Del desastre ecològic a l'experiment natural: resiliència i recuperació parcial de la vegetació aquàtica de l'estany Baciver, Val d'Aran

Abstract

Lake Baciver, located in Pla de Beret (Val d'Aran), was formerly covered by aquatic plants (95% of its surface area). In autumn 1991 the lake was damned, flooding an area equivalent to its original surface and raising the water level by 3.5 meters. This event was catastrophic for the aquatic plants and only 17% of the formerly covered area, survived. This paper discusses the progress of the residual population and the aquatic plant colonization in the newly flooded areas over the past two decades. The study provides data of interest on the Restauration Ecology of soft-water oligotrophic lakes, which is otherwise very difficult to obtain. We found that the quillwort Isoetes lacustris L. can live up to 25 years under extremely low light conditions and sediment instability, but that the residual population does not recruit and is steadily regressing. We have also observed I. lacustris growing a new population from spores in an inoculated formerly terrestrial soil, although space occupation has been very slow, of less than 1 m2 per year on average. Sparganium angustifolium and accompanying species can colonize the new sediments much faster, following exponential progression, and currently occupy 95% of the potential niche for the community. The new status of the lake has changed not only in terms of the landscape, but also in the biomass renewal. Fast growing annuals are taking most of the space against the ecological engineer Isoetes lacustris, which is a slow growing perennial species that plays a key role in controlling sediment biogeochemistry in oligotrophic lake sediments.