Water quality impacts of bridge stormwater runoff from scupper drains on receiving waters: A review.

This article provides insight into the environmental significance of bridge deck stormwater runoff from scupper drains on receiving water bodies through a review of over eighty sources of information including research and review articles, technical reports and government websites. This article discusses sources and impacts of stormwater pollutants and presents potential methods for predicting impacts of stormwater runoff on receiving waters from highways and bridges. Records of similarities and possible differences between highway and bridge deck stormwater runoff are provided, and the significance of scupper drains as points of runoff discharge from bridges is discussed. Factors that influence bridge deck stormwater runoff quality include the location of the bridge, dimensions of the bridge deck, composition of the road surface, age of the bridge, design and maintenance of the drainage system, traffic volume, and intensity and frequency of rainfall events. Several pollutants of concern are discussed, such as heavy metals, polycyclic aromatic hydrocarbons, solids, nutrients, oil, grease, polychlorinated biphenyls, and perfluorinated compounds. This review also discusses available methods for treatment of bridge deck runoff and the challenge of applying these methods for treatment of bridge deck runoff, as compared to treatment of highway runoff. Finally, this article considers the application of the stochastic empirical loading and dilution model (SELDM), a joint product of the U.S. Geological Survey and the Federal Highway Administration, to predict and assess the potential effects of runoff on receiving waters.

Avian species diversity and transmission of West Nile virus in Atlanta, Georgia.

BACKGROUND: The dilution effect is the reduction in vector-borne pathogen transmission associated with the presence of diverse potential host species, some of which are incompetent. It is popularized as the notion that increased biodiversity leads to decreased rates of disease. West Nile virus (WNV) is an endemic mosquito-borne virus in the United States that is maintained in a zoonotic cycle involving various avian host species. In Atlanta, Georgia, substantial WNV presence in the vector and host species has not translated into a high number of human cases. METHODS: To determine whether a dilution effect was contributing to this reduced transmission, we characterized the host species community composition and performed WNV surveillance of hosts and vectors in urban Atlanta between 2010 and 2011. We tested the relationship between host diversity and both host seroprevalence and vector infection rates using a negative binomial generalized linear mixed model. RESULTS: Regardless of how we measured host diversity or whether we considered host seroprevalence and vector infection rates as predictor variables or outcome variables, we did not detect a dilution effect. Rather, we detected an amplification effect, in which increased host diversity resulted in increased seroprevalence or infection rates; this is the first empirical evidence for this effect in a mosquito-borne system. CONCLUSIONS: We suggest that this effect may be driven by an over-abundance of moderately- to poorly-competent host species, such as northern cardinals and members of the Mimid family, which cause optimal hosts to become rarer and present primarily in species-rich areas. Our results support the notion that dilution or amplification effects depend more on the identities of the species comprising the host community than on the absolute diversity of hosts.

Supersuppression: Reservoir Competency and Timing of Mosquito Host Shifts Combine to Reduce Spillover of West Nile Virus.

In the eastern United States, human cases of West Nile virus (WNV) result from spillover from urban epizootic transmission between passerine birds and Culex mosquitoes. In Atlanta, GA, substantial WNV presence in hosts and vectors has not resulted in the human disease burden observed in cities with similar infection pressure. Our study goal was to investigate extrinsic ecological conditions that potentially contribute to these reduced transmission rates. We conducted WNV surveillance among hosts and vectors in urban Atlanta and recorded an overall avian seroprevalence of nearly 30%, which was significantly higher among northern cardinals, blue jays, and members of the mimid family, and notably low among American robins. Examination of temporal Culex feeding patterns showed a marked feeding shift from American robins in the early season to northern cardinals in the late season. We therefore rule out American robins as superspreaders in the Atlanta area and suggest instead that northern cardinals and mimids act as WNV "supersuppressor" species, which slow WNV transmission by drawing many infectious bites during the critical virus amplification period, yet failing to amplify transmission due to low host competencies. Of particular interest, urban forest patches provide spillover protection by increasing the WNV amplification fraction on supersuppressor species.