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Playas in the Rainwater Basin region in Nebraska are globally important wetlands that are continuously threatened by culturally accelerated sedimentation. Using annual habitat survey data and wetland vegetation inventories, inundation and hydrophyte community distributions were evaluated for properties under different types of conservation status. Annual soil erosion rates from surrounding watersheds were calculated to estimate sediment accumulated rates using the Revised Universal Soil Loss Equation 2 (RUSLE2). The slope-length component of the RUSLE2 was derived from 2009 light detection and ranging (LiDAR) data after the methods described by Van Remortel (Computers & Geosciences 30:1043-1053, ). Wetlands enrolled in conservation programs were inundated more and were dominated to a greater degree by hydrophytes than wetlands not enrolled in these programs. The mean estimated soil erosion rate at the Rainwater Basin landscape level was 4.67 tons/ha/year, and the mean estimated sediment accumulation depth for public watersheds was estimated as 0.19 cm/year. Without appropriate conservation actions, the current inundated acres and wetland acres growing hydrophytes would be further reduced by sediment accumulation. The results illustrated the importance of conservation programs to protect wetlands. [ABSTRACT FROM AUTHOR]

Wetlands in the Rainwater Basin in Nebraska are vulnerable to sediment accumulation from the surrounding watershed. Sediment accumulation has a negative impact on wetland quality by decreasing the depth and volume of water stored, and the plant community species composition and density growing in the wetland. The objective of this study was to determine the amount of sediment that has accumulated in five selected wetlands in the Rainwater Basin in Nebraska. Soil cores were taken at five or six locations along transects across each wetland. This study used the fly ash, which is generated by coal-burning locomotives that were present generally in the late 1800s and early 1900s, as a marker to quantify the sediment deposition rates. The cores were divided into 5 cm sections and the soils were analyzed using a fly ash extraction and identification technique. Results indicate that the average depth of sediment ranged from 23.00 to 38.00 cm. The annual average depth of sediment accumulation ranged from 0.18 cm/yr to 0.29 cm/yr. The annual sediment accumulation rate from both wind erosion and water erosion in these five sampling wetlands was between 1.946 and 3.225 kg/ m2/yr. The results of this research can be used to develop restoration plans for wetlands. The fly ash testing technology can also be applied to other areas with the railroads across the United States. [ABSTRACT FROM AUTHOR]

Playa wetlands in Nebraska provide globally important habitats for migratory waterfowl. Inundation condition is an important indicator of playa wetland functionality. However, there is a lack of long-term continuous monitoring records for playa wetlands. The objective of this study was to determine a suitable index for Landsat images to map the playa inundation status in March and April during 1985-2015. Four types of spectral indices—negative normalized vegetation index, Normalized Difference Water Index (NDWI), modified NDWI, and Tasseled Cap Wetness-Greenness Difference (TCWGD)—were evaluated to detect playa inundation conditions from Landsat images. The results indicate that the TCWGD is the most suitable index for distinguishing playa inundation status. By using Landsat images and Google Earth Engine, we mapped the spring inundation condition of Nebraska playas during 1985-2015. The results show that the total inundated areas were 176.79 km2 in spring migratory season, representing 18.92% of the total area of playa wetlands. There were 9898 wetlands inundated at least once in either March or April during the past 30 years, representing 29.41% of a total of 33,659 historical wetlands. After comparing the historical hydric soil footprints and the inundated areas, the results indicate that the hydrological conditions of the majority of playas in Nebraska have changed. The inundated wetlands are candidates for protection and/or partial restoration, and the un-inundated wetlands need more attention for wetland restoration. Wetlands in areas enrolled in conservation easements had a significantly high level of playa inundation status than non-conserved wetlands during spring migratory seasons in the past decades.These conservation easements only count for 4.29% of the total footprint areas, but they have contributed 20.82% of the inundation areas in Nebraska during the past 30 years. [ABSTRACT FROM AUTHOR]