ABSTRACT
Upland areas of southeastern U.S. tidal creek watersheds are popular locations for development, and they form part of the estuarine ecosystem characterized by high economic and ecological value. The primary objective of this work was to define the relationships between coastal development, with its concomitant land use changes and associated increases in nonpoint source pollution loading, and the ecological condition of tidal creek ecosystems including related consequences to human populations and coastal communities. Nineteen tidal creek systems, located along the southeastern United States coast from southern North Carolina to southern Georgia, were sampled during summer, 2005 and 2006. Within each system, creeks were divided into two primary segments based upon tidal zoning: intertidal (i.e., shallow, narrow headwater sections) and subtidal (i.e., deeper and wider sections) and then watersheds were delineated for each segment. Relationships between coastal development, concomitant land use changes, nonpoint source pollution loading, the ecological condition of tidal creek ecosystems, and the potential impacts to human populations and coastal communities were evaluated. In particular, relationships were identified between the amount of impervious cover (indicator of coastal development) and a range of exposure and response measures including increased chemical contamination of the sediments, increased pathogens in the water, increased nitrate/nitrite levels, increased salinity range, decreased biological productivity of the macrobenthos, alterations to the food web, increased flooding potential, and increased human risk of exposure to pathogens and harmful chemicals. The integrity of tidal creeks, particularly the headwaters or intertidally-dominated sections, were impaired by increases in nonpoint source pollution associated with sprawling urbanization (i.e., increases in impervious cover). This finding suggests these habitats are valuable early warning sentinels of ensuing ecological impacts and potential public health and flooding risk from sprawling coastal development. Results also validate the use of a conceptual model with impervious cover thresholds for tidal creek systems in the southeast region.
ABSTRACT
This study investigated the concentrations and potential toxicity of polycyclic aromatic hydrocarbons (PAHs) associated with highway runoff into adjacent estuarine wetlands from road segments representing three levels of average daily traffic (ADT): low (<5,000 ADT), moderate (10,000-15,000 ADT), and high use (>25,000 ADT) based on SC Department of Transportation data. Sediments from three estuarine wetland habitats (tidal creeks, Spartina marsh, and mud flats) adjacent to these road segments were sampled to represent nine highway use class/habitat type combinations. Surficial sediments were collected at 3, 25, and 50 meters from the upland/wetland interface along transects established perpendicular to the road at each site, with additional samples taken from the road berm. Average PAH concentrations, representing 25 compounds, ranged from 3.9 to 11,000 ng/g dry weight. Berm samples had significantly greater total PAH concentrations than samples taken in any of the wetland habitats. Average total PAH concentrations decreased with increasing distance from the road berm within the wetland habitats sampled, but the differences were not statistically significant. Average total PAH concentrations also were not significantly different among the wetland habitats compared. Analysis of PAH profiles indicated that the PAH source was dominated by pyrogenic combustion products rather than from petrogenic sources. This, combined with the presence of dibenzothio-phene, which is a tire oxidation product, indicated that the primary source of PAHs was related to vehicles. Two sites with total PAH concentrations exceeding published bioeffects levels were resampled for bioassay tests using the amphipod Ampelisca verrilli, the polychaete Streblospio benedicti, and the clam, Mercenaria mercenaria, with the first two assays conducted under UV lighting since previous studies had demonstrated enhanced UV toxicity of PAHs for these species. No toxicity was observed in the amphipod or polychaete assays. Toxicity was observed in the juvenile clam assay at one site, possibly due to the combined effects of PAHs and other contaminants present.
