Aquatic bryophytes as ecological indicators of the water quality status in the Tiber River basin (Italy)

A survey of 18 watercourses of the Tiber River basin was carried out to define the ecological niche breadth of some aquatic bryophyte species in relation to environmental factors. Aquatic bryophytes were sampled and water environmental parameters were measured at 99 stations distributed along the catchment (from the headwater regions to the downstream reaches). The datasets of the collected species and environmental data were analyzed by using a multivariate statistical analysis (PCA biplot). Ecological responses of the recorded aquatic bryophytes were obtained using a fuzzy set approach, and were compared with data from literature. The results show that the presence of the aquatic bryophytes in watercourses is affected negatively by the reduction of water velocity, clearness, substratum size and the worsening quality of the water physico-chemical status. In fact, aquatic bryophytes show a general preference for stations characterized by medium-large granulometry, and fast-flowing, clear, oxygenated (mean value 9.2 mg/l), cool waters (mean value 15.0 °C), with low loads of nutrients, particularly ammonia (mean value 0.10 mg/l) and phosphates (mean value 0.09 mg/l). However, ecological responses reveal different patterns in the distribution of aquatic bryophyte species mainly in relation to water physico-chemical parameters (e.g. temperature, conductivity, ammonia, phosphates). E.g. Palustriella commutata var. commutata, Cratoneuron filicinum, Fissidens viridulus and Cinclidotus aquaticus show high preference for clear, turbulent and fast-flowing waters, with temperature below 12 °C, conductivity below 300 μS/cm, and concentrations about 0.01 mg/l for phosphates, not exceeding 0.10 mg/l for ammonium ions and 0.90 mg/l for nitrates. Leptodictyum riparium and Riccia fluitans are for their part more linked to turbid and slow waters affected by eutrophication, showing optimum values for about 0.30 mg/l for ammonia concentration, 0.90 mg/l for nitrates and 0.11 and 0.22 mg/l for phosphates respectively. Conversely, Fontinalis antipyretica is not closely related to specific conditions, showing wide ecological ranges for most of the analyzed environmental factors. This paper has evaluated and discussed the possible use of sampled species as bioindicators for biomonitoring of the water quality.