Environmental control on a land-sea transitional setting: integrated sedimentological, geochemical and faunal approaches

Because of their location at the interface between sea and emerged lands, so-called transitional environments are characterized by strong spatial and temporal variability in terms of sedimentological, physicochemical, and geochemical parameters. An increasing number of studies put forward the use of bioindicators as a tool for environmental monitoring. However, the sensitivity to these environmental parameters is commonly tested separately, even though it is known that interactions are numerous within this complex ecosystem. An integrated methodological study was conducted in Lake Varano (Italy). On the basis of 45 spatially distributed samples throughout the area and selected environmental parameters (trace elements, organic matter, clay mineral assemblages, grain size of sediment, and water characteristics), four factors are identified. The Lake Varano ecosystem is predominantly influenced by terrigenous inputs (first-order factor). The clastic fractions of the sediments supply a large range of trace elements, occasionally in relatively high concentrations. Under such circumstances, despite occasionally exceeding of threshold limits, the trace element pollution can generally be ruled out. The organic content combined with depth is the second key factor. In Lake Varano, the organic content is high and may lead to seasonal eutrophication. As a third-order factor, although only analyzed once, oxygen, ORP, salinity, and pH gradients show that foraminiferal diversity is positively influenced by more saline conditions. The fourth-order factor is the sediment size. To conclude, this paper illustrates the interest in and need to conduct a detailed, integrated, sedimentological study of a site prior to any examination of its ecological status (possible occurrences of sources of pollution).