Use of gene marking to assess stocking success of red drum in Texas bays
No abstract available at this time.
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Geology topics
Research about Texas
Source-linked reports with geographic coverage including Texas.
Seagrasses, dredging and light in Laguna Madre, Texas, U.S.A.
Light reduction resulting from maintenance dredging was the suspected cause of large-scale loss of seagrass cover in deep parts of Laguna Madre between surveys conducted in 1965 and 1974. Additional changes to 1988, together with an analysis of dredging frequency and intensity for different parts of the laguna, were consistent with this interpretation. Intensive monitoring of the underwater light regime and compilation of detailed environmental data for 3 months before and 15 months after a dredging project in 1988 revealed reduced light attributable to dredging in four of eight subdivisions of the study area, including the most extensive seagrass meadow in the study area. Dredging effects were strongest close to disposal areas used during this project but still were detectable on transects >1·2 km from the nearest dredge disposal area. In the subdivision of the study area where most of the dredge disposal occurred, light attenuation was increased throughout the 15 months of observation after dredging. In the seagrass meadow and the transition zone at the outer edge of the meadow, effects were evident up to 10 months after dredging. Resuspension and dispersion events caused by wind-generated waves are responsible for the propagation of dredge-related turbidity over space and time in this system.
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Use of saltwater and freshwater habitats by wintering redheads in southern Texas
Behavioral data were gathered for redheads ( Aythya americana Eyton) using saltwater and freshwater habitats in southern Texas, the northern portion of their major wintering range, in 1989–90. Saltwater and freshwater habitats were used for different purposes by wintering redheads. Approximately 41% of all redheads in saltwater habitats were feeding, while only 0.1% of redheads in freshwater habitats were feeding. Redheads in saltwater habitats drank infrequently (0.3%), but 7.5% of redheads in freshwater wetlands were drinking. Only 23 courting activities were observed, but all occurred in freshwater wetlands. This study showed that redheads depend on saltwater habitats for feeding, which confirmed similar results from recent studies of redheads in the central and southern portions of the Laguna Madre in southern Texas. This study also showed that redheads depend on freshwater wetlands as sources of drinking water. This concurred with data on redhead behavior in the central portion of the Laguna Madre in Texas, but not for redheads wintering in the southern part of the Laguna Madre. Both habitats, saltwater and freshwater, must be considered as integral components of the redhead winter range throughout southern Texas.
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Distribution and status of submerged vegetation in estuaries of the upper Texas coast
Composition and biomass of beds of submerged aquatic vegetation (SAV) in estuaries along the upper Texas coast were examined from bottom core and rake samples taken along 72 line transects during July–August 1987. Substrate composition, salinity, water depth, and water clarity were also measured at each sample station. Halodule wrightii was the dominant species of SAV meadows (69% occurrence), followed by Ruppia maritima (36%). Najas guadalupensis and Vallisneria americana were only found in the shallow (<60 cm), oligohaline (<10 ppt) waters of Trinity Bay. Halophila engelmannii and Thalassia testudinum were only found in the deeper (35–110 cm) euhaline waters (30–40 ppt) of Christmas and Matagorda Bays. H. wrightii and R. maritima occurred across the greatest depth and salinity spectra, with R. maritima more prominent in shallower (<90 cm) mixohaline waters (10–30 ppt) and H. wrightii more prominent in euhaline waters (30–40 ppt). Beds of SAV were more extensive and had greater biomass along south shorelines compared to north shorelines (P<0.045), and depth to which vegetation grew was positively correlated with water clarity (r=0.927, P<0.001). The correlations of water depth, salinity, and water clarity with variation in SAV species composition and distribution suggest that abiotic tolerances documented by previous experimental studies are major factors influencing field distributions. Comparisons with similar field data from the early 1970s corroborate the reported decrease in SAV in the Galveston Bay complex and suggest a slight increase in the Matagorda Bay complex. Decline of SAV in the Galveston Bay complex coincided with major shorefront development and a decline in numbers of wintering redhead ducks Aythya americana . Protection of shorelines of upper coast estuaries is vital to maintaining SAV resources and the dependent fauna. Where possible, barrier island preserves should be established adjacent to beds of-SAV and development restrictions implemented to reduce impacts.
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Reproductive success of barn swallows nesting near a selenium-contaminated lake in east Texas, USA
Reproductive success and contaminant levels in 1986 and 1987 were compared between Barn Swallows nesting at selenium-contaminated Martin Lake, Texas, USA, and swallows nesting at a reference site. Nests were initiated about the same time or earlier at Martin Lake than at the reference site and clutch size was similar between the two locations. Nest success was significantly higher at Martin Lake than at the reference site and no embryo or chick deformities were documented. Selenium concentrations in 14 of 20 eggs from Martin Lake were above background (> 3 ppm, dry weight); two of 20 eggs contained > 5 ppm, a concentration associated with a 20% embryo mortality/deformity rate in some bird species. Selenium concentrations in the kidneys of adult swallows were higher at Martin Lake (mean = 14 ppm dry weight) than at the reference site (5·8 ppm). DDE, the only detected organochlorine compound, was in two of 10 eggs from Martin Lake; these concentrations were below those associated with chronic poisoning and reproductive problems. The maximum mercury concentration in livers of adult Barn Swallows (0·83 ppm, dry weight) was within the range for background levels (>5 ppm).
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40Ar/39Ar chronology and volcanology of silicic volcanism in the Davis Mountains, Trans-Pecos Texas
Field studies and 40 Ar/ 39 Ar dating reveal that silicic volcanism in the Davis Mountains part of the Trans-Pecos Texas volcanic field occurred in six episodes at 0.3 m.y. intervals between 36.8 and 35.3 Ma. Additionally, two groups of silicic intrusions were emplaced at 34.6 and 32.8 Ma. This episodicity is similar to that determined for volcanic fields dominated by ash-flow tuffs, yet voluminous, extensive silicic lavas are considerably more abundant than tuffs in the Davis Mountains, by number of flows and by volume. The preponderance of voluminous silicic lavas over tuffs most likely reflects low water contents and high temperatures of the alkalic and commonly peralkaline Davis Mountains magmas. The earliest episode, at 36.8 Ma, included a widespread and voluminous (possibly >1,000 km 3 ) suite of rhyolite and quartz trachyte lavas, several rhyolite domes, and a strongly rheomorphic, peralkaline ash-flow tuff erupted from a caldera in the northern Davis Mountains. The lava suite extends well beyond the Davis Mountains. Silicic lavas of all episodes probably erupted from widespread, fissure vents. The 36.5 Ma episode consisted of rhyolite to quartz trachyte lavas, also extensive and voluminous (∼200 km 3 ). The 36.3 Ma episode consisted of rhyolite to trachyte tuffs and lavas erupted from a central vent volcano in the southern Davis Mountains. The 35.9 Ma episode consisted of a single, moderately large (∼50 km 3 ) rhyolite lava and a small-volume ash-flow tuff erupted from a caldera in the western Davis Mountains. Rocks emplaced during the 35.6 Ma episode were also rhyolites, including an enigmatic rock that may be strongly rheomorphic ash-flow tuff or a combination of tuff and lava, followed by definite lavas. The 35.3 Ma episode consisted of two ash-flow tuffs, one of which is strongly rheomorphic, and additional voluminous rhyolite lavas (∼120 km 3 ). The rheomorphic tuff erupted from a caldera in the southwestern Davis Mountains. The source of the other tuff is probably in the western Davis Mountains. Intermediate and mafic rocks are minor, except around the southeastern flank of the Davis Mountains, where basalt is abundant. Mafic lavas erupted only during gaps in the silicic activity and on the flanks of the Davis Mountains. Nevertheless, basaltic magma probably drove the silicic magmatism, either by differentiation or by crustal melting, and was present throughout the time of Davis Mountains activity but could not penetrate the low-density silicic magma chambers until they cooled and solidified. The time required for cooling and solidification appears to be 0.1-0.2 m.y.
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Anticholinesterase exposure of white-winged doves breeding in lower Rio Grande valley, Texas
We studied exposure of breeding white-winged doves (Zenaida asiatica) to anticholinesterase compounds (organophosphorus and carbamate pesticides) in the Lower Rio Grande Valley (LRGV), Texas. Widespread use of organophosphorus pesticides and dove population declines prompted the study. We collected breeding adult doves in May and July 1991 (n = 28) and July 1992 (n = 33) at 6 locations. We used depression of whole-brain cholinesterase (ChE) activity (2 SD below control mean) to detect exposure; values from 4 hand-reared doves fed commercial pigeon chow served as the control. Mean brain ChE activity was lower (P lt 0.027) than the control sample at all 6 locations in 1991; 79% of the birds were diagnostic of exposure ( gt 16.1% ChE depression). Pooled 1992 field samples also were lower (P lt 0.036) than were control samples; doves from 4 of the 6 locations had brain ChE activity below (P lt 0.088) controls. Overall, 39% of 1992 doves were diagnostic of exposure to anticholinesterase compounds. Higher exposure rates in 1991 were probably due to increased use of organophosphorus pesticides. Research is needed documenting effects of sublethal exposure on white-winged dove productivity.
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Herbivory on shoalgrass by wintering redheads in Texas
An estimated 80% of redheads ( Aythya americana ) winter on the Laguna Madre of south Texas and Mexico and feed almost exclusively on shoalgrass ( Halodule wrightii ) rhizomes. Shoalgrass abundance has decreased by 60% over the past 30 years, and because the effects of shoalgrass loss on wintering redheads are unknown, we initiated a study to define habitat selection criteria and document the effect of wintering redheads on shoalgrass in the lower Laguna Madre, Texas. Redheads consumed an average of 75% of shoalgrass rhizome biomass at collection sites each winter. When rhizome biomass was grazed to a mean biomass of ltoreq 0.18 g dry mass/core (approximately 10 g dry mass/ml), shoalgrass did not recover to its previous level the following growing season. Thirty-three percent of the sites (10) were grazed below 0.18 g dry mass/core during both years of the study, while 64% (19) were grazed below 0.18 g during 1 or the other of the 2 winters. Ramet number was positively correlated ( P < 0.001, r 2 = 0.54) with rhizome biomass; however, this relationship was influenced by grazing intensity. Heavy grazing reduced the amount of rhizome attached to each ramet compared with ungrazed ramets. Grazing had no effect on root biomass ( P = 0.388), rhizome moisture content ( P = 0.553), or soil magnesium, phosphorous, and potassium ( P = 0.102, 0.499, 0.162, respectively). Redhead presence increased ( P = 0.042) soil nitrogen levels. Foraging areas selected by redheads within the lower Laguna Madre had lower ( P = 0.026) salinities (24 ppt) than areas not selected (35 ppt). Redheads did not select foraging areas in relation to crude protein levels in rhizomes. Shoalgrass habitat in the Laguna Madre should be protected from further losses and enhanced where possible.
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United States Geological Survey, programs in Texas
Meteorologic and physiographic factors in parts of Texas combine to produce some of the most intense rainstorms in the Nation; these rainstorms cause severe, destructive floods somewhere in the State almost every year. A recent example is the catastrophic flooding in the Houston area in October 1994 that resulted in at least 22 deaths, hundreds of millions of dollars in property damage, and substantial environmental damage. When flooding is imminent, the U.S. Geological Survey (USGS) mobilizes field crews that work around the clock making direct measurements of streamflow and water-surface elevations. The data collected by USGS personnel are provided continuously to the National Weather Service and the Federal Emergency Management Agency among others. The data collected during a series of floods provide a chronology of historical peak streamflows and water-surface elevations that aid in flood forecasting and the design of structures to convey or withstand flood waters.
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National Water-Quality Assessment Program - South-Central Texas
In 1991, the U.S. Geological Survey (USGS), Department of the Interior, began a National Water-Quality Assessment (NAWQA) Program. The long-term goals of the NAWQA Program are to describe the status of and trends in the quality of a large, representative part of the Nation's surface- and ground-water resources and to identify the major natural and human factors that affect the quality of these resources. In addressing these goals, the program will produce a wealth of water-quality information that will be useful to policymakers and managers at national, State, and local levels. The NAWQA Program emphasis is on regional water-quality problems. The program will not diminish the need for smaller studies and monitoring presently designed and conducted by Federal, State, and local agencies to meet their individual needs. The NAWQA Program, however, will provide a large-area framework for conducting many of these activities and an understanding about national and regional water-quality conditions that cannot be acquired from individual, local programs and studies. Studies of 60 hydrologic systems that include parts of most major river basins and aquifer systems (study-unit investigations) are the building blocks of the national assessment. Areas of the 60 study units range in size from less than 1,000 to more than 60,000 square miles (mi 2 ) and represent 60 to 70 percent of the Nation's water use and population served by public water supplies. Twenty study-unit investigations were started in 1991, 20 additional started in 1994, and 20 are planned to start in 1997. Assessment activities in the South-Central Texas study area (see fig.) began in 1994.
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Quaternary geologic map of the Dallas 4° x 6° quadrangle, United States
The Quaternary Geologic Map of the Dallas 4° x 6° Quadrangle was mapped as part of the Quaternary Geologic Atlas of the United States. The atlas was begun as an effort to depict the areal distribution of surficial geologic deposits and other materials that accumulated or formed during the past 2+ million years, the period that includes all activities of the human species. These materials are at the surface of the Earth. They make up the ground on which we walk, the dirt in which we dig foundations, and the soil in which we grow crops. Most of our human activity is related in one way or another to these surface materials that are referred to collectively by many geologists as regolith, the mantle of fragmental and generally unconsolidated material that overlies the bedrock foundation of the continent. The maps were compiled at 1:1,000,000 scale.
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Determination of chlorinated insecticides in bottom sediment using an electron-capture gas chromatography screening method, Austin, Texas, 1991 and 1992
Twenty-two bottom-sediment samples were collected from Town Lake in Austin, Texas, in 1991 and 1992 and analyzed for chlorinated insecticides by a reconnaissance-quality, electron-capture gas chromatography screening method developed by the U.S. Geological Survey (USGS). Four different chlorinated insecticides (aldrin, chlordane, dieldrin, and p,p'-DDT) and two degradation products of p,p'-DDT (p,p'-DDD and p,p'-DDE) were detected in these samples. The most significant insecticides detected were chlordane, which was detected in 20 of the 22 samples at concentrations that ranged from 26 to 140 micrograms per kilogram, and p,p'-DDT, which was detected in all 22 samples at concen- trations that ranged from 5 to 40 micrograms per kilogram. Degradation products of p,p'-DDT were detected in all 22 samples. Concentrations of p,p'-DDD ranged from not detected to 117 micrograms per kilogram and for p,p'-DDE from 9 to 97 micrograms per kilogram. Of the 22 samples collected, 15 also were analyzed by the standard USGS laboratory analytical method for chlorinated insecticides to determine the comparability of the two methods. Correlation coefficients were calculated for chlordane (0.8662), p,p'-DDT (0.6393), p,p'-DDD (0.9401), p,p'-DDE (0.8595), and dieldrin (0.3819). A paired sign test at the 95 percent confidence level showed no significant difference between the screening method and laboratory analytical method for all detected insecticides except aldrin. P-values were calculated from the data for chlordane (l.0000), p,p'-DDT (0.1796), p,p'-DDD (l,0000), p,p'-DDE (0.1796), and dieldrin (0.2891).
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Hydrogeologic and water-quality data from wells near the Hueco Bolson Recharge Project area, El Paso, Texas, 1990 and 1991
Tertiary-treated wastewater currently (1991) is being injected into the Hueco bolson aquifer at a site in northeastern El Paso, Texas, to supplement the quantity of available freshwater. Hydrologic data were compiled and water-quality and bacterial data were collected from existing wells near the Hueco Bolson Recharge Project (HBRP) in August and September 1990 and 1991. Borehole tracer tests indicated upward ground-water flow in nearly all tested intervals of several observation wells. The cumulative volume of injected water was less than the volume produced from wells adjacent to the HBRP area. Water levels in three production wells, located more than 1.5 miles from the injection wells, declined at rates comparable to those observed before injection operations. Water levels in wells located within 0.75 mile of the injection-well pipeline declined at a slower rate after HBRP injection operations had begun. Between 1985 and 1991, water levels in observation wells located within 700 feet of an injection well either did not appreciably decline, or declined at smaller rates than water levels in more distant production wells. Trihalomethane compounds were detected in water from 8 of the 16 observation and production wells sampled in 1990 and in 10 of the 17 wells sampled in 1991. Concentrations of trihalomethane compounds in these samples ranged from 0.05 to 1.9 |lg/L (micrograms per liter) in 1990 and from 0.05 to 1.4 |ig/L in 1991. Concentrations of trihalomethane compounds in samples of injected water from two wells were 27.8 and 34.6 |J,g/L respectively, in 1991. Dibromomethane and dichloromethane were detected in water from injection wells and from observation wells within about 700 feet of the injection wells. Aerobic bacteria were determined to be the only bacteria type present in ground water except for samples from two wells, which also contained denitrifying bacteria. The populations of aerobic bacteria determined in ground water ranged from 80 to more than 160,000 most probable number of organisms per milliliter of sample.
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Approximate changes in water levels in wells completed in the Chicot and Evangeline aquifers, 1977-94 and 1993-94, and measured compaction, 1973-93, in the Houston-Galveston region, Texas
This report is one in a series of reports that depict water-level changes since 1977 and compaction of subsurface material since 1973. The report was prepared in cooperation with the City of Houston and the Harris-Galveston Coastal Subsidence District, and presents maps showing the approximate changes in water levels in wells completed in the Chicot and Evangeline aquifers, 1977-94 and 1993-94 (figs. 1-4), extensometer site locations (fig. 5), and measured compaction, 1973-93 (fig. 6), in the Houston-Galveston region. Water-level change maps were prepared previously by Kasmarek and others (1993). The Houston-galveston region includes Harris and Galveston Counties and adjacent parts of Brazoria, Fort Bend, Waller, Montgomery, Liberty, and Chambers Counties.
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