A physical and social analysis of how variations in no-till conservation practices lead to inaccurate sediment runoff estimations in agricultural watersheds

Abstract

Although agricultural influence on sediment runoff is well known, determining what sources of sediment contribute most to stream impairment has remained challenging in agricultural watersheds across the world. Therefore, methods to distinguish the sources of sediment in streams are warranted, particularly methods that incorporate information on anthropogenic practices that affect sediment runoff. In this study we examined how variations in conservation practices contributed to unidentified sources of sediment in an agricultural watershed, where 49% of sediment was sourced from agricultural fields that were assumed to have little erosional runoff. We found that variations in the way no-till agriculture is practiced significantly affected estimates of erosion in the watershed and also led agency managers to overlook sources of sediment in the watershed. In doing this research, we provide a methodological framework that may be useful to researchers who are attempting to identify sources of sediment erosion in watersheds impacted by variations in agricultural conservation practices.

A critical physical geography of no‐till agriculture: Linking degraded environmental quality to conservation policies in an Oregon watershed

“…Glyphosate was detected in 81% of the soil and water samples we collected, at levels above the thresholds put in place to protect ecological and human health. We also found that 49% of sediment came from fields managed with no-till and 51% came from eroding channel banks (Malone and Polyakov 2020). We turn now to our qualitative data to understand the social and political economic processes that can help explain these extreme levels of glyphosate and sediment in the watershed.…”

“…Knowing that herbicide use—and glyphosate, in particular—had increased alongside the expansion of no‐till in the Fifteenmile Watershed, and that sediment runoff continued to be an issue despite the widespread adoption of no‐till, we conducted a suite of interrelated research projects to evaluate the extent of both herbicide and sediment runoff issues. While the methods and results of these studies are described in detail elsewhere (Malone and Foster 2019; Malone and Polyakov 2020), we synthesize them here, as they are central to our CPG approach.…”

“…To identify potential sediment sources, we employed a mixed-methods approach that integrated a cesium-137 sampling study with qualitative data collected via interviews and a survey. Cesium-137, a radioactive isotope present in soils worldwide as a result of atmospheric nuclear testing during the 1950s and 1960s (Nagle and Ritchie 2003), allowed us to identify which sources of sediment contributed the most to streams in the watershed (Malone and Polyakov 2020). For our study, we sampled for cesium-137 on multiple fields on five different farms under no-till management (Figure 4).…”

Achieving cleaner water for UN sustainable development goal 6 with natural processes: Challenges and the future

“…In fact, in the short term, conservation agriculture may prove deficit-inducing (Afshar et al, 2022) and require increased use of herbicide (Laukkanen and Nauges, 2011) as well as the capital investment. There can also be some variability on the improvement expected on the environment such as reduction in soil erosion (Malone and Polyakov, 2020). However, the measures embraced by conservation agriculture have been shown to have positive impacts on reducing soil erosion in the long term and have other important impacts such as reducing the losses of greenhouse gases which also need to be considered when striving to achieve the UN SDGs in their entirety (Lal, 2020).…”