Macrophyte communities in unimpacted European streams: variability in assemblage patterns, abundance and diversity

Macrophytes are an important component of aquatic ecosystems and are used widely within the Water Framework Directive (WFD) to establish ecological quality. In the present paper we investigated macrophyte community structure, i.e., composition, richness and diversity measures in 60 unimpacted stream and river sites throughout Europe. The objectives were to describe assemblage patterns in different types of streams and to assess the variability in various structural and ecological metrics within these types to provide a basis for an evaluation of their suitability in ecological quality assessment. Macrophyte assemblage patterns varied considerably among the main stream types. Moving from small-sized, shallow mountain streams to medium-sized, lowland streams there was a clear transition in species richness, diversity and community structure. There was especially a shift from a predominance of species-poor mosses and communities dominated by liverwort in the small-sized, shallow mountain streams to more species-rich communities dominated by vascular plants in the medium-sized, lowland streams. The macrophyte communities responded to most of the features underlying the typological framework defined in WFD. The present interpretation of the WFD typology may not, however, be adequate for an evaluation of stream quality based on macrophytes. First and most important, by using this typology we may overlook an important community type, which is characteristic of small-sized, relatively steep-gradient streams that are an intermediate type between the small-sized, shallow mountain streams and the medium-sized, lowland streams. Second, the variability in most of the calculated metrics was slightly higher when using the pre-defined typology. The consistency of these results should be investigated by analysing a larger number of sites. Particularly the need of re-defining the typology to improve the ability to detect impacts on streams and rivers from macrophyte assemblage patterns should be investigate

Macrophyte communities of European streams with altered physical habitat

The impact of altering hydro-morphology on three macrophyte community types was investigated at 107 European stream sites. Sites were surveyed using standard macrophyte and habitat survey techniques (Mean Trophic Rank Methodology and River Habitat Survey respectively). Principal Components Analysis shows the macrophyte community of upland streams live in a more structurally diverse physical habitat than lowland communities. Variables representing the homogeneity and diversity of the physical environment were used to successfully separate un-impacted from impacted sites, e.g. homogeneity of depth and substrate increased with decreasing quality class for lowland sites (ANOVA p < 0.05). Macrophyte attribute groups and structural metrics such as species richness were successfully linked to hydro-morphological variables indicative of impact. Most links were specific to each macrophyte community type, e.g., the attribute group liverworts, mosses and lichens decreased in abundance with increasing homogeneity of depth and decreasing substrate size at lowland sites but not at upland sites. Elodea canadensis, Sparganium emersum and Potamogeton crispus were indicative of impacted lowland sites. Many of the indicator species are also known to be tolerant to other forms of impact. The potential for a macrophyte tool indicative of hydro-morphological impact is discussed. It is concluded one could be constructed by combining indicator species and metrics such as species richness and evennes