ABSTRACT
Suspended sediment represents more than 80% of the global riverine sediment flux from continents to the oceans and constitutes an important component of riverine ecosystems. Suspended sediment transport has been disturbed by human intervention in most river systems of the world. While deforestation and conversion to agricultural land leads to increases in suspended sediment loads, dam construction and recently implemented soil conservation measures reduce suspended sediment loads. Here we report on trends in suspended sediment transport in German waterways derived from work-daily sampling data for a monitoring network established by the German Water and Shipping authority in the 1960ies. For this study, we focus on 49 monitoring stations and cover the time period between 1990 and 2010, which represents the time with the largest number of active monitoring stations. Almost all monitoring stations (47 of 49) show a significant reduction in suspended sediment concentration (SSC) on average at a rate of 0.9 mg l-1a-1 since the early 1990ies (at p < 0.05). At some stations this lead to a 50% reduction of the SSC. Our analysis indicates that decreasing suspended sediment concentrations seem to be unrelated to changes (e.g. decreases) in discharge, for which no significant trends could be found for most stations. Our result indicate that decreasing suspended sediment concentrations in German waterways are related to declining sediment supply due to changes in agricultural land use and soil conservation measures, while the construction of dams and reservoirs (which were mainly established before 1980) play a minor role.
