Environmental and community constraints on Elodea nuttallii: implications for early season control in an urban stretch of the Po River (NW Italy)

Invasive aquatic macrophytes represent an increasing concern for freshwater ecosystems, where they alter biodiversity, ecosystem functioning, and water-related services. Among them, the submerged species Elodea nuttallii has rapidly expanded across many European waterbodies, yet its ecology in regulated lowland rivers remains insufficiently explored, particularly compared to that in artificial canals, ponds, and lakes. This study investigates the environmental, hydrological, and biotic factors shaping the occurrence and distribution of E. nuttallii in an urban river system. Field surveys conducted in 2025 documented macrophyte assemblages and habitat conditions in the Po River, the longest Italian river, flowing through the city of Turin. A total of 150 presence-absence points for E. nuttallii were recorded, spaced at least 200 meters apart, along the urban stretch of the river, collecting information on temperature, dissolved oxygen, pH, conductivity, as well as the presence of other macrophytes and the extent of plant populations. The results show that most vegetated patches are dominated by E. nuttallii, which is associated with depositional areas characterised by soft sediments and significantly related to the presence of Myriophyllum spicatum, as demonstrated by Phi correlation analysis. Although interspecific competition appears to limit E. nuttallii’s relative abundance during the seasonal macrophyte community peak, when its mean relative cover drops from 89.2% to 60%, its extended vegetative season likely contributes to its persistence. Moreover, substrate type emerged as the primary abiotic factor shaping spatial distribution in a regulated lowland river, with sand and silt providing optimal conditions for its establishment. We further highlight the need for early season and site-specific management interventions. Given the ecological and recreational significance of the Po River and its role as a dispersal corridor, understanding the invasion dynamics of E. nuttallii is critical for informing management strategies, particularly in light of its designation as an EU-priority alien invasive species.