Effect of Contemporary Harvesting Practices on the Source of Particulate Organic Matter and Sediment in Oregon Coast Range

Forest harvesting and establishment of forest roads tend to increase water and sediment yield.  However, in many studies the source of sediment is often unknown.  The characteristics of sediment and associated organic matter can be used to trace the source of sediment and particulate organic carbon in managed watersheds. Over the last 40 years best management practices have greatly reduced levels of sediment delivered to streams during and after forest harvest.  However, there is still broad concern about stream sediments associated with forest management, particularly with regard to the source of sediment.  By understanding the source of sediment, problem areas can be pinpointed and best management practices improved. We have examined the organic matter characteristics of suspended sediment and endmember soils from harvested (with and without riparian buffers) and unharvested watersheds in the Trask watershed study located in the Oregon Coast Range. We will discuss trends in particulate organic carbon and particulate nitrogen fluxes and sources of sediment and organic matter as determined by %C, C:N, ¹³C, and ¹⁵N.