Drivers of intertidal oyster reef and tidal creek accretion over the last century

Abstract

Salt marshes and intertidal oyster reefs provide valuable ecosystem services but are being lost or altered due to human modifications at the coast. Restoration projects intend to recover ecosystem services, but little is known about the conditions that promote longevity in restoration projects which requires vertical accretion to keep pace with sea-level rise. Furthermore, while there is documentation of the impacts of land-use change on sediment loads in large river systems and sedimentation in estuaries, small coastal tidal creeks have been largely ignored. To address these issues, this work 1. Quantified intertidal oyster reef growth and identified optimal restoration settings across tidal ranges, atmospheric temperatures, and landscape settings, 2. Evaluated land-use change since 1950 CE and associated impacts on tidal creek sedimentation, and 3. Determined how land-use changes affected sediment and carbon accumulation rates of saltmarshes. Chapter one compared the growth of 12 natural intertidal oyster reefs of varying age across two tidal ranges and landscape settings in coastal North Carolina. Peak growth rates were similar among landscape and tidal settings, but flow baffling associated with fringing reefs and higher summer air temperatures contributed to a lower position of the optimal growth zone in the tidal frame. Chapters 2 and 3 were addressed by comparing sediment accumulation rates before and after a land-use change in 12 tidal creeks across two distinct regions in North Carolina, one region of low relief tidal-creek watersheds where land-use change was dominated by fluctuations in forest, silviculture, and agriculture, and another region of high relief tidal-creek watersheds where land-use change was dominated by suburban development. While accumulation rates accelerated within the creek bottom and adjacent fringing marsh sites after a land-use change, the magnitude of the acceleration differed depending on the morphology of the creek basin. There was faster acceleration in accumulation rates at creek sites within coastal prism incised valleys, but slower acceleration for their adjacent fringing salt marshes. Results from this work will provide guidance for oyster reef restoration and coastal watershed management for sedimentation in tidal creeks and salt marshes.Doctor of Philosoph