TY - JOUR T1 - Establishing quantitative benchmarks for soil erosion and ecological monitoring, assessment, and management JF - Ecological Indicators Y1 - 2024 A1 - Webb, N.P. A1 - Edwards, B.L. A1 - Heller, A. A1 - McCord, S.E. A1 - Schallner, J.W. A1 - Treminio, R.S. A1 - Wheeler, B.E. A1 - Stauffer, N.G. A1 - Spiegal, S. A1 - Duniway, M.C. A1 - Traynor, A.C.E. A1 - Kachergis, E. A1 - Houdeshell, C.A. KW - Adaptive management KW - Ecological thresholds KW - Reference site KW - water erosion KW - Wind erosion AB -

Soil erosion can have a multitude of negative impacts on agroecosystems and society and there remains an urgent
need for tools to support its management. Quantitative benchmarks based on holistic understanding of erosion
processes, ecosystem function, and land use objectives can be used with monitoring data and models to inform
assessments and make objective and actionable decisions about erosion management. However, managers
currently lack a framework for establishing benchmarks. Here, we present a framework and evaluation of
different approaches to establishing quantitative benchmarks for soil erosion and ecological monitoring and
assessment that can inform land management decisions. We use monitoring data collected across Chihuahuan
Desert ecosystems in the United States and an aeolian sediment transport model to illustrate how benchmarks
can be established. Approaches include establishing benchmarks from relationships between soil erosion in-
dicators, reference states and land potential, including state-and-transition models, and desired conditions from
existing monitoring data. We discuss the benefits and caveats of the different approaches and show how
combining different benchmarking approaches can help users ensure that benchmarks appropriately reflect
thresholds for soil erosion and achievable management outcomes. We finish by identifying future research needs
to support establishment and application of erosion benchmarks across agroecosystems and recognize the op-
portunity to extend the benchmarking approaches to management of other agroecosystem processes and services.

VL - 159 ER - TY - JOUR T1 - Parameterizing an aeolian erosion model for rangelands JF - Aeolian Research Y1 - 2022 A1 - Edwards, B.L. A1 - Webb, N.P. A1 - Galloza, M. A1 - Van Zee, J.W. A1 - Courtright, E.M. A1 - Cooper, B.F. A1 - Metz, L.J. A1 - Herrick, J.E. A1 - Okin, G.S. A1 - Duniway, M.C. A1 - Tatarko, J. A1 - Tedela, N.H. A1 - Moriasi, D.N. A1 - Newingham, B.A. A1 - Pierson, F.B. A1 - Toledo, D. A1 - Van Pelt, R.S. KW - aeolian KW - Assessment KW - Dust emission KW - Indicators KW - Land management KW - monitoring KW - Wind erosion AB -

Aeolian processes are fundamental to arid and semi-arid ecosystems, but modeling approaches are poorly developed for assessing impacts of management and environmental change on sediment transport rates over meaningful spatial and temporal scales. For model estimates to provide value, estimates of sediment flux that encapsulate intra- and inter-annual and spatial variability are needed. Further, it is important to quantify and communicate transparent estimates of model uncertainty to users. Here, we present a wind erosion and dust emission model parameterized for rangelands using a Generalized Likelihood Uncertainty Estimation framework. Modeled horizontal sediment flux was calibrated using data from five diverse grassland and shrubland sites from the USDA National Wind Erosion Research Network. Observations of wind speed, vegetation height, length of gaps between vegetation, and percent bare ground were used as model inputs. Horizontal sediment flux estimates from 10,000 independently selected parameter sets were compared to flux observations from 44 ∼ month-long collection periods to calculate a likelihood measure for each model. Results show good agreement for individual sampling periods across sites with few observations falling outside prediction bounds and a one-to-one relationship between median predictions and observations. Additionally, combined distributions of sediment flux estimates from all sample periods for a given site closely approximated the probability of observing a given flux at that site. These results suggest AERO effectively represents temporal variability in aeolian transport rates at rangeland sites and provides robust assessments suitable for assessing land health and better predicting changes in air quality and the impacts of land management activities.

VL - 54 ER - TY - JOUR T1 - Vegetation canopy gap size and height: critical indicators for wind erosion monitoring and management JF - Rangeland Ecology and Management Y1 - 2021 A1 - Webb, N.P. A1 - McCord, S.E. A1 - Edwards, B.L. A1 - Herrick, J.E. A1 - Kachergis, E. A1 - Okin, G.S. A1 - Van Zee, J.W. KW - Canopy gap size KW - dust KW - monitoring KW - rangeland health KW - vegetation height KW - Wind erosion AB -

Indicators of vegetation cover and structure are widely available for monitoring and managing rangeland wind erosion. Identifying which indicators are most appropriate for managers could improve wind erosion mitigation and restoration efforts. Vegetation cover directly protects the soil surface from erosive winds and reduces wind erosivity by extracting momentum from the air. The portion of the soil surface that is directly protected by vegetation is adequately described by fractional ground cover indicators. However, the aerodynamic sheltering effects of vegetation, which are more important for wind erosion than for water erosion, are not captured by these indicators. As wind erosion is a lateral process, the vertical structure and spatial distribution of vegetation are most important for controlling where, when, and how much wind erosion occurs on rangelands. These controlling factors can be described by indicators of the vegetation canopy gap size distribution and vegetation height, for which data are collected widely in the United States by standardized rangeland monitoring and assessment programs. In this paper we address why canopy gap size distribution and vegetation height are critical indicators of rangeland wind erosion and health. We review wind erosion processes to explain the physical role of these vegetation attributes. We then address the management implications including availability of data on the indicators on rangelands and needs to make the indicators and model estimates of wind erosion more accessible to the range management community.

VL - 76 ER - TY - JOUR T1 - Comparison of soil-aggregate crushing-energy meters JF - Aeolian Research Y1 - 2020 A1 - Pi, H. A1 - Huggins, D.R. A1 - Webb, N.P. A1 - Sharratt, B. KW - Abrasion KW - Binding energy KW - Dry aggregate stability KW - Dust emission KW - Particle cohesion KW - Wind erosion AB -

Dry aggregate stability (DAS) is an important factor influencing soil wind erosion, dust emission and crop production. Historically and to the present, DAS has been determined using a horizontal- or vertical-plate crushing meter (Soil-Aggregate Crushing-Energy Meter, hereafter SACEM). The intent of this paper was to compare the performance of horizontal-plate SACEM with a commercial penetrometer (Mohr Digi-Test, hereafter MDT). The performance of both instruments was tested on aggregates collected from various soil types, crop rotations, soil amendments, and tillage systems across the inland Pacific Northwest United States (iPNW). Results indicated no consistently significant difference in DAS measured by the MDT and SACEM. However, there was evidence that SACEM under-estimated or MDT over-estimated DAS by 74 to 368% in measuring the stability of strong aggregates (DAS > 3 J kg−1). Both instruments measured higher DAS for no-tillage summer fallow, winter wheat-summer fallow (WW-SF) rotations, and no green manure treatments compared with other tillage practices, oilseed rotations, and green manure treatments. The SACEM that has historically been used in measuring soil DAS can be replaced by the commercial penetrometer (MDT). Nonetheless, differences in the performance of instruments in measuring the stability of strong aggregates poses risks.

VL - 42 ER - TY - Generic T1 - Defining thresholds for wind erosion in desert rangeland STMs T2 - Society for Range Management Y1 - 2020 A1 - Webb, N.P. A1 - Edwards, B.L. A1 - Burke, R. A1 - McCord, S.E. A1 - Van Zee, J.W. A1 - Courtright, E.M. A1 - Cooper, B. KW - desert rangeland STMs KW - thresholds KW - Wind erosion AB -

Within the US, conventional understanding has been that most erosion is occurring in the Great Plains, but our knowledge about the extent and severity of rangeland wind erosion has been limited by monitoring and modeling technologies. Data from air quality monitoring programs like IMPROVE show there was a 75% increase in spingtime fine dust concentrations between 2000 and 2014 across the western states, but we still have a limited understanding of where, when and how much erosion is occurring. Importantly, few tools are available to help managers assess why wind erosion is occurring in responses to land use and management. This information is needed to identify appropriate conservation practices. As a consequence, wind erosion isn't typically considered in assessments of land resource condition despite its importance for plant community dynamics, agroecosystem resilience, regional air quality and climate. To address this problem we developed an Aeolian EROsion (AERO) model designed to run on standardized soil and vegetation monitoring datasets that are collected across the west. AERO is a physically-based model that requires inputs of surface soil texture, bare soil fraction, canopy gap size distribution, average canopy height and time-series or probability distribution of wind speeds for a plot location. By leveraging large standardized monitoring datasets, like those collected by the NRCS NRI and BLM AIM programs, AERO can be used to develop an understanding of potential sediment transport rates and dust emissions across rangelands as influenced by soil properties and the kinds, amounts, proportions and structure of different vegetation species. From AERO applications, we are developing approaches based on the Ecological Land Resource Hierarchy to understand the range of potential wind erosion for different land units at different spatial scales. Our work is then exploring approaches to establish benchmarks based on structural and functional thresholds of concern that enable managers to evaluate how wind erosion responds to changes in the kinds, amounts and proportions of vegetation within ecological sites. By using AERO to integrate the indicators of vegetation structure, the model can also be used to identify functional thresholds for wind erosion and assess whether these thresholds can be generalized across ecological sites and states to inform management at broader spatial scales.

JF - Society for Range Management ER - TY - JOUR T1 - A note on the use of drag partition in aeolian transport models JF - Aeolian Research Y1 - 2020 A1 - Webb, N.P. A1 - Chappell, A. A1 - LeGrand, S.L. A1 - Ziegler, N.P. A1 - Edwards, B.L. KW - Aeolian threshold KW - Dust emission KW - friction velocity KW - Roughness KW - Shear stress partitioning KW - Wind erosion AB -

Sediment transport equations used in wind erosion and dust emission models generally incorporate a threshold for particle motion (u*t) with a correction function to account for roughness-induced momentum reduction and aerodynamic sheltering. The prevailing approach is to adjust u*t by the drag partition R, estimated as the ratio of the bare soil threshold (u*ts) to that of the surface in the presence of roughness elements (u*tr). Here, we show that application of R to adjust only the entrainment threshold (u*t = u*ts/R) is physically inconsistent with the effect of roughness on the momentum partition as represented in models and produces overestimates of the sediment flux density (Q). Equations for Q typically include a friction velocity scaling term (u*n). As Q scales with friction velocity at the soil surface (us*), rather than total friction velocity (u*) acting over the roughness layer, u*n must be also adjusted for roughness effects. Modelling aeolian transport as a function of us* represents a different way of thinking about the application of some drag partition schemes but is consistent with understanding of aeolian transport physics. We further note that the practice of reducing Q by the vegetation cover fraction to account for the physically-protected surface area constitutes double accounting of the surface protection when R is represented through the basal-to-frontal area ratio of roughness elements (σ) and roughness density (λ). If the drag partition is implemented fully, additional adjustment for surface protection is unnecessary to produce more accurate aeolian transport estimates. These findings apply equally to models of the vertical dust flux.

VL - 42 ER - TY - JOUR T1 - Climate change impacts on wind and water erosion on US rangelands JF - Journal of Soil and Water Conservation Y1 - 2019 A1 - Edwards, B.L. A1 - Webb, N.P. A1 - Brown, D.P. A1 - Elias, E. A1 - Peck, D.E. A1 - Pierson, F.B. A1 - Williams, C.J. A1 - Herrick, J.E. KW - climate change KW - rangeland KW - soil erosion KW - water erosion KW - Wind erosion AB -

Soil erosion by water and wind in US rangelands has serious implications for rangeland health and food security and poses significant hazards to human health and communities. Accordingly, understanding how future climate change may impact soil erosion is critical for developing appropriate management strategies that mitigate negative impacts to the extent practical and potentially build resilience. Here, we review potential impacts of climate change on controls of erosion in US rangelands and discuss potential erosion responses. Projected climate changes are expected to have regionally variable effects on important controls of erosion, especially vegetation cover; community composition; frequency, magnitude, and geographical range of fire disturbance; and high intensity, erosive weather events, all of which have the potential to increase rangeland vulnerability to erosion. We identify knowledge gaps relevant to these controls and discuss management considerations to address climate change impacts to soil erosion concerns for US rangelands. In order to improve resilience and the efficacy of climate change adaptation, we recommend that existing monitoring data be used to create assessments of vulnerability, that soil erosion should be explicitly included in management benchmarks and decision support tools, and that no-regrets management options be implemented in anticipation of future impacts.

VL - 74 ER - TY - JOUR T1 - Reducing sampling uncertainty in aeolian research to improve change detection JF - Journal of Geophysical Research: Earth Surface Y1 - 2019 A1 - Webb, N.P. A1 - Chappell, A. A1 - Edwards, B.L. A1 - McCord, S.E. A1 - Van Zee, J.W. A1 - Cooper, B.F. A1 - Courtright, E.M. A1 - Duniway, M.C. A1 - Sharratt, B. A1 - Tedela, N. A1 - Toledo, D. KW - aeolian KW - change detection KW - dust KW - land cover KW - land use KW - Wind erosion AB -

Measurements of aeolian sediment transport support our understanding of mineral dust impacts on Earth and human systems and assessments of aeolian process sensitivities to global environmental change. However, sample design principles are often overlooked in aeolian research. Here we use high‐density field measurements of sediment mass flux across land use and land cover types to examine sample size and power effects on detecting change in aeolian transport. Temporal variances were 1.6 to 10.1 times the magnitude of spatial variances in aeolian transport for six study sites. Differences in transport were detectable for >67% of comparisons among sites using ~27 samples. Failure to detect change with smaller sample sizes suggests that aeolian transport measurements and monitoring are much more uncertain than recognized. We show how small and selective sampling, common in aeolian research, gives the false impression that differences in aeolian transport can be detected, potentially undermining inferences about process and impacting reproducibility of aeolian research.

VL - 124 ER - TY - JOUR T1 - Improving ground cover monitoring for wind erosion assessment using MODIS BRDF parameters JF - Remote Sensing of Environment Y1 - 2018 A1 - Adrian Chappell A1 - Nicholas Webb A1 - Juan Pablo Guerschman A1 - Dean T. Thomas A1 - Gonzalo Mata A1 - Rebecca N. Handcock A1 - John F. Leys A1 - Harry J. Butler KW - Albedo KW - Australia KW - BRDF KW - Ground cover KW - Lateral cover KW - MODIS KW - USA KW - Wind erosion AB -

Measuring and monitoring controls on wind erosion can facilitate detection and prediction of soil degradation important for food security. Ground cover is widely recognised as an important factor for controlling soil erosion by wind and water. Consequently, maintaining ground cover (e.g., vegetation, crop canopy, crop residue) is a recommended management practice which is widely adopted by farmers and land owners. Wind erosion is a lateral or horizontal process and the amount of ground cover needed to maintain lateral cover (Lc = nbh/S where n roughness elements occupy ground area S and have b and h mean breadth and height, respectively) is not well-established. Soil may be removed from beneath or between crop and natural vegetation canopies depending on the width, height and distribution of cover types relative to wind direction and strength. Monitoring by repeated measurement or estimation of ground cover provides information to develop an understanding of its spatial and temporal variation. Fractional cover (fc) retrieved from optical satellite remote sensing (e.g., Moderate Resolution Imaging Spectroradiometer; MODIS) provides a consistent and repeatable measure of ground cover when viewed from above. Therefore, fc provides an areal assessment of components of ground cover. Fractional cover is consequently not the most appropriate approximation of the protection of the soil from wind erosion. Extant wind erosion model parameterisations of Lc already benefit from the use of satellite-derived cover data (Lfc). However, the parameterisations are not well developed. Here, we address the need for a dynamic (multi-temporal), moderate resolution and global metric for wind erosion assessment and modelling. We demonstrate the benefits of using Lc within the context of monitoring ground cover for the assessment of wind erosion and review the basis for estimating ground cover using Lc. We describe a new method for an albedo-based approximation of aerodynamic sheltering (Lω). We use ray-casting of rough surfaces from an existing wind tunnel study to establish a relation between measured Lc and directional hemispherical reflectance ωdir(0°, λ), the so-called ‘black-sky albedo’ and its inverse to estimate shadow. The relation is confirmed to be dependent on the solar zenith angle (θ) and spectral (λ) confounding factors (e.g., soil moisture, soil mineralogy). We reduced the λ dependency of ωdir(0°, λ) by normalising with the MODIS (MCD43A1) BRDF parameter fiso to estimate albedo-based lateral cover (Lω) globally over space (500 m pixels) and time (every 8 days). We compared Lω with fc and Lfc over time for selected locations in Australia and examined Lω across Australia and the USA using national biogeographic regions. Consistent with current approaches to estimating Lc, our results were not field validated due to the dearth of ground-based measurements. However, our results demonstrate that Lω will improve wind erosion models particularly over large areas and Lω is likely to be a valuable source of decision-support information to guide policy makers and land managers on where, when and how to reduce wind erosion.

VL - 204 ER - TY - JOUR T1 - Exploring dust emission responses to land cover change using an ecological land classification JF - Aeolian Research Y1 - 2018 A1 - Magda S. Galloza A1 - Nicholas Webb A1 - Max P. Bleiweiss A1 - Craig Winters A1 - Jeffrey E. Herrick A1 - Eldon Ayers KW - Anthropogenic KW - Dust source KW - Ecological sites KW - State-and-transition models KW - Wind erosion AB -

Despite efforts to quantify the impacts of land cover change on wind erosion, assessment uncertainty remains large. We address this uncertainty by evaluating the application of ecological site concepts and state-and-transition models (STMs) for detecting and quantitatively describing the impacts of land cover change on wind erosion. We apply a dust emission model over a rangeland study area in the northern Chihuahuan Desert, New Mexico, USA, and evaluate spatiotemporal patterns of modelled horizontal sediment mass flux and dust emission in the context of ecological sites and their vegetation states; representing a diversity of land cover types. Our results demonstrate how the impacts of land cover change on dust emission can be quantified, compared across land cover classes, and interpreted in the context of an ecological model that encapsulates land management intensity and change. Results also reveal the importance of established weaknesses in the dust model soil characterisation and drag partition scheme, which appeared generally insensitive to the impacts of land cover change. New models that address these weaknesses, coupled with ecological site concepts and field measurements across land cover types, could significantly reduce assessment uncertainties and provide opportunities for identifying land management options.

VL - 32 ER -