Temporal dynamics of sediment sources in an urbanizing Mediterranean catchment

The identification of sediment sources is important for catchment management, but few studies have been performed in Mediterranean areas. This study uses a multi-proxy sediment fingerprinting approach to explore sources and dynamics of fluvial sediments in a rapidly urbanizing Portuguese peri-urban catchment. X-Ray Fluorescence was used to characterize the elemental geochemistry of sediments collected within the stream network after three storm events in 2012 and 2015. A range of statistical techniques, including hierarchical cluster analysis, was used to identify discriminant sediment properties and similarities between fine bed-sediment samples of tributaries and downstream sites. Quantification of sediment supply from upstream sub-catchments was undertaken using established sediment fingerprinting approaches. The geochemistry of the sediments was found to be influenced by both lithology and land-use changes. In 2012 the sandstone sub-catchment provided 75% of the <63μm and 94% of the 63μm–125μm and 125μm-2000μm sediment, mostly from an Enterprise Park site undergoing deforestation and construction (covering 5% of the catchment area), with most of the remaining sediment deriving from the construction of a major road (1% of the catchment) in the limestone sub-catchment. In 2015, planned and accidental retention basins below the Enterprise Park and major road sites, respectively, prevented some sediment from reaching the stream network, thereby reducing their importance as sediment sources. Sediment mobilization in urban areas with paved roads was small in comparison, but characterized by high heavy metal concentrations. The sediment fingerprinting approach adopted shows promise in identification of the main sources of sediments, necessary to underpin improved peri-urban management strategies.