Sediment profiles and recording the effects of anthropogenic activities

The sediments of streams and rivers partly preserve the records of the activities that surround them. In natural areas, mineral sediments are deposited and organic plant material is carried by rainfall. If in urban or densely cultivated areas, the records are complemented by other organic materials, and chemicals and solid particles from human activities. Studying sediment profiles of small watercourses throughout their hydrological cycle allows us to observe oscillations in sediment inputs and correlate them with the surrounding uses. This makes it possible to observe influences on erosion processes in areas of exposed soil due to agriculture, on the reduction of water flow in primary channels due to soil sealing and on changes in the solid content of sediments due to the incorporation of anthropogenic materials, like microplastics. The methodological procedures presented in this chapter and used in two case studies carried out the obtention of sediment profiles ranging from 12 to 71 cm in length, enabling in-depth analysis of the content of anthropogenic particles. In the urban basin studied, we found up to 5160 part./kg of microplastics, and in the rural basin, there were only a few sparse fragments, highlighting urban waste and activities as the main source of these materials.