Abstract
Suspended particulate matter (SPM) plays an important role in the biogeochemistry of estuaries and wetlands. Recent wetland restoration efforts have targeted tidal wetlands; yet, many questions pertaining to SPM dynamics s remain. A paired in situ optical and acoustical sensor package was deployed for several weeks during the winter in the main channel at Browns Island, CA, in order to identify processes controlling estuarine and marsh sediment dynamics. Turbidity, particle volume concentration and particulate attenuation were employed as surrogates of SPM concentration. The slope of the particulate attenuation spectra, , and laser diffraction were used to study particle size dynamics and flocculation processes. Water samples were collected hourly over one tidal cycle at the end of the study period for SPM concentration and organic content in support of optical measurements. Together these observations helped elucidate the role of tidal wetlands in the cycling of estuarine particles. Tidal action was a driving force of particle dynamics at Browns Island, as fluctuations in tidal water levels controlled wetland inundation and current velocity. SPM surrogates were maximum at the height of the higher high (HH) flood tide and minimum at lower low (LL) tide water level, consistent with the loss of SPM through deposition and/or flocculation due to the interaction of estuarine water with the island. Following HH slack tide, particles smaller than 133 m flocculated into larger particle aggregates. The largest aggregates reached a maximum size of 150 m during the ebb tide. The controlling mechanism for flocculation was likely particle to particle collisions and differential settling in the presence of organic rich pore waters draining from the marsh. The transport of organic rich flocs could be an important mechanism for the export of contaminants and organic matter off of the island and into the estuary.