Assessing the potential of Albufera de València Lagoon sediments for the restoration of charophyte meadows

Albufera de València Lagoon, the largest littoral lagoon on the Iberian Peninsula, has been affected by eutrophication processes since the 1970s due to the direct dumping of sewage waters of industrial, agricultural and urban origin. Consequently, the submerged vegetation that covered the bottom of the lagoon has been lost (charophytes and Potamogeton spp., Myriophyllum spp. and Ceratophyllum spp.). Despite efforts to improve water quality, this vegetation has not recovered. No information about the potential of the recent sediments to host charophyte development is available. In this study, we analysed several sediment cores taken from different areas of the lagoon to determine the spatial distribution of past charophyte communities (based on the fructifications, i.e., oospores and gyrogonites, found in the sediments), to ascertain whether propagules remain in the upper sediments and to determine the potential of the surface sediments (containing pollutants, e.g., organochlorinated pesticides, heavy metals and pharmaceuticals) to host the growth and germination of charophytes if clear water is restored to the lagoon. The study was based on laboratory experiments. Generally, the same species of charophytes were found in all studied areas of the lagoon. The oospores and gyrogonites were located immediately surficially (in the first 5 cm) in certain areas, and these might be capable of germinating in this sediment stratum. The more recent sediment strata (the upper 14 cm), corresponding to the eutrophication period, can support the vegetative growth of Chara hispida and Chara vulgaris and promote the germination of Chara aspera and Chara baltica. We conclude that if the underwater light conditions are improved and nutrient concentrations are reduced in Albufera de València Lagoon, the reestablishment of charophytes might be possible both naturally and through specific management measures (namely, programmes involving seeds as planting stock or large-scale planting activity). This approach necessarily requires an improvement in the water quality of the inputs to the lagoon and an increase in the amount of water discharge to reduce the water residence time. These measures would restore the highly desirable positive feedback between submerged vegetation and water quality.