Environmental factors explaining the distribution and diversity of vascular aquatic macrophytes in a highly heterogeneous Mediterranean region

Abstract

The study of the relationships between vascular aquatic macrophyte occurrence, species richness andthe local environment are central for suitable ecosystem quality assessments, freshwater bodies manage-ment and assistance for macrophyte restoration. Here we quantify the importance of the local factors, bothwater column and sediment, to provide tools for lentic water systems management and conservation in aMediterranean region. We surveyed 90 water bodies along a 2500 m altitudinal gradient in Catalonia (NESpain). Despite its relatively small scale, the area of study exhibits large-scale environmental gradientsmainly related to a diverse geology and climate. In consequence, the response of aquatic macrophytesto a broad range of environmental conditions can be studied without interference of biogeographicalclines. We identified all vascular aquatic macrophytes and analyzed 35 environmental variables at eachsite. Local environmental factors accounted for only 19% of variance in aquatic macrophyte distribution.Even though water column variables explained more variance than sediment variables in a variance par-titioning analysis (pCCA), a mixed model integrating variables of both compartments performed better.The most important variables driving aquatic macrophyte distribution were water conductivity, waterDOC, water K, water pH, water Na, sediment organic matter, sediment Na and water nitrate. CCA betweenspecies and water and sediment variables clearly segregated coastal lagoons, temporary pools and alpinelakes over two main gradients: ionic content and water body productivity. Species richness was low(4.2 species per water body on average) and GAM showed weak correlations with sediment and mostwater column variables. The best factor explaining species richness was the geomorphological typology,but only temporary pools were significantly different from the other types and had the highest speciesrichness. Thus, temporary pools were unique and displayed a high biodiversity, strengthening the needfor their preservation.