Soil particles eroded from the land surface and transported into rivers by runoff are considered one of the main components of non-point source pollution in urban watersheds. These particles also serve as a vector for a wide variety of both organic and inorganic constituents. As a result, the identification of sediment sources in an urban watershed is necessary not only to understand erosion dynamics, but also to help implement more effective measures to control and/or remediate non-point source pollution. The present study employs sediment 'fingerprinting' to determine the main sediment sources in a small residential urban watershed (0.83 km2) on the outskirts of Porto Alegre in southern Brazil. Based on an evaluation spanning 12 rainfall events, the results show that paved and unpaved roads and the stream channel itself contribute, on average, 46%, 23%, and 31%, respectively, to the suspended sediment flux in the watershed. Furthermore, the source contributions varied both between events and over the course of a single event. This appears to imply that source contributions, at least to some extent, depend on local precipitation patterns. The results from this study indicate that the level of uncertainty in source ascription tends to decline with increasing numbers of tracers; hence, successful sediment fingerprinting and source ascription in complex hydrologic environments, such as urban watersheds, may require the use of a large number of chemical and/or physical tracers.
Bibliographical noteFunding Information:
We thank the Brazilian National Research Council (CNPq), CAPES, and the Research Support Foundation of Rio Grande do Sul (Fapergs) for financial support. We thank Dr. Arthur J. Horowitz (US Geological Survey) for a thorough technical and editorial review. Lastly, we thank Dr. Deborah Pinheiro Dick and technicians Alice Rodrigues Cardoso and Christian Cardoso for their field and laboratory support.
- Sediment chemistry
- Sediment sources
- Trace elements
- Urban hydrology