EARTH SURFACE PROCESSES AND LANDFORMS Earth Surf. Process. Landforms 34, 929–940 (2009) Copyright © 2009 John Wiley & Sons, Ltd. Published online 2 March 2009 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/esp.1777 John Wiley & Sons, Ltd. Chichester, UK ESP Earth Surface Processes and Landforms EARTH SURFACE PROCESSES AND LANDFORMS Earth Surface Processes and Landforms The Journal of the British Geomorphological Research Group Earth Surf. Process. Landforms 0197-9337 1096-9837 Copyright © 2006 John Wiley & Sons, Ltd. John Wiley & Sons, Ltd. 2006 Earth Science Earth Science 9999 9999 ESP1777 Research Article Research Articles Copyright © 2006 John Wiley & Sons, Ltd. John Wiley & Sons, Ltd. 2006 Suspended sediment transport in a small Mediterranean agricultural catchment Suspended sediment transport Joan Estrany, 1 * Celso Garcia 1 and Ramon J. Batalla 2,3 1 Department of Earth Sciences, University of the Balearic Islands, Palma de Mallorca, Spain 2 Department of Environmental and Soil Sciences, University of Lleida, Lleida, Spain 3 Forestry and Technology Centre of Catalonia, Solsona, Spain Received 20 May 2008; Revised 30 July 2008; Accepted 12 November 2008 * Correspondence to: Joan Estrany, Department of Earth Sciences, University of the Balearic Islands, E-07122 Palma de Mallorca, Spain. E-mail: joan.estrany@uib.cat ABSTRACT: The aim of this study is to analyze suspended sediment transport in a Mediterranean agricultural catchment under traditional soil and water conservation practices. Field measurements were conducted in Can Revull, a small ephemeral catchment (1.03 km 2 ) on the island of Mallorca. This study uses continuous turbidity records to analyse suspended sediment transport regimes, construct and interpret multiple regression models of total suspended sediment concentration (SSC) and of SSC related to stormflow discharge, and assess the sediment loads and yields of three hydrological years (2004–2005 to 2006–2007). An annual average SSC of 17.3 mg l -1 , with a maximum of 2270 mg l -1 , was recorded in the middle of the winter period when rainfall intensities are high and headwater slopes are ploughed and thus bare. Strong seasonal contrasts of baseflow dynamics associated with different degrees of dilution provide a large scatter in SSC and in the derived rating curves, reflecting that other factors control the supply of suspended sediment. Multiple regression models identify rainfall intensity as the most significant variable in sediment supply. However, under baseflow conditions, physical and biological processes generate sediment in the channel that is subsequently removed during high flow. In contrast, when baseflow is not present, rainfall intensity is the only process that supplies sediment to the channel, mostly from hillslopes. Considering the study period as average in terms of total annual rainfall and intensities, suspended sediment yields were an order of magnitude lower than those obtained in other Mediterranean catchments, a factor that can be related to the historical use of soil conservation practices. Copyright © 2009 John Wiley & Sons, Ltd. KEYWORDS: Suspended-sediment transport; multiple regressions; magnitude and frequency; Mediterranean; agricultural catchment; Mallorca island Introduction Many studies on sediment dynamics and transport have been conducted in forested Mediterranean drainage basins (e.g. Inbar, 1992; Batalla et al., 1995; Llorens et al., 1997; Serrat, 1999; García-Ruíz et al., 2000; Achite and Ouillon, 2007), but despite this previous work, little attention has been paid to sediment transport in agricultural catchments where land use is the major factor affecting erosion processes (Douglas, 1993). Typically, it is necessary to establish a sediment budget to integrate the processes responsible for generating and transporting the sediment of the overall catchment (e.g. Dietrich and Dunne, 1978; Trimble, 1983; Slaymaker, 2003; Walling and Collins, 2008), including implementing soil and water conservation practices that result in reduced sediment loads (cf. Quine et al., 1992). In many situations, these practices are aimed at increasing moisture retention and storage and reducing the on-site impacts of soil erosion linked to reduced soil productivity and crop yields (i.e. Walling, 2006). Histori- cally, traditional soil and water conservation practices, such as terraces and sloping walls on steep slopes (e.g. Grimalt et al., 1992; Zgaier and Inbar, 2005) and under-drainage systems on gentle slopes (cf. Estrany et al., submitted for publication) have been applied to effectively protect cultivated land. Suspended sediment (SS) yields represent the sum of the erosion produced by all active sources within a catchment, although yields cannot be used as reliable indicators of total hillslope erosion due to the difficulties in quantifying sediment storage and identifying the mixture of sources (e.g. Walling and Collins, 2000). SS yield from periodic or infrequent concen- tration data can be computed using one of the approximately 20 existing interpolation- and extrapolation-based load algorithms (cf. Phillips et al., 1999). Interpolation methods make the assumption that the concentration measured in a water sample is representative of conditions in the river for the period between sampling occasions. Extrapolation procedures classically develop a rating relationship between the SS concentration (SSC) and water discharge (Q) based on collecting infrequent samples of SSC. This relationship is then applied to a detailed flow record in order to calculate loads for the period of interest (e.g. Webb et al., 1997). It must be considered, however, that reliable rating curves between Q and SSC in areas with strong seasonal contrast cannot always be established, suggesting that runoff energy is not a predominant factor in soil erosion processes (e.g. Sutherland and Bryan, 1989). Consequently, some authors (e.g. Walling, 1974; Richards and Moore, 2003; Seeger et al., 2004; Francke et al., 2008) have derived multi- variate forms of these rating curves, while others have tried to