Theoretical models of landscape denudation in carbonate terrains are based on an understanding of chemical processes and have allowed an accounting of chemical erosion of carbonate in karst systems and of one sink for atmospheric carbon dioxide. These existing models assume that the mechanical removal of carbonate in karst terrain is negligible. This study will test that assumption by adding mechanical removal of carbonate to the existing geochemical models and will allow more precise accounting of atmospheric CO2 sinks associated with carbonate regions. There are three primary objectives to the project: quantify bed load transport and flux of particulate inorganic carbon, quantify suspended load transport and flux of particulate inorganic carbon, and quantify the flux of dissolved inorganic carbon to compare to the flux of particulate inorganic carbon and to allow calculation of the total flux inorganic carbon. To characterize suspended load flux, direct sampling and computation of the suspended load as the depth-integration of the product of the suspended sediment concentration and the flow velocity will be used. Because it is poorly understood, a major effort of this research will be to describe and quantify bed load flux in karst conduits by determining sediment transport relations for streams with bounded cross sections. The sediment transport relations will be compared to observed bed load movement and to existing models of sediment transport in surface streams. Our expected outcomes are developed relations of bed load transport in karst streams, quantification of the flux of particulate inorganic carbon as bed load and as suspended load, and a better understanding of proportion of carbonate material that is removed from carbonate terrains via physical processes.
Studies of carbonate dissolution in karst settings have clearly demonstrated the significance of the dissolution process as a transient sink in the global carbon cycle due to the loss of carbon dioxide and the creation of bicarbonate. Chemical processes clearly dominate removal of carbonate during low to moderate flow conditions. However, during storm events, the mechanical movement of particles and cobbles of carbonate material (bed load and suspended load) can be a major component of flux of inorganic carbon. Over an annual cycle of storm events, the movement of these particles may account for a large percentage of the annual removal of mass. This study will specifically investigate movement of these particles and improve our understanding of the carbon cycle and of landscape denudation. In addition, this project integrates research and education through the research experience of the Geology Intensive Orientation for Students program at LSU, a program designed to help the incoming Freshmen make the transition to the expectations of college-level course work prior to the start of their first fall semester. The students in the Geology Intensive Orientation for Students will conduct a sediment transport study in the Mississippi River and will be introduction to global carbon cycle.
