Author(s): Justus Hargett; Jon Czuba

Linked Author(s):

Keywords: Sediment; Embeddedness; Gravel bed streams; Freeze thaw cycling; Urbanization; Temporal variation

Abstract: Globally, excess fine sediment (< 2 mm diameter) is recognized as a leading pollutant to freshwater systems. In the United States alone over 250,000 stream kilometers are indicated as impaired by sediment. Furthermore, habitat protections are under threat in the United States that if enacted would be further damaging to endangered and threatened species (Czuba, 2025). Excess fine sediment accumulation can degrade aquatic habitat by filling interstitial space between coarser substrates, causing decreases in surface area, porosity, oxygenation, and habitat reduction for benthic fish, salmonids, and macroinvertebrates (Dubuis and De Cesare, 2023; Wharton et al., 2017; Jones et al. 2011; Kemp et al., 2011). To quantify this degree of fine sediment accumulation around coarser particles in streambeds, ecologists and engineers use a metric often referred to as embeddedness. Physical techniques for measuring embeddedness can be labor intensive and spatially limited. Recent studies by Czuba et al. (2022) have established a relationship between bankfull shear velocity and embeddedness. Building on this concept, Smith et al. (rev) incorporated geospatial data to develop models that remotely estimate embeddedness for the conterminous United States. However, physical measurements are limited to conditions at a single point in time and remote estimates are limited to the average stream embeddedness. Fluvial systems are incredibly dynamic, with stream flow and environmental factors constantly changing. Thus, embeddedness can be expected to fluctuate temporally. In altered watersheds, such as those affected by urbanization and agriculture, these fluctuations can be exacerbated. The goal of this study was to discern how environmental factors contribute to temporal fluctuations in embeddedness and benthic habitat quality in an urbanized watershed. Additionally, we wanted to assess the accuracy of the embeddedness model by Smith et al. (rev) in the face of large temporal variability. Our study area was a heavily monitored stream restoration site located on Stroubles Creek in Blacksburg, Virginia in the United States. The lower extent of this second order stream is typical of those in the Ridge and Valley ecoregion defined by the US Environmental Protection Agency (USEPA). However, the upstream watershed of our site drains much of the Blacksburg area with a resulting drainage composed of 80% urbanized area with the remainder being most ly agricultural pasture and crop land. In the Virginia Ridge and Valley alone, over 2,600 streams of similar size have watersheds comprised of over 75% urban-agriculture combination. With global trends of urbanization and a growing need to supply food, this number is expected to grow. We completed intensive embeddedness surveys every 2-3 weeks from April 2022 to November 2024 to develop a detailed time series of incremental changes in embeddedness, flow regime, and temperature to examine how these factors influenced embeddedness fluctuations. We found that embeddedness displayed substantial patterns in temporal variability with fluctuations between 20 and 80% embeddedness.

DOI: https://doi.org/10.64697/iahr.proc.ise2026.abs.232

Year: 2026