Role of irrigation canal morphology in driving riparian flora in over-exploited catchments

Freshwater plants loss is one of the preeminent issues concerning biodiversity conservation, due to the alteration of inland waters by water regulation and agricultural intensification. At the same time, data suggest a relevant contribution of artificial, lowland aquatic ecosystems in supporting plant diversity. However, the underlying ecological mechanisms remain to be fully understood. To add knowledge to this subject, a wide canal network in the Bologna area (~ 1400 km2, northern Italy) was investigated to analyse the riparian flora in relation to canal morphology. A systematic sampling procedure was adopted by randomly selecting 96 transects (1 m × 10 m) along 79 different canals, classified as small, medium, and large in terms of water depth. Flora was characterised based on the Ellenberg’s humidity and nitrophily indices, life forms, chorotypes, and alien species. The distribution of the number of species and floristic categories between transects and the role of canal depth were explored using linear mixed models and nMDS. 251 plant species were recorded; they were characterised by a broad ecology in terms of soil moisture (71% of the list) and nutrient availability (59%). Wetland and alien species—including invasive ones—were a marginal presence (< 5%, < 6%, respectively)—and canal depth showed a significant effect on compositional dissimilarity between canals, with larger canals characterised by lower diversity rates. This work reinforces the pivotal contribution of heavily modified water bodies in supporting plant richness in oversimplified landscapes, confirming the role of canal depth in driving local flora.