Retention of dissolved silica within the fluvial system of the conterminous USA

Dissolved silica (DSi) is an important nutrient in aquatic ecosystems. Increased DSi retention within the fluvial system due to damming and eutrophication has led to a decrease in DSi exports to coastal waters, which can have severe consequences for coastal areas where ecosystem functioning depends on fluvial DSi inputs. The analysis of fluvial DSi fluxes and DSi retention at regional to global scales is thus an important research topic. This study explores the possibility to empirically assess regional DSi retention based on a spatially explicit estimation of DSi mobilization and fluvial DSi fluxes calculated from hydrochemical monitoring data. The uncertainty of DSi retention rates (rDSi) estimated for particular rivers is high. Nevertheless, for the St. Lawrence River (rDSi = 91 %) and the Mississippi River (rDSi = 13 %) the estimated DSi retention rates are reasonable and are supported by literature values. The variety of sources of the uncertainty in the DSi retention assessment is discussed.