Domestic wastewater causes nitrate pollution in an agricultural watershed, China

• Published in: The Science of the total environment 2022-06, Vol.823, p.153680-153680, Article 153680
• Main Authors: Cao, Meixian, Hu, Anyi, Gad, Mahmoud, Adyari, Bob, Qin, Dan, Zhang, Lanping, Sun, Qian, Yu, Chang-Ping
• Format: Article
• Language: English
• Subjects: agricultural watersheds; aquatic environment; Bayesian theory; Changle River watershed; China; Community-based microbial source tracking; eutrophication; Hydrogeochemical variables; hydrogeochemistry; Land use; microorganisms; municipal wastewater; Nitrate dual stable isotopes; nitrates; nitrogen; pollution; rivers; sewage; SIAR model; soil; stable isotopes; swine
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2022.153680

Excessive quantities of nitrates in the aquatic environment can cause eutrophication and raise water safety concerns. Therefore, identification of the sources of nitrate is crucial to mitigate nitrate pollution and for better management of the water resources. Here, the spatiotemporal variations and sources of nitrate were investigated by stable isotopes (δ15N and δ18O), hydrogeochemical variables (e.g., NO3− and Cl−), and exogenous microbial signals (i.e., sediments, soils, domestic and swine sewage) in an agricultural watershed (Changle River watershed) in China. The concentration ranges of δ15N- and δ18O-NO3− between 3.03‰–18.97‰ and −1.55‰–16.47‰, respectively, suggested that soil nitrogen, chemical fertilizers, and manure and sewage (M&S) were the primary nitrate sources. Bayesian isotopic mixing model suggested that the major proportion of nitrate within the watershed (53.12 ± 10.40% and 63.81 ± 15.08%) and tributaries (64.43 ± 5.03% and 76.20 ± 4.34%) were contributed by M&S in dry and wet seasons, respectively. Community-based microbial source tracking (MST) showed that untreated and treated domestic wastewater was the major source (>70%) of river microbiota. Redundancy analysis with the incorporation of land use, hydrogeochemical variables, dual stable isotope, and exogenous microbial signals revealed domestic wastewater as the dominant cause of nitrate pollution. Altogether, this study not only identifies and quantifies the spatiotemporal variations in nitrate sources in the study area but also provides a new analytical framework by combining nitrate isotopic signatures and community-based MST approaches for source appointment of nitrate in other polluted watersheds. [Display omitted] •Sources of nitrate pollution in the Changle River watershed were identified using multidisciplinary methods.•Manure and sewage contributed to more than 50% of riverine nitrate.•Riverine microbiome was primarily derived from the raw and treated domestic sewage.•Nitrate isotopic signatures highly associated with the sewage-related microbial signals.•Community-based MST could be helpful for identifying nitrate pollution sources.