Environmental drivers of aquatic macrophyte assemblages in ponds along an altitudinal gradient

The aim of this study was to explore the environmental drivers of the aquatic macrophyte assemblage in a large, heterogeneous Spanish region covering a wide altitudinal range. We hypothesized that physicochemical variables affecting assemblages would differ depending on altitude. The study was conducted in 46 plateau ponds and 21 mountain ponds. Our results revealed a shift in hydrophyte assemblage composition and structure along an altitude and water chemistry gradient. However, altitude was not a good predictor of species richness. Conductivity and nutrient concentrations were higher in plateau ponds than in mountain ponds and binary logistic regression showed that conductivity was the best variable for differentiating between both pond types. Canonical correspondence analysis indicated that conductivity was the main factor responsible for the species distribution in both pond types. Generalized linear models showed that in plateau ponds, total phosphorus and mean depth were the strongest predictors of submerged macrophyte coverage, and no model could be created for richness. In the mountain ponds, conductivity and pond area explained coverage of submerged plants, while richness was related to pond area. Our results corroborated the hypothesis to be tested, and the conclusions obtained may be of relevance for making decisions on conservation and restoration.