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At least 775 records · Page 43Linked to original sources
USGS1997

Chemical evolution and estimated flow velocity of water in the Trinity Aquifer, south-central Texas

Three permeable zones with varying lithology and water chemistry compose the Trinity aquifer, a principal source of water in the 5,500- square-mile study area in south-central Texas. The upper permeable zone locally yields small quantities of water to wells and was not included in this study. The middle permeable zone primarily is composed of limestone with minor amounts of dolostone. Terrigenous sand and marine limestone, with minor amounts of dolostone, are the principal lithologic units in the lower permeable zone. Dissolved solids concentrations range from 329 to 1,820 milligrams per liter in water samples from the middle permeable zone and from 518 to 3,030 milligrams per liter in water samples from the lower permeable zone. Principal hydrochemical facies in the middle permeable zone are calcium magnesium bicarbonate and calcium magnesium sulfate. Hydrochemical facies in ground-water samples from the lower permeable zone vary. Tritium concentrations as large as 5.3 tritium units in the southeastern part of the study area are indicative of relatively recent recharge. Results of a geochemical mass balance simulation along a flowpath in the middle permeable zone indicate a mass transfer of 4.25 millimoles per liter of dolomite dissolved, 5.74 millimoles per liter of gypsum dissolved, 0.46 millimole per liter of sodium chloride dissolved, 8.07 millimoles per liter of calcite precipitated, and 0.67 millimole per liter of calcium-for-sodium cation exchange between solid and aqueous phases. These results support dedolomitization as a principal chemical process in the middle permeable zone of the Trinity aquifer. Results of a simulation along a flowpath in the lower permeable zone indicate a mass transfer of 0.41 millimole per liter of dolomite dissolved, 0.001 millimole per liter of gypsum dissolved, 9.58 millimoles per liter of sodium chloride dissolved, 1.09 millimoles per liter of calcite precipitated, and 1.11 millimoles per liter of sodium-forcalcium cation exchange between solid and aqueous phases. Lower permeable zone processes indicate sodium chloride dissolution, dedolomitization, and cation exchange. Ground-water-flow velocities determined from adjusted carbon-14 ages, calculated using NETPATH, for selected flowpaths in the middle and lower permeable zones were about 1.7 feet per year and less than about 4.4 feet per year, respectively.

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USGS1997

Geologic framework of the Edwards Aquifer and upper confining unit, and hydrogeologic characteristics of the Edwards Aquifer, south-central Uvalde County, Texas

The stratigraphic units of the Edwards aquifer in south-central Uvalde County generally are porous and permeable. The stratigraphic units that compose the Edwards aquifer in south-central Uvalde County are the Devils River Formation in the Devils River trend; and the West Nueces, McKnight, and Salmon Peak Formations in the Maverick Basin. The Balcones fault zone is the principal structural feature in Uvalde County; however, the displacement along the fault zone is less in Uvalde County than in adjacent Medina and Bexar Counties to the east. The Uvalde Salient is a structural high in south-central Uvalde County, and consists of several closely connected crustal uplifts that bring Edwards aquifer strata to the surface generally forming prominent hills. The crustal uplifts forming this structural high are the remnants of intrusive and extrusive magnatic activity. Six primary faults—Cooks, Black Mountain, Blue Mountain, Uvalde, Agape, and Connor—cross the length of the study area from the southwest to the northeast juxtaposing the Lower Cretaceous Salmon Peak Formation at the surface in the northwestern part of the study area against Upper Cretaceous formations in the central part of the study area. In the study area, the porosity of the rocks in the Edwards aquifer is related to depositional or diagenetic elements along specific stratigraphic horizons (fabric selective) and to dissolution and structural elements that can occur in any lithostratigraphic horizon (not fabric selective). Permeability depends on the physical properties of the rock such as size, shape, distribution of pores, and fissuring and dissolution. The middle 185 feet of the lower part of the Devils River Formation, the upper part of the Devils River Formation, and the upper unit of the Salmon Peak Formation probably are the most porous and permeable stratigraphic zones of the Edwards aquifer in south-central Uvalde County.

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USGS1997

Analysis of minimum 7-day discharges and estimation of minimum 7-day, 2-year discharges for streamflow-gaging stations in the Brazos River basin, Texas

The minimum 7-day, 2-year discharge (7Q2) was estimated for each of 97 streamflow-gaging stations in the Brazos River Basin, Texas, with at least 10 years of unregulated or 10 years of regulated discharge data using the Pearson Type III distribution fitted by L-moment statistics of the annual minimum 7-day discharges. Forty-six stations have at least 10 years of unregulated discharge data only, 26 stations have at least 10 years of regulated discharge data only, and 25 stations have at least 10 years of unregulated and 10 years of regulated discharge data. Statistical tests were applied to the annual minimum 7-day discharges to determine if the unregulated and regulated data have trends; and to determine if the data before regulation are significantly different from the data after regulation. Results of the Mann-Kendall test indicate a significant trend at the 95-percent confidence level for 8 of the 46 unregulated-only stations, for 6 of the 26 regulated-only stations, and for 5 stations before regulation and for 10 stations after regulation of the 25 stations with both unregulated and regulated data. Results of the Wilcoxon rank-sum test indicate a significant difference between the unregulated and regulated annual minimum 7-day discharges at the 95-percent confidence level for 16 of the 25 stations with both types of data. The 7Q2 is zero for 31 of the 46 unregulated-only stations and for 9 of the 26 regulated-only stations. The 7Q2 also is zero for 9 stations before regulation and for 3 stations after regulation of the 25 stations with both unregulated and regulated data. The 7Q2 ranges from 33 to 631 cubic feet per second for the eight regulated-only stations on the mainstem Brazos River. For the seven stations on the mainstem Brazos River with at least 10 years of unregulated and 10 years of regulated discharge data, the 7Q2 ranges from 0 to 568 cubic feet per second before regulation and from 0.30 to 670 cubic feet per second after regulation. The 7Q2 increased during regulation for 19 of the 25 stations with both unregulated and regulated data. The effect of regulation for most stations generally was an increase in the magnitude of the 7Q2.

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USGS1997

Water-quality assessment of the Trinity River Basin, Texas — Nutrients and pesticides in the watersheds of Richland and Chambers Creeks, 1993-95

A study of nutrients and pesticides was conducted during February-August 1995 in the west-central part of the Trinity River Basin, where land commonly is used for growing crops. Water and bed-sediment samples were collected at 8 small reservoir sites in the headwaters (known as Natural Resources Conservation Service reservoirs), at 5 stream sites, and at 3 Richland-Chambers Reservoir sites. The analysis included data from the Chambers Creek near Rice site (08064100), which was sampled repeatedly during March 1993-September 1995. Total nitrogen concentrations in the Natural Resources Conservation Service reservoirs were less than 1.0 milligram per liter, as nitrogen, except in 2 of the 8 reservoirs. For the five stream sites, total nitrogen concentrations at the beginning of the study ranged from 0.5 to 1.8 milligrams per liter. Peaks were noted in all stream sites during either March or April; the greatest peak concentration was 4.8 milligrams per liter, as nitrogen. By the end of the study, concentrations decreased to less than 1.2 milligrams per liter, as nitrogen. In the Richland-Chambers Reservoir, the February-March and June sampling showed total nitrogen concentrations of about 0.6 milligram per liter, as nitrogen. At the beginning of the study, all five of the stream sites had total phosphorus concentrations less than 0.04 milligram per liter, as phosphorus. Peak concentrations in the streams occurred in the May sampling except at one site. Two sites had concentrations greater than 0.2 milligram per liter, as phosphorus. By the end of the study, concentrations decreased to less than 0.04 milligram per liter, as phosphorus, except at one site where the concentrations were about 0.08 milligram per liter. Concentrations in the Richland-Chambers Reservoir were less than 0.04 milligram per liter, as phosphorus. Total nitrogen and total phosphorus concentrations generally increased with streamflow and with the percentage of cropland in the drainage area upstream from the sampling site. Herbicides were detected in the streams much more often than insecticides were. Nineteen herbicides and 9 insecticides were detected at the 08064100 Chambers Creek near Rice site. Atrazine and metolachlor, the most commonly detected herbicides, occurred in all samples at this site. Other herbicides detected in 25 percent or more of the samples were alachlor, fluometuron, prometon, simazine, trifluralin, and 2,4-D. At the beginning of the study, the number of herbicides detected in the five stream sites was 4 or 5. The greatest number of herbicides detected in the streams occurred in May samples, ranging from 7 to 10. The number of herbicides detected in the Richland-Chambers Reservoir ranged from 6 to 8. Generally, more herbicides were detected in high-streamflow samples than in low-streamflow samples. However, a consistent relation between the number of herbicides in samples and the percentage of cropland in a drainage area was not evident. At the beginning of the study, atrazine concentrations at the stream sites were less than 0.4 microgram per liter, except at one site. In the streams, concentrations peaked in March and April; the greatest peak concentration was 20 micrograms per liter. By the end of the study, atrazine concentrations decreased to less than 0.4 microgram per liter at all the stream sites. In the Richland-Chambers Reservoir, the concentrations were about 1 microgram per liter during February-March and about 3 micrograms per liter in June. Atrazine concentrations tended to increase with increasing streamflow. A consistent relation between atrazine concentrations and the percentage of cropland in a drainage area was not evident. The greatest number of insecticides detected in water samples was two. Diazinon, the most frequently detected insecticide, had slightly greater concentrations in May and June - between 0.01 and 0.02 microgram per liter. The only organochlorine insecticides detected in bed-sedime

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USGS1997

Hydrogeologic framework and geochemistry of the Edwards aquifer saline-water zone, south-central Texas

The Edwards aquifer supplies drinking water for more than 1 million people in south-central Texas. The saline-water zone of the Edwards aquifer extends from the downdip limit of freshwater to the southern and eastern edge of the Stuart City Formation. Water samples from 16 wells in the Edwards aquifer saline-water zone were collected during July–September 1990 and analyzed for major and minor dissolved constituents, selected stable isotopes, and radioisotopes. These data, supplemental data from an extensive water-quality data base, and data from other previous studies were interpreted to clarify the understanding of the saline-waterzone geochemistry. Most of the isotope and geochemical data indicate at least two distinct hydrological and geochemical regimes in the saline-water zone of the Edwards aquifer. On the basis of hydrogen and oxygen isotopes and radiocarbon data, the shallower updip regime is predominantly meteoric water that has been recharged probably from the freshwater zone within recent geologic time (less than tens of thousands of years). Also, on the basis of hydrogen and oxygen isotope data, water in the hydrologically stagnant regime (downdip) has been thermally altered in reactions with the carbonate rocks of the zone. The deeper water probably is much older than water in the shallow zone and is nearly stagnant relative to that in the shallow zone. The geochemical grouping observed in the wellwater data from well samples in the saline-water zone indicates that the zone is hydrologically compartmentalized, in part because of faults that function as barriers to downdip flow of recharge water. These fault barriers also probably impede updip flow. Flow compartmentalization and the resulting disparity in geochemistry between the two regimes indicate that updip movement of substantial amounts of saline water toward the freshwater zone is unlikely. Estimated in-place temperature of the samples collected indicates an increase with depth and (or) distance from the downdip limit of freshwater. The pH of the samples decreases with increasing distance from the downdip limit of freshwater, but the decrease is caused partly by the increase in temperature. Dissolved major ions and dissolved solids concentrations all indicate a progressive but monotonic increase in salinity from updip to downdip. The alkalinity of the water samples is predominantly bicarbonate because the low-molecular weight aliphatic-acid anion concentrations are small relative to the bicarbonate concentrations. The dissolved organic carbon concentrations also are lower than expected for an aquifer with economic amounts of oil and gas hydrocarbons.

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USGS1997

Hydrology of the shallow aquifer and uppermost semiconfined aquifer near El Paso, Texas

The availability of fresh ground water in El Paso and adjacent areas that is needed to meet increased demand for water supply concerns local, State, and Federal agencies. The Hueco bolson is the principal aquifer in the El Paso area. Starting in the early 1900s and continuing to the 1950s, most of the municipal and industrial water supply in El Paso was pumped from the Hueco bolson aquifer from wells in and near the Rio Grande Valley and the international border. The Rio Grande is the principal surface-water feature in the El Paso area, and a major source of recharge to the shallow aquifer (Rio Grande alluvium) within the study area is leakage of flow from the Rio Grande. The shallow aquifer and the underlying Hueco bolson aquifer are in general hydrologic connection, but wells that penetrate these aquifers have different water levels and water quality. The configuration (slope) of the predevelopment (pre- 1903) water table indicates that ground water in the Hueco bolson flowed south from the Texas-New Mexico State line toward the El Paso Valley and the Rio Grande. There the water moved upward from the Hueco bolson fill through the alluvium and discharged as seepage at the land surface or through evapotranspiration on the river flood plain. Subsequent (post-January 1903) development of the Hueco bolson has caused water levels to decline in both the bolson aquifer and the shallow aquifer, and these declines have reversed the original vertical hydraulic gradient and now cause vertical leak- 1 Hydrologist, U.S. Geological Survey. 2 Geologist, El Paso Water Utilities-Public Service Board. age downward. Water-level declines in the shallow aquifer have in turn induced increasing amounts of leakage from the Rio Grande and from irrigation canals. The reversal from upward to downward in vertical hydraulic gradient between the Rio Grande alluvium and the underlying Hueco bolson aquifer has induced shallow water in the alluvium to move downward into the deeper aquifer. The introduction of water from the alluvium probably has led to a gradual water-quality deterioration of ground water in the Hueco bolson aquifer. The extent of any deterioration is a major concern because the dissolved solids concentration in water from some wells is approaching 1,000 milligrams per liter and already has exceeded this limit in other wells.

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USGS1997

Migration chronology and distribution of redheads on the lower Laguna Madre, Texas

An estimated 80% of redheads (Aythya americana) winter on the Laguna Madre of southern Texas and Mexico. Because there have been profound changes in the Laguna Madre over the past three decades and the area is facing increasing industrial and recreational development, we studied the winter distribution and habitat requirements of redheads during two winters (1987-1988 and 1988-1989) on the Lower Laguna Madre, Texas to provide information that could be used to understand, identify, and protect wintering redhead habitat. Redheads began arriving on the Lower Laguna Madre during early October in 1987 and 1988, and continued to arrive through November. Redhead migration was closely associated with passing weather fronts. Redheads arrived on the day a front arrived and during the following two days; no migrants were observed arriving the day before a weather front arrived. Flock size of arriving redheads was 26.4 ± 0.6 birds and did not differ among days or by time of day (morning midday, or afternoon). Number of flocks arriving per 0.5 h interval (arrival rate) was greater during afternoon (21.7 ± 0.6) than during morning (4.3 ± 1.2) or midday (1.5 ± 0.4) on the day of frontal passage and during the first day after frontal passage. Upon arrival, redhead flocks congregated in the central portion of the Lower Laguna Madre. They continued to use the central portion throughout the winter, but gradually spread to the northern and southern ends of the lagoon. Seventy-one percent of the area used by flocks was vegetated with shoalgrass (Halodule wrightii) although shoalgrass covered only 32% of the lagoon. Flock movements seemed to be related to tide level; redheads moved to remain in water 12-30 cm deep. These data can be used by the environmental community to identify and protect this unique and indispensable habitat for wintering redheads.

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USGS1997

Wetland losses related to fault movement and hydrocarbon production, southeastern Texas coast

Time series analyses of surface fault activity and nearby hydrocarbon production from the southeastern Texas coast show a high correlation among volume of produced fluids, timing of fault activation, rates of subsidence, and rates of wetland loss. Greater subsidence on the downthrown sides of faults contributes to more frequent flooding and generally wetter conditions, which are commonly reflected by changes in plant communities {e.g., Spartina patens to Spartina alterniflora) or progressive transformation of emergent vegetation to open water. Since the 1930s and 1950s, approximately 5,000 hectares of marsh habitat has been lost as a result of subsidence associated with faulting. Marsh- es have expanded locally along faults where hydrophytic vegetation has spread into former upland areas. Fault traces are linear to curvilinear and are visible because elevation differences across faults alter soil hydrology and vegetation. Fault lengths range from 1 to 13.4 km and average 3.8 km. Seventy-five percent of the faults visible on recent aerial photographs are not visible on photographs taken in the 1930's, indicating relatively recent fault movement. At least 80% of the surface faults correlate with extrapolated subsurface faults; the correlation increases to more than 90% when certain assumptions are made to compensate for mismatches in direction of displacement. Coastal wetlands loss in Texas associated with hydrocarbon extraction will likely increase where production in mature fields is prolonged without fiuid reinjection.

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USGS1997

Community involvement in a multimedia outreach project for Caddo Lake, Texas

Caddo Lake is located in northeast Texas and northwest Louisiana and is the largest freshwater lake in Texas. A portion of the lake in Texas has been designated a "Wetland of International Significance" under the Ramsar Convention of the United Nations. The human community in the watershed has experienced a number of hydrological alterations to Caddo Lake over the last 100 years by the Federal Government. Thus, many landowners in the area have become organized to protect Caddo Lake against what some view as harmful further alterations. In 1992, the U.S. Congress appropriated funds for an initiative to conduct baseline studies of the natural resources of Caddo Lake in order to foster ecotourism and economic development in the surrounding counties. For the information gathering part of the initiative and in response to negative criticism of the Caddo Lake Initiative expressed at a public meeting, the U.S. Geological Survey's National Wetlands Research Center invited public participation in developing a multimedia outreach system to improve the understanding of the natural resources at Caddo Lake and provide information about the studies. In the development of the outreach system we sought to strengthen working relationships with the State of Texas, local governments, and grassroots citizens groups. The outreach system consisted of an MS Windows-based interactive CD-ROM package that incorporated pictures, sound, animation, and video footage of the lake and the local culture. Public involvement in system development served as a catalyst for changing community perceptions about Federal and states studies at Caddo Lake and fostered community endorsement of the Caddo Lake Initiative.

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USGS1996

Sediment quality triad assessment survey of the Galveston Bay, Texas system

To characterize the quality of sediments at key sites in the Galveston Bay Estuary, sediment samples were collected concurrently for chemical and physical analyses, toxicity testing and an assessment of benthic community structure. Significant toxicity, as determined by the sea urchin ( Arbacia punetulata ) pore water embryological development assay, was observed at 12 of the 24 sites investigated in this study. No toxicity was observed at any of the sites with the amphipod ( Grandidierella japonica ) solid-phase test. There were a number of sites with elevated levels of trace metals and petroleum hydrocarbons. The chemistry, toxicity and benthic data were ranked by station and a scaled rank sum was calculated to facilitate comparisons among the stations. Five sites exhibited strong evidence of contaminant-induced degradation, while 15 stations showed no evidence of contaminant-induced degradation. At eight additional sites the sediment quality triad (SQT) data indicated that unmeasured chemicals or conditions were stressing the system. Contaminant impacts could be reduced or eliminated by alternative regulatory and management practices, including the restriction of produced water discharges into coastal estuaries and the use of dredge material disposal practices that minimize the reintroduction of sediment-associated contaminants to the bays.

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USGS1996

Identifying water-quality trends in the Trinity River, Texas, USA, 1969-1992, using sediment cores from Lake Livingston

Chemical analyses were done on cores of bottom sediment from three locations in Lake Livingston, a reservoir on the Trinity River in east Texas to identify trends in water quality in the Trinity River using the chemical record preserved in bottom sediments trapped by the reservoir. Sediment cores spanned the period from 1969, when the reservoir was impounded, to 1992, when the cores were collected. Chemical concentrations in reservoir sediment samples were compared to concentrations for 14 streambed sediment samples from the Trinity River Basin and to reported concentrations for soils in the eastern United States and shale. These comparisons indicate that sediments deposited in Lake Livingston are representative of the environmental setting of Lake Livingston within the Trinity River Basin. Vertical changes in concentrations within sediment cores indicate temporal trends of decreasing concentrations of lead, sodium, barium, and total DDT (DDT plus its metabolites DDD and DDE) in the Trinity River. Possible increasing temporal trends are indicated for chlordane and dieldrin. Each sediment-derived trend is related to trends in water quality in the Trinity River or known changes in environmental factors in its drainage basin or both.

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USGS1996

DDE decreases in plasma of spring migrant peregrine falcons, 1978-94

Mean p,p'-DDE (DDE) residues in plasma of combined adult and subadult female peregrine falcons (Falco peregrinus) decreased significantly in spring migrants captured at Padre Island, Texas, between 1978 and 1979 (1.00 μg /g wet wt), 1980 (0.57), 1984 (0.50), and 1994 (0.34). No other organochlorine pesticides were detected (detection limit, 0.02 μ g/g) in 1994. Mirex, oxychlordane, dieldrin, heptachlor epoxide, and the parent material DDT were routinely found in plasma samples in earlier years. Polychlorinated biphenyls (PCBs) were found in 75% of the adult females in 1994, but PCB data collected in 1984 were not comparable. The decrease in organochlorine pesticide residues was associated with peregrine population increases in the Arctic and elsewhere in North America. The arctic peregrine ( F. p. tundrius ) was removed from the list of Threatened and Endangered Species by the U.S. Fish and Wildlife Service in 1994. Satellite telemetry and plasma sampling provide new insight into continuing sources of DDE and PCBs. Chemicals that replaced organochlorine pesticides require additional investigation in North and South America.

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USGS1996

Occurrence of polycyclic aromatic hydrocarbons in urban streams as assessed using semipermeable membrane devices, Dallas-Fort Worth metropolitan area, Texas

One of the primary goals of the U.S. Geological Survey's National Water Quality Assessment (NAWQA) Program is to determine the occurrence and distribution of contaminants in stream sediments and tissues of aquatic organisms (Crawford and Luoma, 1993). Metals and persistent organic contaminants are of principal concern. Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds that occur abundantly in the environment, are toxic and often carcinogenic to organisms, and could represent a long-term source of contamination. PAHs are metabolized and excreted by most higher vertebrates, particularly fishes, often making assessment of tissues concentrations impossible. Major sources of PAHs are the incomplete combustion of carbonaceous materials and oil spills. The objectives of this fact sheet are to summarize the occurrence of water-borne PAHs in three urban streams in the Dallas- Fort Worth metropolitan area and to assess the use of semipermeable membrane devices (SPMDs) as PAH samplers. One site on each of three streams was selected for monitoring the occurrence of PAHs (fig. 1). The sites were chosen to reflect varied urban land uses and the influences of point- and nonpointsource pollution. The monitoring was done using SPMDs during a 30-day period in late May and June 1994.

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USGS1996

Pesticides in urban and agricultural streams, 1993-95

Nonpoint sources of pesticides are a national issue and are a major interest in the U.S. Geological Survey National Water-Quality Assessment (NAWQA) Program because of their potential toxicity to humans and aquatic life. Using the water-quality data collected by the Trinity River Basin NAWQA study-unit team, an analysis of pesticides in urban and agricultural streams was made by aggregating and grouping data from several networks. The samples were collected during March 1993 through September 1995. About 70 samples were collected from urban streams and 70 from agricultural streams. The urban dataset consists of sampling sites in the Dallas-Fort Worth metropolitan area where more than 3.5 million people lived in 1990. Land use in the sampled urban watersheds is primarily residential, but there are commercial areas, such as shopping centers and office complexes along major highways and streets. The agricultural dataset consists of sampling sites in the watershed of Richland-Chambers Reservoir, an area in the west-central part of the Trinity River Basin where fertile soils are extensively cultivated. The land use is mostly cropland and pasture with some rangeland. In the cultivated areas, the major crops are corn, cotton, and sorghum. In the rangeland areas, cattle are the dominant livestock. In the pasture areas, hay is grown along with grass for cattle feed. None of the crops are irrigated. The material in this fact sheet is condensed from a report by Land and Brown (1996) where the study is presented in greater detail.

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USGS1996

Water-quality trends using sediment cores from White Rock Lake, Dallas, Texas

The U.S. Geological Survey National Water-Quality Assessment (NAWQA) Program has three objectives, one of which is "to define trends (or lack of trends) in water quality" (Leahy and others, 1990). Water-quality trends are of interest for at least three reasons: First, trends can improve our understanding of the influence of human activities on water-quality conditions; second, trends can indicate the effectiveness of environmental regulations; and third, trends can provide a warning of additional degradation of water quality in the future. A common approach for determining water-quality trends in streams is to apply statistical tests to historical data; however, historical water-quality data have several limitations. These include lack of data, inconsistent sampling and analytical methods, numerous measurements below detection levels, and questionable accuracy. If historical data are lacking or are inappropriate for statistical trend testing, water-quality records can be partly reconstructed using sediment cores from receiving water bodies such as reservoirs. The purpose of this fact sheet is to summarize the principal findings documented in a report on water-quality trends in White Rock Creek Basin using dated sediment cores from White Rock Lake (Van Metre and Callender, in press). The study used dated sediment cores to reconstruct water-quality conditions. More specifically, the changes in water quality associated with the watershed’s change from agricultural to urban land use and with the implementation of environmental regulations were identified.

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