Comparative test of ecological assessment methods of lowland streams based on long-term monitoring data of macrophytes

Spatially Structured Environmental Variation Plays a Prominent Role on the Biodiversity of Freshwater Macrophytes Across China

Different non-mutually exclusive mechanisms interactively shape large-scale diversity patterns. However, our understanding of multi-faceted diversity and their determinants in aquatic ecosystems is far from complete compared to terrestrial ones. Here, we use variation partitioning based on redundancy analysis to analyze the relative contribution of environmental and spatial variables to the patterns of phylogenetic, taxonomic, and functional diversity in macrophyte assemblages across 214 Chinese watersheds. We found extremely high spatial congruence among most aspects of biodiversity, with some important exceptions. We then used variation partitioning to estimate the proportions of variation in macrophyte biodiversity explained by environmental and spatial variables. All diversity facets were optimally explained by spatially structured environmental variables, not the pure environment effect, implying that macrophyte are taxonomically, phylogenetically, and functionally clustered in space, which might be the result of the interaction of environmental and/or evolutionary drives. We demonstrate that macrophytes might face extensive dispersal limitations across watersheds such as topography and habitat fragmentation and availability.

Integrating river hydromorphology and water quality into ecological status modelling by artificial neural networks

The aim of the study was to develop predictive models of the ecological status of rivers by using artificial neural networks. The relationships between five macrophyte indices and the combined impact of water pollution as well as hydromorphological degradation were examined. The dataset consisted of hydromorphologically modified rivers representing a wide water quality gradient. Three ecological status indices, namely the Macrophyte Index for Rivers (MIR), the Macrophyte Biological Index for Rivers (IBMR) and the River Macrophyte Nutrient Index (RMNI), were tested. Moreover two diversity indices, species richness (N) and the Simpson index (D) were tested. Physico-chemical parameters reflecting both water quality and hydromorphological status were utilized as explanatory variables for the artificial neural networks. The best modelling quality in terms of high values of coefficients of determination and low values of the normalized root mean square error was obtained for the RMNI and the MIR networks. The networks constructed for IBMR, species richness and the Simpson index showed a lower degree of fit. In all cases, modelling quality improved by adding two hydromorphological indices to the pool of explanatory variables. The significant effect of these indices in the models was confirmed by sensitivity analysis. The research showed that ecological assessment of rivers based on macrophyte metrics does not only reflect the water quality but also the hydromorphological status.

Responses of aquatic macrophytes to anthropogenic pressures: comparison between macrophyte metrics and indices

Macrophyte responses to anthropogenic pressures in two rivers of Central Spain were assessed to check if simple metrics can exhibit a greater discriminatory and explanatory power than complex indices at small spatial scales. Field surveys were undertaken during the summer of 2014 (Duraton River) and the spring of 2015 (Tajuña River). Aquatic macrophytes were sampled using a sampling square (45 × 45 cm). In the middle Duraton River, macrophytes responded positively to the presence of a hydropower dam and a small weir, with Myriophyllum spicatum and Potamogeton pectinatus being relatively favored. Index of Macrophytes (IM) was better than Macroscopic Aquatic Vegetation Index (MAVI) and Fluvial Macrophyte Index (FMI) in detecting these responses, showing positive and significant correlations with total coverage, species richness, and species diversity. In the upper Tajuña River, macrophytes responded both negatively and positively to the occurrence of a trout farm effluent and a small weir, with Leptodictyum riparium and Veronica anagallis-aquatica being relatively favored. Although IM, MAVI, and FMI detected both negative and positive responses, correlations of IM with total coverage, species richness, and species diversity were higher. Species evenness was not sensitive enough to detect either positive or negative responses of aquatic macrophytes along the study areas. Overall, traditional and simple metrics (species composition, total coverage, species richness, species diversity) exhibited a greater discriminatory and explanatory power than more recent and complex indices (IM, MAVI, FMI) when assessing responses of aquatic macrophytes to anthropogenic pressures at impacted specific sites.