Is water quality or the presence of aquatic macrophytes more important for supporting taxonomic and functional macrozoobenthic diversity in lowland running waters?

To address this question, we sampled for a year 12 water streams in the Po Plain. At each site and sampling station, three samples were collected across four seasons: spring (May), summer (July), autumn (October), and winter (January). We also recorded abiotic parameters (water temperature, pH, conductivity, dissolved oxygen percentage, and stream speed), presence or absence of aquatic macrophytes, and landscape attributes (riparian naturalness and surrounding land use). Physicochemical parameters were measured in situ using appropriate instruments, while chlorophyll was estimated in the laboratory from water samples collected on site. Macrozoobenthos was collected using a Surber sampler and subsequently identified in the laboratory, both taxonomically and according to trophic/functional traits.

The highest mean abundance of individuals per m² was recorded at sites with high water quality and macrophytes, followed by sites with high water quality but no plants. Interestingly, however, the highest values of both taxonomic and functional diversity were observed at sites without macrophytes, suggesting that their presence may increase competition among functional groups.

Multidimensional scaling (MDS) clearly highlights a differentiation between the 10 natural rivers and the 2 artificial channels, as well as a longitudinal gradient across the Po Plain (upper, intermediate, and lower sections), indicating a general deterioration of the studied systems approaching the Adriatic Sea.