Identifying subsoil sediment sources with carbon and nitrogen stable isotope ratios

Abstract

Abstract:Increased sediment loads from accelerated catchment erosion significantly degrade waterways worldwide. In the South East Queensland region of Australia, sediment loads are degrading Moreton Bay, a Ramsar listed wetland of international significance. In this region, like most parts of coastal Australia, sediment is predominantly derived from gully and channel bank erosion processes. A novel approach is presented that uses carbon and nitrogen stable isotope ratios and elemental composition to discriminate between these often indistinguishable subsoil sediment sources. The conservativeness of these sediment properties is first tested by examining the effect of particle size separation (testing for consistency during transport) and the effect of sampling at different times (testing for temporal source consistency). The discrimination potential of these sediment properties is then assessed with the conservative properties, based on the particle size and temporal analyses, modelled to determine sediment provenance in three catchments. Nitrogen sediment properties were found to have significant particle size enrichment and high temporal variance indicative of non-conservative behaviour. Conversely, carbon stable isotopes had very limited particle size and temporal variability highlighting their suitability for sediment tracing. Channel erosion was modelled to be a significant source of sediment (μ 51%, σ 9%) contrasting desktop modelling research that estimated gully erosion is the predominant sediment source. To limit the supply of sediment to Moreton Bay, channel bank and gully erosion must both be targeted by sediment management programs. By distinguishing between subsoil sediment sources, this approach has the potential to enhance the management of sediment loads degrading waterways worldwide.

Do forests represent a long-term source of contaminated particulate matter in the Fukushima Prefecture?

“…C, N, C þ N) to quantify source contributions. The discrimination potential of these particulate matter parameters was similar to other applications in sediment tracing research (Fox and Papanicolaou, 2007;Laceby et al, 2015b;Mukundan et al, 2010;Papanicolaou et al, 2003).…”

“…The only properties that were not enriched were TOC and TN in forest soils and d 15 N in cultivated sources. Laceby et al (2015b) also reported a similar significant, though minor enrichment for d 13 C across multiple particle size fractions. These authors also reported a significant enrichment in TOC and TN when combining multiple source samples (e.g.…”

“…Three combinations of particulate matter parameters were modelled: 1) TN and d 15 N (the N model); 2) TOC and d 13 C (the C model); 3) all 4 properties (the C þ N model). These combinations were used to quantify relative source contributions with a concentration weighted distribution modelling approach (Laceby et al, 2015b;Le Gall et al, 2016):…”

“…cultivated, subsoil, forest) are quantified with the analyses and modelling of total organic carbon (TOC), total nitrogen (TN) and carbon and nitrogen stable isotope ratios (d 13 C and d 15 N). These parameters have been effectively used to trace the source of sediment and particulate matter (Fox and Papanicolaou, 2007;Laceby et al, 2015b;McConnachie and Petticrew, 2006). Soil d 15 N increases with depth in the soil profile (Amundson et al, 2003;Natelhoffer and Fry, 1988) whereas TOC and TN decrease Owens et al, 2006).…”

A 300-year record of sedimentation in a small tilled catena in Hungary based on δ13C, δ15N, and C/N distribution

“…The δ N values also could have a distinct vertical distribution within a soil/sediment profile, depending on differences in the sediment and decomposition rates. Therefore, they could be a useful tracer for sediment fingerprinting, especially for the identification of sediments eroded by gully or subsoil erosion (Laceby et al 2015).…”