High-resolution sedimentary record of anthropogenic deposits accumulated in a sewer decantation tank

Abstract

To test the extent to which sediments accumulated in sewers may serve as high-resolution archives of urban evolution, this study examined a sedimentary succession deposited in a decantation tank of the combined sewer network of Orleans (France). The focus was on a 1.43 m sediment core drilled after 10 months of operation since the last cleaning. Sediments were stratigraphically organised into three distinct facies. The lower unit comprised organic remains, the middle unit gravels and sands and the upper unit was fine sands. The evolution of radionuclide activities, bile acid concentrations, and glass microspheres enabled sediments from wastewater and stormwater inputs to be distinguished. Precipitation events that affected the area were the main control on sediment deposition with organic-rich sediments accumulating from wastewater during dry weather and coarser, mineral sediments accumulating from stormwater during precipitation events. These results enable development of a chronological framework for sediment deposition. These findings reveal the potential of sewer sediment accumulations to record relevant information on the evolution of urban socio-ecosystems on monthly to annual scales with a relatively high time resolution.