David A. Haukos

EFFECTS OF SEDIMENTATION ON PLAYA WETLAND VOLUME

Over 50% of the wetlands in the conterminous United States have been lost; however, few studies have investigated the more insidious effects of sedimentation on wetland volume. We examined the effects of sedimentation on playa wetland volume in the Southern High Plains (Texas, USA). We compared 20 playas with watersheds dominated by rangeland to 20 playas that had cropland watersheds. Playas were located in fine- and medium-texture soil zones. Playas with cultivated watersheds contained more sediments than those with rangeland watersheds. Playas with cultivated watersheds had lost all of their original volume, on average, whereas playas with rangeland watersheds had lost only about one third of their volume. Of the ≈30000 playas in the region, most have cultivated watersheds, and therefore the hydroperiod of playas has been drastically altered over the last 60 yr, changing the structure and function of these ecosystems. Also, sedimentation in playas in the medium-texture soil zone was greater than in the ...

The importance of playa wetlands to biodiversity of the Southern High Plains

Abstract We describe the landscape of the Southern High Plains, including the important remaining native feature of the area; playa wetlands. Playas are ephemeral wetlands on the prairie occupying approximately 2% of the landscape. Playas re-charge the Ogallala aquifer, are incorporated in farming irrigation systems, and represent the predominant wildlife habitat of the area. The importance of playas to mammalian, avian, other vertebrate, and floral biodiversity is detailed. Potential threats to playas are described and include chemical contamination, physical modication, and grazing. Recommended avenues for conservation of playas include nationwide recognition of the importance of playas, increased emphasis on basic research, and development of management plans for landscape biodiversity.

Ecosystem services provided by playas in the High Plains: potential influences of USDA conservation programs

Playas are shallow depressional wetlands and the dominant wetland type in the non-glaciated High Plains of the United States. This region is one of the most intensively cultivated regions in the Western Hemisphere, and playas are profoundly impacted by a variety of agricultural activities. Conservation practices promoted through Farm Bills by the U.S. Department of Agriculture (USDA) that influence playas and surrounding catchments impact ecosystem functions and related services provided by wetlands in this region. As part of a national assessment, we review effects of agricultural cultivation and effectiveness of USDA conservation programs and practices on ecosystem functions and associated services of playas. Services provided by playas are influenced by hydrological function, and unlike other wetland types in the United States, hydrological function of playas is impacted more by accumulated sediments than drainage. Most playas with cultivated catchments have lost greater than 100% of their volume from sedimentation causing reduced hydroperiods. The Conservation Reserve Program (CRP) has the largest influence on playa catchments (the High Plains has >2.8 million ha), and associated sedimentation, of any USDA program. Unfortunately, most practices applied under CRP did not consider restoration of playa ecosystem function as a primary benefit, but rather established dense exotic grass in the watersheds to reduce soil erosion. Although this has reduced soil erosion, few studies have investigated its effects on playa hydrological function and services. Our review demonstrates that the Wetlands Reserve Program (WRP) has seldom been applied in the High Plains outside of south-central Nebraska. However, this is the primary program that exists within the USDA allowing conservation practices that restore wetland hydrology such as sediment removal. In addition to sediment removal, this practice has the greatest potential effect on improving hydrologic function by reducing sedimentation in vegetative buffer strips. We estimate that a 50-m native-grass buffer strip could improve individual playa hydroperiods by up to 90 days annually, enhancing delivery of most natural playa services. The potential for restoration of playa services using USDA programs is extensive, but only if WRP and associated practices are promoted and playas are considered an integral part of CRP contracts.

PAST AND FUTURE IMPACTS OF WETLAND REGULATIONS ON PLAYA ECOLOGY IN THE SOUTHERN GREAT PLAINS

Playa wetlands provide functions critical to the existence of life on the High Plains portion of the Great Plains, including surface drainage, aquifer recharge, and wildlife habitat. These small, circular, isolated depressional wetlands with closed watersheds have a dynamic, unpredictable hydroperiod, which is essential to the maintenance of biodiversity. Most numerous in the Southern High Plains of northwestern Texas and eastern New Mexico, playas have been impacted by sedimentation, pit excavation, road construction, industrial and municipal wastewater, feedlot runoff, urban development, overgrazing, and deliberate filling. Despite being declared, as a wetland class, jurisdictional “waters of the United States” since 1977, regulations and laws for conservation of wetland functions have seldom been applied to playas. The January 2001 Supreme Court decision, Solid Waste Agency of Northern Cook County (SWANCC) v. United States Army of Corps of Engineers, likely eliminated federal regulation of impacts covered by the Clean Water Act in all but a few playas. Although still subject to the Federal “Swampbuster” provision enacted by the 1985 Food Security Act, extended natural dry periods allows for frequent cultivation and other activities in playas without incurring violation, contributing to the continued degradation of playa functions. None of the states with significant numbers of playas have regulations for the conservation of playa functions. Suggestions for the successful future conservation of playas and their associated functions include (1) increased promotion and implementation of existing federal and state conservation programs specifically for playas; (2) proposed state regulations for playa conservation; (3) recognition of agricultural impacts on wetland determinations; (4) creation of Wetland Management Districts to preserve intact, functioning playas; and (5) increased public education on the value of playas.

Sources of recently deposited sediments in playa wetlands

There are more than 20,000 playa wetlands in the Southern High Plains of Texas and New Mexico. Playas with cropland watersheds have lost most of their basin volume due to sedimentation, and they have lost more volume than playas with rangeland watersheds. To determine the source (wind vs. water transport) of sedimentation in playas and develop management recommendations to lessen sediment impacts, we examined the particle size distribution (PSD) of soils in 8 playas with rangeland and cropland watersheds. The distribution curves of sand in playa sediments plotted against relative distance coincided with playa elevational profiles, and the PSD of deeper sediments contained more sand, especially at the playa margins. In contrast, more clay had been deposited in the central portion of the playa basin, and clay content decreased with sediment depth. Sand content at playa edges was greater in crop than in range playas. Sediments eroded from the surrounding watershed resulted in deposition of coarser soil particles at the playa margin, whereas finer particles dominated playa centers. Because most sediments in playa wetlands orginate from the immediate watershed and are deposited through water erosion, management activities should concentrate on practices that reduce watershed erosion.

Reducing sedimentation of depressional wetlands in agricultural landscapes

Depressional wetlands in agricultural landscapes are easily degraded by sediments and contaminants accumulated from their watersheds. Several best management practices can reduce transport of sediments into wetlands, including the establishment of vegetative buffers. We summarize the sources, transport dynamics, and effect of sediments, nutrients, and contaminants that threaten wetlands and the current knowledge of design and usefulness of grass buffers for protecting isolated wetlands. Buffer effectiveness is dependent on several factors, including vegetation structure, buffer width, attributes of the surrounding watershed (i.e., area, vegetative cover, slope and topography, soil type and structure, soil moisture, amount of herbicides and pesticides applied), and intensity and duration of rain events. To reduce dissolved contaminants from runoff, the water must infiltrate the soil where microbes or other processes can break down or sequester contaminants. But increasing infiltration also diminishes total water volume entering a wetland, which presents threats to wetland hydrology in semi-arid regions. Buffer effectiveness may be enhanced significantly by implementing other best management practices (e.g., conservation tillage, balancing input with nutrient requirements for livestock and crops, precision application of chemicals) in the surrounding watershed to diminish soil erosion and associated contaminant runoff. Buffers require regular maintenance to remove sediment build-up and replace damaged or over-mature vegetation. Further research is needed to establish guidelines for effective buffer width and structure, and such efforts should entail a coordinated, regional, multi-scale, multidisciplinary approach to evaluate buffer effectiveness and impacts. Direct measures in “real-world” systems and field validations of buffer-effectiveness models are crucial next steps in evaluating how grass buffers will impact the abiotic and biotic variables attributes that characterize small, isolated wetlands.

Avian response to vegetative pattern in playa wetlands during winter

Abstract Breeding-bird communities inhabiting northern prairie wetlands have been shown to have higher densities and diversities in wetlands with a well-interspersed 50:50 vegetative cover:water ratio than in those wetlands with a higher or lower proportion of cover. Potential reasons for such a response include increased food or visual isolation and spacing of breeding birds. We manipulated cover:water ratios (75:25, 50:50, 25:75) in Southern Great Plains playas and examined avian response (i.e., species richness, non-waterfowl bird density, and waterfowl density) to these patterns in winter. We found the highest species richness and generally the highest waterfowl densities in the 50:50 cover:water treatment. Because the amount of vegetative food was similar among treatments and waterfowl inhabiting playas during winter are forming pair bonds, it is most likely that the optimal edge and visual isolation provided in the 50:50 cover:water treatment contributed to its high use and richness. Nonwaterfowl bird density was not different among the treatments. Many nonwaterfowl birds using playas in winter, such as McCowns longspur (Calcarius mccownii), occur as nonbreeding feeding flocks, are not forming pair bonds, and likely are not responding to particular cover:water treatments. Playa wetland biologists should create a well-interspersed 50:50 cover:water ratio to optimize waterfowl use and avian species richness.

Toxicity of a glufosinate- and several glyphosate-based herbicides to juvenile amphibians from the Southern High Plains, USA

Pesticide toxicity is often proposed as a contributing factor to the world-wide decline of amphibian populations. We assessed acute toxicity (48 h) of a glufosinate-based herbicide (Ignite 280 SL) and several glyphosate-based herbicide formulations (Roundup WeatherMAX, Roundup Weed and Grass Killer Super Concentrate, Roundup Weed and Grass Killer Ready-To-Use Plus on two species of amphibians housed on soil or moist paper towels. Survival of juvenile Great Plains toads (Bufo cognatus) and New Mexico spadefoots (Spea multiplicata) was reduced by exposure to Roundup Weed and Grass Killer Ready-To-Use Plus on both substrates. Great Plains toad survival was also reduced by exposure to Roundup Weed and Grass Killer Super Concentrate on paper towels. New Mexico spadefoot and Great Plains toad survival was not affected by exposure to the two agricultural herbicides (Roundup WeatherMAX and Ignite 280 SL) on either substrate, suggesting that these herbicides likely do not pose an immediate risk to these species under field conditions.

Opinion: Endogenizing culture in sustainability science research and policy

Integrating the analysis of natural and social systems to achieve sustainability has been an international scientific goal for years (1, 2). However, full integration has proven challenging, especially in regard to the role of culture (3), which is often missing from the complex sustainability equation. To enact policies and practices that can achieve sustainability, researchers and policymakers must do a better job of accounting for culture, difficult though this task may be.

The Predicted Influence of Climate Change on Lesser Prairie-Chicken Reproductive Parameters

The Southern High Plains is anticipated to experience significant changes in temperature and precipitation due to climate change. These changes may influence the lesser prairie-chicken (Tympanuchus pallidicinctus) in positive or negative ways. We assessed the potential changes in clutch size, incubation start date, and nest survival for lesser prairie-chickens for the years 2050 and 2080 based on modeled predictions of climate change and reproductive data for lesser prairie-chickens from 2001–2011 on the Southern High Plains of Texas and New Mexico. We developed 9 a priori models to assess the relationship between reproductive parameters and biologically relevant weather conditions. We selected weather variable(s) with the most model support and then obtained future predicted values from climatewizard.org. We conducted 1,000 simulations using each reproductive parameter’s linear equation obtained from regression calculations, and the future predicted value for each weather variable to predict future reproductive parameter values for lesser prairie-chickens. There was a high degree of model uncertainty for each reproductive value. Winter temperature had the greatest effect size for all three parameters, suggesting a negative relationship between above-average winter temperature and reproductive output. The above-average winter temperatures are correlated to La Niña events, which negatively affect lesser prairie-chickens through resulting drought conditions. By 2050 and 2080, nest survival was predicted to be below levels considered viable for population persistence; however, our assessment did not consider annual survival of adults, chick survival, or the positive benefit of habitat management and conservation, which may ultimately offset the potentially negative effect of drought on nest survival.