Luettich Lab Research

• Observing and modeling the blue crab spawning migration

The Luettich lab is studying the migration of female blue crabs Callinectes sapidus from adult habitats in North Carolina estuaries to coastal larval release (“spawning”) locations. During this migration, ovigerous crabs use ebb-tide transport, a vertical migratory behavior in which crabs ascend into the water column during ebb tides and descend to the bottom during flood tides, to move seaward. The lab is using a variety of methods for this work: tracking migratory crabs with ultrasonic telemetry, tethering crabs in a local estuary to observe vertical ascent patterns, and coupling models of crab behavior to a hydrodynamic model of local estuaries. These NSF-funded studies are being used to determine the relationship of vertical migrations to local currents, the influence of vertical migrations on horizontal transport, migratory trajectories in the estuaries, spatial patterns in migratory success, the residence times of crabs in different estuarine regions, and larval release locations.

• ADCIRC circulation model

Luettich has collaborated with Dr. J. Westerink (Univ. Notre Dame) on the development of the ADCIRC circulation model, which solves the shallow water equations for either two- or three-dimensional flows using a finite element discretization in space; it is highly parallelized to run on multiprocessor/high performance computers. Consequently, ADCIRC is very well suited for applications covering large areas while at the same time providing detailed representations of coastal areas including inlets, sounds and estuaries. The model is widely used in the academic, governmental and private sector for tidal and storm surge studies. Data bases developed with ADCIRC by Luettich and colleagues are also widely used to provide offshore tidal boundary conditions for localized coastal modeling studies. Recent significant applications of ADCIRC by Luettich and colleagues include: a comprehensive study of hurricane induced flooding in the southern Louisiana/New Orleans region, tidal characteristics in the South Atlantic Bight, physical flow characteristics and associated biological transport in the vicinity of Beaufort Inlet, NC, and a nowcast/forecast system for tides and storm surge in the Western Atlantic and Gulf of Mexico. Luettich’s laboratory has also engaged actively in inner shelf observational studies (Figure 3.32), including a detailed study of current patterns in the vicinity of Beaufort Inlet, a coupled bio-physical study of blue crab migration in the Bogue Sound/Beaufort Inlet system (discussed above) and a study of the seiching characteristics of Pamlico Sound, NC. [Collaborators: J. Westerink, Univ Notre Dame; R. Forward, DUML; D. Lynch, Dartmouth; D. Eggleston, NCSU; H. Seim, C. Werner, B. Blanton, J.Hench, H. Paerl, various students, UNC-CH. Funding: NSF, NOPP, EPA, US Army COE.]

Figure 3.32. Left: An example time series of water column properties collected by a profiling buoy system deployed in 7 m of water near the mouth of the Neuse River Estuary. Data indicate that during relatively low winds (< 10 m/s) the water column is density stratified with reduced oxygen concentrations below the pycnocline, relatively low turbidity and a diurnally migrating chl-a maximum. At higher winds (> 10 m/s) the water column mixes rapidly and bottom material is resuspended throughout the water column. Right: The initial deployment of the Lookout Shoals research buoy, January, 2005. The buoy was deployed from IMS’s 48’ RV Capricorn, seen in the background starting for home.

• Profiling Buoy System for Shallow Waters (Rick Luettich, H. Paerl, students) (EPA).

Luettich has developed a profiling buoy system for shallow inner shelf and estuarine studies. It is comprised of a buoy mounted, computer controlled winch system that raises and lowers a CTD/multi-parameter probe. Cell phone communications enable near real time transmission of data to shore. Two of these systems have been deployed in the Neuse River Estuary over the past several years and have documented the occurrence of wind driven upwelling along the shores of the estuary and the role that this plays in bringing low oxygen water to the surface (potentially impacting pelagic fisheries populations in the system). These profiling buoys have also documented a pervasive vertical migration of the chl-a maximum in the water column from near surface to near bottom on a daily time scale and characterized the meteorological conditions for which the system becomes well-mixed over the depth. Under these mixing conditions the chl-a maximum is completely disbanded and bottom resuspension is widespread.

• Offshore Buoy and Mooring System (Rick Luettich, H. Seim, students) (SEACOOS)

As part of the SEACOOS program, Luettich is also collaborating with H. Seim to develop the Lookout Shoals Research Buoy. An uninstrumented buoy was deployed in early January off the Cape Lookout Shoals; this will soon be followed up with a fully instrumented buoy (Figure 3.35). The completed buoy system will consist of a bottom tripod containing a CTD and ADCP measuring mean currents through the water column and the surface wave field. The buoy will host a mid-depth and near surface CTD, and an extensive array of meteorological sensors. The buoy and bottom tripod will communicate via an acoustic modem and the buoy will communicate with shore via an Iridium satellite communications system and a cellular phone system.

Fig. 3.35. Schematic of buoy/mooring deployed off Cape Lookout, NC.

• ModMon: a Comprehensive, Long Term Water Quality Modeling and Monitoring Program for the Neuse River Estuary (Hans Paerl, Rick Luettich) (North Carolina Department of Environment and Natural Resources)

ModMon is a coordinated, multidisciplinary state, university and industry estuarine environmental modeling and monitoring program. This effort is a result of the Senate Select Committee hearings on River Water Quality and Fish Kills, legislative requests for assistance from university scientists in solving state environmental problems, and university initiatives to enhance research in areas of critical importance to state water quality management and planning. ModMon has been designed to provide a water quality model of the Neuse River Estuary (NRE) that is evaluating alternatives for reducing nitrogen loading. ModMon is also a crucial source of data for evaluating a Total Maximum Daily (nitrogen) Load (TMDL), required by the EPA for controlling unwanted symptoms of eutrophication in the NRE (algal blooms, hypoxia, food web disruption). To achieve these goals, the monitoring component is obtaining field data for calibrating and verifying the model and advancing our understanding of relationships between nutrient loading, eutrophication and water quality. Field data are obtained by both ship-based and in stream continuous multiple sensor (YSI 6800) measurements of temperature, salinity, pH, turbidity, dissolved oxygen and chlorophyll (fluorescence), complemented by laboratory analyses of inorganic and organic nutrients (C, N, P), diagnostic (of algal taxonomic groups) photopigments, and molecular markers for microbial groups involved in nutrient cycling and production dynamics.