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Light exposure along particle flowpaths in large rivers

July 26, 2019

Sunlight is a critical resource in aquatic systems driving photosynthesis, photodegradation of organic matter and contaminants, animal behavior, and the activity of human pathogens. In rivers, solutes, materials, and organisms are turbulently mixed across the water column during downstream transport and exposed to highly variable sunlight. However, there are no measurements of suspended particles' sunlight exposure during downstream transport to characterize this variability, and it is unclear if current measurement approaches and optical theory capture the light exposure of suspended particles. We deployed neutrally buoyant drifters and stationary buoys in the Upper Mississippi (WI, U.S.A.) and Neuse Rivers (NC, U.S.A.) to measure underwater sunlight from the perspective of suspended particles. In our study sites, underwater sunlight varied more along flowpaths measured by drifters than over time measured by fixed‐site buoys; sunlight exposure along flowpaths was dominated by bursts of light (sunflecks) that accounted for 62–99% of the cumulative sunlight exposure; and modeled sunlight exposure using optical theory was consistently 56–1700% higher than measured sunlight exposure along flowpaths. Our results suggested that suspended particles in the study reaches experienced darker conditions than predicted and have important implications for how to quantify underwater sunlight in rivers.

Citation Information

Publication Year 2020
Title Light exposure along particle flowpaths in large rivers
DOI 10.1002/lno.11256
Authors John R. Gardner, Scott H. Ensign, Jeffrey N. Houser, Martin W. Doyle
Publication Type Article
Publication Subtype Journal Article
Series Title Limnology and Oceanography
Series Number
Index ID 70208348
Record Source USGS Publications Warehouse
USGS Organization Upper Midwest Environmental Sciences Center