Mississippi Basin Carbon Project Science Plan

Summary

Understanding the carbon cycle is one of the most difficult challenges facing scientists who study the global environment. Lack of understanding of global carbon cycling is perhaps best illustrated by our inability to balance the present-day global CO₂ budget. The amount of CO₂ produced by burning fossil fuels and by deforestation appears to exceed the amount accumulating in the atmosphere and oceans. The carbon needed to balance the CO₂ budget (the so-called "missing" carbon) is probably absorbed by land plants and ultimately deposited in soils and sediments. Increasing evidence points toward the importance of these terrestrial processes in northern temperate latitudes. Thus, efforts to balance the global CO₂ budget focus particular attention on terrestrial carbon uptake in our own North American "backyard."

The USGS Mississippi Basin Carbon Project conducts research on the carbon budget in soils and sediments of the Mississippi River basin. The project focuses on the effects of land-use change on carbon storage and transport, nutrient cycles, and erosion and sedimentation throughout the Mississippi River Basin. Particular emphasis is placed on understanding the interactions among changes in erosion, sedimentation, and soil dynamics. The project includes spatial analysis of a wide variety of geographic data sets, estimation of whole-basin and sub-basin carbon and sediment budgets, development and implementation of terrestrial carbon-cycle models, and site-specific field studies of relevant processes. The USGS views this project as a "flagship" effort to demonstrate its capabilities to address the importance of the land surface to biogeochemical problems such as the global carbon budget.

Two hypotheses are being examined: (1) that carbon burial in terrestrial environments is accelerated by human influences on erosion and sediment deposition; and (2) that significant amounts of carbon are fixed from the atmosphere and supplied to sites of enhanced erosion and deposition, and to soils and sediments enriched by modifications of hydrologic systems and nutrient supplies. Study of these hypotheses is inherently historical, requiring mass balance estimates over time scales ranging from specific flood events to millennia. Similarly, the project requires consideration of a broad range of spatial scales. At the hillslope and small watershed scale, field studies are conducted to understand the processes that control local carbon erosion, transport, and accumulation. Results of these studies are integrated with data that are more readily applied over larger areas (for example, digital elevation models, inventories of dams and reservoirs, records of land use and land cover, fluvial discharge records, and soil and climate databases). This integration is being prototyped in several river sub-basins and will ultimately extend to characterization of relevant properties of the land surface over the whole basin. Modeling is inherent in every aspect of the project, both as a tool for understanding at discrete spatial and temporal scales, and as a method for integrating mass-balance calculations over time and space. To assure that our work is always guided by the need to extrapolate beyond field and sub-basin scales, we include whole-basin and global analyses even in the early stages of the project.

This science plan is intended to serve as a rationale and guide for project participants and as a source of information about the project for managers and potential collaborators. The activities described in this plan will be carried to a level of detail that depends on funding, the project lifetime, and the development of arrangements for collaboration and review by non-USGS scientists. Essential goals of the project are testing the two central hypotheses, estimating whole-basin carbon budgets, and linking these estimates to the global CO₂ budget. Studies of carbon, sediment, and nutrient budgets in the Mississippi Basin will also provide valuable information relevant to many other problems associated with human land use. Agricultural productivity is threatened by increasing erosion and declining fertility of soils. Erosion and sedimentation are primary concerns in the management of water supplies and quality. Natural organic compounds play a critical role in the transport and storage of contaminants in waters and sediments. Carbon compounds account for most of the oxygen depletion associated with anoxia and eutrophication in lakes, streams, and coastal waters. An improved understanding of interactions between changes in the land surface and changes in the carbon cycle is essential to predicting and coping with global environmental change.

	Contents
	(Beginning)
	Background