Water quality of artificial canals used for agricultural purposes affected by urban and agricultural activities through a chemical and microbial perspective

Water from artificial canals in reclaimed floodplains is primarily used for crop irrigation; however, its quality is often compromised by chemical and microbial hazards, which may pose a threat to crop safety and quality. The main objectives of the present work were a) to analyse the chemical and microbial properties of water in a network of artificial canals; b) to identify the relationships among such parameters; and c) to detect spatial shifts in water quality (upstream and downstream) along some key canals. The canals were grouped into four sectors based on water origin: Sector A (urban), Sector B (wastewater treatment plants), Sector C (rural), and the Canale Emiliano Romagnolo (CER, Po River). The three years data showed a concentration decrease of most of the chemical targets, with the following order, sector B > sector A > sector C > CER. For microbial parameters, Sectors A and B exhibited higher biological pollution than Sector C and CER. Results were generally under the Italian legislation limits for water reuse. The multiple linear regression models revealed a generally positive correlation between microbial populations and sectors influenced by urban activities (Sectors A and B), while the relationships between microbial populations and chemical properties were less clear. Sodium adsorption ratio was the main parameter distinguishing canals in Sector B, whereas canals in sector A were characterized by overall higher P–PO₄ and N–NO₃ concentrations compared to sector C and CER. Upstream-downstream comparison generally indicated either stable or improved water quality, with the exception of a canal affected by the intrusion of poor-quality water. Overall, this study demonstrates that wastewater likely plays a dominant role in shaping water quality within artificial floodplain canals, highlighting the pronounced vulnerability of these canals to point-source pollution. • Water of canals affected by urban and agricultural activities has been investigated. • Higher load of nutrients and microbes in urban- than in agricultural-affected water. • Unresponsiveness of microbial population to water chemical properties. • Vulnerability of artificial canal system to pollution from point sources.