An integrated hydrogen and carbon stable isotope approach

12 We present a novel application for quantitatively apportioning sources of organic matter in streambed 13 sediments via a coupled δH and δC compound-specific isotope analysis (CSIA) of leaf wax n14 alkane biomarkers using a Bayesian mixing model. Leaf wax extracts of 13 plant species were 15 collected from across three sub-environments (aquatic, bankside and terrestrial) and four plant 16 functional types (trees, herbaceous perennials and C3 and C4 graminoids) from the agricultural River 17 Blackwater catchment, Norfolk, UK. Nine isotopic ratio and n-alkane chain length fingerprints were 18 derived, which successfully differentiated 93% of individual plant specimens by plant functional type. 19 The δH values were the strongest discriminators of plants originating from different functional 20 groups, with trees (mean values ranging from -208‰ to -164‰) and C3 graminoids (mean values 21 ranging from -259‰ to -221‰) providing the largest contrasts. The δC values provided strong 22 distinction between C3 and C4 plants, and successfully discriminated between natural and cultivated 23 vegetation. n-Alkane chain length metrics complemented hydrogen and carbon isotope data by 24