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Contaminants in Bed Sediment and Tissue - Acadian-Pontchartrain NAWQA
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Contaminants in Bed Sediment and Fish Tissues

A study examining the occurrence and distribution of trace elements and organic compounds in southern Louisiana fish and streambeds

Study Description

Bed-sediment and fish tissue studies are the primary means by which trace elements and hydrophobic organic contaminants are initially assessed by NAWQA. Concentrations in bed sediments and fish and their areal distribution are assessed to identify sources and potential needs for more detailed study. Hydrophobic organic compounds preferentially adhere to bed sediments and fish (and other organisms) rather than occurring dissolved in water. Nevertheless, water is one of the primary means for these compounds to move around in the larger environment. Trace elements (i.e., heavy metals, either naturally occurring or man-made) are also moved by water from source areas through the larger environment. In the summer of 1998, bed sediments and fish tissues were collected from 21 sites around south Louisiana to determine the occurrence and distribution of a variety of organic compounds and trace elements present in freshwater environments.

Sites

Sites selected include our Fixed Sites and additional sites to form a broad picture for a one-time sampling. These sites cover a range of physiographic areas, land uses, and stream sizes and types. The Bed Sediment and Tissue section of the NAWQA design methods ("Design of the National Water-Quality Assessment Program: Occurrence and Distribution of Water-Quality Conditions, Circular 1112") describes how sites are selected, generalized methods for collection and analysis, and objectives in sampling.

Small graphic of bed sediment and tissue site locations.
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The following sites were sampled in summer of 1998:
Site NameStation ID
Tchefuncte River near Covington at US-19007375050
Bogue Falaya River at Covington at US-19007375170
Tangipahoa River near Robert at US-19007375500
Tickfaw River near Liverpool at LA-Hwy 3807375800
Dawson Creek at Bluebonnet Blvd., Baton Rouge07379960
Amite River at Port Vincent at LA-Hwy 4207380120
Bayou Des Allemands at Des Allemands at US-9007380300
Bayou Lafourche below weir at Thibodaux07381002
Bayou Grosse Tete at Rosedale at LA-Hwy 7607381440
Bayou Boeuf at Amelia at US-90073814675
Bayou Teche near St. Martinville at Keystone Lock07385700
Vermilion River at Perry at LA-Hwy 8207386980
Bayou Des Cannes near Eunice at US-19008010000
Bayou Nezpique near Basile at US-19008012000
Mermentau River at Mermentau at US-9008012150
Bayou Queue de Tortue near Riceville at LA-Hwy 9108012300
Bayou Lacassine near Lake Arthur at LA-Hwy 1408012470
Whiskey Chitto Creek near Oberlin at LA-Hwy 2608014500
Calcasieu River near Kinder at US-19008015500
Turtle Bayou near Bayou Penchant293524091041300
Bayou Segnette 4.6mi south of Westwego294957090095300

Methods and Analysis

Fish were collected by electroshocking along a stretch of each waterbody, as close to or overlapping the water-sampling site. Fish species we collected included largemouth bass (Micropterus salmoides), longear sunfish (Lepomis megalotis), bluegill sunfish (Lepomis macrochirus), white crappie (Pomoxis annularis), warmouth sunfish (Lepomis gulosus), and common carp (Cyprinus carpio). A composite of six to eight fish of a given species were used for analyses to ensure a sufficient amount of material, particularly for the smaller species. Some sites had more than one species collected, and we submitted multiple composited tissue samples for comparison between species.

For all species, we analyzed trace elements (including mercury) in livers and in fillets, separately, as well as organic compounds in whole bodies. Trace elements are primarily stored in liver tissue in organisms, and the analysis of these tissues gives an idea of the total suite of metals that fish are exposed to. Fillets were collected to determine the amounts and kinds of metals that accumulated in edible portions of fish. Organic compounds, particularly hydrophobic ones, accumulate in fatty tissues of organisms, which are distributed across the whole body.

Bed sediments were collected according to methods published in "Guidelines for Collecting and Processing Samples of Stream Bed Sediment for analysis of trace elements and organic contaminants for the National Water-Quality Assessment Program, Open-File Report 94-458". Since trace elements and organic compounds are often moved through stream systems attached to sediment, areas of recent deposition indicate which chemicals are being transported in the present time. Deep cores of sediment can indicate a time series of deposition, and show changes in trace element concentrations over time.

Areas of recent sediment deposition in streams were identified for sources of samples. These areas tend to have backwater conditions or other kinds of slow flow that allow sediment to settle out, usually along streambanks or other shallow areas in Louisiana streams. An interpretive report will soon be available analyzing bed sediment occurrence and distribution. Raw data will also be available in our Annual Report.

Constituents analyzed:
  • Trace Elements in bed sediments
  • Organic Compounds in bed sediments
  • Trace Elements in Fish Tissue
  • Organic Compounds in Fish Tissue

For questions about our Bed Sediment and Fish Tissue Survey, please contact Dennis Demcheck [ddemchec@usgs.gov], 225-298-5481.

Information on fish consumption advisories, and contamination of fish can be found at the following pages:


U.S. Department of the Interior, U.S. Geological Survey, Baton Rouge, Louisiana, USA
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