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Austin, Texas is among the most rapidly urbanizing regions in the U.S., posing challenges to the resilience of its water resources. Geochemical differences between stream water from relatively pristine (rural) and impacted (urban) watersheds indicate several distinct controls on stream water compositions, including extent of urbanization, extent of failure of the city’s municipal water infrastructure, and differences in bedrock composition and permeability. We focus here on the largely unstudied evolution of municipal water once it leaves the infrastructure and enters the natural hydrologic system as groundwater and/or surface water. We use the distinct Sr isotope values (⁸⁷Sr/⁸⁶Sr) and other compositional differences between municipal waters, natural stream and spring water, limestone bedrock, and soils as tracers of the sources of and processes by which four Austin-area streams and springs acquire their dissolved constituents. These processes include 1) fluid-mixing between municipal and natural surface water and groundwater, 2) multiple mineral-solution reactions, including dissolution and water-rock interaction (WRI) processes of precipitation, incongruent dissolution, and recrystallization, and 3) varying groundwater residence times. Stream water in two urbanized watersheds have high⁸⁷Sr/⁸⁶Sr values and ion compositions close to values for municipal water, whereas stream and spring water in two rural watersheds have compositions close to natural stream water. Urbanized stream water compositions can be accounted for by models of municipal water contributions followed by dissolution of bedrock minerals. By contrast, rural stream water compositions are consistent with a model sequence of dissolution followed by extensive WRI with limestone. The results of this study indicate significant contributions to streams from the municipal infrastructure. We find that the evolution of this municipal water in the natural hydrologic system comprises multiple fluid-mixing processes and mineral-solution reactions, which are influenced by differences in bedrock geology. This composite evolution advances our understanding of the complexities of “Urban Stream Syndrome”. 

Various spatiotemporal, hydraulic, and water quality parameters can affect the microbial community composition of water within drinking water distribution systems (DWDSs). Although some relationships between various paravmeters and microbial growth are known, the effects of spatial and temporal trends on particle-associated microbial communities in chlorinated DWDSs remain poorly understood. The objectives of this study were to characterize the microbial community composition of both particle-associated bacteria (PAB) and total bacteria (TB) within a full-scale chlorinated DWDS, and assess relationships between microbiavvl community and various spatiotemporal, hydraulic, and water quality parameters. Bulk water samples were collected from the treatment plant, a storage tank, and 12 other sites in a rural chlorinated DWDS at varying distances from the treatment plant on four sampling dates spanning six months. Amplicon sequencing targeting the 16S rRNA gene was performed to characterize the microbial community. Gammaproteobacteria dominated the DWDS, and hydraulic parameters were well-correlated with differences in microbial communities between sites. Results indicate that hydraulic changes may have led to the detachment of biofilms and loose deposits, subsequently affecting the microbial community composition at each site. Spatial variations in microbial community were stronger than temporal variations, differing from similar studies and indicating that the highly varied hydraulic conditions within this system may intensify spatial variations. Genera containing pathogenic species were detected, withLegionellaandPseudomonasdetected at every site at least once andMycobacteriumdetected at most sites. However, only one sample had quantifiablePseudomonas aeruginosathrough quantitative polymerase chain reaction (qPCR), and no samples had quantifiableLegionella pneumophilaorMycobacterium avium, indicating a low human health risk. This study establishes spatial variations in PAB associated with varied hydraulic conditions as an important factor driving microbial community within a chlorinated DWDS.