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

The discussed case study is represented by the Reno river basin, in northern Apennines (Italy), where a hydrological and geochemical monitoring has been carried out for three of the major tributaries: Lavino, Savena and Sillaro streams, where the gauging stations were built from 1997 to 2000yr’ at the outlet of the mountain basins. Each monitoring station was equipped with an ultrasonic flow meter, interfaced to an automatic pumped sampler. The rising interest for nutrients migration and the availability of more than 1500 water samples/river, have led to the analysis for total nitrogen, nitrate and phosphorus and grain size on the suspended sediment collected during flood events. The monitored watersheds, although very close, are different for lithology and anthropogenic contamination levels. These differences are recognizable in the particle size distribution and in the nutrient level of the water samples collected. Suspended sediment from the Savena torrent shows a higher component of coarser material (26% sand and 22% clay) than Sillaro and the Lavino rivers which have higher clay-silt content. Aggregates dominate the suspended sediment load and catchments lithology and soil type are thought to be important controls on the effective particle size characteristics of suspended sediment mobilized from the main sub-catchments. This study shows the results of a detailed analysis concerning suspended sediment concentration and particle size distribution in water samples collected mainly during storm events from three tributaries of the Reno River and it gives interesting elements on behavior of the concentration of total Nitrogen and Phosphorous to grain size. Concentration of Ntot and Ptot in sediments increases from Sillaro to Lavino to Savena. Relationships of nutrient concentration with soil use, agricultural and anthropic activity are expected to exist, possibly with the presence of a seasonality component. Despite their close geographical proximity, analyses of nutrient in the streams and a detailed study of data set have revealed dissimilar properties, which have been related to the different agricultural, geological and hydrological properties of catchments.