Rivers and the Carbon Cycle

My primary research interests include river morphodynamics, geomorphologic controls on the carbon cycle, and tectonic geomorphology.

Rivers are sensitive recorders of landscape change, and can serve as a profound signal for active tectonic, climatic, biotic, and anthropogenic processes. Rivers traverse vast distances and elevation gradients, and in doing so they serve as a nexus between the geosphere, hydrosphere, cryosphere, atmosphere, and biosphere. Chemical reactions at Earth’s surface largely involve water, and so rivers record catchment-scale chemical processes and we can take advantage of these systems to understand the dynamics of the surrounding landscape.

My current natural laboratory is the Rio Bermejo in northern Argentina. The Rio Bermejo is a special river because it has no tributaries for ~1000 km and it has suspended sediment concentrations exceeding 10 g/L at depth. This is a river that can and should be investigated further to answer questions about source-sink processes and the relationship between hydraulic conditions and river planform change. The Bermejo transports a significant volume of sediment and terrestrial organic carbon from the Andes to the Parana River, which makes its way to the Atlantic Ocean. The primary research questions I am tackling include:

  1. Is dynamic topography influencing the planform geometry and flow regime of river systems draining the eastern flank of the Andes?
  2. How do rivers modulate the type and amount of organic carbon delivered from source to sink?
  3. Over what timescales is sediment and organic carbon transferred from source to sink, and how do fluvial dynamics control this timescale?

To answer these questions, I apply numerous methods in geochemistry, sedimentology, and morphometry:

  • Field sampling of river suspended sediment and ADCP profiling to obtain hydraulic conditions
  • Suspended load characterization (grain size, sediment concentration, mineralogy (XRD))
  • Total organic carbon and bulk stable isotope analysis of river suspended sediment
  • Biomarker stable isotope analysis of river suspended organic carbon and floodplain soil organic carbon
  • Cosmogenic nuclide geochemistry, specifically meteoric 10Be/9Be of river sediment
  • River planform analysis, including meander migration rate calculation from high temporal resolution satellite image data.
  • Remote sensing analysis of precipitation, vegetation, high-resolution elevation across a river catchment
Source to sink model for leaf wax biomarker transport in the Rio Bermejo fluvial system (Marisa Repasch, 2017)

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