title: Differentiating the sources of fine sediment, organic matter and nitrogen in a subtropical Australian catchment.
abstract: Understanding the sources of sediment, organic matter and nitrogen (N) transferred from terrestrial to aquatic environments is important for managing the deleterious off-site impacts of soil erosion. In particular, investigating the sources of organic matter associated with fine sediment may also provide insight into carbon (C) and N budgets. Accordingly, the main sources of fine sediment, organic matter (indicated by total organic carbon), and N are determined for three nested catchments (2.5km2, 75km2, and 3076km2) in subtropical Australia. Source samples included subsoil and surface soil, along with C3and C4vegetation. All samples were analysed for stable isotopes (δ13C, δ15N) and elemental composition (TOC, TN). A stable isotope mixing model (SIAR) was used to determine relative source contributions for different spatial scales (nested catchments), climatic conditions and flow stages. Subsoil was the main source of fine sediment for all catchments (82%, SD=1.15) and the main N source at smaller scales (55-76%, SD=4.6-10.5), with an exception for the wet year and at the larger catchment, where surface soil was the dominant N source (55-61%, SD=3.6-9.9), though contributions were dependent on flow (59-680m3/s). C3litter was the main source of organic C export for the two larger catchments (53%, SD=3.8) even though C4grasses dominate the vegetation cover in these catchments. The sources of fine sediment, organic matter and N differ in subtropical catchments impacted by erosion, with the majority of C derived from C3leaf litter and the majority of N derived from either subsoil or surface soil. Understanding these differences will assist management in reducing sediment, organic matter and N transfers in similar subtropical catchments while providing a quantitative foundation for testing C and N budgets.
authors.affiliation: Australian Rivers Institute, Griffith University, 170 Kessels Road, Nathan, Brisbane, QLD 4111, Australia. Electronic address: a.garzongarcia@griffith.edu.au.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Garzon-Garcia
authors.affiliation: Australian Rivers Institute, Griffith University, 170 Kessels Road, Nathan, Brisbane, QLD 4111, Australia; Laboratoire des Sciences du Climat et de l'Environnement, Unité Mixte de Recherche (CEA/CNRS/UVSQ), Gif-sur-Yvette 91198, France. Electronic address: placeby@lsce.ipsl.fr.
authors.forename: J Patrick
authors.initials: JP
authors.lastname: Laceby
authors.affiliation: Australian Rivers Institute, Griffith University, 170 Kessels Road, Nathan, Brisbane, QLD 4111, Australia. Electronic address: j.olley@griffith.edu.au.
authors.forename: Jon M
authors.initials: JM
authors.lastname: Olley
authors.affiliation: Australian Rivers Institute, Griffith University, 170 Kessels Road, Nathan, Brisbane, QLD 4111, Australia. Electronic address: s.bunn@griffith.edu.au.
authors.forename: Stuart E
authors.initials: SE
authors.lastname: Bunn
keywords: Carbon; Erosion; Fingerprinting; Nitrogen; Stable isotopes; Vegetation litter