Quantifying sources of suspended sediment in three size fractions

Abstract

Purpose Identifying of the sources, stores and pathways of sediments in a catchment is essential to accurately target management actions designed to reduce sediment delivery to receiving waters. Fingerprinting the source of sediment using geochemical properties has increasingly been accepted as an accurate approach for quantifying the contribution of different sources to river sediment discharge. In this study, we seek to examine the effect of particle size and location of the sources on their contribution to suspended sediments. Materials and methods Geochemical tracers (n=41) were employed to calculate proportional contributions of sediment to Emu Creek, a predominantly pastoral catchment (911 km 2 ) in south-eastern Queensland, Australia. The study focused on two high flow events (10-and 6-year return periods) and some lower flow events which occurred during the 18 months from October 2011 to March 2013. Source contributions were determined at eight spatially distributed sites in major tributaries and along the main channel of Emu Creek. Source determination at the in-stream sites was done using end member samples (based on the underlying rock type) collected upstream of the site of interest, thus indicating how different sources dominate at different locations downstream. To examine whether different size fractions shared similar provenances, three size fractions of both source and suspended samples including fine silt and clay (<10 μm), silt (10-63 μm) and fine sand (63-212 μm) were analysed. Results and discussionThe source apportionment results using the distribution mixing model indicate that particle size and location of sources within a catchment are major factors that affect the measured contribution of sources to suspended sediments. The closer a suspended sediment sampling site is to a potential source, the more likely it is that source of sediment will dominate the material being sampled. Conclusions For all size fractions, proximal sources of sediment make a higher contribution to suspended sediments than distal sources. This indicates that management actions should be focused on the more proximal sources to the point of interest/impact. Although proximal soil sources were major contributor of sediments in all three size fractions, the percentage of contribution greatly vary in different size fractions, emphasising the need to trace the size fraction which is causing the downstream problems.

Coarse and fine sediment sources in nested watersheds with eucalyptus forest

“…In a nested watershed with distint geological materials, Haddadchi et al () observed proximal sources tended to contribute more to a given river sampling point than more distal sources. Minella et al () observed that the budget calculations indicate that rural small watershed had a sediment delivery ratio of ∼15%, whereas in our watershed study, a sediment delivery ratio was only 0.71% (Rodrigues, ).…”

“…forests on water and land resources are not well known, and there are uncertainties about the ability of production land to support planted forests without degrading those natural (Reichert et al, ; Rodrigues et al, ). Sediment in suspension and bedload sediment cause environmental problems (Bilotta & Brazier, ; Haddadchi, Olley, & Pietsch, ; Owens et al, ). Sediment sources identification contributes to maintaining natural resources quality in forest production systems, the management of resources, and the establishment of proper use and management techniques to limit or reduce degradation, especially on the watershed scale.…”

“…Coarse sediment fractions are transported to greater distances only during intense flow and to very short distances during low flow, whereas finer fractions are transported to long distances in low intensity and energy flow events. The processes of disaggregation, transport, and deposition are all size‐selective (Koiter, Owens, Petticrew, & Lobb, ), and this selectivity depends on soil, erosion, and rain parameter in the watershed (Haddadchi et al, ).…”

“…For sediment sources correct identification, we should consider the proportion of individual sources to the sediment mixture, where erosive processes in the watershed cause time and spatial variability in sediment type and size distribution (Minella, Merten, Walling, et al, 2009) and of rock-type sources (Haddadchi et al, 2015) and processes of soil formation. Furthermore, identification of coarser sediment sources has received very little attention.…”

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

“…Although this difference seems minor, it was significant and likely mitigated by the 71 particulate matter samples. In comparison, Haddadchi et al (2015) reported that there was an absolute mean difference of 14% (SD 8%) between the <10 mm and the 10e63 mm and 13% (SD 9%) between the <10 mm and the 63e212 mm fraction. The larger mean differences and standard deviations reported by these authors likely relates to the fact that they compared isolated fraction ranges, they used elemental geochemistry which is inherently more complex, and they modelled only 8 sediment samples for comparison.…”