Drivers of Antibiotic Resistance Gene Abundance in an Urban River

In this study, we sought to profile the abundances and drivers of antibiotic resistance genes in an urban river impacted by combined sewage overflow (CSO) events. Water samples were collected weekly during the summer for two years; then, quantitative PCR was applied to determine the abundance of resistance genes associated with tetracycline, quinolones, and β-lactam antibiotics. In addition to sampling a CSO-impacted site near the city center, we also sampled a less urban site ~12 km upstream with no proximal sewage inputs. The tetracycline genes tetO and tetW were rarely found upstream, but were common at the CSO-impacted site, suggesting that the primary source was untreated sewage. In contrast, ampC was detected in all samples indicating a more consistent and diffuse source. The two other genes, qnrA and blaTEM, were present in only 40-50% of samples and showed more nuanced spatiotemporal patterns consistent with upstream agricultural inputs. The results of this study highlight the complex sources of ARGs in urban riverine ecosystems, and that interdisciplinary collaborations across diverse groups of stakeholders are necessary to combat the emerging threat of antibiotic resistance through anthropogenic pollution.

Effects of combined sewer overflow on water quality: a case study of Hatirjheel Lake in Dhaka

Abstract

This paper presents a case study focusing on the impacts of combined sewer overflows on the water quality of the receiving water body, Hatirjheel. Hatirjheel, the largest surface water body in Dhaka City with an area of about 1.012 km2, receives discharges from nine combined sewer overflow (CSO) structures. The water quality of Hatirjheel is poor throughout the year, but particularly during the wet season (June to October) near the CSO structures through which significant rainwater-sewage overflows. The water has been found to contain high concentrations of 5-day biochemical oxygen demand (BOD5) and chemical oxygen demand; some of the BOD5 values exceed the national discharge standards for treated effluents. Total ammonia concentration in Hatirjheel water increases during the wet season, often exceeding 20 mg/l; the concentration continues to increase after the end of the wet season, most likely due to the ammonification process. Nitrate concentration in Hatirjheel water increases at the end of the wet season, possibly due to nitrification; subsequent reduction in nitrate and ammonia concentration is possibly due to incorporation of nitrogen into algal mass. Excessive phosphorus in Hatirjheel promotes eutrophication, resulting in the visible greenish color of the water. This study highlights the significant adverse impact of combined sewer overflows, particularly for a densely populated city like Dhaka, where most of the rainfall occurs within a relatively short period during monsoon.

ArticleHighlights

Influence of storms on the emission of pollutants from sewage into waters

During heavy precipitation, chemical and biological pollutants from urban and agricultural areas enter the waters from storm overflows as a result of infiltration and inflow, as well as via uncontrolled outflows from water treatment plants. Infiltration and inflow of rainwater into sewers is an especially popular and major worldwide problem. Climate forecasts indicate changes in climatic conditions towards an increase in the intensity and frequency of torrential rainfalls. It may therefore be assumed that the negative impact of rainwater on water quality will increase. This article attempts to address the question of the impact of pollution from wastewater introduced into water during rainy weather to the receiver. The assessment of the impact of rainfalls on a receiver was carried out on the basis of a simulation of pollution loads from sewage introduced into a river by storm overflows based on data from monitoring the amount of rainfall and simulating the operation of storm overflows using Environmental Protection Agency Storm Water Management Model (EPA SWMM). The obtained results were compared with the pollutant loads discharged at the same time from the sewage treatment plant (STP). In addition, the article assesses possible improvement solutions to reduce the negative impact of storm overflows on water.

Evaluation of a multivariate analysis modeling approach identifying sources and patterns of nonpoint fecal pollution in a mixed use watershed

Surface waters listed on impaired waters (303 d) lists due to pathogen contamination pose a significant environmental and public health burden. The need to address impairments through the Total Maximum Daily Load (TMDL) process has resulted in method developments that successfully identify nonpoint fecal pollution sources by maximizing available resources to improve water quality. However, the ability of those methods to effectively and universally identify sources of fecal pollution requires further evaluation. The objective of this research was to assess the usefulness of a previously described multivariate statistical approach to identify common patterns influencing fate and transport of fecal pollutants from sources to receiving streams using the Tuckasegee River watershed in Western North Carolina as a test watershed. Two streams were routinely monitored using a targeted sampling approach to assess fecal pollution extent and identify nonpoint sources using canonical correlation and canonical discriminant analyses. Fecal pollution in the watershed varied spatially and temporally with significantly higher fecal coliform concentrations observed in Scott Creek (f = 9.49, p = 0.002) and during the summer months (f = 14.8, p < 0.0001). Canonical correlations described 62-67% of water quality variability and indicate that fecal pollution in portions of the watershed are influenced by stormwater runoff and fecal indicator bacteria resuspension from sediment, while fecal pollution in other portions are influenced by soil erosion and surface runoff. Canonical discriminant analyses indicate that LULC significantly influences the nature and extent of fecal pollution. These results demonstrate that chemical parameters are useful predictors of fecal pollution and can help identify nonpoint fecal pollution sources in relation to land use patterns and land management practices. This approach to water quality monitoring program design and data analysis may effectively and efficiently identify parameters that best predict fecal pollution to aid in development and implementation of effective TMDLs to remediate impaired waters.

The Role of Sewer Network Structure on the Occurrence and Magnitude of Combined Sewer Overflows (CSOs)

Combined sewer overflows (CSOs) prevent surges in sewer networks by releasing untreated wastewater into nearby water bodies during intense storm events. CSOs can have acute and detrimental impacts on the environment and thus need to be managed. Although several gray, green and hybrid CSO mitigation measures have been studied, the influence of network structure on CSO occurrence is not yet systematically evaluated. This study focuses on evaluating how the variation of urban drainage network structure affects the frequency and magnitude of CSO events. As a study case, a sewer subnetwork in Dresden, Germany, where 11 CSOs are present, was selected. Scenarios corresponding to the structures with the lowest and with the highest number of possible connected pipes, are developed and evaluated using long-term hydrodynamic simulation. Results indicate that more meshed structures are associated to a decrease on the occurrence and magnitude of CSO. Event frequency reductions vary between 0% and 68%, while reduction of annual mean volumes and annual mean loads ranged between 0% and 87% and 0% and 92%. These rates were mainly related to the additional sewer storage capacity provided in the more meshed scenarios, following a sigmoidal behavior. However, increasing network connections causes investment costs, therefore optimization strategies for selecting intervention areas are needed. Furthermore, the present approach of reducing CSO frequency may provide a new gray solution that can be integrated in the development of hybrid mitigation strategies for the CSO management.

Land Cover and Water Quality Patterns in an Urban River: A Case Study of River Medlock, Greater Manchester, UK

Urban river catchments face multiple water quality challenges that threaten the biodiversity of riverine habitats and the flow of ecosystem services. We examined two water quality challenges, runoff from increasingly impervious land covers and effluent from combined sewer overflows within a temperate zone river catchment in Greater Manchester, North-West UK. Sub-catchment areas of the River Medlock were delineated from digital elevation models using a Geographical Information System. By combining flow accumulation and high-resolution land cover data within each sub-catchment and water quality measurements at five sampling points along the river, we identified which land cover(s) are key drivers of water quality. Impervious land covers increased downstream and were associated with higher runoff and poorer water quality. Of the impervious covers, transportation networks have the highest runoff ratios and therefore the greatest potential to convey contaminants to the river. We suggest more integrated management of imperviousness to address water quality, flood risk and, urban wellbeing could be achieved with greater catchment partnership working.

Land Use Contributions to Adverse Biological Effects in a Complex Agricultural and Urban Watershed: A Case Study of the Maumee River

Agricultural and urban contaminants are an environmental concern because runoff may contaminate aquatic ecosystems, resulting in stress for exposed fish. The objective of the present controlled, field-based study was to assess the impacts of high-intensity agriculture and urban land use on multiple life stages of the fathead minnow (Pimephales promelas), using the Maumee River (Toledo, OH, USA) as a case study. Laboratory cultured adult and larval fathead minnows were exposed for 21 d, and embryos were exposed until hatching to site-specific water along the lower reach of the Maumee River. Adult minnows were analyzed for reproduction and alterations to hematologic characteristics (vitellogenin, glucose, estradiol, 11-ketotestosterone). Water and fish tissue samples were analyzed for a suite of multiresidue pesticides, hormones, and pharmaceuticals. Contaminants were detected in every water and tissue sample, with 6 pesticides and 8 pharmaceuticals detected in at least 82% of water samples and at least half of tissue samples. Effects differed by exposed life stage and year of exposure. Fecundity was the most sensitive endpoint measured and was altered by water from multiple sites in both years. Physiological parameters associated with fecundity, such as plasma vitellogenin and steroid hormone concentrations, were seldom impacted. Larval fathead minnows appeared to be unaffected. Embryonic morphological development was delayed in embryos exposed to site waters collected in 2016 but not in 2017. A distinction between agricultural and urban influences in the Maumee River was not realized due to the great overlap in contaminant presence and biological effects. Differences in precipitation patterns between study years likely contributed to the observed biological differences and highlight the need for environmental exposure studies to assess the environmental risk of contaminants. Environ Toxicol Chem 2019;00:1-17. © 2019 SETAC.

Spatial variations of pollutants from sewer interception system overflow

Sewer interception systems have been built along rivers in rapidly urbanizing areas to collect unregulated sewage discharges due to misconnections between storm sewers and sanitary sewers. During storm events, combined sewage might overflow from these systems into rivers through orifices and deteriorate water quality in rivers. Interception system overflows (ISOs) from different orifices in a sewer interception system might interact with each other, therefore pollutants from ISOs show a spatial variation. This paper aims to understand the spatial variation of pollutants from ISOs for informed decision making. In this study, an urbanized catchment in China is chosen as the study area, and the Storm Water Management Model (SWMM) is used to examine the spatial variation of pollutants from ISOs and to analyze the effect of sewer separation on ISOs. The results obtained from the case study indicate that: (1) Critical rainfall amounts which trigger overflows decrease downstream in an interception system while annual ISO volumes and pollutant loads from ISOs increase downstream; additionally, these variations are influenced by sizes and slopes of interceptors; (2) Runoff is the main source of COD from ISOs while sewage is the main source of NH₃-N, and ratios of pollutants from sewage to ISOs increase downstream; (3) Sewer separation can significantly reduce pollutant loads from sewage to ISOs, but it cannot significantly reduce pollutant loads from runoff. In order to mitigate ISO pollution, it is suggested to increase conveyance capacities of interceptors in the downstream, separate sewage from runoff, and promote source control for urban runoff in highly urbanized areas.