Influence of canal use purpose on water quality: A case study in the floodplain area of the Life Green4Blue project

Floodplain ecosystems worldwide have largely been reclaimed for urbanization and agriculture. In these reclaimed areas, water is managed through artificial canals that serve various purposes, including irrigation, soil drainage, flood safety, and biodiversity support. This study aimed to assess how the use of artificial canals (irrigation and receiving canals) within the floodplain area of the Life Green4Blue project (LIFE18 NAT/IT/000946) affects water quality. The study was conducted in the Po Plain (Italy), an area that has undergone extensive agricultural reclamation in the past century. The irrigation canals are supplied with water from the Canale Emiliano Romagnolo, which diverts water from the Po River during the summer months (April to September). The larger receiving canals primarily act as discharge routes for both irrigation and drainage canals, and to a lesser extent, for irrigation. During autumn and winter (October to March), both types of canals are used to maintain hydraulic safety by lowering the water levels.

Water quality was monitored monthly from January 2020 to December 2023. Cluster analysis (CA) showed a clear distinction between the water in receiving canals and irrigation canals. Principal component analysis (PCA) identified that the differences were mainly due to nutrient and salt concentrations. Water in receiving canals exhibited higher levels of nutrients (such as N-NH4, Ca, K, Mg, P, and S) and higher electrical conductivity (EC) values. The poorer quality of water in the receiving canals is attributed to its origin—soil leachates and water from irrigation canals that have already traveled across agricultural lands—and the lack of freshwater input. Consequently, the water quality index (WQI) was higher for irrigation canals (67) compared to receiving canals (61).

Both canal types showed a decline in water quality during the autumn and winter (AW) seasons, as indicated by the PCA. This decline was linked to higher nutrient and EC concentrations compared to the spring and summer (SS) seasons. The increased nutrient load in the AW seasons is likely due to greater soil leaching caused by higher rainfall. Additionally, the reduced water flow during AW seasons hindered dilution, allowing for more significant exchange of cations and anions from the bed sediments. Interestingly, the decline in water quality was more pronounced in irrigation canals than in receiving ones, suggesting that freshwater input plays a crucial role in maintaining water quality in irrigation canals.

This study underscores the influence of canal usage on water quality and highlights the need for continuous freshwater input throughout the year to sustain the ecosystem services provided by floodplain areas.