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In cooperation with the Pueblo De Cochiti

Deposition and Chemistry of Bottom Sediments in Cochiti Lake, North-Central New Mexico

By Jennifer T. Wilson and Peter C. Van Metre

U.S. Geological Survey
Water-Resources Investigations Report 99–4258

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pdf (684 KB)


Contents

Abstract

Introduction

Purpose and scope

Methods

Quality control

Deposition of bottom sediment

Sediment surveys

Core lithology, grain size, and organic carbon content

Estimating age of sediments and rates of deposition

Chemistry of bottom sediments

Major elements

Trace elements

Organochlorine compounds

Polychlorinated biphenyls (PCB’s)

DDT, DDD, and DDE

Polycyclic aromatic hydrocarbons

Radionuclides

Conclusions

References cited

Figures

1.   Map showing contributing area of Cochiti Lake and location of sediment coring sites
2–12.   Graphs showing:
  2.   (A) Longitudinal profile of reservoir showing historical sedimentation and migration of sediment front. (B) Suspended-sediment discharge of the Rio Grande at Otowi Bridge, N. Mex.
  3.   Grain size in a gravity core at site R1 (A) and box cores (B) and percentage of organic carbon in a gravity core (C) and box core at site R1 (D) from Cochiti Lake
  4.   Major element concentrations in a gravity core and box core at site R1 from Cochiti Lake
  5.   Major element concentrations in box cores from Cochiti Lake
  6.   Trace-element concentrations in a gravity core and box core at site R1 from Cochiti Lake
  7.   Trace-element concentrations in box cores from Cochiti Lake
  8.   Concentrations of DDT and its metabolites in a gravity core (A) and box cores (B) from Cochiti Lake
  9.   Polycyclic aromatic hydrocarbon (PAH) concentrations (A-D), PAH sums (E), and the ratio of the sum of 2- and 3-ringed PAH’s to total combustion PAH (F) in a gravity core from Cochiti Lake
  10.   Polycyclic aromatic hydrocarbon (PAH) concentrations (A-D), PAH sums (E), and the ratio of the sum of 2- and 3-ringed PAH’s to total combustion PAH (F) in box cores from Cochiti Lake
  11.   Uranium and thorium radionuclide activities in a gravity core from Cochiti Lake
  12.   Uranium and thorium radionuclide activities in box cores from Cochiti Lake
13.   Plutonium activities in a gravity core (A and B) and box cores (C and D) from Cochiti Lake

Tables

1.   Parameters analyzed for and their reporting levels in Cochiti Lake bottom-sediment samples
2.   Polycyclic aromatic hydrocarbons (PAH’s) analyzed for, number of detections, and range and median of concentrations, in micrograms per kilogram, in Cochiti Lake bottom-sediment samples
3.   Counting and total errors of radionuclide analyses
4.   Trace-element sediment-quality guidelines compared to concentration ranges, in micrograms per gram, in Cochiti Lake gravity core
5.   Concentrations of polychlorinated biphenals (PCB’s), in micrograms per kilogram, in Cochiti Lake gravity core from site R1 and box cores from all sites
6.   Organic sediment-quality guidelines compared to concentration ranges, in micrograms per kilogram, in Cochiti Lake gravity core

CONVERSION FACTORS AND VERTICAL DATUM

Multiply By To obtain
foot 0.3048 meter
ton 0.9072 metric ton

Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929—a geodetic datum derived from a general adjustment of the first-order level nets of the United States and Canada, formerly called Sea Level Datum of 1929.


Abstract

Bottom sediments were sampled at seven sites in Cochiti Lake in September 1996. Sediment cores penetrating the entire lacustrine sediment sequence were collected at one site near the dam. Surficial sediments were sampled at the near-dam site and six other sites located along the length of the reservoir. Analyses included grain size, major and trace elements, organochlorine compounds, polycyclic aromatic hydrocarbons (PAH’s), and radionuclides. Concentrations of trace elements, organic compounds, and radionuclides are similar to those in other Rio Grande reservoirs and are low compared to published sediment-quality guidelines. Most elements and compounds that were detected did not show trends in the age-estimated sediment cores with the exception of a decreasing trend in total DDT concentrations from about 1980 to 1992. The mixture of PAH’s suggests that the increase is caused by inputs of fuel-related PAH and not combustion-related PAH.




U.S. Department of the Interior, U.S. Geological Survey
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Last modified: Friday, September 16 2005, 04:24:01 PM
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