The earth’s mountains continue to lose water. Glaciers are melting and mountain snow/rain balance tilts increasingly liquescent. Water is running off sooner—sometimes overfilling reservoirs, causing flooding, and setting the stage for late-season shortages. One adaptive strategy is to recover and enhance water-storage capacities of headwater riparian systems. Grazing, a common use of headwater lands, affects both soils and vegetation. To better understand how grazing might affect water storage and other ecosystem services of high elevation riparian wetlands, we measured soil-profile temperatures, soil organic matter (SOM), and phytomass at six sites in the upper Sweetwater River sub-basin of Wyoming, USA, where fence lines allowed us to contrast grazing management. We found grazed wetlands consistently had warmer soils than fenced wetlands. We found added evidence that SOM is important in both soil temperature control and water-storage potential of wetlands. We review evidence that warmer soil temperatures and drying cause loss of SOM with the implied concomitant C losses through erosion and emissions. We recommend land managers of temperate-climate headwater systems consider the need to end growing seasons with full stands of riparian vegetation to reduce soil warming and to build organic matter—particularly on lands where municipalities and other downstream water users are seeking long-term increases in water yields and less flooding.
Increasing human population and intensive land use combined with a warming climate and chronically diminished snowpacks are putting more strain on water resources in the western United States. Properly functioning riparian systems slow runoff and store water, thus regulating extreme flows; however, riparian areas across the west are in a degraded condition with a majority of riparian systems not in proper functioning condition, and with widespread catastrophic erosion of water-storing peat and organic soils. Headcuts are the leading edge of catastrophic channel erosion. We used aerial imagery (1.4-3.3-cm pixel) to locate 163 headcuts in riparian areas in the Sweetwater subbasin of central Wyoming. We found 1-m-the generally available standard resolution for land management-and 30-cm pixel imagery to be inadequate for headcut identification. We also used Structure-from-Motion models built from ground-acquired imagery to model 18 headcuts from which we measured soil loss of 425-720 m3. Normalized by channel length, this represents a loss of 1.1-1.8 m3 m(-1) channel. Monitoring headcuts, either from ground or aerial imagery, provides an objective indicator of sustainable riparian land management and identifies priority disturbance-mitigation areas. Image-based headcut monitoring must use data on the order of 3.3 cm ground sample distance, or greater resolution, to effectively capture the information needed for accurate assessments of riparian conditions.
A warming earth has lost substantial mountain-stored frozen fresh water, thus generating a pressing need for greater liquid-water storage within upperelevation riparian systems. Liquid-water storage can be enhanced by avoiding microtopographic channels that facilitate land drainage and rapid runoff. A number of authors have attributed certain forms of wetland hummocks and inter-hummock channels to grazing livestock but there is little evidence in the scientific literature for a cause and effect mechanism. We used comparisons at six fencelines on four meadow and wetland complexes to test the null hypothesis that grazing management makes no difference in hummocks and inter-hummock channels measured as surface roughness. Surface roughness was measured both photogrammetrically (photo) and with an erosion bridge (EB), and the measurements expressed as surface roughness indices (SRIs). Wetland surface roughness inside fenced areas was 44 (EB) and 41 (photo). Wetland surface roughness outside fenced areas was more than 50 % higher (p \ 0.0001), measuring 76 (EB, n = 6) and 62 (photo, n = 4). The site with the longest period of conservation management (50? years) had the lowest inside EB SRI at 27. The two independent measurement methods, EB and photo, yielded similar, correlated results (R = 0.71, n = 8). Historical aerial photography provides supporting evidence for our findings. We reject the null hypothesis and while we suspect macrotopography, hydrology, soil type, and climate are factors in hummock formation, our evidence supports the thesis that hummocks formed surface-down by inter-hummock channels result primarily from grazing by domestic livestock.
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