California Watersheds Research Articles

Dry Weather Flow Contribution of Metals, Nutrients, and Solids from Natural Catchments

Dry weather flow can be a substantial source of pollutants, particularly in urbanized areas such as southern California. To effectively evaluate and manage watershed-based pollutants, it is essential to understand the contribution of constituents from both developed and natural areas. Such information can be used by managers to set appropriate regulatory targets and to better evaluate severity of anthropogenic effects. This study quantified levels of suspended solids (TSS), metals, and nutrients from nineteen representative natural (undeveloped) streams in ten watersheds in southern California. Dry-weather concentrations and fluxes were typically one to two orders of magnitude lower than those from developed catchments. Constituent concentrations varied based on the catchment characteristics, with geologic type being the dominant factor that influenced variability among constituent levels. Concentration and flux values were independent of latitude, elevation, and catchment size suggesting that results from this study can be extrapolated to provide regional estimates of background water quality.

COMPARISON OF MOSQUITO CONTROL PROVIDED BY THE ARROYO CHUB (GILA ORCUTTI) AND THE MOSQUITOFISH (GAMBUSIA AFFINIS)

Two 6-wk trials were conducted in 28-m2 earthen ponds to compare the efficacy of the arroyo chub, Gila orcutti, to the mosquitofish, Gambusia affinis, as a biological control agent for mosquitoes and a possible replacement for the mosquitofish in sensitive watersheds of southern California. The mosquitofish population growth rate was 1.73 times greater than the arroyo chub population growth rate; however, greater reproduction by the mosquitofish did not result in significantly better reduction of mosquitoes than was provided by the comparatively small populations of arroyo chub. On average across a 6-wk study in the spring, both larvivorous fishes reduced the abundance of 3rd and 4th instars by 4- to 5-fold compared to that observed in the control ponds that lacked fish but contained few invertebrate predators. The abundance of nontarget microinvertebrates in ponds containing the mosquitofish was only 7% of that in ponds containing the arroyo chub during the summer, but did not differ significantly between the fish species treatments when zooplankton was comparatively more abundant during the spring. Even though the number of individuals produced by each fish species during 6 wk in the spring was greater than for fish stocked in the summer, species-specific population growth rates in the spring study (individuals/individual/d; mosquitofish, 0.077; arroyo chub, 0.044) were only slightly higher than in the summer (individuals/individual/d; mosquitofish, 0.068; arroyo chub, 0.039) indicating that differences in the number of fish stocked contributed primarily to the differences in final population size between spring and summer studies. The arroyo chub is native to the South Coastal drainages in California and should be considered as a viable alternative to the mosquitofish for integrated mosquito management programs in riverine wetlands and sensitive watersheds of southern California.

Developing Effective Stakeholder Based Total Maximum Daily Loads for Multiple Pollutants

Developing Effective Stakeholder Based Total Maximum Daily Loads for Multiple PollutantsLocated in Ventura County California, the Calleguas Creek Watershed (CCW), though relatively small in area, suffers from more water quality impairments than most California watersheds, as defined by the USEPA's 303(d) list. Local stakeholders, along with the Los Angeles Regional Water Quality Control Board (LARWQCB), began a watershed planning process over eight years ago to develop a better...Author(s)Chris MintonSourceProceedings of the Water Environment FederationSubjectArticlesDocument typeConference PaperPublisherWater Environment FederationPrint publication date Oct, 2007ISSN1938-6478SICI1938-6478(20071001)2007:5L.55;1-DOI10.2175/193864707786619297Volume / Issue2007 / 5Content sourceTMDLS ConferenceFirst / last page(s)55 - 63Copyright2007Word count79

16S rRNA-based assays for quantitative detection of universal, human-, cow-, and dog-specific fecal Bacteroidales: A Bayesian approach

We report the design and validation of new TaqMan ® assays for microbial source tracking based on the amplification of fecal 16S rRNA marker sequences from uncultured cells of the order Bacteroidales. The assays were developed for the detection and enumeration of non-point source input of fecal pollution to watersheds. The quantitative “universal” Bacteroidales assay BacUni-UCD detected all tested stool samples from human volunteers (18 out of 18), cat (7 out of 7), dog (8 out of 8), seagull (10/10), cow (8/8), horse (8/8), and wastewater effluent (14/14). The human assay BacHum-UCD discriminated fully between human and cow stool samples but did not detect all stool samples from human volunteers (12/18). In addition, there was 12.5% detection of dog stool (1/8), but no cross-reactivity with cat, horse, or seagull fecal samples. In contrast, all wastewater samples were positive for the BacHum-UCD marker, supporting its designation as 100% sensitive for mixed-human source identification. The cow-specific assay BacCow-UCD fully discriminated between cow and human stool samples. There was 38% detection of horse stool (3/8), but no cross-specificity with any of the other animal stool samples tested. The dog assay BacCan-UCD discriminated fully between dog and cow stool or seagull guano samples and detected 62.5% stool samples from dogs (5/8). There was some cross-reactivity with 22.2% detection of human stool (4/18), 14.3% detection of cat stool (1/7), and 28.6% detection of wastewater samples (4/14). After validation using stool samples, single-blind tests were used to further demonstrate the efficacy of the developed markers; all assays were sensitive, reproducible, and accurate in the quantification of mixed fecal sources present in aqueous samples. Finally, the new assays were compared with previously published sequences, which showed the new methodologies to be more specific and sensitive. Using Bayes’ Theorem, we calculated the conditional probability that the four assays would correctly identify general and host-specific fecal pollution in a specific watershed in California for which 73 water samples had been analyzed. Such an approach allows for a direct comparison of the efficacy of different MST methods, including those based on library-dependent methodologies. For the universal marker BacUni-UCD, the probability that fecal pollution is present when the marker is detected was 1.00; the probability that host-specific pollution is present was 0.98, 0.84, and 0.89 for the human assay HF160F, the cow assay BacCow-UCD, and the dog assay BacCan-UCD, respectively. The application of these markers should provide meaningful information to assist with efforts to identify and control sources of fecal pollution to impaired watersheds.

A spatial analysis of cumulative habitat loss in Southern California under the Clean Water Act Section 404 Program

Habitat loss is the leading cause of biodiversity reduction in the world today, with wetlands having experienced especially large losses in the United States and elsewhere. Using remote sensing and GIS techniques, this study quantified cumulative habitat loss in two Southern California watersheds associated with Clean Water Act Section 404 permits, primarily for developments, issued by the U.S. Army Corps of Engineers from 1984 to 2002. While the majority of habitat loss occurred outside of explicitly 404-authorized developments, non-explicitly authorized development represented a substantial fraction of observed habitat loss. The spatial distribution of habitat loss and 404 permits were analyzed statistically. In almost all cases, percent habitat loss was significantly correlated with variables representing 404 authorizations. These correlations may indicate the presence of incidental authorizations, suggesting that 404 authorizations within the study area may have indirectly facilitated nearby development (i.e., growth-inducing impacts). This study expanded the use of remote sensing, GIS, and spatial statistics for the purpose of regulatory-driven cumulative impact assessment. Until resource agencies quantify cumulative impacts in a spatially explicit manner and analyze those data statistically, there can be little rigorous scientific basis for formulating regulatory or policy decisions regarding cumulative impacts.

Distinguishing between Invasions and Habitat Changes as Drivers of Diversity Loss among California's Freshwater Fishes

Many of California's native populations of freshwater fish are in serious decline, as are freshwater faunas worldwide. Habitat loss and alteration, hydrologic modification, water pollution, and invasions have been identified as major drivers of these losses. Because these potential causes of decline are frequently correlated, it is difficult to separate direct from indirect effects of each factor and to appropriately rank their importance for conservation action. Recently a few authors have questioned the conservation significance of invasions, suggesting that they are "passengers" rather than "drivers" of ecological change. We compiled an extensive, watershed-level data set of fish presence and conservation status, land uses, and hydrologic modifications in California and used an information theoretic approach (Akaike's information criterion, AIC) and path analysis to evaluate competing models of native fish declines. Hydrologic modification (impoundments and diversions), invasions, and proportion of developed land were all predictive of the number of extinct and at-risk native fishes in California watersheds in the AIC analysis. Although nonindigenous fish richness was the best single predictor (after native richness) of fishes of conservation concern, the combined ranking of models containing hydrologic modification variables was slightly higher than that of models containing nonindigenous richness. Nevertheless, the path analysis indicated that the effects of both hydrologic modification and development on fishes of conservation concern were largely indirect, through their positive effects on nonindigenous fish richness. The best-fitting path model was the driver model, which included no direct effects of abiotic disturbance on native fish declines. Our results suggest that, for California freshwater fishes, invasions are the primary direct driver of extinctions and population declines, whereas the most damaging effect of habitat alteration is the tendency of altered habitats to support nonindigenous fishes.

Mist Net Effort Required to Inventory a Forest Bat Species Assemblage

Abstract: Little quantitative information exists about the survey effort necessary to inventory temperate bat species assemblages. We used a bootstrap resampling algorithm to estimate the number of mist net surveys required to capture individuals from 9 species at both study area and site levels using data collected in a forested watershed in northwestern California, USA, during 1996–2000. The mean number of simulated surveys required to capture individual species varied with species' rarity and ranged from 1.5 to 44.9. We retrospectively evaluated strategies to reduce required survey effort by subsampling data from 1996 to 1998 and tested the strategies in the field during 1999 and 2000. Using data from 1996 to 1998, the mean number of simulated surveys required to capture 8 out of 9 species was 26.3, but a 95% probability of capture required >61 surveys. Inventory efficiency, defined as the cumulative proportion of species detected per survey effort, improved for both the study area and individual sites by conducting surveys later in summer. We realized further improvements in study area inventory efficiency by focusing on productive sites. We found that 3 surveys conducted between 1 July and 10 September at each of 4 productive sites in this 10‐km2 study area resulted in the capture of 8 species annually. Quantitative estimation of the survey effort required to assess bat species occurrence improves the ability to plan and execute reliable, efficient inventories. Results from our study should be useful for planning inventories in nearby geographical areas and similar habitat types; further, the analytical methods we used to assess effort are broadly applicable to other survey methods and taxa.

STAKEHOLDER DEVELOPED TOTAL MAXIMUM DAILY LOADS

STAKEHOLDER DEVELOPED TOTAL MAXIMUM DAILY LOADSLocated in Ventura County California, the Calleguas Creek Watershed (CCW), though relatively small in area, suffers from more water quality impairments than most California watersheds, as defined by the USEPA's 303(d) list. Local stakeholders, along with the Los Angeles Regional Water Quality Control Board (LARWQCB), began a watershed planning process over eight years ago to develop a better...Author(s)Chris MintonSourceProceedings of the Water Environment FederationSubjectSession 52: TMDL: A Four Letter WordDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2007ISSN1938-6478SICI1938-6478(20070101)2007:14L.3932;1-DOI10.2175/193864707787973987Volume / Issue2007 / 14Content sourceWEFTECFirst / last page(s)3932 - 3940Copyright2007Word count434

The Relationship Between Productivities of Salmonids and Forest Stands in Northern California Watersheds

Abstract Productivities of resident salmonids and upland and riparian forests in 22 small watersheds of coastal northern California were estimated and compared to determine whether: 1) upland site productivity predicted riparian site productivity; 2) either upland or riparian site productivity predicted salmonid productivity; and 3) other parameters explained more of the variance in salmonid productivity. Upland and riparian site productivities were estimated using Site Index values for redwood (Sequoia sempervirens) and red alder (Alnus rubra), respectively. Salmonid productivity was indexed by back-calculated length at age 1 of the largest individuals sampled and by total biomass. Upland and riparian site indices were correlated, but neither factor contributed to the best approximating models of salmonid productivity. Total salmonid biomass was best described by a positive relationship with drainage area. Length of dominant fish was best described by a positive relationship with percentage of hardwoods within riparian areas, which may result from nutrient and/or litter subsidies provided by red alder. The inability of forest productivity to predict salmon productivity may reflect insufficient variation in independent variables, limitations of the indices, and the operation of other factors affecting salmonid production. The lack of an apparent relationship between upland conifer and salmonid productivity suggests that management of land for timber productivity and component streams for salmonid production in these sites will require separate, albeit integrated, management strategies.

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.

Assessing genetic diversity of protected coho salmon (Oncorhynchus kisutch) populations in California

California coho salmon (Oncorhynchus kisutch) are under legal protection owing to significant declines in abundance over the last decades. Previously, California coho salmon were characterized as having low genetic diversity and weak population subdivision, attributable potentially to homogenization by out-of-basin hatchery releases. Here, diversity at seven highly polymorphic microsatellite DNA markers is assessed within and among 32 collections of coho salmon from 16 California watersheds. In 71% of local populations, genotypic composition deviates significantly from that expected under the assumption of random mating. We develop and apply methods to adjust for two potential causes of deviation from random mating expectations: (i) Wahlund effects, owing to heterogeneous collections of individuals, and (ii) the "Allendorf–Phelp's effect", owing to closely related juveniles in samples. Such population-level "adjustments" reduce within-region and increase among-region variance; after adjustment, we find strong concordance of genetic and geographic distances. We conclude that stock transfers have had minimal impact on population structure and that California coho salmon populations likely comprise small numbers of endemic breeders, potentially experiencing high levels of genetic drift and inbreeding.

PREFIRE AND POSTFIRE EROSION OF SOIL NUTRIENTS WITHIN A CHAPARRAL WATERSHED

Prescribed burns are an effective and increasingly popular strategy for inhibiting wildfires. The goal of this study was to characterize soil nutrient loss after a prescribed fire within a chaparral watershed in southern California. The study compared hillslope sediments for approximately 1 year before the fire with those during the year after the fire. Samples were collected in 11 sediment traps located randomly along fall line transects throughout a steep, 0.65-ha watershed (∼65% average slope). Concentrations of soluble ammonium nitrogen, nitrate nitrogen, phosphate phosphorus, Ca, Mg, K, and Na, exchangeable ammonium nitrogen, and total C and N were analyzed. Sediment production averaged approximately 1600 g per sediment trap for the entire year before the fire but increased to approximately 10,700 g for the year after the fire. The average sedimentation rates for the less than 2-mm fraction doubled from a prefire rate of 2.7 to 7.5 g d−1 after the fire and increased to 86 g d−1 after the first major rain event after the fire. The greatest concentrations of soluble and exchangeable base cations (Ca, Mg, K, Na) in the eroded sediment were measured at the first sampling date after the fire. Input and microbial mineralization of fresh organic matter approximately 4 months after the fire is believed to be the source of increases in the concentrations of soluble nitrate nitrogen and phosphate phosphorus and exchangeable ammonium nitrogen. Our findings indicate that prescribed fire may cause less loss of N and P than wildfires.

Suspended-sediment transport in an intensively cultivated watershed in southeastern California

The purpose of this study is to investigate the variation of sediment movement at multiple spatial and two temporal scales of an agricultural watershed in southeastern California where surface runoff is primarily supplied by irrigation. An extensive turbidity and stage monitoring program based on grab sampling using 500-mL plastic bottles and in situ monitoring using both turbidity sensors and pressure transducers was designed to capture the spatial and temporal heterogeneities of suspended-sediment loads. The obtained turbidity values and stages at weekly and 5-min time scales were subsequently converted to suspended-sediment concentrations and water discharges, respectively, using established calibration methods. Weekly data were analyzed using a mass-balance approach to distinguish erosion and deposition processes in drain channels at various spatial scales. Further analysis on weekly data led to an empirical model describing the process of sediment transport at various spatial scales. The model revealed that drain channels at larger spatial scales (i.e. downstream channels) tended to be dominated by weekly net deposition, while those at smaller spatial scales (i.e. upstream channels) were controlled by weekly net erosion. However, analysis of the 5-min data showed that in small-scale drain channels, large amount of sediment was indeed deposited over a short period of one week (about one day). In the rest of the week, low-intensity erosion prevailed. Therefore, sediment transport in the study watershed was generally controlled by deposition, which supports the necessity of on-going drain-channel dredging by Imperial Irrigation District.

Watershed Environmental Hydrology Model: Environmental Module and Its Application to a California Watershed

A newly developed watershed environmental hydrology (WEHY) model is presented as a state-of-the-art nonpoint source (NPS) model. The model consists of hydrologic and environmental modules, and describes environmentally relevant hydrologic processes based upon physically based governing equations to model the fate of pollutants such as sediment and phosphorus in the watershed. Unlike other physically based NPS models, the WEHY model is unique in its upscaling approach to the governing equations of hydrologic and environmental processes, which results in the governing equations that are compatible with the computational grid resolution while accounting for subgrid heterogeneities through upscaled model parameters. Upscaling was performed by means of a technique called ensemble averaging. The model was tested at the Ward Creek Watershed in Lake Tahoe Basin for its performance in a subalpine watershed setting. Comparisons of predicted and observed values were in good agreement and showed good promise of the approach used in the development of the model. Because of the physical basis of the WEHY model and its use of upscaled conservation equations, the model has the advantage of being applicable to ungauged basins and to large watersheds.

A Coupled Upland-Erosion and Instream Hydrodynamic-Sediment Transport Model for Evaluating Sediment Transport in Forested Watersheds

This article describes a prototype modeling system for assessing forest management-related erosion at its source and predicting sediment transport from hillslopes to stream channels and through channel networks to a watershed outlet. We demonstrate that it is possible to develop a land management tool capable of accurately assessing the primary impacts of spatiotemporally varied forest management practices on sediment yield and delivery at hillslope to watershed scales in a single simulation. The modeling system consists of four components: (1) the TOpographic ParameteriZation (TOPAZ) model for discretizing hillslope and channel elements, (2) the Water Erosion Prediction Project (WEPP) model for evaluating hillslope-scale surface erosion processes, (3) the National Center for Computational Hydrodynamics and Engineering's one-dimensional (CCHE1D) hydrodynamic-sediment transport model, and (4) an interface program to manage relational databases and data transfer between modules. The coupled models were calibrated and validated with observed flow and sediment load data from the North Fork Caspar Creek Experimental Watershed in coastal northern California. The coupled models' predictions of peak flow rate and total flow volume were not significantly different from observed values. Predicted sediment concentrations were significantly different from observed values, but within typical ranges for sediment transport equations. We recommend that the WEPP model be improved to allow access to sub-daily time scale results so that it can be better integrated with other watershed models.

Effects of urbanization on California’s fish diversity: Differentiation, homogenization and the influence of spatial scale

Human development of freshwater ecosystems has lead to drastic changes in freshwater fish faunas, including the loss of many native species and the gain of non-natives. Typically conservation ecologists view these two opposing forces as contributing to biological homogenization, and consider homogenization as one of the principle negative consequences of urbanization. However, homogenization is only one outcome out of many that can result from the loss and gain of species. In particular, it is possible for invasions and extinctions to lead to differentiation; a process whereby two (or more) regions become less similar to one another through time. Using the freshwater fishes of California, we show that urbanization is highly positively correlated to both the endangerment of native fish and the invasion of non-native fish within watersheds. Despite this, the fish faunas of California’s watersheds have differentiated from one another through time. Furthermore, the degree of differentiation is positively correlated with measures of urbanization, which is contrary to expectation. We suggest that this result reflects: (1) the haphazard manner in which non-native fishes have been introduced into California watersheds, (2) the difficulty that both native and non-native fishes have in expanding their geographical ranges, and (3) the continued presence of vestiges of formerly distinct regional faunas. This pattern of differentiation among watersheds is likely a matter of scale, as previous work on freshwater fishes has demonstrated homogenization at both larger and smaller spatial scales. In addition the observed pattern is probably a short-term (temporal) phenomena and will disappear with continued invasion and extinction. We suggest that similar patterns may occur for other taxa that have limited natural dispersal abilities and that are idiosyncratically released as non-natives via human activities (e.g. herptiles).

Prediction of sediment‐bound nutrient delivery from semi‐arid California watersheds

Soil carbon (C), nitrogen (N), and phosphorus (P) are lost from hillslopes in particulate forms through soil erosion. The fate of the eroded C (e.g., sequestration or oxidation) may affect the global C budget, and delivery of N and P to waterbodies can lead to eutrophication. Whereas the magnitude of particulate nutrient losses may be similar to or greater than dissolved losses, it is rarely estimated. We couple a sediment delivery model with measurements of C, N, and P in soil to account explicitly for hillslope sediment transport processes that yield sediment‐bound nutrients to fluvial networks. The model is applied to a site in California dominated by coastal sage scrub and gopher‐rich grasslands. Although the magnitude of sediment delivery predicted by the model has been tested with reservoir sedimentation records, no data exist to test the predicted rates of nutrient delivery. Nevertheless, the model results are provocative; it predicts that losses of particulate C from sage covered hillslopes (23 kg/ha/yr) are nearly double that from grassland hillslopes (13 kg/ha/yr), despite a lower annual sediment yield from the sage hillslopes. The model predicts similar average annual N and P losses for sage and grasslands but dramatic differences in the frequency and magnitude of delivery events. Nutrient delivery from grasslands is chronic whereas delivery from the coastal sage is highly episodic, with large pulses driven by fire frequency. These results suggest that changes in the vegetation community can alter the delivery regime of sediment‐bound C, N, and P.

Rapid Detection of Enteroviruses in Small Volumes of Natural Waters by Real-Time Quantitative Reverse Transcriptase PCR

Despite viral contamination of recreational waters, only bacterial, not viral, indicators are monitored routinely, due to a lack of rapid and cost-effective assays. We used negatively charged filters to capture enteroviruses from seawater and freshwater. Viral RNA was extracted using a commercial kit, and the viruses were quantified by real-time quantitative reverse transcriptase PCR (qRT-PCR). Poliovirus (6.6 to 330,000 virus particles/ml) was added to samples from watersheds in Los Angeles, California, and analysis showed that with 50-ml samples, a cellulose acetate/nitrate (HA) filter yielded final recovery of 51% (r2= 0.99) in fresh water and 23% (r2= 0.90) in seawater. However, for additions of low levels of virus (more likely to represent field samples; <10(4) enterovirus particles/ml), the recovery was lower and more variable, with HA being best in freshwater (17%, r2= 0.97) and the type GF/F glass filter having higher average recovery in seawater (GF/F, 17%; r2= 0.93; HA 12%, r2= 0.87). The optimized method was used with 1-liter field samples from two very different freshwater "creeks" that drain into Santa Monica Bay, California: Topanga Creek (TC), a relatively pristine mountain creek, and Ballona Creek (BC), a concrete-lined urban storm drain. One TC site out of 10 and 2 BC sites out of 7 tested significantly positive for enteroviruses, with higher enterovirus concentrations in BC than in TC (ca. 10 to 25 versus 1 equivalent enterovirus particle/ml). The presented filtration-qRT-PCR approach is fast (<8 h from sampling to results), sensitive, and cost efficient and is promising for monitoring viral contamination in environmental water samples.

Trace Metal Pollutant Load in Urban Runoff from a Southern California Watershed

In order to implement efficient and effective management strategies for coastal water quality in Southern California, it is important to consider the relative pollutant contributions from urban dry-weather flow (DWF) and wet-weather flow (WWF). This study uses both historical flow coupled with water quality monitoring data and computer modeling to characterize the annual DWF and WWF discharges from an urban catchment in Los Angeles, Calif. The DWF and WWF pollutant loading of the trace metals copper, lead, nickel, and chromium for 6 water years dating from 1991 to 1996 is predicted. The results indicate that DWF contributes a considerable amount of flow and pollutants. Approximately, 9–25% of the total annual Ballona Creek flow volume is DWF. The simulations indicate DWF accounts for 54, 19, 33, and 44% of the average annual load of total chromium, copper, lead, and nickel, respectively. In the dry season, the simulations indicate DWF accounts for 89, 59, 58, and 90% of the load of total chromium, copper, lead, and nickel, respectively. This research suggests DWF controls may be an important part of pollution mitigation plans for urban stormwater drainage systems in Southern California.

Evaluation of antibiotic resistance analysis and ribotyping for identification of faecal pollution sources in an urban watershed

The accuracy of ribotyping and antibiotic resistance analysis (ARA) for prediction of sources of faecal bacterial pollution in an urban southern California watershed was determined using blinded proficiency samples. Antibiotic resistance patterns and HindIII ribotypes of Escherichia coli (n = 997), and antibiotic resistance patterns of Enterococcus spp. (n = 3657) were used to construct libraries from sewage samples and from faeces of seagulls, dogs, cats, horses and humans within the watershed. The three libraries were analysed to determine the accuracy of host source prediction. The internal accuracy of the libraries (average rate of correct classification, ARCC) with six source categories was 44% for E. coli ARA, 69% for E. coli ribotyping and 48% for Enterococcus ARA. Each library's predictive ability towards isolates that were not part of the library was determined using a blinded proficiency panel of 97 E. coli and 99 Enterococcus isolates. Twenty-eight per cent (by ARA) and 27% (by ribotyping) of the E. coli proficiency isolates were assigned to the correct source category. Sixteen per cent were assigned to the same source category by both methods, and 6% were assigned to the correct category. Addition of 2480 E. coli isolates to the ARA library did not improve the ARCC or proficiency accuracy. In contrast, 45% of Enterococcus proficiency isolates were correctly identified by ARA. None of the methods performed well enough on the proficiency panel to be judged ready for application to environmental samples. Most microbial source tracking (MST) studies published have demonstrated library accuracy solely by the internal ARCC measurement. Low rates of correct classification for E. coli proficiency isolates compared with the ARCCs of the libraries indicate that testing of bacteria from samples that are not represented in the library, such as blinded proficiency samples, is necessary to accurately measure predictive ability. The library-based MST methods used in this study may not be suited for determination of the source(s) of faecal pollution in large, urban watersheds.