Flora and plant communities across a complex network of heavily modified water bodies: geographical patterns, land use and hydrochemical drivers in a temperate overexploited plain

The decline of freshwater flora due to alteration, reclamation and trophic perturbation of lowland wetlands is among the most relevant issues in biological conservation. The contribution of heavily modified water bodies (HMWBs) in preserving plant diversity is notable, but the underlying ecological mechanisms are not completely explored. To contribute to this debate and expand the knowledge on the role of HMWBs in maintaining wetland biodiversity in overexploited agroecosystems, a canal network of about 1150 km (SE Po valley, N-Italy) was analysed to study the geographical patterns of riparian flora and plant communities, and their land use and hydrochemical drivers. A systematic sampling procedure was adopted by randomly selecting 96 transects (10 ­m 2 ) along 79 drainage canals. Additionally, 22 transects were sampled for water quality evaluation. Flora was characterised based on species richness and presence of threatened, alien and invasive species. We also studied the contribution of land use and water quality in explaining plant richness and composition. Slope and aspect of canals do not significantly affect plant species composition, whereas the «proximity to protected areas» seems to have a negative influence. Both threatened and alien plants richness decrease approaching protected areas. Among land use types, only agro-zootechnical settlements influence plant species composition, favoring nitrophilous species, as demonstrated by water parameters (the spatial patterns of nitrophilous species mirrored the progressive worsening of canal waters). This work confirms the key role of HMWBs in sustaining plant species diversity in oversimplified landscapes, highlighting complex regulation mechanisms that need further investigations.