Assessing sediment dynamics of the Middle St. Johns River Basin, Lake Jesup, Florida, USA

Lake Jesup is a shallow, hypereutrophic lake located in the middle St. Johns River basin that received large loads of secondary effluent prior to 1985 and experiences tidal, tributary and wind influenced flow. To date we have assessed the use of several different types of sediment traps at different water depths within this shallow basin (typically less than 2.5 m). Each system deployed has its advantages, but deployments in shallow systems present unique challenges. We have augmented our sediment traps with additional observation and data collection systems to evaluate our approach for studying sedimentation rates in the basin. These systems include a floating barge platform to collect daily water samples for suspended particles, weather stations for wind direction and velocity current (flow) meter and acoustic Doppler water velocity systems (ADVs). Results from 2009 to 2010 show mass accumulation rates ranging between 200 g dw m^-2 d^-1 to 1200 g dw m^-2 d^-1. Trap material was analyzed for nutrients to better understand fluxes of carbon, nitrogen, and phosphorus. Sediment oxygen demand was measured during incubation experiments to determine potential effects on water column oxygen concentrations during resuspension events. In the second phase of this project (2010 to 2011) we will measure radioisotopes to better estimate the source of resuspended particles. Our goal is to use the deployed instrumentation to show how hydrodynamics affect sediment transport in this basin. Studying the sediment dynamics of highly productive fresh water end members of estuary systems is critical to better quantify biogeochemical fluxes necessary for effective restoration management. This paper will present a model of nutrient flux and accumulation rates, sediment oxygen demand, correlations between sediment flux and potential driving forces, and initial results from radioisotope sourcing.