Some sedimentological and chemical features of the seafloor in front of the Tiber River

Abstract

26 sediment samples, collected Oct 3d-4th, 1978 off the Tiber River mouth (Tyrrhenian Sea) were analyzed for grain size parameters, nutrients (inorganic and extractable P, NH₃, extractable Si) and organic matter (org C, N, P) in order to study the influence of the biogeochemical cycles on global ecological processes. Three depositional facies were recognized from grain size and Geomorphology of the submersed delta: a) nearshore sands area, with nearly constant high energy; b) delta front with prevailing sands and silty clays deposited directly off the river mouth (flocculation area); c) prodelta slope, with prevailing silty clays and presence of mass movement processes. The comparison with other coastal areas of the Mediterranean Sea and the study of the linear correlation coefficients among all parameters indicate: a) the organic matter content, mostly of fluvial origin, is higher in the finest grained sediments; good correlation was found between this group and phosphorus compounds, whose organic fraction is also strongly correlated with silt; b) pH and redox, directly correlated with the coarser fraction, are very useful for contouring reducing areas with conditions for the mineralization of org N and a likely increase in phosphate release from sediments; c) ammonia is totally independent from any other parameter. Its areal distribution shows direct influence from fresh water input rather than "in situ" biochemical transformation mechanism. A preliminary conclusion emphasizes the delta front as the best target area for the study of the influence of sediments on the coastal water quality.