Integrating rangeland health and stream stability in assessments of rangeland watersheds

Authors: MEEHAN, MIRANDA - North Dakota State University; O'Brien, Peter; HECKER, GARRETT - North Dakota State University; PRINTZ, JEFFERY - Retired Non ARS Employee

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2020
Publication Date: 1/16/2021
Citation: Meehan, M.A., O'Brien, P.L., Hecker, G.A., Printz, J.L. 2021. Integrating rangeland health and stream stability in assessments of rangeland watersheds. Rangeland Ecology and Management. 75:104-111. https://doi.org/10.1016/j.rama.2020.12.005.
DOI: https://doi.org/10.1016/j.rama.2020.12.005

Interpretive Summary: Watersheds are hydrologic units that define the area of land that all drains to a common outlet, and they may consist of a variety vegetation cover, soil types, slopes, and land use. The entire area is linked by hydrology, but the relationship of other ecological processes and functions within the watershed is not well understood. In fact, no single assessment tool is available to describe the ecological status of both terrestrial upland sites (i.e., those outside of the stream terrace) and riparian complexes (i.e., sites along streambanks) in a single watershed. We investigated the overall ecological status of watersheds by integrating a tool commonly used for upland sites, the Interpreting Indicators of Rangeland Health protocol (IIRH), with surveys to assess stream stability. The basis of the IIRH is to identify how the land is functioning compared to a historical reference condition, which is based on expected vegetation, water movement, and soil properties. The qualitative values from the IIRH protocol were different among upland sites associated with 35 seasonally-flowing streams in North Dakota, USA. The stream surveys included measuring characteristics like stream width, stream depth, diameter of material in the stream bed, the shape of stream curves, and width of the stream valley. Stream stability, as determined using those stream characteristics, had a relationship with all three attributes of rangeland health, Soil & Site Stability, Hydrologic Function, and Biotic Integrity. This relationship suggests that upland sites that are not functioning in the same way as a historical reference condition are typically associated with unstable streams, which have a high risk of stream bank collapse and are more likely to change in depth, width, and flow paths. We found that unstable streams were found along upland sites with departures from the reference state in soil compaction, erosion, amount of bare ground, litter dynamics, water infiltration, and invasive species. These findings suggest that changes in these IIRH indicators should be monitored and managed by land managers to ensure that streams continue to perform critical ecosystem functions. Future research must continue to investigate the link between upland and riparian functions within a watershed, with special emphasis on vegetation dynamics. In the meantime, integrating these two watershed assessments is useful in providing land managers with vital information about maintaining ecological function throughout the watershed.

Technical Abstract: Watersheds are distinct hydrologic units that comprise a range of terrestrial upland and riparian complex ecological sites. Since the hydrologic function of the entirety of the watershed is linked, other ecological functions and processes are also likely linked. No single assessment tool is available to describe the ecological status of both terrestrial upland sites and riparian complexes in a single watershed. We investigated the relationship by integrating two tools, Interpreting Indicators of Rangeland Health protocol (IIRH) and stream geomorphic surveys. The qualitative values from the IIRH protocol were different among upland sites associated with 35 intermittent stream reaches in North Dakota, USA. Riparian complex sites were separated using three metrics of stream stability, stream channel type, bank-height ratio, and Bank Erosion Hazard Index. Stream channel type had the strongest relationship with two attributes of rangeland health, Soil & Site Stability and Hydrologic Function, while bank-height ratio had the strongest relationship with the Biotic Integrity attribute. The influences of individual indicators were identified using a principal components analysis, which revealed unstable streams were typified by departures from the reference state in compaction, soil loss, bare ground, litter dynamics, infiltration, and invasive species. These findings suggest that changes in these IIRH indicators should be monitored and managed by land managers to ensure that riparian function and ecosystem services are not compromised. Future research must continue to investigate the link between upland and riparian functions within a watershed, with special emphasis on vegetation dynamics. In the meantime, integrating these two watershed assessments to provide land managers with vital information about maintaining ecological function throughout the watershed.