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The source characterization of nitrate (NO3−) in groundwater of Muling-Xingkai Plain (MXP) and the influence of NO3− on the water environment were studied by hydrogeochemical and multivariate statistical analysis. A total of 164 groundwater samples were collected, and the samples were classified into three clusters by using hierarchical cluster analysis. Cluster 1 (C1), accounting for 13% of total samples, was mainly located in local residential zones where the top soils were the medium-textured sediments. Cluster 2 (C2) and cluster 3 (C3) were mainly located in farmlands and residential zones where the clay sediments were overlaying the aquifers. The soil media covering the aquifers was an important factor controlling the concentration of NO3− in groundwater, which determined the infiltration rate of wastewater and the redox environment of aquifers. Only the samples in C1 exceeded the WTO standards for NO3− (50 mg/L), and the samples in C2 and C3 had low NO3− concentration (less than 10 mg/L). The excessive NO3− in groundwater was observed in the shallow groundwater under local residential zones, and it was closely related to the anthropogenic activities since the 1950s. The domestic sewage was responsible for the elevated NO3− contents in the MXP. Then, it was still necessary to construct the sewage disposal system in rural areas to further protect the groundwater resource to avoid the formation of extensive nitrogen pollution. At present, NO3− in the groundwater mainly shows a fertilizer and natural rainwater origin and is not demonstrating the significant deterioration of groundwater qualities and water environment.

Water-rock interactions occurring during fracturing and flowback in shale gas reservoirs may dominate some chemical and isotopic compositions of hydraulic fracturing flowback fluids (HFFF) by imparting characteristic compositions of the continental shale to the HFFF. In this paper, a simple conservative mixing model (SCMM) and a progressive conservative mixing model (PCMM) were developed to evaluate and understand the impacts of geochemical processes on forensic indicators (δ11B, 87Sr/86Sr, and Ba/Sr) of HFFF produced from the Dameigou Shale. Application of the paired sample T-test showed that the measured values of δ11B, 87Sr/86Sr, Ba, and Sr in HFFF produced from the Dameigou Shale were all significantly (p 1.45) in HFFF. Therefore, 87Sr/86Sr and Ba/Sr show potential as indicators of continental HFFF produced from carbonate-poor shales and provide a clear distinction from rapidly-circulating shallow groundwater mainly recharged by rainwater (87Sr/86Sr: 0.70903–0.70914 and Ba/Sr

Responses of hydrochemical parameters, bacterial community structures, and microbial activities during the natural biodegradation of hydrocarbons leaking from a crude oil pipeline at a site in northeastern China were studied using the hydrochemical method, the polymerase chain reaction amplification of 16S rDNA genes, and denaturing gradient gel electrophoresis (DGGE).The concentrations of PHs and the main physicochemical characteristics (Eh and pH) were increased gradually at longitudinal ZK1–ZK3–ZK6 section in June 2010, suggesting that the degree of biodegradation decreased gradually from the pollutant source to downstream. The electron acceptor (SO42−) participated in biodegradation process responds identical trend to the degree of biodegradation at the same section while the biodegradation reduction products (Fe2+, Mn2+, and HCO3 −) respond to it in opposite trend. The concentrations of Fe2+, Mn2+, and SO4 2− at wells ZK1 and ZK3 indicate that sulfate-reducing biodegradation was the dominant process experienced at contaminated sites rather than iron–manganese reduction processes. The dynamic changes of hydrochemical parameters suggest that the degree of biodegradation would be intensified at the center of pollutant plume and iron–manganese reduction processes experienced earlier than sulfate-reducing biodegradation. The community diversities and microbial activities in different soil depths were responded to PHs, but the relationship is not simply linear. The community diversities and microbial activities increased significantly with rise in PH concentration of soil until about 20 mg/kg and then peaked off sharply, suggesting that community succession would be occurred in microhabitat when the PH concentration in soil exceeds 20 mg/kg. The major DGGE bands found in the soil samples were sequenced. One sequence affiliated with γ-Proteobacteria showed high similarities to uncultured bacteria which had been found in offshore oil pollution environment. These bacterial species were found to have similar petroleum degradation functions to the bacteria at the sites studied here.