Mathematical modelling of sediment chemico-physical parameters in a coastal lagoon to estimate high density seagrass meadow (Ruppia cirrhosa) distribution

In spring 2003, the pH, redox potential (Eh), grain-size (G), Total Nitrogen (TN), Total Phosphorus (TP) and Total Organic Carbon (TOC) were measured in superficial sediment samples from 83 sampling stations equally and randomly distributed inside the Orbetello lagoon. Localisation of the seagrass meadows (Ruppia cirrhosa) and the estimation of biomasses were carried out at the same time. A Landsat 7 multiband image of the study area was used to improve the spatial localisation of the sediment sampling sites and seagrass meadow distribution (GRASS GIS). Spatial distribution maps of the sediment measured values (pH, Eh, G, TN, TP and TOC) and seagrass meadow distribution and density were built using a geo-statistics software (g-stat). A simple mathematical model, based on the measured physical and chemical parameters of the sediment (Eh, pH, TP, G), was constructed to estimate seagrass meadow density and distribution in the Orbetello lagoon. Results of the model were used to elaborate a georeferenced map which was superimposed on the map constructed with seagrass density obtained in the field in order to evaluate the predictive power of the model. We found good agreement between the distribution of meadows recorded in the field with the suitable areas predicted by the model. Therefore, the constructed model could be a valid instrument for planning and evaluating management activities carried out in this lagoon.