Effective size characteristics of suspended sediment and nutrient concentrations during flood events in the Reno River tributaries (Northern Italy).

摘要

In this study, we carry out a detailed analysis concerning Suspended Sediment Concentration (SSC) and particle size distribution in water samples collected mainly during storm events in the Reno river basin, in northern Apennines (Italy). At the outlet of mountain basins of the three major tributaries, Lavino, Savena and Sillaro, a hydrological monitoring has been started up. A total of 766 samples with maximum SSC were selected for this study to determine the nutrient level on the solid fraction. The samples were taken during flood events occurred from the year 2000 to 2009. By considering the physicochemical properties and nutrient constituents as the most important characteristics of the river conditions, total Nitrogen (Ntot), total Phosphorus (Ptot), particle size and SSC were selected for testing. The monitored watersheds are different for lithology, land cover and anthropogenic contamination levels. These differences were recognizable in the particle size distribution and in the nutrient level of the SSC in the water samples. Suspended sediment of the Savena stream showed a higher component of coarser material, Sillaro and the Lavino samples have higher clay content, 46% and 43% respectively. Concentration of Ntot and Ptot in the stream suspended sediments increases from Sillaro to Lavino to Savena. There is a statistically significant relationship between Ptot and Ntot (P≤0.05) and both nutrients showed significant linear relationships versus silt particle sizes. Silt appears to be the preferential vector of nutrients, confirming that finer particles and their aggregates have been proved to be the preferential vehicle for nutrients. Despite their close geographical proximity, analyses of grain size and nutrient in the streams have revealed dissimilar properties, which have been related mainly to the anthropogenic contamination levels, different cover land, agricultural and lithology properties of catchments.