Sources, Sinks and Yield of Organic Constituents In Managed Headwaters of Mississippi.

Managed, forested headwaters in Mississippi constitute more than 20 million acres and are a crucial part of watershed dynamics because they comprise more than 60-80% of stream networks and watershed land areas.  Headwater streams contribute suspended solids, OM, and nutrients such as nitrogen to downstream fluvial environments and these constituents are frequently cited as contributing to river impairment in Mississippi.  Flux of these materials from headwaters is difficult to quantify and few studies have examined the source of these materials.  In particular, the relationships among origin, storage, and consumption and export of OM with stream discharge and subsurface interflow represent significant gaps in our understanding of headwater processes. OM serves a vital function as a regulator of bacterial productivity, dissolved oxygen DO concentrations, nutrient cycling, and food web productivity however excess terrestrial input of OM and associated nutrients can contribute to eutrophication and hypoxia in waters that are deficient in DO. This project augments current research efforts concerning hydrologic and hydrologically-mediated functions in managed, forested headwaters of Mississippi.  This study quantifies the yield, source, and transport of organic carbon (OC) and nutrients within managed watersheds in order to better constrain the flux of OC, nutrients, and contaminants that bind to OM.  Objectives are to (1) quantify exports of sediment, POM, POC , and PON, (2) determine whether C and N are derived from a similar source using stable isotope ratios, (3) determine the source of DOC and DON, and (4) determine whether additional process are occurring at a larger scale.  Preliminary data linking TSS to soils from one year of sampling across four management intensities will be presented.  These data will be of value to forested-watershed managers in their efforts to weight the environmental cost vs. nutrient cycling benefit of organic inputs resulting from silvicultural activities.