In situand high frequency monitoring of suspended sediment properties using a spectrophotometric sensor

Abstract

It is well known that sediment properties, including sediment-associated chemical constituents and sediment physical properties, can exhibit significant variations within and between storm runoff events. However, the number of samples included in suspended sediment studies is often limited by time-consuming and expensive laboratory procedures after stream water sampling. This restricts high frequency sampling campaigns to a limited number of events and reduces accuracy when aiming to estimate fluxes and loads of sediment-associated chemical constituents. In this study, we address the potential of a portable ultraviolet-visible spectrophotometer (220-730 nm) to estimate suspended sediment properties in a resource efficient way. Several field deployable spectrophotometers are currently available for in-stream measurements of environmental variables at high temporal resolution. These instruments have primarily been developed and used to quantify solute concentrations (e.g. dissolved organic carbon and NO 3 -N), total concentrations of dissolved and particulate forms (e.g. total organic carbon) and turbidity. Here we argue that light absorbance values can be calibrated to estimate sediment properties. We present light absorbance data collected at 15-min intervals in the Weierbach catchment (NW Luxembourg, 0.45 km 2 ) from December 2013 to January 2015. In this proof-of-concept study, we performed a local calibration using suspended sediment loss-on-ignition (LOI) measurements as an example of suspended sediment property. We assessed the performance of several regression models that relate light absorbance measurements with the percentage weight LOI. The MM-robust regression method presented the lowest standard error of prediction (0.48%) and was selected for calibration (adjusted r 2 = 0.76 between observed and predicted values). The model was then used to predict LOI during a storm runoff event in December 2014. This study demonstrates that spectrophotometers can be used to estimate suspended sediment properties at high temporal resolution and for long-time spans in a simple, non-destructive and affordable manner.

Sediment transport modelling in riverine environments: on the importance of grain-size distribution, sediment density, and suspended sediment concentrations at the upstream boundary

“…The threshold for initiating the motion of non-cohesive sediment is based on the ratio of a critical bed shear stress and the submerged grain weight. Many studies proposed less empirical parameterizations based on the weight and (angular) surface of the sediment grain but eventually showed results quite similar to those obtained when using the original Shields curve (Zanke, 2003;Miedima, 2010). Consequently, one can argue that the Shields curve can still be considered a good means for assessing the threshold of non-cohesive sediment mobility.…”

Fingerprinting the sources of water-mobilized sediment threatening agricultural and water resource sustainability: Progress, challenges and prospects in China

“…The diversity of fingerprint properties has expanded continuously, representing an important methodological development of the fingerprinting approach driven by the expansion in the range of sources that need to be discriminated and recent advances in analytical capabilities (Walling, 2013), such as mid-, near-infrared and ultraviolet visible spectroscopy (Reeves and Smith, 2009;Martínez-Carreras et al, 2016). To date, common tracer properties applied in fingerprinting studies include physical properties (e.g., particle size, density and color) (Martínez-Carreras et al, 2010;Erskine, 2013;Barthod et al, 2015), geochemical constituents (e.g., major, minor, rare earth elements) (Theuring et al, 2015), geogenic (e.g., 40 K, 238 U, 232 Th) radionuclides, fallout (e.g., 137 Cs, excess 210 Pb, 7 Be) radionuclides (Shala et al, 2017), mineral magnetism (Rowntree et al, 2017), bulk stable isotopes (e.g., δ 13 C, δ 15 N ) (Parnell et al, 2010;McCarney-Castle et al, 2017), and biomarkers (e.g., fatty acids, n-alkanes) Upadhayay et al, 2017).…”

Sediment transport modelling in riverine environments: on the importance of grain-size distribution, sediment density and boundary conditions

“…SSC is generally measured punctually whereas models require continuous input data time series. In this context, turbidity data is often recognized as a good proxy for estimating continuous the time series of SSC (Martínez-Carreras et al, 2016). In this 15 study, the turbidity is monitored every 5 minutes at the downstream boundary using an YSI 600 OMS turbidimeter.…”

“…dredged and removed from them (Kanbar et al, 2017)., During flood events, the remobilization of these riverbed sediments can strongly impact water and even soil quality (Carter et al, 2006;Hissler and Probst, 2006;Martínez-Carreras et al, 2016).…”