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Sibley Nature Center Presents Geology of the Playas and Ogallala Aquifer of the Llano Estacado by Steven Schafersman, Ph.D. CyberComputing Sciences and Llano Estacado Chapter of the Texas Master Naturalists Introduction to the Llano Estacado The Llano Estacado is Spanish and literally means the Staked Plain or Plain of Stakes. But "staked" or “stakes” for several reasons that have long been the subject of controversy. The region was named the Llano Estacado by Spanish explorer Francisco Vasquez de Coronado in 1541, when he crossed what is now the Texas panhandle. The name still holds today, but why he named it this is not clear. Pronounce the name as the Spanish do: “Yano Estacado,” not “Lano Estacado.” Introduction to the Llano Estacado The most common explanation is that the original Spanish explorers would drive stakes into the ground to mark their trail to find their way back, a common practice when exploring an unknown flat, featureless landscape, which certainly describes the Llano Estacado. A second idea has it that Coronado’s men had to tether their horses at night using stakes, because if they wandered off they couldn’t be tracked on the soft, short grass. A third suggestion is that the abundant yucca stalks make it appear that the land is “staked.” Playas and Playa Lakes There is a fourth explanation. Spanish explorer Francisco Vasquez de Coronado in 1541 was the first European to see the playa lakes. He named them playas because some playas have sandy shores, and playa means “beach” in Spanish. Coronado’s trail through the Texas Panhandle—only 49 years after Columbus discovered the New World for Spain—is the brown one on the map above. He also was the first European to visit the Pueblo Indians of New Mexico. Introduction to the Llano Estacado The fourth hypothesis is that the original word was Estacando, not Estacado. This word means “stagnant,” “pond,” or “many ponds,” and if this hypothesis is correct, would refer to the many thousands of playa lakes that are a prominent feature of the Llano Estacado. Coronado was the first European to see playas. The small ponds eventually dry up and become stagnant mud pits before turning into typical dry playas. A simple misspelling may explain it all. Coronado intended to name the region the Llano Estacando, the “Plain of Many Ponds,” but somehow the “n” got left out of the name by mistake, leaving it spelled Estacado! Unfortunately, no one knows precisely which of these explanations for the origin of the name Llano Estacado is correct! Introduction to the Llano Estacado Where is the Llano Estacado? The Llano Estacado is about ¾ in West Texas and ¼ in eastern New Mexico. The cities of Amarillo, Lubbock, and Midland are printed in red. It is bounded on the north by the Canadian River, on the southwest by the Pecos River, on the east by the Caprock Escarpment, and on the west by the Mescalero Escarpment. Introduction to the Llano Estacado What is the Llano Estacado? The Llano Estacado is a plateau, a regional landmass consisting of horizontally-bedded sedimentary rocks or strata that stands higher in elevation than the surrounding land areas. Some plateaus are the result of regional uplift, while others—like the Llano Estacado—are the result of the differential erosion of surrounding land areas, leaving the plateau higher only because the surrounding land has eroded downward. Introduction to the Llano Estacado The best example of an uplifted plateau in the United States is the giant Colorado Plateau of southern Utah and Colorado and northern Arizona and New Mexico, the famous Four Corners Area. The Llano Estacado is a smaller version of the Colorado Plateau, but there are some important differences. In particular, the Colorado Plateau was uplifted by tectonic forces while the Llano Estacado sits higher only because the surrounding land has eroded downward. Introduction to the Llano Estacado Characteristically, millions of years of weathering and erosion create beautiful and scenic landforms on plateaus, such as canyons, buttes, mesas, and pinnacles. Depending on the age and timing and amount of uplift, these landforms can have high relief (relief is the difference in elevation between the highest and The famous East and West Mitten lowest areas) as in the Colorado Buttes in Monument Valley, Arizona. Plateau, seen in the photo at right. Note the high relief. Introduction to the Llano Estacado Landforms can also have low topographical relief, as is the case with the Llano Estacado. Low relief means the area is relatively flat (see photo), and this certainly characterizes the Llano Estacado. Topography refers to mapping the land in terms of elevation and relief, so a topographic map shows a region’s elevation and relief to one who Rattlesnake Racetrack, just off can read it. The entire U.S. has Rankin Highway in Midland County, been mapped topographically. has low relief. Introduction to the Llano Estacado Canyons on the Colorado Plateau are deep with steep canyon walls, such as the Grand Canyon, but “canyons” on the Llano Estacado are relatively shallow with gentle slopes and low bluffs that can simply be termed stream valleys (or draws), not canyons. The reason is because the Colorado Plateau has undergone recent uplift, so erosion now is extremely active, while the Llano Estacado has never uplifted, so erosion by now has worn down the Playa Lake on the Llano Estacado. land to a condition of low relief. Note the shallow depression on otherwise flat topography (low relief). Introduction to the Llano Estacado High relief in the Llano Estacado? Yes! The Llano Estacado does have some areas of high topographic relief. These are found along the edges of the plateau, where the land drops precipitously from the top of the plateau to the valley below. These steep edges or cliffs are called escarpments. The eastern edge in Texas is the Caprock Escarpment, and the western edge in New Mexico is the Mescalero Escarpment. The escarpments were created by headward erosion by streams cutting into the Llano Estacado. Introduction to the Llano Estacado High relief in the Llano Estacado? The Caprock Escarpment near Amarillo and Canyon, Texas, is so scenic that a state park was created to protect the area: Palo Duro Canyon State Park. The small Prairie Dog Town Fork of the Red River created the huge Palo Duro Canyon by slowly cutting into the Caprock Escarpment over millions of years. Spectacular landforms, such as famous Lighthouse Rock at left, can be found in the park. Introduction to the Llano Estacado Palo Duro Canyon State Park The Caprock Escarpment is visible in the photo at right. This wall of horizontally-layered sedimentary rock is the eastern edge of the Llano Estacado. The red color indicates that the sediments were originally deposited in non-marine environments, such as river channels and alluvial plains, and contain an oxidized form of iron called hematite (blood-mineral), a mineral which is ground to form a red pigment. Introduction to the Llano Estacado The Mescalero Escarpment The Mescalero Escarpment is visible in the photo at right. This wall of horizontally-layered sedimentary rock is the western edge of the Llano Estacado or southern High Plains. Here it drops off into the Pecos River Valley just south of Tucumcari, New Mexico. Once again, note the considerable topographic relief between the top of the plateau and the river valley below. Introduction to the Llano Estacado Characteristics of the Llano Estacado The Llano Estacado plateau occupies approximately 37,000 square miles (22 million acres). It is larger than the combined states of Maryland, Massachusetts, New Jersey, and Rhode Island, and larger than the single state of South Carolina! The region is devoid of native trees except for the tiny shin oak and mesquite. As the Southern High Plains, the Llano is cut off from the Great Plains to the north by the Canadian River Valley. The Llano slopes gently to the southeast by 8-10 feet per mile. With no geological relief, the only changes in elevation are the approximately 34,000 shallow depressions called playas. The Llano Estacado is the largest, isolated non-mountainous geological area in North America, which is why endemic plants and animals are found here. Introduction to the Llano Estacado Most students are told that we live in the Permian Basin, but they do not know what the Permian Basin really is. Also, isn't a basin a depression rather than an elevated area? The Permian Basin is actually a sedimentary rock sequence, with horizontal (flat-lying) strata (sedimentary rock layers) found deep underground. Millions of years ago, the Permian ocean basin was depressed, filled with marine water, and collected sediment, but now we live on top of the rocks of the Permian Basin, not in it. Introduction to the Llano Estacado The Permian Basin The “Permian Basin” is actually an informal name that describes a number of subsurface geologic features: the Midland Basin, the Delaware Basin, the Central Basin Platform between them, and several mountain ranges composed of the same strata that have been uplifted by various events that are scattered around and inside the major basins. The name “Permian Basin” was given to this area because it contains an enormous amount of oil and gas found primarily in strata of Permian age. Introduction to the Llano Estacado Most of this Permian strata (stratified sedimentary rock) is deep underground and isn’t visible anywhere on the surface except in mountain ranges where it has been uplifted and eroded, such as the Guadalupe Mountains, adjacent to the Llano Estacado. So we don’t really live in a basin or depression, we live on an elevated plateau created by differential erosion. We don’t live in the Permian Basin, we live on the Llano Estacado! Introduction to the Llano Estacado Description of the Llano Estacado The Llano Estacado is an elevated plateau—created by differential erosion of surrounding rock—in a dry region of the United States, so its habitats are characterized by slight elevation or depression, low amount of water, and the consequences of wind and water erosion. Availability of water is the most important factor. Most threatened animal species on the Llano Estacado are endangered because humans have taken so much groundwater that springs have dried up, not because of over-hunting. Excessive groundwater removal is an example of habitat destruction, the most common reason why plants and animals become endangered or extinct. Introduction to the Llano Estacado The Llano Estacado is a semi-arid region that receives more rainfall than arid regions, such as deserts, but less rainfall than moist or wet regions, such as forests. A desert receives between 0 and 10 inches of rain a year, and a forested region receives over 30 inches a year. So, a semi-arid region— usually a grassland—receives between 10 and 30 inches (25-75 cm) of rain annually. The amount of rainfall is one of the two primary controls on biomes, ecosystems, and habitats. The other is temperature, controlled by either latitude or altitude (elevation). Introduction to the Llano Estacado Temperature and rainfall amount (mean annual temperature and precipitation) have been carefully measured by scientists and are used to describe ecological zones and regions. The chart above—a climograph—illustrates this concept. Introduction to the Llano Estacado The Southern Great Plains was originally short-grass and mid-grass prairie. Domestic cattle were introduced to the region in the 1870s by the first ranchers— grazing on endless square miles of grasses—and most crops started to be cultivated during the 1920s. Over- cultivation and over-grazing of the land replaced the drought-resistant natural plants with crop plants that required abundant rainfall, making the topsoil susceptible to wind erosion when the 1930s drought began. Introduction to the Llano Estacado The massive wind erosion of the loose topsoil resulted in the “Dust Bowl,” a period of great hardship for the farmers that forced many of them to leave the region and migrate to California in the later 1930s. The Dust Bowl wind erosion damage was centered in two areas: (1) the Llano Estacado in Texas and (2) southeastern Colorado and southwestern Kansas. The land must be constantly protected to prevent further damage. Introduction to the Llano Estacado Water is also the primary agent responsible for erosion and the creation of landforms. This is true even in deserts, a fact that most people don’t realize (they incorrectly think wind is totally responsible). All of the canyons, gorges, buttes, mesas, pinnacles, and columns of desert regions are the result of water erosion, not wind erosion, acting slowly over time. The photos at right show the effects of water erosion in a semi-arid Palo Duro Canyon State Park, Texas region. Habitats of the Llano Estacado Canyons and “The Breaks” “The Breaks” are the semi-arid canyons that cut into the eastern and western edges of the Llano Estacado Plateau, the Caprock and Mescalero Escarpments. Here, water erosion over millions of years has sculpted the brightly-colored rocks into spectacular landforms, providing an unlimited number of niches and microhabitats for organisms. Introduction to the Llano Estacado Water is abundant in the Llano Estacada only in aquifers, streams, springs, and playa lakes, not in rainfall. In the case of the playas, the water is ephemeral, that is, the water is not permanent but rather seasonal or even episodic, lasting only for a few weeks or months. Despite the temporary nature of this water, it is nevertheless very important for the plants and animals of the region and their habitats. Birds use this water during their migrations, for example. Playa Lakes, Llano Estacado Playas and Playa Lakes Playa lakes are the unique, freshwater wetlands of the Southern Great Plains. Playas are circular depressions on clay soil that hold water for several months after a rain. There are about 30,000 playas and playa lakes on the Llano Estacado Playas and Playa Lakes The existence of playas is closely associated with both rainfall and the freshwater aquifer of the region, the Ogallala Aquifer. Playas dot the landscape on the High Plains states, providing a unique natural resource. Playas and Playa Lakes The number of playas in the Great Plains has been estimated to be between 25,000 and 50,000. Most of these, about 85%, are found in the Southern High Plains, that is, on the Llano Estacado. Along with the prairie grasslands, the playas are the major, defining habitat of the Llano Estacado. Playas and Playa Lakes Scattered across the western prairie landscape are thousands of playa lakes. Playa lakes are the most numerous wetlands in the region, totaling more than 40,000 in eastern New Mexico, Colorado and Wyoming, western Kansas, Nebraska and Oklahoma, and the Texas Panhandle combined. More than 95 percent of the world's playa lakes are located in the western Great Plains. Playas and Playa Lakes Thousands of small playas with clay soil dot the Llano Estacado. Playas are circular depressions; when filled with rain water, they are termed playa lakes. Playas are actually small, round, and shallow individual wetlands that average 17 acres in size. They have clay-lined basins and naturally fill with water periodically from rainfall and its associated runoff. These small depressions hold water for several months after a rain. Playas and Playa Lakes To get a good idea of the number and distribution of playas on the Llano Estacado, please examine this map of the playas around Lubbock, Texas. Much of the Llano is covered by this density of playas. Note that these rounded playas are not very large—most average about 17 acres in area. Also, remember that these playa “lakes” are only filled with water in the spring and early summer. They are shallow, dry depressions most of the year. Playas and Playa Lakes Playas on the Llano Estacado provide over 400,000 acres of wetland habitat. Playas and playa lakes occupy only approximately 2- 3% of the total landscape, but they are vital for the survival of many birds, mammals, and many other plants and animals. Playas support 37 mammal species, more than 200 bird species, 13 amphibian species, 124 aquatic invertebrates, and more than 340 species of plants. Playas and Playa Lakes Playa lakes may be the most important wetland habitat type for birds on the Great Plains. Playas are wintering places for many species of ducks, geese, and cranes. In the summer, some ducks and wading birds nest in or near playas with water. Playas and Playa Lakes Playa lakes are a vital habitat for wildlife, especially for migrating birds that depend on the region's resources to "refuel" for their journey between Canada, the United States and South America. More than 200 species of birds use playas during the breeding, wintering or migrating seasons. Given the diversity of wildlife found on playas, the wetlands offer rich experiences for wildlife-watchers, photographers, and other naturalists. Playas and Playa Lakes Big salt playas (playas with very alkaline or salty water) are not as common on the Llano Estacado. Thousands of Sandhill Cranes winter on the salt playas from Muleshoe to Midland. No plants live on the bottom of a salt playa. The cranes do not feed on playa vegetation, but fly to them to roost at night for protection from predators. During the day, they feed on surrounding fields, then return to the playa in the evening Watching the flocks of Sandhill Cranes fly in to to roost for the night. roost in the evening is one of the great local birding sights. Playas and Playa Lakes Playa lakes are shallow, usually round, wetlands with clay floors that lie in the lowest point of a generally large, closed watershed and collect rainfall and associated runoff from surrounding uplands. Their average size is 17 acres, and all playa lakes combined make up about 2 to 5 percent of the total western prairie landscape. Playa lakes in the Texas Panhandle. Playas and Playa Lakes The majority of playa lakes are located in or adjacent to farms, grazing lands and feedlots, which can create a number of impacts on playas including: pesticide and fertilizer runoff, contaminants from feedlot runoff, overgrazing, and sedimentation. Sedimentation is the primary threat to playa lakes. Sediment runoff into playa basins reduces the volume of water they can hold and may disrupt the wet-dry cycles necessary for vegetation growth. Playas and Playa Lakes Additional impacts on playas include: development, oil field water dumping, and altered water cycles and basin structure. Most playa basins have been manipulated to increase storage capacity for irrigation purposes. The presence of additional water from irrigation runoff also alters natural playa hydrology. Many playas are pumped for irrigation (photo at right). Playas and Playa Lakes Playas are ephemeral, or seasonal, in nature and hold water only after rainfall or runoff events. Most of the time, they are dry, which is partially why many people don't recognize them as wetlands. Playa lakes are sometimes mistakenly referred to as buffalo wallows, mud pits or evaporation pans. But they are, in fact, an important type of wetland that is essential for the natural health of the land, plants, and animals. Playas and Playa Lakes Plants in clay playas must adapt to being covered with water for months in the spring and early summer, and then being dry for many more months the rest of the year. Note the mud cracks in the dry playa at right, into which rain water can infiltrate and recharge the aquifer. Playas and Playa Lakes The landscape of Texas is subject to frequent episodes of below- average precipitation and recurrent intervals of prolonged, severe drought. Since 1996, much of the west-central portion of Texas has experienced severe drought conditions with annual precipitation falling to less than 60 percent of normal. Drought has affected regional ranching operations and the harvests of important cash crops. In addition, statewide reservoir storage levels have fallen to a 16-year low in a state experiencing a booming economy and rapid population growth. Playas and Playa Lakes Playa Lakes in Texas High Plains An even closer inspection of drought conditions is offered by the imagery acquired by the LANDSAT Earth- mapping satellite. During the early summer of 1999, substantial rainfall occurred in the High Plains from the area near Lubbock north to Amarillo. Water accumulated in small playa basins throughout the region. By the winter of 2000, however, following several months of reduced rainfall, dramatic changes were visible in the concentration of surface water. Many basins have completely dried by early January. July 5, 1999 January 13, 2000 Playas and Playa Lakes August 6, 1999 January 13, 2000 Decreasing Water Availability Larger playa basins and reservoirs in the southern High Plains exhibit similar changes during the same period. LANDSAT imagery registered to the same coordinate system can be used for change detection analysis of surface water availability during drought conditions. Information of this kind forms a valuable supplement to field reports of rain gages, water well levels, stream flows and reservoir capacities. Note above how playa lake shorelines have retreated due to lack of rainfall during drought conditions. Playas and Playa Lakes An important natural resource in any state are its aquifers. Aquifers are bodies of rock just below the surface which contain fresh water. If you drill a well into the aquifer, the well bore will fill up with water that you can pump. The top of the water in the well and the aquifer are at the same depth. This depth is termed the water table. The land above the aquifer is called the recharge area. This is where rainwater enters the aquifer and keeps it filled. Introduction to the Llano Estacado Most of the habitats and organisms of the Llano depend on the presence of water during some time of the year. Aquifers are fresh water-bearing rocks in the shallow subsurface. In this case, the water is not ephemeral, but constant. However, it is recharged by rainfall at slow rates, and is thus subject to being extracted too quickly for replacement. Springs are fed by aquifers, and the springs dry up when the aquifers become depleted due to drought and human over-use. This is the case on the Llano Estacado. Playas and Playa Lakes The Ogallala Aquifer (pronounced oh-ga-la’-la) is one of the largest aquifer systems in the world. It stretches across all or portions of eight states generally from north to south to include South Dakota, Nebraska, Wyoming, Colorado, Kansas, Oklahoma, New Mexico, and Texas, and underlies about 174,000 square miles. The aquifer is named after the formation it occupies, and this was named in 1899 after the town of Ogallala, Nebraska. Introduction to the Llano Estacado Development of irrigation technology during the 1940s enabled the exploitation of the Ogallala Aquifer, now being depleted at unsustainable rates. Since World War II, the Llano Estacado has experienced expanded cultivation, making the Llano one of the most agriculturally-impacted regions in the Western Hemisphere. North of the Canadian River near Amarillo, the Ogallala Aquifer is recharged in the foothills of the Rocky Mountains. But only rain that actually falls on the Llano Estacado recharges the Ogallala Aquifer here, so it has been depleted much more rapidly. The Ogallala Aquifer Introduction to the Llano Estacado Another name for the Ogallala Aquifer is the High Plains Aquifer. Remarkably, this enormous aquifer lies beneath the driest grassland in the United States, allowing it to be used for agriculture irrigation, even during cycles of drought. This is one of our country’s greatest natural resources, but few people know about it, and few protect it. Cotton, wheat, corn, and sorghum are the dominant crops, all watered using groundwater from the aquifer. Livestock are grazed on the uncultivated rangelands. The High Plains or Ogallala Aquifer Introduction to the Llano Estacado The Ogallala or High Plains Aquifer is the largest aquifer in the world. Much of the water taken from this natural resource was unregulated by either state or federal agencies. Before depletion became a problem, the Ogallala held more fresh water than all the lakes and streams on Earth. Water Saturation of the Ogallala Aquifer Introduction to the Llano Estacado The law in Texas allowed landowners to extract as much groundwater as they wished, and many took too much. The result was a depletion of the aquifer, lowering its top (the water table) hundreds of feet since the 1940s when irrigation began. Now, this great aquifer is in danger of permanent damage. This law—termed the right of capture—is still in effect! Depletion of the Ogallala Aquifer Playas and Playa Lakes Texas has many major and minor aquifers. Two of the largest are the Ogallala Aquifer (blue) and the Edwards Aquifer (light green) shown on the map at left. The Ogallala Aquifer underlies the Llano Estacado is the major source for irrigation water to support agriculture in this area. Most crops could not be grown here without irrigation water from the aquifer. Note the location of the Ogallala Aquifer in Andrews County. Playas and Playa Lakes The map of Texas Minor Aquifers shows a second aquifer in Andrews and Ector County, the Dockum Group, which is Triassic in age and lies beneath the Ogallala Aquifer in this region. MRT, June 3, 2008, p. 1A, WCS officials continue education campaign, “…information from a geologist about how the site is dry and does not sit over an aquifer.” “In this particular area, there are no active geological processes that would compromise the site.” Geologist: Robert M. Holt, U Miss. Is this statement really true? Current active geological processes: earthquakes, fracturing, wind erosion, stream flooding, water erosion. Playas and Playa Lakes The Ogallala Aquifer lies relatively near the land surface in most of its area with a maximum thickness of about 1,000 feet with a few hundred feet more the norm. Even in those areas of only a few feet of thickness, the aquifer can almost always be counted on to yield water to a well drilled into it. Some wells yield only a few gallons of water per minute, while others yield 1,000 gallons of water per minute or more. The Ogallala Aquifer not only includes the portion of the Ogallala that is saturated with water, but may also include saturated portions of the overlying and underlying formations that are hydraulically connected to the Ogallala. Water in the aquifer on the Southern High Plains flows from northwest to southeast at about 150 feet per year under natural conditions. This rate of movement can be altered by discharge from the aquifer by pumping wells. Playas and Playa Lakes Deposition of the Ogallala Formation began 10 to 12 million years ago during late Tertiary (Miocene/Pliocene) geologic time. Sand, gravel, silt, and clay eroded from upland areas to the west and north were deposited over the land surface of the present-day High Plains by primarily eastward flowing streams. The surface on which the sediments were deposited would have been much like the present area located east of the High Plains escarpment characterized by low hills, relatively shallow valleys, and meandering streams. The uppermost layer of the Ogallala Formation is typically a caliche layer described as the “Caprock Caliche.” This layer locally varies in thickness and has been reported to be as much as 60 feet thick in some areas. The caliche layer formed about one million years ago after the land surface stabilized and soils formed. Playas and Playa Lakes Playas and Playa Lakes Playas and Playa Lakes Playas and Playa Lakes Playas and Playa Lakes Playas and Playa Lakes The Ogallala Aquifer underlies approximately 174,000 square miles of the Great Plains region, primarily in Texas, New Mexico, Oklahoma, Kansas, Colorado and Nebraska. The Ogallala has long been a major source of water for municipalities, industries, and most notably agricultural development since the turn of the century. In 1990, the aquifer was measured to contain about 3.270 billion acre-feet of water. Pumping for irrigation is the primary use of the aquifer. In 1949, the Ogallala irrigated 3 million acres; by 1997 it irrigated 14 million acres. Playas and Playa Lakes The natural recharge rate for the Ogallala Aquifer on the Llano Estacado is ¾ inch a year, far less water than is being removed each year for irrigation. Consequently, the aquifer's water supply has declined steadily since the 1940s. Recent measurements show a 1.35 feet drop per year from 1992 to 1997. Use of the Ogallala began at the turn of the century, but the rate was small, probably not greater than recharge. During World War II, however, irrigation technology improved, and reliance on the Ogallala now steadily increased. During this time, the Ogallala water supply progressively declined: From 1950 to 1980 water levels dropped 9.9 feet, and from 1980 to 1999 they dropped 3.2 feet, according to the U.S. Geological Survey. Playas and Playa Lakes Although current dry land farming techniques have resulted in reduced pumping, the amount of groundwater being withdrawn still greatly surpasses the aquifer's natural rate of recharge. In many places in Texas, the water table— the top of the water level in the Ogallala Aquifer—has dropped hundreds of feet, and pores in the rock are in danger of collapsing or being permanently damaged. Playas and Playa Lakes Over the past several decades, researchers have gathered substantial evidence pointing to playas lakes as the primary source of recharge for the Ogallala Aquifer. This is big news for western Great Plains states, which have relied on pumping the Ogallala for agricultural, municipal and industrial use since the turn of the century. Although this research has been going on for quite some time, the results are relatively unknown to the general public and even to conservation professionals. Since about 99 percent of playa lakes are located on private land, this information is crucial for farmers, ranchers, and natural resource managers who hope to conserve water and maintain agricultural economies of the region. Playas and Playa Lakes Examine the cross-section of an idealized playa above. The playa is shallow, only 1’-3’ deep. The water (blue) enters from the surrounding watershed when it rains. These watersheds are usually agricultural land, so the entering water can contain chemicals. The water is held in the playa by a clay layer (brown) that gradually thickens over the years. The clay comes from sediment mixed in the water from the surrounding land. The water in the playa lake both slowly evaporates and infiltrates, and the playa gradually dries up. Playas and Playa Lakes According to studies conducted in the Southern High Plains region of Texas and New Mexico, natural recharge occurs throughout much of the landscape above the Ogallala Aquifer but is focused through playa wetlands. When a dry playa lake receives rainfall or associated runoff, water flows into the playa basin and penetrates the clay layer through deep cracks and plant root openings in the floor. Water then flows through fissures in the cap rock layer, ultimately reaching the Ogallala formation. Cracks in the playa lake floor eventually swell shut as the clay absorbs more water, limiting or diminishing recharge through the basin. Playas and Playa Lakes Aquifer recharge occurs both within playas and along the perimeter of playas. When a dry playa receives a surge of water from rainfall or associated runoff, water flows into the playa basin and penetrates the clay layer. These cracks eventually swell shut and become impermeable as the clay absorbs more water. Once a playa is full, recharge also occurs along playa perimeters where clay is thin or non-existent. Current research on playas in the Southern High Plains of Texas found that recharge rates in playa basins exceeds three inches per year in unaltered playas. More than 70 percent of playas have been altered from their natural state by tilling, pitting, intentional filling, or filling through sedimentation. Playas and Playa Lakes Recharge also occurs along the wetland's perimeter where clay is thin or non- existent. It is here that playa permeability increases (permeability is a measure of how easily a substance transmits fluids). Landscape-wide recharge to the Ogallala in the Southern High Plains is about 11 mm of water per year, and about 9.2 mm of that is focused through playa lakes. This means that 85-90 percent of all recharge is occurring on 2-3% of the landscape, amounting to about 3-6 inches per year under playa lakes. This is why preserving playas is so important. Playas and Playa Lakes Sedimentation is the most critical threat to playa lake function, especially in regard to groundwater recharge. Sedimentation occurs on all playas that are surrounded by tilled lands. Water from rain and irrigation carry soil into playas, gradually filling them. Sediment build up reduces the volume of water playas can hold and increases the rate of water loss through evaporation, thus limiting recharge. Incorrect land use by farmers—such as improper tilling—can lead to playa lake damage. Playas and Playa Lakes Playas and Playa Lakes Playas and Playa Lakes Playas and Playa Lakes The important of playas and playa lakes is now so well recognized, that a multi-state organization has formed to study and protect playa lake wetlands. This is the Playa Lakes Joint Venture (PLJV). The PLJV’s mission is to conserve playa lakes, other wetlands and associated landscapes through partnerships for the benefit of birds, other wildlife and people. The PLJV works in portions of six states: Colorado, Kansas, Nebraska, New Mexico, Oklahoma and Texas. PLJV Website: www.pljv.org Playas and Playa Lakes The PLJV operates similarly to a business, devoting attention to communications, fundraising, and infrastructure as well as biology. The PLJV was established in 1989, and is the seventh of 13 habitat joint ventures throughout the United States, which cover nearly every eco-region in North America. Joint ventures were originally conceived by the U.S. Fish and Wildlife Service in 1986 to implement the North American Waterfowl Management Plan. But with the recent advent of other bird conservation plans for waterbirds, shorebirds, and landbird species, many joint ventures, such as the PLJV, are now incorporating an "all bird" approach to their work.
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