Species Composition and Diversity of Macroinvertebrates in Two Playa Lakes on the Southern High Plains, Texas

-Two playa lakes on the Southern High Plains of West Texas were sampled over a 2-year period to determine the species composition and diversity of macroinvertebrates. Sixty species were collected in one or more developmental stages with Insecta dominant and Crustacea poorly represented. Diversity index values ranged from 1.5 to 4.0 and were generally higher for a modified basin than a relatively undisturbed lake. The Southern High Plains of West Texas and eastern New Mexico are dotted with small, flat-floored, undrained depressions called playa lakes which collect rainfall or agricultural run-off. Evaporation and percolation are the only natural means of water loss. These ephemeral to semipermanent bodies of water occur at a frequency of 900-1,000 per county and are primary reservoirs in a region with an average rainfall of 35.5-45.7 cm (Reeves, 1970). Considerable work has been done on the geomorphology and physiogomy of playa lakes on the Southern High Plains of Texas but little is known of their biology and ecology. Sublette and Sublette (1967) conducted a physiochemical and macroinvertebrate study of 23 playa lakes in eastern New Mexico and West Texas. They collected over 60 macroinvertebrate taxa and described basic successional patterns. Richardson (1971) investigated the general ecology and macroinvertebrate fauna of a desert playa lake in southern New Mexico. Home (1974) reported on the salinity and phyllopod fauna of some of the saline playas on the Southern High Plains. Parks (1975) examined the accuracy of various successional models in predicting the diversity and seasonal occurrence of macroinvertebrates in three playa lakes near Lubbock. Sweazy et al. (1977) revealed the toxic effects of wastewater effluent on tiger salamanders (Ambystoma tigrinum [Green]) at a playa lake in Lubbock County. Continual usage of insecticides, herbicides, and fertilizers on the High Plains of Texas has increased interest in monitoring and protecting dwindling water resources. Physiochemical analyses of water samples taken to the laboratory to evaluate prevailing environmental conditions are often expensive and laborious to perform, and the results only indicate conditions at the time tests are conducted. Therefore, baseline knowledge of the fauna of playas in agro-ecosystems is essential in assessing seasonal and long-term environmental change. This study was undertaken to survey the macroinvertebrates in two West Texas playas surrounded by farmland and to provide baseline diversity information for future studies. 'Coll. of Agric. Sci., Texas Tech Univ.. Manuscript No. T-10-119. HE SOUTHWESTERN NATURALIST 26(2):153-158 MAY 21, 19 This content downloaded from 207.46.13.111 on Sat, 21 May 2016 06:22:09 UTC All use subject to http://about.jstor.org/terms The Southwestern Naturalist STUDY AREA.-Two playas near Lubbock, Texas, were selected for study because of their relatively long life, faunal diversity, and location in an intensive farming area. Site A was located 12.5 km south and 0.5 km east of Hwy. 87 and 114th St. junction. The circular playa covered approximately 8.6 ha when full. A dense growth of pink smartweed (Persicaria bicorne Raf. and P. lapathifolium L.) surrounded the basin, with arrowhead (Sagittaria longiloba Engelm.) occurring sporadically in areas less dominated by pink smartweed. The playa margin supported a variety of trees, shrubs, and forbs, including water willow (Salix nigra Marsh), saltcedar (Tamarix aphylla Karst.), and ironweed (Prionopsis ciliata Nutt.). Study site B was located 10.9 km south and 0.8 km east of Hwy. 87 and 98th St. junction. Unlike site A, which was in a relatively natural condition, site B was highly modified and filled more quickly than site A. The rectangular basin at site B had very steep banks and covered approximately 3.9 ha when full. At either end the general contour became less formidable, giving the basin a scooped-out appearance. The steep banks restricted aquatic vegetation to the shallower ends. Both species of pink smartweed occurred but were far less abundant than at site A. The playa margin supported saltcedar, water willow, and a thick growth of Aster subulatus Mich. The soil at both sites was deep Amarillo fine sandy loam which is moderately coarse-textured and permeable. METHODS AND MATERIALS.-Weekly population sampling was started in early summer 1977 when the playas began filling and continued until they had completely dried. Rainfall and runoff events were monitored throughout the study. Six sampling sites encircling the playas were established at depths of 0.1 to 0.7 m. Most sampling sites were in the littoral zone since water 0.3 m deep supporting submergent vegetation was preferred macroinvertebrate habitat. The location of the sixth sample was always downwind to compensate for any clumping effect. Macroinvertebrates were collected by taking two 180° sweeps with a d-frame net. The first sweep captured free-swimming forms and mixed approximately 2.5 cm of bottom sediments into the water column. The second sweep contained primarily sediments and benthos dwellers. In the laboratory, samples were washed through a large mesh screen (12 mm) to remove large leaves and twigs. Samples were then placed in 70% ethanol for 10 minutes and rinsed again. The remaining material was placed in a concentrated sugar solution (1.1 kg sugar/3.81 1 water) following the modified sugar flotation technique of Anderson (1959). Floating macroinvertebrates were strained off the surface and preserved in 70% ethanol. Remaining bottom debris was examined for organisms such as gastropods that were not adequately separated by sugar flotation. RESULTS AND DISCUSSION. Basin Filling. -Precipitation records for the 2 years of study are shown in Fig. 1. The first samples were taken on 13 May 1977 when the maximum depths for playas A and B were 0.8 m and 2.1 m, respectively. An additional 8.9 cm of rainfall during June through mid-July increased the depths to 1.0 m in playa A and 3.0 m in playa B. By the end of July, water levels began to substantially decline, with maximum depths of 0.07 m in playa A and 1.2 m in playa B. By 5 August sampling of playa A was restricted to a small depression and the basin was completely dry by 19 August. Sampling of playa B continued in water 0.07 0.1 m deep until 2 September when drying was complete. Both playas began refilling in mid-June, 1978, and sampling was renewed. Maximum depths were initially comparable to those in 1977, but limited rainfall during late June and early July resulted in reduced midsummer levels. By 30 June, sampling in playa A was restricted to the same depression present in August 1977, with drying complete a week later. Extensive pumping of water from playa B for irrigation in late June and early July resulted in noticeable water level fluctuations, whereas similar activity during 1977 caused no appreciable fluctuations. Sampling of playa B continued until complete drying on 15 July, which occurred a month and a half earlier than in 1977. 154 vol. 26, no. 2 This content downloaded from 207.46.13.111 on Sat, 21 May 2016 06:22:09 UTC All use subject to http://about.jstor.org/terms Merickel and Wangberg-Playa Lake Macroinvertebrates 12.70JAN 1977JUNE 1978