ACCRETION OF A NEW-ENGLAND (USA) SALT-MARSH IN RESPONSE TO INLET MIGRATION, STORMS, AND SEA-LEVEL RISE

Sediment accumulation rates were determined at several sites throughou t Nauset Marsh (Massachusetts, U.S.A.), a back-barrier lagoonal system , using feldspar marker horizons to evaluate short-term rates (1 to 2 year scales) and radiometric techniques to estimate rates over longer time scales (Cs-137, Pb-210, C-14). The barrier spit fronting the Spar tina-dominated study site has a complex geomorphic history of inlet mi gration acid overwash events. This study evaluates sediment accumulati on rates in relation to inlet migration, storm events and sea-level ri se. The marker horizon technique displayed strong temporal and spatial variability in response to storm events and proximity to the inlet. S ediment accumulation rates of up to 24 mm year(-1) were recorded in th e immediate vicinity of the inlet during a period that included severa l major coastal storms, while feldspar sites remote from the inlet had substantially lower rates (trace accumulation to 2.2 mm year(-1)). Du ring storm-free periods, accumulation rates did not exceed 6.7 mm year (-1), but remained quite variable among sites. Based on Cs-137 (3.8 to 4.5 mm year(-1)) and Pb-210 (2.6 to 4.2 mm year(-1)) radiometric tech niques, integrating sediment accumulation over decadal time scales, th e marsh appeared to be keeping pace with the relative rate of sea-leve l rise from 1921 to 1993 of 2.4 mm year(-1) At one site, the Pb-210-ba sed sedimentation rate and rate of relative sea-level rise were nearly similar and pear rhizome analysis revealed that Distichlis spicata re cently replaced this once S. patens site, suggesting that this portion of Nauset Marsh may be getting wetter, thus representing an initial r esponse to wetland submergence. Horizon markers are useful in evaluati ng the role of short-term events, such as storms or inlet migration, i nfluencing marsh sedimentation processes. However, sampling methods th at integrate marsh sedimentation over decadal time scales are preferab le when evaluating a systems response to sea-level rise. (C) 1997 Acad emic Press Limited.