Seasonal and spatial variability of water quality parameters in the lagoon of Venice

The paper presents the results of the statistical analysis of a set of seven water quality parameters, which were collected in 2001 within the frame of a more comprehensive monitoring program of the lagoon of Venice. The program, which began in September 2000 and ended its first phase in August 2003, includes the monthly sampling of 32 water quality parameters in 30 stations. Multivariate techniques and gridding methods were used for investigating the spatial and seasonal variability of the data and for characterizing the trophic evolution of the basin in 2001. The results of the multivariate analysis indicate that the 30 stations can be classified into seven groups, based on the similarity of the temporal evolution of nutrients and chlorophyll a. Furthermore, these groups reflect the geographic distribution of stations since those closer to the tributary discharges and the ones which are located in southern part of the lagoon were classified into clearly distinct clusters. The analysis of the temporal evolutions of the spatial distributions of the most important water quality parameters confirms such an interpretation and evidences the role of the tributaries and of the exchanges with the sea in determining the water quality and the dynamics of the ecosystem. The key role of these factors is also clearly demonstrated and established in quantitative terms by the results of the regression analysis between a trophic indicator, identified in the multivariate analysis, and the yearly averaged values of salinity and residence time, that is of physical parameters which give a measure of the influence of the rivers and of the tidal mixing. (C) 2004 Elsevier B.V. All rights reserved.