Characteristics of storm runoff and sediment dispersal in the San Pedro Channel, southern California.

In-site measurements of particle size spectra were obtained from three offshore cruises to evaluate the physical consequences of increased sediment transport and deposition offshore which was caused by episodic storm runoff water from the Santa Ana River watershed, a highly urbanised coastal watershed in southern California. Of the total annual runoff discharge to the coastal ocean, 89.2% occurred in the 2003/2004 winter season, and 0.22 Mt of sediment mass was transported during the storm events. The runoff plume at surface taken offshore by cross-shore currents progressed rapid aggregation and sedimentation, while the initially high concentration of suspended sediment discharged from the river outlet was dominated by small particles. Vertical profiles of particle size spectra revealed two separated plumes near the river outlet and turbidity plume along the bottom consisted of an abundance of very fine and dense particles. It would appear to support the theory that even if the storm runoff does not carry a high concentration of sediment being capable of generating negative buoyancy, sediment deposition on the shelf might mobilise in dense, fluid mud transported offshore by gravity. In a coastal pollution context, sediment particle size spectra information may offer potentially useful means of characterising particle-associated pollutants for purposes of source tracking and environmental interpretation.

Decadal and shorter period variability of surf zone water quality at Huntington Beach, California.

The concentration of fecal indicator bacteria in the surf zone at Huntington Beach, CA, varies over time scales that span at least 7 orders of magnitude, from minutes to decades. Sources of this variability include historical changes in the treatment and disposal of wastewater and dry weather runoff, El Niño events, seasonal variations in rainfall, spring-neap tidal cycles, sunlight-induced mortality of bacteria, and nearshore mixing. On average, total coliform concentrations have decreased over the past 43 years, although point sources of shoreline contamination (storm drains, river outlets, and submarine outfalls) continue to cause transiently poor water quality. These transient point sources typically persist for 5-8 yr and are modulated by the phase of the moon, reflecting the influence of tides on the sourcing and transport of pollutants in the coastal ocean. Indicator bacteria are very sensitive to sunlight therefore, the time of day when samples are collected can influence the outcome of water quality testing. These results demonstrate that coastal water quality is forced by a complex combination of local and external processes and raise questions about the efficacy of existing marine bathing water monitoring and reporting programs.

Generation of enterococci bacteria in a coastal saltwater marsh and its impact on surf zone water quality.

Elevated levels of enterococci bacteria, an indicator of fecal pollution, are routinely detected in the surf zone at Huntington State and City Beaches in southern California. A multidisciplinary study was carried out to identify sources of enterococci bacteria landward of the coastline. We find that enterococci bacteria are present at high concentrations in urban runoff, bird feces, marsh sediments, and on marine vegetation. Surprisingly, urban runoff appears to have relatively little impact on surf zone water quality because of the long time required for this water to travel from its source to the ocean. On the other hand, enterococci bacteria generated in a tidal saltwater marsh located near the beach significantly impact surf zone water quality. This study identifies a potential tradeoff between restoring coastal wetlands and protecting beach water quality and calls into question the use of ocean bathing water standards based on enterococci at locations near coastal wetlands.

Pathogen filtration, heterogeneity, and the potable reuse of wastewater.

Filtration is commonly employed in water and wastewater treatment to remove particles and reduce the concentration of microbial pathogens. All physical models of packed-bed filtration are based on a proportional relationship between particle removal per unit depth of bed and the local particle concentration, dC/dz = -C/l, where l is the filtration length scale. Although l is known to vary with time and filter depth for heterogeneous suspensions or "dirty" beds, this paper demonstrates that the filtration rates of even seemingly monodisperse particle suspensions under clean-bed filtration conditions cannot be described with a single filtration length scale. A new model is derived for particle filtration that accounts for heterogeneity at two different spatial scales. Heterogeneity at the scale of the pathogen and/or collector (microscale heterogeneity) leads to a slow power-law decay of contaminant concentration with distance, instead of the fast exponential decay predicted by the standard model. Heterogeneity at the filter scale (macroscale heterogeneity) provides another level of complexity that can be evaluated once microscale heterogeneity effects are characterized. This model for microscale and macroscale heterogeneous particle filtration is verified by filtration experiments on a recombinant analogue of the waterborne pathogen Norwalk virus.

Prevalence of enterohemorrhagic Escherichia coli in raw and treated municipal sewage.

Municipal sewage was screened for DNA encoding Shiga-like Toxin (SLT) II, a key protein involved in the virulence of enterohemorrhagic Escherichia coli. PCR analysis of sewage concentrates showed that DNA encoding SLT II was present in a single sample of untreated sewage and absent in all other samples tested (n = 6). Thermotolerant E. coli cultured from the sewage (n = 1,520) also tested negative for SLT II by colony hybridization.