Tracking the Sources of Antibiotic Resistance Genes in an Urban Stream during Wet Weather using Shotgun Metagenomic Analyses.

Stormwater runoff has been known to cause increases in bacterial loadings in urban streams. However, little is known about its impacts on antibiotic resistance genes (ARGs) in urban watersheds. This study was performed to characterize the ARG composition of various environmental compartments of an urban watershed and to quantify their contributions of microbes and ARGs to an urban stream under wet weather conditions. Shotgun metagenomic results showed that the ARG abundance in wet weather flow was significantly higher than in base flow. Multidrug resistance genes were the most common ARG type across environmental samples. Vancomycin resistance genes were abundant in embankment soil and street sweeping samples. Analyses using SourceTracker estimated storm drain outfall water to be the biggest contributor of microbes (54-57%) and ARGs (82-88%) in the urban stream during wet weather flows. Furthermore, results on street sweepings showed that wash-off from streets was the biggest known contributor of microbes (41-45%) and ARGs (92-96%) in storm drain outfall water. Pantoea and Pseudomonas were associated with the highest numbers of ARGs and were most abundant in stormwater-related samples. Results from this study can advance our knowledge about ARGs in urban streams, an important medium linking environmental ARGs to the general public.

Quantifying the Relative Contributions of Environmental Sources to the Microbial Community in an Urban Stream under Dry and Wet Weather Conditions.

Investigating sources of microbial contamination in urban streams, especially when there are no contributions from combined sewer overflows or sewage effluent discharges, can be challenging. The objectives of this study were to identify the sources of microbes in an urban stream and quantify their relative contributions to the microbial community in the stream under dry and wet weather conditions. A microbial source tracking method relying on the 16S rRNA gene was used to investigate the microbial communities in water samples of an urban stream (i.e., from 11 dry and 6 wet weather events), as well as in streambed sediment, soils, street sweepings, sanitary sewage, an upstream lake, and feces of animals and birds collected between 2013 and 2015. The results showed that the Escherichia coli levels in the stream were significantly higher in wet weather flow than in dry weather flow. The upstream lake contributed approximately 93% of the microbes in dry weather flows. Water discharged from storm drain outfalls was the biggest source of microbes in wet weather flows, with a median contribution of approximately 90% in the rising limb and peak flow and about 75% in the declining limb of storms. Furthermore, about 70 to 75% of the microbes in the storm drain outfall water came from materials washed off from the street surfaces in the watershed. Fecal samples did not appear to contribute substantially to the microbes in environmental samples. The results highlight the significance of street surfaces in contributing microbial loads to urban streams under wet weather conditions.IMPORTANCE Identifying the sources of microbial contamination is important for developing best management practices to protect the water quality of urban streams for recreational uses. This study collected a large number of water samples from an urban stream under both dry and wet weather conditions and provided quantitative information on the relative contributions of various environmental compartments to the overall microbial contamination in the stream under the two weather conditions. The watershed in this study represents urban watersheds where no dominant fecal sources are consistently present. The findings highlight the importance of reducing the direct contribution of microbes from street surfaces in the watershed to urban streams under wet weather conditions. The methods and findings from this study are expected to be useful to stormwater managers and regulatory agencies.

Flow and transport effect caused by the stalk contraction cycle of Vorticella convallaria.

Vorticella convallaria is a protozoan attached to a substrate by a stalk which can contract in less than 10 ms, translating the zooid toward the substrate with a maximum Reynolds number of ∼1. Following contraction, the stalk slowly relaxes, moving the zooid away from the substrate, which results in creeping flow. Although Vorticella has long been believed to contract to evade danger, it has been suggested that its stalk may contract to enhance food transport near the substrate. To elucidate how Vorticella utilizes its contraction-relaxation cycle, we investigated water flow caused by the cycle, using a computational fluid dynamics model validated with an experimental scale model and particle tracking velocimetry. The simulated flow was visualized and analyzed by tracing virtual particles around the Vorticella. It is observed that one cycle can displace particles up to ∼190 µm with the maximum net vertical displacement of 3-4 µm and that the net transport effect becomes more evident over repeated cycles. This transport effect appears to be due to asymmetry of the contraction and relaxation phases of the flow field, and it can be more effective on motile food particles than non-motile ones. Therefore, our Vorticella model enabled investigating the fluid dynamics principle and ecological role of the transport effects of Vorticella's stalk contraction.

Yard waste compost as a stormwater protection treatment for construction sites.

Runoff water quality improvement from three yard waste compost erosion control treatments were compared with two conventional treatments and an untreated control on plots of 3:1 slope during two growing seasons, using natural events and simulated rainfall. Runoff volume, suspended solids, nutrients, biomass, turf shear strength, and turfgrass color scale were monitored. The most effective compost treatment, a 5-cm thick blown compost blanket, produced 12.7 times less runoff and 9.8 times less sediment load than a straw mat and silt fence treatment. The compost treatments generated eight times more biomass than the straw mat treatments. Root development was significantly better on the compost treatments based on turf shear strength measurements. Tilled-in compost was not as effective as a compost blanket at reducing sediment loss, particularly before the establishment of grass on the plot. The cost of compost treatments was similar to that of straw mat with silt fence treatments.