The development of rare earth element-labelled potassium-depleted clays for use as cohesive sediment tracers in aquatic environments

Abstract

Purpose Understanding the transport behaviour of fine cohesive sediment is fundamental to the sustainable management of aquatic environments. Sediment tracing techniques are widely used for measuring the transport pathways of sand-sized material in the field. However, the development of tracers, including geochemically labelled clays, for fine, cohesive sediment is more problematic. Such tracers should have chemical signatures that can be easily detected following significant dilution in the field and should remain constant for the duration of the tracer study. Materials and methodsWe have examined the potential of rare earth element (REE)-labelled phlogopite and hydrobiotite as cohesive sediment tracers. Clays were first treated with sodium tetraphenylborate to extract interlayer potassium and enhance their cation exchange capacity. Ho, La and Sm were then sorbed to the clays in batch experiments. Desorption of the chemical signature in both fresh and saline conditions was examined after 1 and 10 days. Results and discussion Potassium extraction enhanced REE sorption, resulting in REE concentrations in excess of 40,000 mg kg −1 in the labelled clays, and these signatures should be easily detected following dilution in the aquatic environment. In both fresh and saline conditions, over 90% of the tracer signature was retained over a 1-day period. However, over longer time scales, there was considerable loss of the REE signature. Conclusions Over short time scales, there is considerable potential to use these materials as cohesive sediment tracers. Over longer time scales, although much of the label is lost, the tracers could still provide qualitative information identifying net sediment transport pathways.

Recent advances and future directions in soils and sediments research

“…Blake et al 1999;Saari et al 2010), and in developing new tracers, such as rare earth elements (REE) and natural and artificial fluorescence (e.g. Polyakov and Nearing 2004;Granger et al 2007Granger et al , 2011Stevens and Quinton 2008;Spencer et al 2011). Many of these newer tracers are showing considerable promise, particularly for tracing sediment movement on hillslopes, although further refinement and testing are required to prove their suitability at medium to large spatial scales such as the landscape and river basin scales, and at the interface between freshwater and brackish/saltwater environments.…”

Everything goes somewhere; tracking the movement of contaminated sediments in an industrialised estuary using dual signature sediment tracers

“…labelled with one or more signatures in order that they may be unequivocally identified following release [1,2]. Measurable and uniquely identifiable signatures have in the past included the use of radioactive tracers [3,4] and Rare Earth elements [5], fluorescent coated sands [6], fluorescent silts [7][8][9]. Synthetic, polymer-based have also been developed (e.g.…”

From green to transparent waters : Managing eutrophication and cyanobacterial blooms by geo-engineering

“…Contrary to Spencer et al 2011who found substantially more La desorbed after day ten than day one, we did not observe a temporal effect in FLa concentration. However, Spencer et al (2011) found the similar leaching behaviour in freshwater suggesting a potentially additional labile La component not present within the bentonite clay interlayers. Yuan et al (2009) reported a La release from La modified clays of 0.006% at pH 6.1, and of 0.0007% at pH 7.85 and referred to it as the trivalent (free) La-ion.…”