The main objective of the ISEO project is the identification and quantitative assessment of the synergic effects on the water quality of local pressures, in the watershed
and along the shoreline, and global warming, pursuing the following five aims:
(1) to measure the most relevant P inputs to the lake and to evaluate P pollution potential of the different anthropic activities in the watershed. So far, the importance of these fundamental tasks has been underrated;
(2) to map and evaluate the ecological features of SAV meadows, in order to exploit their diagnostic power to evaluate P contamination/sources and to assess their capacity to retain and contrast the inflowing P;
(3) to understand the lake circulation and its effect on the lake actual water renewal time, that controls the residence of nutrients in the hypolimnion. Although deep sub-alpine lakes are oligomictic, in Lake Iseo water overturn seems less frequent and the mixing depth shallower than in the past decades. Accordingly, there is a need of understanding the mechanisms that control winter mixing, with the aid of mathematical models.
(4) to identify innovative and effective management strategies, on the basis of the results of the monitoring and modeling activity. To this purpose, a coupled hydrodynamic–ecological model will be usedas a management tool to quantify the effects of loadings reduction on nutrient concentrations in the lake and to explore alternative recovery strategies.
(5) to set up a synoptic monitoring system of the lake, in order to detect acute pollution events, control the potential occurrence of algal bloom and provide distributed satellite data that can be fundamental for the research issues.
Our unit contributed to objectives 1), 2) 4) and 5).
Silica (Si) is an essential nutrient and the molar ratio of Si relative to N and P is relevant in the eutrophication process of aquatic ecosystems because it determines species composition. Lakes and reservoirs are biogeochemical reactors that recycle, store, remobilize and transform material. However, related to the well-studied nitrogen and phosphorous, only few works have examined factors controlling Si loads, retention and stoichiometry in lakes.
In the frame of the project ISEO: Improving the lake Status from Eutrophy towards Oligotrophy we analyzed Si, N and P loads and recycling in Lake Iseo. More specifically the purpose of this work was threefold; 1) to evaluate the role of the lake in regulating Si availability along the hydrographic network, 2) to understand how the lake influence N:P:Si ratios in river waters and 3) to analyze the spatial and temporal variability of benthic metabolism and Si fluxes in the littoral zone colonized by different primary producers communities.
Quantification of incoming (2536 ton TSi y-1) and outcoming Si loads (622 ton TSi y-1) suggests that Lake Iseo is a net Si sink and retains 78% of total load. Intact core incubations of different substrates collected from the littoral zone during the summer vegetative period indicate that the littoral zone mainly recycles DSi to the water column, but the intensity of Si regeneration differs among investigated habitats. Bare sediment colonized by benthic microalgae and rooted macrophytes show the highest release (121 µmol m-2 h-1) while rocky shores colonized by epilithon have the capacity to store Si during the all period (-29 µmol m-2 h-1).