A characterization of seasonal pools in Central Oregon's high desert Public Deposited



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  • Seasonal wetlands in arid and semi-arid lands provide an important source of surface water in otherwise dry lands. Central Oregon's high desert, located in the Northern Great Basin (NGB) is dotted with hundreds of seasonal pools, locally called playas. The playas hold water or snow during parts of winter and spring but typically dry up during summer months. The mechanisms of seasonal pool hydrology, especially in the NGB, are poorly understood and have not been thoroughly examined. There is high seasonal variability and inter-annual variability in surface water amounts in the playas. Historical over-grazing and a century of fire suppression have caused serious long-term ecological damage throughout the NGB ecoregion. A large portion of playas located on the Bureau of Land Management (BLM) Prineville District lands have been excavated to capture and retain increased water for livestock use. These dug-out playas exhibit an altered ponding regime, affecting the depth and duration of water on the surface. Playa excavations have affected the hydrologic behavior on the playas, possibly altering the vegetation communities. Playa habitat is important to many different species, including the greater sage-grouse (Centrocercus urophasianus), a candidate for protection under the federal Endangered Species Act. To obtain my objectives of fostering a greater understanding of the ecology of the playa systems and to begin documenting the variability across the landscape I explored various methods to characterize and monitor the playas. I analyzed field data collected by the BLM, including ecological site inventory. Because of the knowledge gap in playa ecology, I created a method to support and improve data collection to describe these unique wetlands. I created a field manual to characterize playas that will give land managers and scientists a tool to obtain and contribute useful information about the playas. The information can be used to answer a variety of questions concerning subjects such as: the perceived sensitivity of a site for livestock grazing, the relative importance of a playa to various wildlife species, and whether or not the site is appropriate for livestock troughs or wind turbines. Working with the BLM I helped to develop experimental habitat improvement strategies. To monitor the success of the habitat improvement strategies I used Electromagnetic induction (EMI) to map subsurface soil physical properties, looking specifically at salinity to gain information about hydrologic patterns. I compared hydrologic patterns of playas before and after habitat improvement strategies using EMI data. From initial visual observations of the EMI data, water appears to be distributed across the playas in greater areal extent following habitat improvement strategies. To further characterize the variability in the playas across Central Oregon's high desert, I examined whether relative ash concentration in the soil samples had an effect on the apparent physical characteristics of a playa. There were no discernable differences in relative ash concentration between any of the soil samples. Land managers have an inclination towards orchestrating restoration activities on the altered playas aimed at habitat improvement goals. I recommend caution and patience with restoration activities. Attempts to return systems to within their historical range of biotic and abiotic characteristics and processes may not be possible. Management activities directed at removing undesirable features of a system may perpetuate new undesirable systems. Directing management goals towards promoting biological diversity and hydrological functionality may be more successful focus. I recommend continuing to characterize these unique systems to facilitate the understanding of the role of these features in the high desert.
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