Title of Document : TRANSPORT , SOURCES , AND QUALITY OF SESTON IN A PIEDMONT HEADWATER STREAM

Title of Document:TRANSPORT, SOURCES, AND QUALITY OFSESTON IN A PIEDMONT HEADWATERSTREAMDavid Charles Richardson, Doctor of Philosophy2008Directed By:Dr. Margaret Palmer, Marine, Estuarine andEnvironmental Science, Chesapeake BiologicalLaboratoryDr. Louis A. Kaplan, Stroud Water ResearchCenter Streams transport and process particulate organic carbon (POC) within thesuspended load (seston) after terrestrially-fixed (allochthonous) carbon enters loticecosystems or as instream (autochthonous) production is suspended from thestreambed. POC provides a basal resource for upstream food webs, but can alsosupport heterotrophic metabolism in downstream rivers. Yet, the controls ontransport, sources, and biological availability (quality) of POC from headwaters arepoorly understood. I examined seston and POC dynamics in a3-order headwaterstream in SE Pennsylvania. I studied the temporal controls on seston transport,composition, and sources, and the biological quality of POC.I present evidence that seasonal patterns in seston and POC transport andcomposition reflect stream organism activity and cycles of autumnal leaf litter inputs and vernal algal production. This work also provides the first evidence of recurrentnighttime peaks of seston transport; I attribute this pattern to bioturbation ofstreambed sediments that suspends particles during stream-organism nest digging,foraging, and movement. I present the first effort to demonstrate that streamsalamanders contribute to ecosystem level processes such as modification of sestonand organic carbon flow.Mixing model analyses of seston composition indicate that seston in smallstreams is predominantly mineral-core particles; however, POC fluxes are primarilyorganic-core particles. Furthermore, the traditional view of headwater POC as leafdetritus should be expanded to include algal-derived particles, even in forestedheadwater streams. Finally, I report a new method for measuring the quality ofsuspended POC from aquatic environments using heterotrophic respiration as a metricfor lability. Heterotrophic respiration rates for suspended POC measured using thismethod were an order of magnitude higher than respiration rates previously reportedfor benthic POC.The results from this research highlight the importance of seston for bothheadwater streams and as a longitudinal linkage of allochthonous and autochthonousorganic matter to downstream ecosystems. The magnitude of this connection iscontrolled by the quality, quantity, and timing of POC delivery. TRANSPORT, SOURCES, AND QUALITY OF SESTON IN A PIEDMONTHEADWATER STREAM