure 1 & 2).

Figure 2. Wetland lakes within the headwaters of the Amazon, Peru.                                            

Objectives

This project will focus on improving our understanding of the aquatic carbon cycle in the Pastaza-Marañón Foreland Basin (PMFB) within the headwaters of the Amazon in Peru. Quantifying the aquatic carbon cycle requires monitoring a range of processes, such as the spatial and temporal variation in DOC in the water column and the biodegradation potential of DOC. Monitoring these processes is particularly important in the PMFB as high concentrations of DOC are usually associated with peat and wetlands and they could be a substantial, as yet undocumented carbon source within the province.

The major objectives of this project are therefore to:

  1. Measure concentrations of DOC and other aquatic C components in lakes and tributaries of the PMFB. In conjunction with project partners IIAP, establish a regular monitoring programme of DOC sampling in key rivers of the PMFB (e.g. Amazon (Iquitos), Ucayali/Maranon (Nauta) and Rio Tigre (Nueva York)) to understand seasonal variation in concentrations and spatial variation among different rivers (associated with shallow/deep peatlands or seasonally flooded non-peatland forests).
  2. Investigate DOC biodegradation potential in DOC ‘hotspots’, either in-situ using continuous measurement of dissolved carbon dioxide (CO2) and oxygen (O2) or in controlled laboratory experiments.
  3. Estimate the regional flux of carbon from rivers and lakes to the atmosphere.

Potential for high impact outcome

At the global scale, carbon cycling and climate change are interrelated. We are in a unique position at Leeds to answer important unresolved questions about how aquatic carbon cycling in the Amazon may impact upon climate change. The research topic is high profile and has immediate policy-relevance: the peatlands of the PMFB are currently largely intact but threatened by both agricultural and infrastructure development, and monitoring aquatic carbon is an important indicator of broader ecosystem health. We therefore anticipate the project generating several papers with at least one being suitable for submission to a high impact journal.

Training

The student will develop a range of research skills including field sampling, chemical analysis, statistical analysis, data interpretation and presentation skills. Training will be provided in field/laboratory health and safety procedures and the use of field and analytical equipment. The student will benefit from spending time based at the Instituto de Investigaciones de la Amazonia Peruana, Iquitos Peru and the School of Geography at Leeds and benefit from this interaction. The student will have the opportunity to develop their research profile through publication and presentation of results at national and international conferences. The successful PhD student will have access to a broad spectrum of training workshops put on by the Faculty of Environment at the University of Leeds that include an extensive range of training workshops in statistical analysis, through to managing your degree, to preparing for your viva (http://www.emeskillstraining.leeds.ac.uk/).

Student profile

The prospective student should have (or expect to receive) a minimum of a first class BSc (or high 2i plus MSc) degree in an appropriate discipline, and be prepared to spend time in remote field sites in Peru.

Partner

Our Project Partners at IIAP made some of the first descriptions of the PMFB and has decades of experience in working within this region. IIAP comprises active research groups studying the forests, aquatic ecosystems and terrestrial biodiversity of northwest Amazonia and developing strategies for the sustainable management of these ecosystems. The School of Geography at Leeds has collaborated with IIAP for more than ten years on a range of ecological and socio-economic projects, and IIAP will play an important role in providing local scientific expertise, logistical support, and links to stakeholders during this studentship.

References

Aufdenkampe, A.K., Mayorga, E., Hedges, J.I., Llerena, C., Quay, P.D., Gudema, J., Krusche, A.V. and Richey, J.E., 2007. Organic matter in the Peruvian headwaters of the Amazon: Compositional evolution from the Andes to the lowland Amazon main stem. Organic Geochem. 38(3), 337-384.

Draper, F. C.; Roucoux, K. H.; Lawson, I. T.; Mitchard, E. T.; Honorio, E. N.; Lähteenoja, O.; Torres-Montenegro, L.; Valderrama-Sandoval, E.; Zárate, R. & Baker, T. R. 2014. The distribution and amount of carbon in the largest peatland complex in Amazonia. Environmental Research Letters 9: doi:10.1088/1748-9326/9/12/124017.

Hulatt, C.J., Kaartokallio, H., Oinonen, M., Sonninen, E., Stedmon, C.A. and Thomas, D.N., 2014, Radiocarbon dating of fluvial organic matter reveals land-use impacts in boreal peatlands. Environ. Sci. Technol. 48, 12543-12551.

Mayorga, E., Aufdenkampe, A.K., Masiello, C.A., Krusche, A.V., Hedges, J.I., Quay, P.D., Richey, J., Brown, T.A., 2005a. Young organic matter as a source of carbon dioxide outgassing from Amazonian rivers. Nature 436, 538–541.

Meybeck, M., 1982. Carbon, nitrogen, and phosphorus transport by world rivers. Am.J. Sci. 282 (4), 401–450.

Richey, J.E.,Hedges, J.I.,Devol,A.H., Quay, R.D., Victoria,R., Martinelli, L., Forsberg,B.R., 1990. Biogeochemistry of carbon in the Amazon River. Limnol. Oceanogr. 35 (2), 352–371.

Seidel M., Yager, P.L, Ward, N.D., Carpenter, E.J, Gomes, H.R., Krusher, A.V., Richey, J.E., Dittmar, T and Medeiros, P.M., 2015. Molecular-level changes of dissolved organic matter along the Amazon River-to-ocean continuum. Mar. Chem.177, 218-233.

Ward, N.D., Krusche, A.V., Sawakuchi, H.O., Brito, D.C., Cunha, A.C., Moura, J.M.S., da Silva,R., Keil, R.G., Richey, J.E., 2015. The compositional evolution of dissolved and particulate organic matter along the lower Amazon River-Óbidos to the ocean. Mar. Chem.177, 244–256.

Related undergraduate subjects:

  • Chemistry
  • Earth science
  • Ecology
  • Environmental science
  • Geography