Portfolio VII: Understanding ContaminantsAchievements And ImpactsScientific achievements over the course of the TRP research supported a variety of topics relevant to understanding (1) fate (2) transport and (3) effects that representative toxicants have upon organisms and ecological processes are summarized below.
(1) Fate of Contaminants TRP funded research has provided a number of insights into how sediment physics and biogeochemistry interact to regulate contaminant release and resuspension. Many of these processes were poorly understood for estuarine ecosystems prior to this work. Geochronological techniques were utilized to examine long sediment cores from the Bay. Sharp peaks of heavy metal concentrations are found below the surface layers of the cores, indicating declines in lead, copper and zinc loads in recent years. The data suggested that management strategies to reduce metal loading have been effective. In particular, lead in the sediments is now approximately half of that seen in the sediments during the period of peak loading in the 1970s. Microbial ecology studies provided some of the first direct evidence for degradation and mineralization of some chlorinated aromatic compounds by microbial consortia in Baltimore Harbor and mid-Chesapeake Bay sediments. Researchers investigating physical processes provided the first data showing that resuspension of surface, organic-rich sediments occurs frequently during wind events and surprisingly, at significant rates during periods of average tidal flow. When organic rich, toxic-containing sediments are resuspended decomposition of the organic material occurs at a more rapid pace, releasing the toxins into the water column once more. (2) Transport and Trophic Transfer TRP support enabled researchers to make some of the first reliable measurements of PCB congeners and other HOCs in the dissolved and particulate phases in the water column, as well as in phyto- and zooplankton in Chesapeake Bay. Data on HOC distributions in plankton size fractions indicated increasing concentrations with larger particles. Thus zooplankton are bioaccumulating contaminants from smaller sized particles. Phytoplankton also appear to be an important source of PCB loading to oysters which absorb more PCBs from food than indigestible clay or mineral particles filtered simultaneously. Determinations of mass transfer rates for the uptake of HOCs by phytoplankton were also used in the development of models of toxic bioaccumulation and transport. With regard to toxic metals, while trace metal fluxes between sediments and the water column are geochemically significant and can produce detectable (even substantial) changes in the water column concentrations, they did not produce sufficiently elevated levels likely to induce major biological effects. Food quantity and quality, or other natural stresses such as low oxygen appear to significantly outweigh the effects of toxics from the sediments, making direct assessments of the ecological effects of the toxics problematic. Elevated concentrations of toxic trace elements in sediments are to some extent responsible for accumulation of these elements in important forage food species, (grass shrimp and mummichogs). However, researchers noted that the degree of enrichment is controlled by a complex system involving the biogeochemical processes important for each contaminant and by biological factors such as preferred food, nutritional and growth status, and basic physiological differences among species. (3) Effects of Contaminants on Oysters While TRP "effects" research focused upon a number of organisms, studies of contaminant impacts on oysters were particularly important given ongoing emphasis on both the natural fishery and aquaculture efforts. Researchers found environmental conditions such as temperature and salinity greatly influenced the impact of toxins on oysters. Measurements of metallothionein production were used as a biomarker for metal exposure and response. The results and associated technology used are highly applicable to managers developing guidelines for the management of aquatic environments, and to identifying potential water bodies suitable for oyster aquaculture. Estuarine biofilms were found to concentrate copper and cadmium at sufficient levels to inhibit larval set and metamorphosis. This study emphasized that the bioconcentrating activity of estuarine biofilms is a significant factor that must be considered when establishing heavy metal contamination criteria in Chesapeake Bay. The devastating effects of dermo and MSX on Chesapeake Bay oyster populations is well-documented, however interactions between immune response and pollutant loading has not been well understood. TRP funded research documented the increase in susceptibility of oysters to dermo in the presence of tributyltin. ImpactsAs one of the longest sustained effort to fund research addressing contaminant issues in Chesapeake Bay, the TRP has had strong impacts. It has provided the scientific foundation for understanding how biogeochemistry and ecological processes regulate the storage and mobilization of contaminants within the ecosystem. Funding to individual projects dispersed across a number of institutions around the Bay has helped to build an infrastructure within the research community. The CBEEC partnership and the strong programmatic and administrative support from joint activities of Maryland and Virginia Sea Grant have been key to this effort. The group of scientists funded through the TRP routinely provide strong input to managers within their respective states as well as to the relevant subcommittees within the EPA Bay Program charged with developing contaminant monitoring and assessment protocols. It can be argued that subsequent efforts to focus the TRP and develop new models for this type of research would not have been as successful had this scientific foundation and its links to stakeholders been facilitated. Recognition of both the strengths and data gaps from the TRP led CBEEC to implement a process that has enfranchised numerous stakeholders and resulted in the development of the new TPP strategic plan. Impacts of this effort are still building; however, the tangible structure of the CERP effort is a strong outcome. In, many respects, we view this as a national model for:
Projecting to the future, it is clear that issues pertaining to the effects of contaminants in sediments will become extremely important in the coming years. Public debate over dredging in Baltimore Harbor and dredge spoil disposal sites has been played out on the front pages of local and national newspapers. The role of science in these debates has been key and at times contentious. The CERP model and its scientific outcomes will ultimately provide critical information as decisions are made regarding this issue. |
