Current research projects are:

• Mixing and circulation in river plumes

• Transport of fish and crab larvae in a coastal environment

• Residence times and mixing within estuaries

Mixing and circulation in river plumes

Rivers are a major source of nutrients, pollutants, and other land-based material to the coastal ocean. Our work concentrates on the processes that control the vertical and lateral mixing within a river plume during strong wind events. The mixing and circulation within river plumes are governed by winds, tides, river discharge and a myriad of other mechanisms. A better understanding of the mixing processes is essential for more accurate insight into the dynamics responsible for pollutant transport, harmful algal blooms, and larval transport in the coastal ocean.

In this NSF-sponsored study, we are using an innovative combination of dye injection, surface drifters, moored current meters, and numerical modeling to measure the small-scale circulation and mixing within a plume.

Vertical mixing within the water column is not well understood, primarily due to a lack of accurate measurements. One of the goals of our research is to provide oceanographers with more data in which to examine this phenomenon. To determine an estimate of the vertical mixing in a river plume, we have injected a dye into plume formed by the Delaware River and observe how the dye mixed. By measuring the diffusion and advection of the dye within the plume, we can estimate the vertical mixing rates and circulation within the plume. A better understanding of river plume dynamics enables us to determine the fate of river-borne material and their effects on the coastal environment.

Transport of fish and crab larvae in a coastal environment

Much of marine life is dependent on ocean currents for the transport of their larvae from habitat to habitat. The dispersal of fish and crab larvae on the continental shelf and their eventual transport back to estuarine nurseries play a major role in the size of adult populations. Unfortunately, the physical and biological processes that control this transport are not well understood. Our work focuses on the genesis and maintenance of larval patches in coastal waters as well as the relationship between wind forcing and larval transport.

We are presently examining the effects of winds, river discharge, and diffusion on larval recruitment within estuaries and bays in Georgia , Delaware , and Korea . A number of recent studies have determined that blue crabs spawned in estuaries such as Delaware and Chesapeake Bays , leave the estuaries in the larval stage concentrated in a 'larval patch', and return 20-30 days later. To determine the effects of the physical environment on the transport and evolution of the patches we use a number of techniques ranging from satellite-tracked drifters that allow us to follow the patches to numerical models of the coastal environment to the centuries-old technique of plankton net towing.

Residence times and mixing within estuaries

Estuaries and coastal salt marshes are particularly susceptible to pollution, nutrient loading and anoxia. Estuaries whose waters are quickly replaced by either strong tides or substantial river input (i.e. short residence time) can be expected to quickly recover from inputs of pollution; however, those with weak tidal mixing or little freshwater inflow (i.e. long residence times) are at great risk from the ever expanding coastal populations.

In this Sea Grant-supported investigation, we are using satellite-tracked drifters, hydrographic surveys, and numerical modeling of physical and biological processes to examine the residence times and mixing within the Satilla River , a black water stream on the coast of Georgia.