Water quality of two first order forested watersheds in coastal South Carolina

Understanding watershed hydrology and the concentrations of nutrients in stream waters are fundamental considerations for assessing water quality. Despite the fact that forests are generally recognized for providing clean water and used as a baseline for assessing the effects of other land uses, especially urbanization, there are ongoing concerns about the effects of forest management practices on receiving waters. Two First-order forested watersheds (?KS 80 and WS 77) on poorly drained pinehardwood stands at the USDA Forest Service Santee Experimental Forest in the South Carolina Coastal Plain have been monitored since mid-1960s to characterize their hydrology, water quality and vegetation dynamics. This study examined the nutrient concentrations and loading dynamics of these two watersheds using both outflow and concentration data collected since 2003. WS 80 remained as a reference throughout the study period, whereas WS 77 underwent a prescribed burning of the understory vegetation in May 2003 for Red-cockaded Woodpecker (Picoides barcalis) habitat management. Both watersheds were highly responsive of rainfall events with 8 to 46% of the annual rainfall lost to stream outflows depending upon years. Prescribed burning contributed to as much as 72% (147 mm) increase in outflows in 2005 for the treatment watershed (WS 77) compared to the pre-burning levels. However, by the First half of 2006 the effect reduced to only 13 mm increase. No difference was found in nutrient concentrations between the two watersheds, except for the NH4-N, which seem to have increased. Both the nutrient concentrations and loading rates measured were small and were lower than the values published for pine forests in eastern North Carolina. Historic data and the data presented herein may serve as baseline information for assessing developmental impacts in the region and for assessing the Total Maximum Daily Loads (TMDLs).