Investigating changes in proglacial stream suspended sediment concentration and their drivers using large scale remote sensing

Abstract

Glaciers are prolific sediment producers, and quantifying trends in proglacial suspended sediment concentration (SSC) is critical for understanding the evolution of sediment dynamics in glacierized systems, a task impeded by sparse in situ observations in these often-remote environments. In this study, we use Landsat-derived spectral reflectance to quantify how SSC changed between 1984 and 2023 across a range of proglacial river systems (n = 54) in Alaska and northwestern Canada. We investigated how observed SSC changes were related to upstream proglacial lakes, as well as glaciological factors. We found that 54 % of all study sites underwent statistically significant SSC changes (median rate of statistically significant change = −1.8 mg L⁻¹ yr⁻¹ or − 0.7 % yr⁻¹; IQR = −8.4 to 0.5 mg L⁻¹ yr⁻¹). Streams below proglacial lakes are more likely to have significant changes than systems without lakes (60 % of sites with upstream lakes vs 42 % of sites without upstream lakes). SSC declines dominate statistically significant trends for sites with upstream lakes, while increasing SSC is dominant for rivers with no upstream proglacial lake. We perform statistical analyses to investigate potential physical drivers of SSC change and find a direct association between glacier area and a site's median SSC as one of the few significant correlations. Proglacial lake area and its change are poor predictors for both downstream median SSC and SSC change. Together, these findings show clear changes in sediment dynamics in glacierized watersheds over ~40 years, with proglacial lakes playing a notable but complicated role in downstream sedimentary processes.