b'10Integration of geochemical and isotopic biomarker tracers to apportion functionally similar sediment sources at catchment scaleUpadhayay HR1, Micale M1,2 and Collins AL11Sustainable Agriculture Sciences, Rothamsted Research, North Wyke, Okehampton,EX20 2SB, UK.2Department of Agriculture, Universit degli Studi Mediterranea di Reggio Calabria,Feo di Vito 89122 Reggio Calabria - Italy Sediment source apportionment at catchment scale is often limited by: (1) lack of robusttracers to separate potential sources, and; (2) catchment complexity including that associated with land use rotation. Here, we use integrated tracers (geochemistry and compound-specific stable isotopes) in a source fingerprinting approach to differentiate functionally similar sources in a mixed-land use catchment (4.5 km2) in the South-West of England. Source samplingtargeted arable fields, pasture fields, woodland, damaged road verses and stream banks.All source and sediment (deposited and time-integrated suspended) samples were analysed for geochemistry and isotopic biomarkers (alkanes and fatty acids). An advanced Bayesian Isotope Mixing Model (MixSIAR) was used to integrate the tracers for estimating source apportionment. Land use rotation means that pasture and arable sources are interchangeable over the duration of crop rotations with the result that geochemical tracers alone have limited capability forseparating these two sources. Integration of land use-based isotopic biomarkers in the tracer set can significantly improve source differentiation and thereby estimated source apportionment. This study will provide an expanded understanding of tracer utility for source apportionment in lowland agricultural landscapes in the UK and will assist catchment managers in targeting interventions for reducing sediments and associated organic matter or pollutant transfer to the aquatic ecosystem.54'