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Source-linked reports with geographic coverage including Texas.

At least 829 records · Page 46Linked to original sources
USGS1995

Water-quality assessment in the Trinity River Basin, Texas: Nutrient concentrations in streams winter and spring 1994

A consistent, basin-wide set of data for streams in the Trinity River Basin is a necessary baseline to compare current conditions with historical data and to provide a reference for future studies. In addition, the basin-wide surveys begin the process of addressing the cause-effect relations for water quality in the basin. Effects of land use, geology, vegetation, soils, and reservoirs on water quality were considered in selection of sites. Seasonal differences were addressed by conducting two surveys, the first during the winter low-flow period and the second during the late spring high-flow period.

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USGS1995

Index of stations— Surface-water data-collection network of Texas, September 1993

The U.S. Geological Survey's investigations of the water resources of Texas are conducted in cooperation with the Texas Water Development Board, river authorities, cities, counties, U.S. Army Corps of Engineers, Bureau of Reclamation, International Boundary and Water Commission, and others. Investigations are under the general direction of R.O. Hawkinson, District Chief, Texas District. The address of the Texas District office is 8011 Cameron Road, Austin, TX 78754. As of September 30, 1993, the surface-water data-collection network of Texas (table 1 at end of the report) included 342 continuous-recording streamflow stations (D), 36 gage-height record only stations (G), 18 crest-stage partial-record stations (C), 62 floodhydrograph partial-record stations (H), 28 low-flow partial-record stations (L), 2 continuous-recording temperature stations (Ml), 12 continuous-recording temperature and conductivity stations (M2), 5 continuous-recording temperature, conductivity, and dissolved oxygen stations (M3), 20 continuous-recording temperature, conductivity, dissolved oxygen, and pH stations (M4), 23 daily chemical-quality stations (Q), 158 periodic chemical-quality stations (Qp), 20 lake surveys for water quality (Qs), and 75 continuous or daily reservoir-content stations (R). Plate 1 shows the location of the stations listed in table 1. Table 1 shows the station number and name, latitude and longitude, type of station, and the office principally responsible for collection of the data. An 8-digit permanent numerical designation for all gaging stations has been adopted on a nationwide basis; stations are numbered and listed in downstream order. In the downstream direction along the main stem, all stations on a tributary entering between two main-stem stations are listed between them. A similar order is followed in listing stations by first rank, second rank, and other ranks of tributaries. The rank of any tributary with respect to the stream to which it is an immediate tributary is indicated by an indention in the table. Each indention represents one rank. This downstream order and system of indention shows which gaging stations are on tributaries between any two stations on a main stem and the rank of the tributary on which each gaging station is situated.

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USGS1995

Coal geology of the Paleocene-Eocene Calvert Bluff Formation (Wilcox Group) and the Eocene Manning Formation (Jackson Group) in east-central Texas: Field trip guidebook for the Society for Organic Petrology, Twelfth Annual Meeting, The Woodlands, Texas, August 30, 1995

The Jackson and Wilcox Groups of eastern Texas (fig. 1) are the major lignite producing intervals in the Gulf Region. Within these groups, the major lignite-producing formations are the Paleocene-Eocene Calvert Bluff Formation (Wilcox) and the Eocene Manning Formation (Jackson). According to the Keystone Coal Industry Manual (Maclean Hunter Publishing Company, 1994), the Gulf Coast basin produces about 57 million short tons of lignite annually. The state of Texas ranks number 6 in coal production in the United States. Most of the lignite is used for electric power generation in mine-mouth power plant facilities. In recent years, particular interest has been given to lignite quality and the distribution and concentration of about a dozen trace elements that have been identified as potential hazardous air pollutants (HAPs) by the 1990 Clean Air Act Amendments. As pointed out by Oman and Finkelman (1994), Gulf Coast lignite deposits have elevated concentrations of many of the HAPs elements (Be, Cd, Co, Cr, Hg, Mn, Se, U) on a as-received gm/mmBtu basis when compared to other United States coal deposits used for fuel in thermo-electric power plants. Although regulations have not yet been established for acceptable emissions of the HAPs elements during coal burning, considerable research effort has been given to the characterization of these elements in coal feed stocks. The general purpose of the present field trip and of the accompanying collection of papers is to investigate how various aspects of east Texas lignite geology might collectively influence the quality of the lignite fuel. We hope that this collection of papers will help future researchers understand the complex, multifaceted interrelations of coal geology, petrology, palynology and coal quality, and that this introduction to the geology of the lignite deposits of east Texas might serve as a stimulus for new ideas to be applied to other coal basins in the U.S. and abroad.

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USGS1995

Summary statistics and graphical comparisons of specific conductance, temperature, and dissolved oxygen data, Buffalo Bayou, Houston, Texas, April 1986-March 1991

Buffalo Bayou is the major stream that drains the Houston, Texas, metropolitan area. The U.S. Geological Survey has provided specific conductance, temperature, and dissolved oxygen data to the City of Houston for three sites along a 7.7-mile reach of Buffalo Bayou since 1986. Summary statistics and graphical comparisons of the data show substantial variability in the properties during 1986-91. Specific conductance ranged from about 100 microsiemens per centimeter at 25 degrees Celsius at each of the three sites to 17,100 microsiemens per centimeter at 25 degrees Celsius at the most downstream site, at the headwaters of the Houston Ship Channel. Water temperatures ranged from 5 to 33 degrees Celsius. Temperatures were very similar at the two upstream sites and slightly warmer at the most downstream site. Dissolved oxygen ranged from zero at the most downstream site to 11.7 milligrams per liter at the most upstream site.

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USGS1995

Water-quality assessment of the Trinity River Basin, Texas— Analysis of available information on nutrients and suspended sediment, 1974-91

The U.S. Geological Survey is conducting an assessment of water quality in the Trinity River Basin as part of the National Water-Quality Assessment Program. During the planning phase of this study, existing information on nutrients and suspended sediment was compiled and analyzed. A total of about 5,700 water-quality samples were analyzed from local, State, and Federal agencies. Of these, about 4,200 were from streams and about 1,500 were from wells. Additionally, atmospheric deposition data for two locations were obtained and analyzed. Spatial variations in nutrient concentrations in streams are related primarily to point sources and reservoirs. Median total nitrogen concentrations downstream from major point sources, downstream from reservoirs, and on tributaries were 6.0, 1.3, and 2.4 milligrams per liter, respectively. Median total phosphorus concentrations for the same three settings were 1.6, O. 1, and 0.2 milligrams per liter, respectively. The largest concentrations occurred at low flow downstream from Dallas, Texas, when streamflow dominated by treated wastewater from point sources. The smallest concentrations occurred immediately downstream from reservoirs, which act as sinks for nutrients. Nutrient concentrations in agricultural areas were positively correlated to percent of drainage in agricultural land use and to discharge, indicating washoff of nutrients from nonpoint sources during storms. As with concentrations, nutrient loads were related to the presence of point sources and reservoirs. Loads increased substantially in the Dallas-Fort Worth area with the addition of nutrients from point sources; loads decreased substantially as flow passed through Livingston Reservoir. Concentrations of total nitrogen and total phosphorus did not change significantly, at the 95 percent confidence level, from 1974 to 1991 at most sites. The exception was a decrease in phosphorus concentrations at two sites downstream from major wastewater-treatment plants in the Dallas area. Concentrations of organic nitrogen and ammonia declined and concentrations of nitrite plus nitrate increased at sites below major wastewater-treatment plants. These changes are indicative of improvements in wastewater treatment that converts organic nitrogen and ammonia to nitrite and finally nitrate. Because nitrogen conversion reactions consume oxygen, the occurrence of these reactions at the treatment plants instead of in the streams resulted in reduced loading of biochemical oxygen demand to the streams. The only nutrient measured in ground water was nitrate. Nitrate concentrations varied by aquifer with the largest median concentrations in the Queen City and Nacatoch aquifers. There was a significant rank correlation between nitrate concentrations and depth of well for all seven aquifer groups sampled, with largest concentrations present in shallow wells. The large concentrations could result from nonpoint sources of nitrate associated with agricultural and urban land use; however, attempts to correlate nitrogen fertilizer application rates and agricultural land use to concentrations of nitrate in ground water were inconclusive. Only limited suspended-sediment data were available. Four sites had daily sediment-discharge records for three or more water years (October 1 to September 30) between 1974 and 1985. An additional three sites had periodic measurements of suspended-sediment concentrations. There are differences in concentrations and yields among sites; however, the limited amount of data precludes developing statistical or cause-and-effect relations with environmental factors such as land use, soil, and geology. Data are sufficient, and the relation is pronounced enough, to indicate trapping of suspended sediment by Livingston Reservoir.

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USGS1995

Water-quality assessment of the Trinity River Basin, Texas - Review and analysis of available pesticide information, 1968-91

In 1991 the Trinity River Basin study unit was among the first 20 study units in which work began under full-scale program implementation of the National Water-Quality Assessment Program. A retrospective assessment was undertaken to review and analyze existing pesticide data and related environmental factors. Population and land-use data indicate human modifications to the landscape and hydrologic system of the study area during the period 1968–91. A variety of crops treated with pesticides were identified, with wheat and cotton accounting for the largest number of acres treated annually (541,250 and 519,870 acres, respectively). Agricultural-use estimates for the later period covered by this report (1988–90) indicate that 105 different pesticides were used and that 24 pesticides accounted for 75 percent of average agricultural use in the study area. Sorghum was treated by the largest number of the 24 mostused pesticides, and cotton was treated by the second largest number of those pesticides. Dimethoate and methyl parathion were the most heavily used of the organophosphate class pesticides. The herbicide 2,4–D was the most heavily used chlorophenoxy pesticide. Carbamate pesticides are used extensively in the study area, with carbaryl, carbofuran, methomyl, and thiodicarb accounting for the majority of the use of this class of pesticide. Miscellaneous pesticides included alachlor, arsenic acid, picloram, and glyphosate, among others. The data indicate that herbicide use generally is proportionally higher in the study area than in the Nation, and that insecticide use in the study area generally is proportionally lower than in the Nation. Eight different agencies collected the waterquality data used in this report. Samples were collected by all agencies at a combined total of 155 surface-water sites and 121 ground-water sites. The sampled media included water, bed sediment, and tissues of fish and other aquatic wildlife. Some 273 samples for analysis of the herbicide 2,4–D were collected as part of the city of Arlington’s data-collection program. The herbicide was detected in 74 percent of the samples, but none exceeded the Maximum Contamination Level for drinking water. Dallas Water Utilities collected pesticide samples during a storm in February 1977. Samples were collected at 17 sites with detections of some pesticides in over 50 percent of the samples. Diazinon was detected in 56 percent of samples and 2,4–D was found in 56 percent of samples. Texas Parks and Wildlife Department collected samples from fish tissue for analyses of organochlorine pesticides from 15 sites in the Dallas-Fort Worth area. Chlordane concentrations in some of the samples exceeded the Food and Drug Administration’s action level of 300 micrograms per kilogram. The Texas Water Commission collected ground-water samples in the study area during 1990 for the major types of pesticides and none were detected. No arsenic was detected in samples from 121 wells in or near the study area. Organochlorine and organophosphate samples were collected beginning in 1974 and ending in 1991. Concentrations of organochlorine pesticides in bed sediment decrease with increasing distance downstream from the Dallas-Fort Worth urban area. Pesticide samples collected by the U.S. Geological Survey indicated significant rank correlation between number of detects of chlordane and the percent of the contributing watershed classified as urban land use. Dieldrin in bed sediment samples, and lindane, diazinon, and malathion, in water samples, also were significantly correlated with urban land use. Chlordane and dieldrin were significantly correlated with distance downstream from the Dallas-Fort Worth urban area. Review of all available data showed that pesticides were detected to a substantial degree in various sample media over the time period covered by this report. The authors were able to locate little pesticide-sample data for ground water or for tributary streams because sampling efforts historically have been concentrated on the mainstem Trinity River.

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USGS1995

Geologic framework and hydrogeologic characteristics of the Edwards Aquifer recharge zone, Bexar County, Texas

In Bexar County, residential and commercial development on the Edwards aquifer recharge zone is increasing. The aquifer possibly can be contaminated by spills, leakage of hazardous materials, or runoff from the rapidly developing urban areas that surround, or are built on, the intensely faulted and fractured, karstic limestone outcrops characteristic of the recharge zone. Furthermore, some of the hydrogeologic subdivisions that compose the Edwards aquifer have greater effective porosity than others. The areas where the most porous subdivisions crop out might provide efficient avenues for contaminants to enter the aquifer. The Edwards aquifer recharge zone has relatively large permeability resulting, in part, from the development or redistribution of secondary porosity. Lithology, stratigraphy, diagenesis, and karstification account for the effective porosity and permeability in the Edwards aquifer outcrop. Karst features that greatly enhance effective porosity in the outcrop area include sinkholes and caves. Hydrogeologic subdivision VI, the Kirschberg evaporite member, appears to be the most porous and permeable subdivision within the Kainer Formation. Hydrogeologic subdivision HI, the leached and collapsed members, undivided, is the most porous and permeable subdivision within the Person Formation. Hydrogeologic subdivision II, the cyclic and marine members, undivided, is moderately permeable, with both fabric- and not-fabric-selective porosity. The faults in northern Bexar County are part of the Balcones fault zone. Although most of the faults in this area trend northeast, a smaller set of cross-faults trend northwest. Generally, the faults are en echelon and normal, with the downthrown blocks typically toward the coast.

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USGS1995

Geology and hydrogeology of Naval Air Station Chase Field and Naval Auxiliary Landing Field Goliad, Bee and Goliad counties, Texas

The geologic formations that crop out near Naval Air Station Chase Field and Naval Auxiliary Landing Field Goliad military bases consist of fluvial to fluvial-deltaic sediments of Tertiary and Quaternary age. These formations include the Fleming and Goliad Formations of Miocene age, Lissie Formation of Pleistocene age, fluvial terrace deposits of Pleistocene to Holocene age, and alluvium of Holocene age. The lithology of these formations consists of sand, sandstone, silt, and clay, with lesser amounts of gravel and caliche in the outcrops. The freshwater aquifers underlying the study area are the unconfined Evangeline (watertable) aquifer, comprising the upper sandy parts of the Fleming Formation and Goliad Formation, and confined Fleming aquifers, comprising the thick sandstone beds of the Fleming Formation. Both military bases withdraw potable water from one of the confined aquifers. At Naval Air Station Chase Field, the transmissivity and storativity of the confined aquifer where the base withdraws its public water supply are 1,060 feet squared per day and 1.2x10 -4 , respectively, as computed from the results of a 74-hour constant-discharge aquifer test. Selected water-quality field measurements of specific conductance, pH, and temperature indicate that each of the three aquifers at Naval Air Station Chase Field are somewhat insulated from one another by the intervening confining units. Large vertical hydraulic-head gradients are present between the unconfined Evangeline aquifer and confined Fleming aquifers at Naval Air Station Chase Field and Naval Auxiliary Landing Field Goliad. These gradients, together with the results of the aquifer test at Naval Air Station Chase Field and assumed characteristics of the confining units, indicate that downward flow of ground water probably occurs from the water-table aquifer to the underlying aquifers. The rate of downward flow between the two confined Fleming aquifers (from A-sand to B-sand) can be approximated using an estimate of vertical hydraulic conductivity of the intervening confining unit obtained from assumed storage characteristics and data from the aquifer test. Under the relatively high vertical hydraulic-head gradient induced by the aquifer test, ground-water movement from the A-sand aquifer to the B-sand aquifer could require about 490 years; and about 730 years under the natural gradient. Future increases in ground-water withdrawals from the B-sand aquifer might increase downward flow in the aquifer system of the study area.

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USGS1995

Nutrient loading to Lewisville Lake, north-central Texas, 1984-87

Concentrations of nutrients in the streams of the 1,660-square-mile Lewisville Lake drainage basin have some association with the two types of physiographic regions in the basin prairie regions and cross timbers regions. Total nitrogen and phosphorus concentrations generally are larger in streams draining the prairie regions than in streams draining the cross timbers regions, a characteristic that might be accounted for in part by the fact that prairie regions tend to have more nutrient-rich, less-permeable soils than cross timbers regions. Most of the variability in nutrient loads is associated with variability in discharge. During a low-flow synoptic survey, the largest contributor of total nitrogen and total phosphorus (at the downstream-most site) was Isle du Bois Creek (815 pounds per day of total nitrogen and 146 pounds per day of total phosphorus). During a high-flow synoptic survey, the largest contributor of total nitrogen and total phosphorus (at the downstream-most site) was Elm Fork Trinity River (4,620 pounds per day of total nitrogen and 210 pounds per day of total phosphorus). On the basis of results of stormflow and periodic sampling, the total nitrite plus nitrate nitrogen that entered the reservoir on the average each day during 1986 was 5,640 pounds per day, and during 1987,4,480 pounds per day. During the same period, about one and one-half as much nitrogen in the form of total ammonia plus organic nitrogen entered the reservoir (8,530 pounds per day in 1986 and 7,020 pounds per day in 1987); and about one-fourth as much total phosphorus entered the reservoir during the period (1,310 pounds per day in 1986 and 1,080 pounds per day in 1987). Point sources accounted for small fractions (probably less than 10 percent) of the total nutrient load from Clear Creek, Little Elm Creek, Hickory Creek, and Elm Fork Trinity River. Most of the point-source load to Lewisville Lake could originate at a few sewage-treatment plants discharging to ungaged streams close to the reservoir. The estimated long-term (1974-89 water years) average annual total nitrogen load (excluding loads from sewage-treatment plants in ungaged areas) is 11,800 pounds per day. The estimated long-term (1974 89 water years) average annual total phosphorus load (excluding loads from sewage-treatment plants in ungaged areas) is 1,100 pounds per day.

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USGS1995

Geology and hydrology of the Edwards Aquifer in the San Antonio area, Texas

The Edwards aquifer, which is the sole source of water for the city of San Antonio, is one of the most permeable and productive carbonate aquifers in the United States. The aquifer is composed of extensively faulted, fractured, and cavernous limestone and dolomite of Early Cretaceous age lying within the Balcones fault zone a series of normal en echelon strike faults that separate the Edwards Plateau from the Gulf Coastal Plain in south Texas. Along segments of some faults, the entire thickness of the aquifer is displaced vertically, and these faults then act as barriers to downdip ground-water flow. The large porosity and exceptional permeability of the unconfined part of the Edwards aquifer result from the dissolution of limestone by circulating ground water and development of a cavernous network along fractures. The large porosity and permeability of the freshwater part of the confined Edwards aquifer result primarily from dedolomitization. The small permeability of the saline-water part of the confined aquifer is caused by the limited interconnection between the pores in the rock matrix and by the lack of substantial dissolution along fractures. The large transmissivity of the Edwards aquifer is indicated by the hundreds of highyielding wells, small hydraulic gradients, and large spring discharges. The determined transmissivity throughout most of the confined freshwater aquifer ranges from 430,000 to 2,200,000 feet squared per day; the determined transmissivity of the unconfined aquifer generally is less than 430,000 feet squared per day. Faulting causes the aquifer to be highly anisotropic, and simulation indicates anisotropy ratios ranging from 0.0:1 to 1:1. The ground-water-flow system of the Edwards aquifer includes several components. These include a catchment area on the Edwards Plateau where the unconfined aquifer receives direct recharge, an area of confining beds crossed by streams draining the Edwards Plateau, a major recharge area within the Balcones fault zone where streams lose flow directly into the unconfined Edwards aquifer, and the confined Edwards aquifer that consists of the freshwater and salinewater zones. Water entering the Edwards aquifer in the Balcones fault zone moves downdip in a generally southeasterly direction into the confined parts of the aquifer. In the confined aquifer, flow is toward the east and northeast under low hydraulic gradients through fractured, highly transmissive limestone and ultimately discharges at large springs and wells. All of the base flow and some of the storm runoff of streams crossing the recharge area infiltrates to the unconfined aquifer. On the basis of streamflow losses, the average annual recharge for 1934-88 was 635,500 acre-feet. Freshwater discharges from the Edwards aquifer primarily from wells, springs, and seeps. Beginning in 1968, annual discharge from the aquifer has consistently exceeded average annual recharge largely because of a doubling of well pumpage. However, total springflow also increased because of greater-than-average recharge during most years since the late 1960's. The total volume of circulating freshwater in the Edwards aquifer is about 45 million acrefeet. Long-term hydrographs at San Antonio indicate no net decline in ground-water levels during 1911-87; thus, there was no net loss of water from storage in the freshwater zone of the Edwards aquifer during that long-term period, assuming the San Antonio hydrograph represents the entire aquifer. However, short-term changes in water levels result largely from the variability of precipitation as indicated by severe declines during the drought of the late 1940's to middle 1950's and by rises to record highs during the abnormally wet years in the 1970's and 1980's. The principal components of the groundwater budget (recharge, springflow, and pumpage) have varied greatly over 55 years (1934-88) of pertinent hydrologic records. Annual recharge varied from about 44,000 to 2,000,000 acre-feet. Annual springflow varied from about 70,000 acrefeet to about 580,000 acre-feet. Pumpage increased from about 100,000 acre-feet annually in the early 1930's to more than 500,000 acre-feet annually during some years in the 1980's. However, the average annual recharge of 635,500 acrefeet is about equal to the sum of the average annual springflow (359,500 acre-feet) and average annual pumpage (273,000 acre-feet), indicating no longterm decrease in ground-water storage because of springflow and pumpage.

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USGS1995

Documented and potential extreme peak discharges and relation between potential extreme peak discharges and probable maximum flood peak discharges in Texas

The U.S. Geological Survey, in cooperation with the Texas Department of Transportation, conducted a study of extreme flood potential for Texas. Potential extreme peak discharges, derived from the relation between documented extreme peak discharges and their contributing drainage areas, can provide valuable information concerning the maximum expected peak discharge that could occur at a stream site. Documented extreme peak discharges and associated data were aggregated for 832 sites with and without streamflow-gaging stations in natural basins in Texas. A potential extreme peak discharge curve was developed for each of 11 hydrologic regions in Texas and for the State as a whole, based on documented extreme peak discharges and associated contributing drainage areas. The curve envelops, for a large range of drainage areas, the largest documented extreme peak discharges. Potential extreme peak discharges estimated from the curves were compared to probable maximum flood peak discharges estimated from various simulation models.

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USGS1995

Geologic framework and hydrogeologic characteristics of the Edwards Aquifer outcrop, Hays County, Texas

All of the hydrogeologic subdivisions within the Edwards aquifer outcrop in Hays County have some porosity and permeability. The most porous and permeable appear to be hydrogeologic subdivision VI, the Kirschberg evaporite member of the Kainer Formation; hydrogeologic subdivision III, the leached and collapsed members, undivided; and hydrogeologic subdivision II, the cyclic and marine members, undivided, of the Person Formation. The two types of porosity in the Edwards aquifer outcrop are fabric selective, which is related to depositional or diagenetic elements and typically exists in specific stratigraphic horizons; and not fabric selective, which can exist in any lithostratigraphic horizon. Permeability, the capacity of porous rock to transmit water, depends on the physical properties of the rock such as size, shape, and distribution of pores, and fissuring and dissolution. Two faults, San Marcos Springs and Mustang Branch, completely, or almost completely, offset the Edwards aquifer by juxtaposing Edwards aquifer limestone against nearly impermeable upper confining units along parts of their traces across Hays County. These faults are thought to be barriers, or partial barriers, to groundwater flow where the beds are juxtaposed. In Hays County, the Edwards aquifer probably is most vulnerable to surface contamination in the rapidly urbanizing areas on the Edwards aquifer outcrop. Contamination can result from spills or leakage of hazardous materials; or runoff on the intensely faulted and fractured, karstic limestone outcrops characteristic of the recharge zone.

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USGS1995

Residues and trends of organochlorine pesticide and polychlorinated biphenyls in birds from Texas, 1965-88

Concentrations of DDE (a metabolite of DDT) in birds decreased during recent years in most areas of the continental United States. Organochlorine pesticides were widely used in agriculture in Texas from the early 1950s to the 1970s. I used previously published data to determine whether concentrations of DDE and polychlorinated biphenyls (PCBs) in birds from Texas have followed a decreasing trend similar to that in birds from other areas in the United States. A total of 2,669 bird samples was collected between 1965 and 1988 from diverse locations in Texas and was analyzed for organochlorines and other environmental contaminants. The brown pelican ( Pelecanus occidentalis ), peregrine falcon ( Falco peregrinus ), laughing gull ( Larus atricilla ), black skimmer ( Rynchops niger ), and European starling ( Sturnus vulgaris ) were the most frequently studied species. DDE and PCBs were the most commonly detected organochlorines in bird tissues. Mean DDE concentrations ranged from 0.4 to 61.00 parts per million (ppm) wet weight (ww) and PCBs from 0.02 to 32.00 ppm ww. Concentrations of DDE in eggs and carcasses of black skimmers decreased significantly during 1970-84 and dropped from approximately 10 to nearly 3 ppm ww. PCBs decreased from approximately 7 ppm ww to 1 ppm ww in eggs and carcasses. DDE concentrations in eggs of brown pelicans varied from more than 3 ppm ww in 1970 to approximately 1 ppm ww in 1983; and PCB concentrations diminished from about 10 to 1 ppm ww. Decreasing trends in concentrations of DDE and PBCs were observed in most species, although in some cases, the estimated trends were not significantly different from zero. Concentrations of DDE in birds from the Texas coast decreased from more than 6.0 ppm in 1978 to below 0.5 ppm in 1985. The decreasing ratios in selected species varied from approximately 2.0 to 12.0 (DDE) and from 4.5 to 9.0 (PCBs). The results indicate that in general from 1965 to 1988, DDE and PCBs declined in birds from Texas.

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