Sediment sources, sediment dis-connectivity and rates of denudation and land-to-sea solute and sedimentary fluxes in selected Mediterranean catchment systems in eastern Spain

The Pou Roig-Quisi and Mascarat catchments in eastern Spain (Calpe) are located as neighbouring catchment systems in a Mediterranean, mostly mountainous and anthropogenically modified environment. The catchments drain directly into the Mediterranean sea. The selected study areas are characterized by a mild Mediterranean climate with a mean annual air temperature of ca. 18°C and a mean annual precipitation sum around 400 mm (measured slightly above sea level). During the coldest months (January, February) frost and snow can occur in the highest elevations although the mountain ranges are situated close to the coast. In contrast, maximum summer temperatures (July, August) can easily exceed 30°C and south-facing hillslopes and rockwalls are exposed to high solar radiation. The lithology in the area is clearly dominated by marine limestones. Elevation ranges from sea level up to 1126 m a.s.l. Geomorphological processes include chemical and mechanical weathering, rock falls, debris flows, splash and slope wash, fluvial erosion, and fluvial solute, suspended sediment and bedload transport.

This ongoing GFL research is focussed on sediment sources, sediment (dis-)connectivity, spatiotemporal variability and rates of contemporary denudational processes and land-to-sea solute and sedimentary fluxes. Our work includes detailed field and remotely sensed geomorphological mapping and computing of morphometric catchment parameters combined with the extended statistical analysis of high-resolution meteorological and rock temperature data and the observation and monitoring of sediment-transfer, runoff and fluvial transport events. In the field, we are using a combination of different observation, monitoring and sampling techniques, including different tracer techniques and sediment traps in stream channels, remote time-laps cameras, and event-based high-resolution field monitoring combined with frequent water and sediment samplings. Sediment connectivity is significantly reduced by extended terraced areas within the catchment systems. Sediment transfers, the intermittent runoff, and fluvial transport and land-to-ocean fluxes are almost entirely controlled by pluvial events. High runoff during extreme rainfall events forms a relevant hazard particularly in the lowest parts of the catchment systems. Mechanical fluvial denudation shows a higher spatiotemporal variability than chemical denudation. Altogether, drainage-basin wide chemical denudation dominates over drainage-basin wide mechanical fluvial denudation which is explained by partly limited sediment availability, long-term sediment storage at defined locations, and by the predominant marine limestones found in the catchment areas.