AQUAFLORA: A predictive model based on diatoms and macrophytes for streams water quality assessment

According to the Water Framework Directive phytobenthos (diatoms) and macrophytes are part of the same biological element, the aquatic flora, which should be used in monitoring programs for rivers ecological assessment. However, they have been treated separately over time, and different indices are used to reach an Ecological Quality Status. Here we build a predictive model (the AQUAFLORA) based on communities composed of diatoms and macrophytes, with the aim of determining if these two elements of the aquatic flora could be combined in a single model to evaluate the streams ecological quality. For that we used biological and environmental information from 200 reference and 171 disturbed sites distributed through the entire Portuguese mainland territory. After clustering analysis, 5 biological reference groups significantly different (ANOSIM Global R = 0.685; p < 0.001, 999 permutations) were established, corresponding to sub-sets of reference condition. The most contributive taxa to within groups Bray-Curtis similarity (determined by SIMPER analysis) are a mixture of macrophytes and diatoms. The groups were well discriminated (72%) by the environmental descriptors. Generally, groups 1, 2 and 3 are permanent siliceous rivers located in the north where precipitation is higher and temperatures are lower; while reference groups 4 and 5 correspond to southern streams with higher temperatures, low precipitation with a higher degree of temporality and high hardness and alkalinity. A 5-classes quality system based on Bray-Curtis dissimilarities between the observed flora and the reference groups communities, translated well the human pressures affecting the streams and highlighted the sensitivity of the aquatic flora to other pressures that are not usually considered (hydromorphological, land use).