Research:

Investigating subsidence versus sediment accumulation and erosion effects on coastal marsh elevation: the Fritchie and Pearl River Marshes, Louisiana (pending)

Summary:

Losses of coastal wetlands are staggering, as high as 90 km² yr^-1 for the Louisiana delta plain and 20 ha yr^-1 in the Pearl River marsh. Implications of these losses are wide ranging and severe, including loss of fin and shellfish habitat, diminished protection from storm surge and decreased pollutant filtration. Land losses are due to a range of factors including sea level rise; sediment starvation; faulting; withdrawal of water, oil, and natural gas, coastal erosion, sediment compaction; unfavorable tidal asymmetry; and loss of vegetation. Both of these marshes are dissected by normal faults, anticipated to influence rates of subsidence. These contiguous marshes, while contrasting in restoration history and hydrology, share geologic composition and geomorphic and tectonic settings, making them ideal for this research.

Objectives:

1. Measure/differentiate changes in marsh elevation due to subsidence vs. sediment erosion/compaction;

2. Assess role of restoration in influencing parameters measured in objective 1.;

3. Measure marsh sediment accretion/erosion;

4. Develop approach to allow for widespread field and planning applications.

Evaluation of the impacts of dredging activities on the fate of dioxin in the Houston Ship Channel, Texas (ongoing)

Summary:

Sedimentary processes and activities which modify or impact them are key components in determining the fate of dioxins. Contamination of the Houston Ship Channel (HSC) and Galveston Bay (GB) with dioxins is a serious issue, impacting both human and ecosystem health. Polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs), collectively referred to as dioxins, are persistent contaminants. In oxic sediments, half-lives of dioxins are on the order of decades. Dioxins are known to cause a variety of damaging biochemical, immunological, and reproductive effects in animals and are suspected carcinogens in humans. Dioxins bio-accumulate, particularly in the aquatic food chain, posing significant risks to human health. Study includes the HSC from confluence of the San Jacinto River to upper GB (see map). Dioxin toxic equivalents (TEQs) at sampling sites near dredge sites 1, 2, 4, 5 and 6 significantly exceed the target limits of 470 ng kg^-1. One transect will be studied in this general area, in addition to an un-dredged location near the mouth of the Trinity River.

Objectives:

1. Compare/contrast dredged vs. undredged sites and spoil islands in terms of sediment composition and dioxin contents;

2. Determine effects of dredging on dioxin concentrations, source or sink?;

3. Assess role of dredging in TMDL framework.

Factors regulating microbial degradation of dioxins and dioxin-like compounds in estuarine sediments: the Houston Ship Channel and Galveston Bay, Texas (ongoing)

Summary:

The Houston Ship Channel (HSC) and upper Galveston Bay (GB) are polluted with dioxins derived from industrial, municipal and agricultural effluents (see graphic). Hypotheses to be tested include: H₁ Dioxins are sequestered in sediments and can be attenuated by increased biodegradation under reducing geochemical conditions; and H₂ Dioxins fate is inextricably linked to geochemical and microbial settings of host sediments; therefore physical mixing (bioturbation, dredging, commerce) makes dioxins more available for bioaccumulation, while reducing prospective rates of biodegradation via resulting perturbations (including change from reducing to oxidizing conditions).

Objectives:

1. Evaluate natural, microbially-mediated degradation of dioxins in sediments;

2. Develop an interdisciplinary and comprehensive understanding of processes which accentuate and inhibit microbial degradation of dioxins in sediments;

3. Develop a sedimentary dioxin budget, extrapolated to the field scale.

Quantification of sediment sources of the Nueces-Corpus Christi Estuary System (ongoing)

Summary:

The quantity and quality of sediment supplied to estuaries plays a pivotal role in overall water quality in terms of: turbidity, transport/sequestration of pollutants and maintenance of associated environments (tidal flats, marsh lands, etc.). This research applies radiochemical and geochemical techniques to quantify sources of sediment to the estuary. Sediment samples have been collected from the estuary, throughout the Nueces River basin, the Gulf Intracoastal Waterway (GIW) and from the Gulf of Mexico (GOM). A suite of radionuclides will be determined in all sediment samples, including ¹³⁷Cs, ²¹⁰Pb, ²²⁶Ra, ²²⁸Ra, ²³²Th, ²³⁰Th and ²²⁸Th. Isotopic signatures for sediment samples will be used to investigate both environmental controls which influence sediment radiochemical signatures (lithology, land use, water chemistry) and to quantify the contributions of various source areas to the estuary sediment supply.

Objectives:

1. Determine importance of marine vs. terrestrial sources of sediment to the estuary;

2. Measure large scale sedimentation in the delta and bays of the estuary;

3. Measure suspended sediment concentrations throughout the Nueces River basin and estuary;

4. Determine dissolved anions which may influence isotopic adsorption.