In cooperation with the U.S. Air Force
Spatial Distribution and Trends in Trace Elements, Polycyclic Aromatic Hydrocarbons, Organochlorine Pesticides, and Polychlorinated Biphenyls in Lake Worth Sediment, Fort Worth, Texas
By Glenn R. Harwell, Peter C. Van Metre, Jennifer T. Wilson, and Barbara J. Mahler
U.S. GEOLOGICAL SURVEY
Water-Resources Investigations Report 03–4269
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Contents
Abstract
Introduction
Purpose and Scope
Study Area
Acknowledgments
Methods and Preliminary Computations/Analyses
Collection of Bottom Sediment Samples
Analytical Methods
Age Dating and Mass Accumulation Rates
Normalization Techniques and Statistical Tests
Grain Size and Organic Carbon
Spatial Distribution and Historical Trends of Selected Hydrophobic Contaminants
Trace Elements
Regression Results
Spatial Distribution of Trace Elements
Historical Trends in Trace Elements
Polycyclic Aromatic Hydrocarbons
Spatial Distribution of PAHs
Historical Trends in PAHs
PAH Assemblage
Organochlorine Pesticides
Polychlorinated Biphenyls
Spatial Distribution of PCBs
Historical Trends in PCBs
Possible Sources of PCBs
Summary
References Cited
Figures
1. |
Map showing location of study area and approximate sampling locations in Lake Worth, Fort Worth, Texas, 2000–2001 | |
2–9. |
Graphs showing: | |
2a–e. |
Cesium-137 profiles in gravity core samples from Lake Worth, Fort Worth, Texas, 2000–2001 | |
3. |
Depth versus cesium-137 date in gravity core sample from background site upstream from IH–820 bridge in Lake Worth, Fort Worth, Texas, 2000–2001 | |
4a–x. |
Sediment characteristics and selected major elements in gravity core samples from Lake Worth, Fort Worth, Texas, 2000–2001 | |
5. |
Comparison of cadmium concentrations in lake sediment from selected areas of Lake Worth, Fort Worth, Texas, 2000–2001 | |
6a–f. |
Regression analyses to describe spatial distribution of trace elements in sediment from Lake Worth, Fort Worth, Texas, 2000–2001 | |
7a–g. |
Historical trends of trace elements in gravity core samples from Lake Worth, Fort Worth, Texas, 2000–2001 | |
8. |
Comparison of total polycyclic aromatic hydrocarbon (PAH) and total combustion PAH concentrations in lake sediment from selected areas of Lake Worth, Fort Worth, Texas, 2000–2001 | |
9a–i. |
Historical trends of total polycyclic aromatic hydrocarbon (PAH) and total combustion PAH concentrations, PAH source ratios, and organic carbon in gravity core samples from Lake Worth, Fort Worth, Texas, 2000–2001 | |
10. |
Map showing spatial distribution of total polychlorinated biphenyls (PCBs) in surficial sediment samples from Lake Worth, Fort Worth, Texas, 2000–2001 | |
11a–d. |
Graphs showing historical trends of polychlorinated biphenyls (PCBs) in gravity core samples from Lake Worth, Fort Worth, Texas, 2000–2001 |
Tables
1. |
Descriptive information for sediment sampling locations in Lake Worth, Fort Worth, Texas, 2000–2001 |
2. |
Mass accumulation rates computed from cesium-137 concentrations in gravity core sediment samples from Lake Worth, Fort Worth, Texas, 2000–2001 |
3. |
Concentrations of selected major and trace elements, grain size, and forms of carbon in sediment samples from Lake Worth, Fort Worth, Texas, 2000–2001 |
4. |
Kendall's tau correlation coefficients between trace elements and potential normalizing variables in sediments from Lake Worth, Fort Worth, Texas |
5. |
Linear regression equations used to estimate background trace element concentrations and anthropogenic contributions in sediment from Lake Worth, Fort Worth, Texas |
6. |
Concentrations of selected polycyclic aromatic hydrocarbons (PAHs) in sediment samples from Lake Worth, Fort Worth, Texas, 2000–2001 |
7. |
Concentrations of selected organochlorine pesticides and polychlorinated biphenyls (PCBs) in sediment samples from Lake Worth, Fort Worth, Texas, 2000–2001 |
Abstract
In spring 2000, the Texas Department of Health issued a fish consumption advisory for Lake Worth in Fort Worth, Texas, because of elevated concentrations of polychlorinated biphenyls (PCBs) in fish. In response to the advisory and in cooperation with the U.S. Air Force, the U.S. Geological Survey collected 21 surficial sediment samples and three gravity core sediment samples to assess the spatial distribution and historical trends of selected hydrophobic contaminants, including PCBs, and to determine, to the extent possible, sources of hydrophobic contaminants to Lake Worth. Compared to reference (background) concentrations in the upper lake, elevated PCB concentrations were detected in the surficial sediment samples collected in Woods Inlet, which receives surface runoff from Air Force facilities and urban areas. Gravity cores from Woods Inlet and from the main part of the lake near the dam indicate that the concentrations of PCBs were three to five times higher in the 1960s than in 2000. A regression method was used to normalize sediment concentrations of trace elements for natural variations and to distinguish natural and anthropogenic contributions to sediments. Concentrations of several trace elements—cadmium, chromium, copper, lead, and zinc—were elevated in sediments in Woods Inlet, along the shoreline of Air Force facilities, and in the main lake near the dam. Concentrations of these five trace elements have decreased since 1970. Polycyclic aromatic hydrocarbons also were elevated in the same areas of the lake. Concentrations of total polycyclic aromatic hydrocarbons, normalized with organic carbon, were mostly stable in the upper lake but steadily increased near the dam, except for small decreases since 1980. The Woods Inlet gravity core showed the largest increase of the three core sites beginning about 1940; total polycyclic aromatic hydrocarbon concentrations in post-1940 sediments from the core showed three apparent peaks about 1960, 1984, and 2000. The concentrations of organochlorine pesticides were low relative to consensus-based sediment-quality guidelines and either decreased or remained constant since 1970. The two likely sources of hydrophobic contaminants to the lake are urban areas around the lake and the drainage area of Meandering Road Creek that contributes runoff to Woods Inlet and includes Air Force facilities.
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