Dissolved and particulate humic substances in water channels in the historic centre of Venice

The presence of humic substances, both in solution and as particulate, was studied in channels of the historic centre of Venice. The amount of particulate, its composition (organic and inorganic fraction) and the ratio between organic matter and humic substances were also considered. The sampling campaign was planned in 2001–02 from November to May. Three samplings in 20 stations representative of a large typical urban area were performed. The results obtained show that the composition of the particulate is variable, whereas the concentration of both dissolved and particulate humic substances is relatively homogeneous. Fulvic acids present in particulate are less homogeneous than dissolved forms; furthermore, the humification rate of organic matter is variable. Humic acids are absent, both in particulate and in dissolved forms.