POC TRANSPORT BY HEADWATER STREAMS IN THE PIEDMONT OF SOUTH CAROLINA

Because freshwater ecosystems cover such a small percentage of the Earth’s surface, they have often been overlooked as important quantitative components of the carbon cycle, on both regional and global levels. However, preliminary studies have shown that these freshwater ecosystems are very dynamic and are important sinks and sources of carbon. First-order headwater streams are a particularly important, but frequently overlooked, component of the freshwater ecosystem because they constitute the majority of stream length in river systems. Thus, the transport and storage of carbon in these streams is critical to understanding carbon cycling in river systems. In this study, we investigated the effects of storm events on particulate organic carbon (POC) transport in three residential headwater streams. We collected samples periodically throughout seven storm events using an automated sampler and compared results to base flow samples. Samples were filtered through 0.7 micron glass microfiber filters and loss on ignition was used to estimate percent organic matter. Filtered samples were compared to a Munsell soil color chart in order to quantify change in sediment type throughout a given storm event. During base flow conditions, total suspended sediment remained low in all three streams, rarely reaching more than 30 mg/L, with 20-30% POC. During storm events, total suspended sediment peaked immediately, ranging from 190 mg/L to 3000 mg/L depending on stream location and size of storm event. POC peaked 30 minutes to 2 hours after the storm event peak, reaching a maximum of about 60% of the total suspended sediment, with concentrations ranging from 50mg/L to 1500mg/L. At the beginning a storm event, the sediment was strong brown in color but, as the POC increased, the color became light yellowish brown, before returning to pale yellow as the stream returned to base flow conditions. Total suspended sediment and percent POC both significantly increase during storm events, showing that POC transport is much greater during these events, but POC stays in suspension longer than mineral sediment. Variations of suspended sediment and POC appear to be a function of geological differences and historical land-use practices. The data suggests that head water streams can be an important source of downstream POC.