Research Interests

My scientific research is centered on large-scale river biogeochemistry, particularly of carbon and nutrients.

Global River Nutrient Exports and Human Pressures

In my recent work with Sybil Seitzinger and the Global NEWS team, I coordinated with colleagues in the US and Europe to examine recent and possible future trajectories (1970 2050) in global, spatially distributed river carbon and nutrient export to the oceans under a range of climate, hydrological, land use, agricultural and population pressures representing the Millennium Ecosystem Assessment scenarios. We also made preliminary steps towards towards quantitatively linking river nutrient exports to coastal effects such as eutrophication and occurrence of harmful algal blooms (Glibert et al., 2008); such linkage will help to constrain the impact on coastal ecosystem health from climate change and human activity on watersheds. Finally, we extended the annual-scale Global NEWS models to more mechanistic, sub-annual, and sub-basin scale approaches through a collaboration led by the University of New Hampshire's Water Systems Analysis Group (WSAG).

Carbon in Amazonian Rivers

My Ph.D. work focused on Amazonian rivers and was conducted with the long-standing CAMREX project, led by my Ph.D. advisor, Jeff Richey (University of Washington). My isotopic (14C and 13C) and related biogeochemical research in the Amazon basin (in collaboration with Anthony Aufdenkampe, Stroud Water Research Center) has shed light on a range of carbon sources and processes operating in this continental-scale basin that encompasses both semi-arid environments in the Andean cordillera and lowland rain forests. In lowland rivers, extensive analysis on organic and inorganic fractions indicate that dissolved CO2 is predominantly contemporary (< 5 years in age) and originates in the respiration of a labile organic matter subfraction that is a very small component of bulk organic fractions (Mayorga et al. 2005); this work provides critical insight regarding controls on the observed high CO2 evasion fluxes from rivers to the atmosphere (Richey et al. 2002) and potential human impacts from deforestation. In contrast, cycling of particulate organic carbon from high mountains to lowlands is intimately tied to sediment dynamics, involving the erosion of aged soil and fossil carbon, deposition and storage in lowland floodplains hundreds of kilometers downstream, and subsequent remobilization to the river after extensive transformations over hundreds to thousands of years (Mayorga et al. 2005; Aufdenkampe et al. In prep.).