Changes in aquatic plants in the Italian volcanic-lake system detected using current data and historical records

Lake littoral ecosystems help to preserve a significant degree of local and regional species richness. However, lakes are subjected to a range of human impacts that dramatically affect the local biota structurally and functionally. Unfortunately, the data available for numerous taxonomic groups in many river and lake systems are still somewhat scanty, especially in the Mediterranean area. We conducted a floristic study in 2010 and compared our data with historical data recorded over the last century (1908–2006) in six Italian volcanic lakes (central-southern Italy). Floristic data about charophytes and vascular plants were collected according to standardized sampling procedures along randomly selected transects and were partitioned into four functional groups (emergent species, floating-leaved, submerged and free-floating macrophytes). A total of 49 aquatic taxa was recorded, including 11 taxa of charophytes, emphasizing the contribution of local stoneworts to regional and European species richness. Temporal trends in macrophyte species richness and distribution over the last century mirrored trends in lakeshore development and catchment land use, and water quality. In the long term, a clear reduction in emergent species and submerged macrophytes richness was recorded in some lakes; on the other hand, in recent decades a progressive improvement of water quality supports the partial recovery of aquatic plant richness in others. As a result, the loss of native aquatic plants is concentrated along the lakeshores and in the first meters of depth.