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

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 component 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 in the Amazon is poorly understood and requires further study if we are to improve our understanding of how strongly the Amazon acts 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 (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 Maranon Province of 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 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 would anticipate that much higher concentrations would be observed in the lakes and rivers of the upper Amazon. The relatively low concentrations of DOC in the lower reaches of the Amazon suggest that much of the DOC soured from the peatland and wetlands in its headwaters is removed from the water column during transport via a number of mechanisms such as biodegradation to CO2, loss to bottom sediments via adsorption to mineral particles or flocculation.
When peats are drained or otherwise disturbed DOC losses of considerable age have been observed in rivers (Hulatt et al., 2014), thus indicating destabilisation of peat as a long-term carbon store. Considering this potential sensitivity of peat and the relatively large carbon stock that is contained in the PMFB, there is a need to improve our understanding of aquatic DOC dynamics in this area of the Amazon basin.
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. This will be achieved by carrying out field work and monitor a range of processes, such as: the rate of carbon deposition to lake floors, the spatial and temporal variation in DOC in the water column; the source of the DOC (recent/old peat, terrestrial or aquatic vegetation) and the biodegradation of the DOC. Monitoring these processes is particularly important in Datum de Maranon province and 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.

Further information can be found here http://www.nercdtp.leeds.ac.uk/projects/index.php?id=529 or contact Pippa Chapman ([Email Address Removed])