Determining contemporary and historical sediment sources in a large drainage basin impacted by cumulative effects: the regulated Nechako River, British Columbia, Canada

Abstract

Purpose Sediment dynamics in most large river basins are influenced by a variety of different natural and anthropogenic pressures, and disentangling these cumulative effects remains a challenge. This study determined the contemporary and historical sources of fine-grained (< 63-μm) sediment in a large, regulated river basin and linked changes in sources to activities in the basin. The river has seen declines in chinook salmon, sockeye salmon, and the endangered Nechako white sturgeon populations, and sediment (both fine-grained and sands) transport and deposition have been identified as potential causes of these declines. Materials and methods Samples of suspended sediment and potential source materials were collected from numerous sites distributed throughout the upper Nechako River Basin in British Columbia, Canada. A floodplain sediment core was also collected in order to reconstruct sediment sources over the last~70 years. Discriminating fingerprint properties were used within the MixSIAR model to apportion sources among sub-basins and land-use types. Results were compared to records of precipitation and Nechako River discharge trends, and to changes in landscape development. Results and discussion Contributions from the erosion of channel banks dominated the suspended sediment load at most sites. Changes in sediment sources during the 2015 field season reflected snowmelt and patterns of water release from the Nechako Reservoir that affected the sediment-carrying capacity of tributaries and the Nechako River main stem. Spatial variations in 2015 also reflected the distribution of land use (e.g., forested or agricultural land) as well as topography (e.g., slope steepness). Over the last~70 years, variations in sediment sources and the characteristics of the sediment (e.g., organic matter content and particle size composition) were linked to the construction of the Kenney Dam (operational in 1954) and the impacts of deforestation by the forestry and agricultural industries. Superimposed on these have been wildfires and a major mountain pine beetle infestation leading to higher erosion rates in the affected areas. Conclusions The sediment source fingerprinting technique, in combination with historical information on the hydrometeorology and the land use and river management in the basin, has provided valuable information with which to understand sediment dynamics in the Nechako River Basin. Such an approach can help to disentangle how large river systems respond to a combination of natural and anthropogenic pressures.

Preface—evaluating the response of critical zone processes to human impacts with sediment source fingerprinting

“…Progressing downstream, there was an increase in sediment derived from erosion processes on agriculture and forested landscapes consistent with the changing land use in the catchment. Gateuille et al (2019) also found that the construction of a dam in the 1950s resulted in a significant alteration of the sediment transport capacity in the Nechako River Basin, resulting in a change in sediment source dynamics. Overall, Gateuille et al (2019) demonstrated that the sediment source fingerprinting technique can be utilized to investigate how the cumulative effects of anthropogenic and natural disturbances affect sediment source dynamics in a large river basin over short (i.e., annual) and longer (i.e., decadal) temporal scales.…”

“…Gateuille et al (2019) also found that the construction of a dam in the 1950s resulted in a significant alteration of the sediment transport capacity in the Nechako River Basin, resulting in a change in sediment source dynamics. Overall, Gateuille et al (2019) demonstrated that the sediment source fingerprinting technique can be utilized to investigate how the cumulative effects of anthropogenic and natural disturbances affect sediment source dynamics in a large river basin over short (i.e., annual) and longer (i.e., decadal) temporal scales. Gellis et al (2019) apportion sediment using elemental analysis and the sediment fingerprinting approach and age-date sediment with fallout radionuclides in the agricultural Walnut Creek Basin (Iowa, USA).…”

“…Importantly, Mahoney et al (2019) provide six important conclusions for helping develop these new coupled models that will help drive future research programs. Gateuille et al (2019) combine fallout radionuclides ( 137 Cs and 210 Pb xs ) with elemental geochemistry to investigate the main sediment sources (i.e., stream bank, agricultural, and forest) in the Nechako River Basin in British Columbia, Canada. Not only did these authors investigate how these erosion sources vary spatially across this catchment, but they also investigated how these sources changed over time based on the analyses of a sediment core from an island on the main stem of the Nechako River.…”

“…To further advance our understanding of the critical zone, we believe it is important for sediment source fingerprinting research to capitalize on combining multiple sediment source fingerprints to explicitly investigate Earth system science processes. In particular, the multi-fingerprint research in this special issue that simultaneously incorporates temporal fingerprints (e.g., 7 Be, 210 Pb xs ) with erosion process and spatial fingerprints (Gateuille et al 2019;Gellis et al 2019) outlines a potentially effective technique to investigate the response of critical zone processes to anthropogenic activities over multiple temporal scales. For example, short-term fingerprints such as 7 Be may provide information on erosion processes occurring on intra-annual temporal scales or even the individual rainfall event scale.…”

The representation of sediment source group tracer distributions in Monte Carlo uncertainty routines for fingerprinting: An analysis of accuracy and precision using data for four contrasting catchments

“…For example, Motha, Wallbrink, Hairsine, and Grayson () and Collins, Walling, Webb, and King () used source group means and standard deviations and this approach remains widely used in international literature (e.g. Aliyanta & Sidauruk, ; Brosinsky, Foerster, Segl, & Kaufmann, ; Chen, Fang, & Shi, ; Dahmardeh Behrooz, Gholami, Telfer, Jansen, & Fathabadi, ; Gateuille et al, ). Krause, Franks, Kalma, Loughran, and Rowan (), Wilkinson et al (); Wilkinson, Hancock, Bartley, Hawdon, and Keen (), Haddadchi, Olley, and Pietsch (, ), Laceby and Olley () and Palazón et al () all used a Student's t ‐distribution which gave more weighting to the tails of the distribution than a normal distribution and was considered more appropriate when sample numbers were low.…”