Nutrient loading and spatial–temporal dynamics of phytoplankton guilds in a Southern Italian Coastal Lagoon (Lake Alimini Grande, Otranto, Italy)

Abstract

The importance of external and internal P-loading to the structural organization and dynamics of phytoplankton guilds in a Southern Italy coastal lagoon (Lake Alimini Grande) was investigated. To this end, phosphorus external loading through localized freshwater inputs was measured, P-release through detritus decomposition on sediments was evaluated, and phytoplankton abundance, biomass and taxonomic composition were quantified at 33 sites and 12 sampling times from September 1998 to September 1999. P-loading in the area was greater in the winter (26.5 µM P m−2 d−1) than in the summer (18.4 µM P m−2 d−1). In the winter, external inputs were 61.7% of the total, while in summer, internal inputs accounted for 99.8% of the total. Phytoplankton biomass was related to P inputs. In particular, the spatial distribution of phytoplankton biomass was related to external inputs in winter–spring, and to internal inputs in summer–autumn. A total of 228 phytoplankton taxa were identified of which 13 taxa accounted for more than 80% of phytoplankton abundance. The spatial and temporal dynamics of 13 taxa were related to P-availability and habitat heterogeneity.