Changes in aquatic macrophyte flora over the last century in Catalan water bodies (NE Spain)

Landscape and aquatic environments have suffered increasing threats over the last century with major impacts on lentic waters and, presumably, on its inhabiting life. This study aims to evaluate changes in occurrence of aquatic macrophyte flora in lentic waters in Catalonia (NE Spain), emphasizing the last 20 years, with particular reference to vulnerable species. We conducted a survey (2005–2009) identifying macrophytes from 215 lentic water bodies (from eight different geomorphological typologies) and compared the data obtained with a historical compilation (1879–2006) from the Biodiversity Data Bank of Catalonia (BDBC). Vascular hydrophyte species were present in 53.5% of the sampled water bodies and only 69.7% of species cited in the BDBC were re-sampled in the recent survey. Significant changes in species occurrence were also found, particularly for those endangered macrophytes where the ratio of re-sampling was lower (52%). Hydrophyte flora of 36 water bodies has changed over the last 20 years and richness clearly tends to decrease. However, trends are different in each typology; while richness is stable in alpine lakes, it drops for coastal lagoons, ponds and karstic lakes. The threats most correlated with hydrophyte disappearance are water extraction and regulation and desiccation/drainage. To sum up, we detect a loss of hydrophyte diversity at a local and regional scale. Conservation actions are needed to preserve remaining water bodies and flora.