| dc.description.abstract | A large part of the total sediment transport in a river occurs as fine sediment transport. During its transport through the river system fine sediment can be temporarily stored on the floodplain or in the channel bed.
Besides playing a large part in the sediment budget of a river, storage of fine sediment in the gravel bed can also affect the ecology of a river. There can be contaminants attached to the sediment and infiltration of fine sediment in the gravel bed can reduce oxygen levels and limit nutrient exchange by clogging the pores. In this study, the infiltration and storage of fine sediment in a gravel bed was measured in the Geul River catchment in Limburg, the Netherlands. In addition, the distribution of zinc and lead contamination in the catchment was assessed. The fine sediment, transported by the Geul River, contains zinc and lead, due to historical mining activities. To measure the infiltration of fine sediment, traps were placed in the gravel bed of the river. These traps contained ‘clean’ gravel between which fine sediment was captured. The mass of the captured fine sediment was used to determine the fine sediment infiltration flux. Changes in the sediment flux could be related to changes in discharge. In addition, a second method to determine the sediment infiltration flux was tested. This method utilizes the metal concentrations in the sediment. Fluxes determined with this method were comparable to those determined with the other, gravimetric, method, with a fluxes of 0.49 ± 0.19 kg/m2/day and 0.54 ± 0.22 kg/m2/day respectively. Distribution patterns of zinc and lead in the channel and on the floodplain were analyzed. In general the concentrations decreased in the downstream direction, though both in the channel and on the floodplain fluctuations in concentrations were encountered. The highest zinc and lead concentrations in the channel were measured near the Dutch-Belgian border. The lowest lead concentrations were found at the measurement location furthest downstream, 18 km from the border. Yet, the lowest zinc concentrations were measured only 5 km from the border, lead concentrations at this location were also lower than those measured a few kilometers further downstream. These fluctuations can occur by input of sediment with a different metal content, through for instance bank erosion. The distribution pattern is also affected by differences in the mobility of the elements, and by the historical production rates of the mines. | |
