High\xa0frequency un-mixing of soil samples using a submerged spectrophotometer in a laboratory setting\u2014implications for sediment fingerprinting

Niels F Lake,Adrian L Collins,Núria Martínez-Carreras,Peter J Shaw

doi:10.1007/s11368-021-03107-6

Abstract

PurposeThis study tests the feasibility of using a submersible spectrophotometer as a novel method to trace and apportion suspended sediment sources in situ and at high temporal frequency.MethodsLaboratory experiments were designed to identify how absorbance at different wavelengths can be used to un-mix artificial mixtures of soil samples (i.e. sediment sources). The experiment consists of a tank containing 40 L of water, to which the soil samples and soil mixtures of known proportions were added in suspension. Absorbance measurements made using the submersible spectrophotometer were used to elucidate: (i) the effects of concentrations on absorbance, (ii) the relationship between absorbance and particle size and (iii) the linear additivity of absorbance as a prerequisite for un-mixing.ResultsThe observed relationships between soil sample concentrations and absorbance in the ultraviolet visible (UV–VIS) wavelength range (200–730 nm) indicated that differences in absorbance patterns are caused by soil-specific properties and particle size. Absorbance was found to be linearly additive and could be used to predict the known soil sample proportions in mixtures using the MixSIAR Bayesian tracer mixing model. Model results indicate that dominant contributions to mixtures containing two and three soil samples could be predicted well, whilst accuracy for four-soil sample mixtures was lower (with respective mean absolute errors of 15.4%, 12.9% and 17.0%).ConclusionThe results demonstrate the potential for using in situ submersible spectrophotometer sensors to trace suspended sediment sources at high temporal frequency.

Highlights

Suspended sediment (SS) plays an essential role in the hydrological, geomorphological and ecological functioning of aquatic ecosystems (Owens et al 2005; Bilotta and Brazier 2008; Wohl et al 2015; Vercruysse et al 2017)
The results demonstrate the potential for using in situ submersible spectrophotometer sensors to trace suspended sediment sources at high temporal frequency
The measured concentrations inside the tank were generally lower than the theoretical concentrations intended (Fig. 3); measured concentration decreased with increasing particle size

Summary

Introduction

Suspended sediment (SS) plays an essential role in the hydrological, geomorphological and ecological functioning of aquatic ecosystems (Owens et al 2005; Bilotta and Brazier 2008; Wohl et al 2015; Vercruysse et al 2017). Sediment fingerprinting is one direct approach to estimating SS contributions from catchment sources. This approach compares properties of potential source materials with properties of SS, using distinct diagnostic signatures or so-called composite fingerprints comprising several constituent properties These properties are selected on the basis that they are clearly distinctive between individual sources, allowing for the un-mixing of SS to estimate source proportions

Methods

Results

Discussion

Conclusion