SURFICIAL SEDIMENT TRANSPORT AND DEPOSITION PROCESSES IN A JUNCUS-ROEMERIANUS MARSH, WEST-CENTRAL FLORIDA

Flow speed, water level, total suspended solid (TSS) concentration and sediment deposition were measured on the surface of a Juncus roemeria nus marsh in west-central Florida in order to: (1) determine magnitude and direction of suspended material transport across the marsh surfac e; (2) identify the processes controlling this transport and; (3) rela te water column processes to net surficial deposition. Flow data, meas ured by hot-film anemometry speed sensors, indicate that (1) Bow speed is inversely related to distance from the creek edge, and (2) the dur ation of slack-high water is limited to less than 30 minutes. TSS conc entrations measured on the levee generally reflect those measured with in the creek itself (15 to 20 mg/l). However, as distance from the cre ek increases, current speeds decrease and a corresponding decrease in TSS concentration is observed. Low current speeds in the overland flow promote deposition throughout the entire inundation event until the l ast parcel of water leaving the marsh surface has a minimum TSS concen tration of approximately 6-8 mg/l. Rates of total deposition per tidal cycle (tc) were calculated from petri-dish sediment traps deployed ov er both fortnight and single tidal cycles. The results indicate that d eposition rates me affected by proximity to the tidal creek and also b y season. Levee deposition rates average 24 +/- 9 g/m(2)/tc and exceed depositional rates measured 10 meters From the creek edge (9.5 +/- 3 g/m(2)/tc). When divided into seasonal components, mean deposition rat es are greater for both the levee (31 +/- 17 g/m(2)/tc) and the inner (18 +/- 4 g/m(2)/tc) marsh sites during the summer than those measured in the winter (18 +/- 3 g/m(2)/tc and 6.7 +/- 2 g/m(2)/tc, respective ly). The trap data also indicate that during the winter, surficial dep osition is significantly affected by storm activity. Surficial sedimen t fluxes derived from TSS concentration, water level, and Bow speed da ta agree with deposition rates determined from trap data and suggest t hat direct settling accounts for almost all surficial deposition measu red by the traps. Other potential sediment sources (e.g., fecal materi al and plant liner) appear to contribute little overall to marsh surfa ce accretion on the time scales considered for this study. Despite the fact that the observed deposition rates are less than those reported for other marshes on the Gulf of Mexico and the southeast U.S. coastli nes, vertical accretion rates (extrapolated from bulk density measurem ents of surficial sediments and deposition rates in the study area) su ggest that the west-central Florida marshes are accreting at rates com parable to local rates of sea-level rise.