STUDY DESIGN AND DATA COLLECTION

Stream Chemistry

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The primary objectives of the stream chemistry component of study were to assess the relation between land use and chemical constituents in surface water and to evaluate fluxes of contaminants in the Snake River. Synoptic studies were designed to assess sources and fluxes of contaminants during selected hydrologic conditions. Intensive sites were monitored for pesticides during a 2-year period from 1993 to 1995.

Stream Ecology

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The primary objective of the stream ecology component of study was to assess the surface-water quality by integrating the chemical, physical, and biological factors. Stream ecology sites were distributed among major ecoregions and dominant land uses, which included irrigated agriculture, forested land, and rangeland. The stream types sampled represented wadable streams, large rivers, and least-disturbed springs and streams. Sites were classified as intensive or synoptic on the basis of the level of the sampling effort or the number of years data were collected.

Basic sites--
general water chemistry

Streamflow, nutrients, major ions, organic carbon, suspended sediment, water temperature, specific conductance, pH, and dissolved oxygen to describe concentrations and seasonal variations. Stable isotopes and tritium sampled quarterly.

Streams draining basins representative of common land-use types. Also large-river sites that integrate multiple types of land use.

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Monthly plus additional high streamflow samples
Apr. 1993-Aug. 1995

Intensive sites-- pesticides

In addition to the above constituents, dissolved concentrations of 87 pesticides to describe seasonal variations.

Subset of basic sites draining areas of predominantly agricultural land use.

2

Weekly to monthly
Apr. 1993-Aug. 1995

Synoptic sites--water chemistry

Streamflow, nutrients, dissolved concentrations of 87 pesticides, suspended sediment, selected isotopes, water temperature, specific conductance, pH, and dissolved oxygen to describe concentrations, assess spatial variability, and determine chemical and sediment fluxes.

Additional main-stem sites, varied land-use sites, and sites in the Rock Creek watershed. Snake River sites between Milner Dam and King Hill.

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13

May and June 1994

August 1995

Intensive
assessments

Fish, macroinvertebrates, algae, instream and riparian habitat to assess aquatic biological community structure. Continuous summer water temperature and field parameters collected.

Contaminants in bed sediments: Total PCBs, 32 organochlorine pesticides, 78 semivolatile organic compounds, and 44 trace elements to determine occurrence and spatial distribution.

Contaminants in bottom-feeding aquatic biota: Total PCBs, 30 organochlorine pesticides, and 24 trace elements to determine occurrence and spatial distribution. Organic contaminants in whole fish. Trace elements in fish livers and caddisflies. Organic contaminants and trace elements in fillets of gamefish (one basic site).

All basic sites.

All basic sites.

All basic sites.

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Once in 1993;
6 sites multiple years (1993-95);

2 sites multiple reach

6 sites multiple years;

1 site multiple reach

6 sites multiple years;

1 site multiple reach

Synoptic studies

Similar to the intensive assessment sites, except only one reach per site sampled to assess spatial distribution and reference conditions of aquatic communities and associated habitats.

Contaminants in bottom-feeding aquatic biota and in bed sediments.

Least-disturbed reference sites.

Some least-disturbed reference sites, some spring sites, and some basic sites.

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10

Once in 1993

Once

(mostly in 1992-94)

Regional Study Unit surveys

Major ions, nutrients, 87 pesticides, volatile organic compounds, and radon to assess occurrence. Data collected in cooperation with the Idaho Statewide Ground-Water Monitoring Program.

Domestic, irrigation, stock, and public supply wells from a wide range of well depths.

Snake River Plain, Idaho.

Tributary valleys, Idaho.

Jackson Valley, Wyoming.

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Once in 1994

Once in 1995

Once in 1995

Local land-use studies

Major ions, nutrients, 87 pesticides, 60 volatile organic compounds, radon, and selected isotopes to assess the effects of land use and hydrogeology on ground-water quality in locally important aquifers of the basin.

Mostly domestic wells.

A&B study area, mean well depth 230 feet.

Minidoka study area, mean well depth 40 feet.

Jerome/Gooding study area, mean well depth 240 feet.

Eden study area, mean well depth 380 feet.

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15

Once in 1993

Once in 1993

Once in 1994

Once in 1995

Springs between Milner Dam and King Hill: water chemistry and aquatic biota assessment

Nutrients, pesticides, and selected isotopes to determine source water of springs and nutrient loads from ground water to
the Snake River. Aquatic habitat and communities of fish, macroinvertebrates, and algae in least-disturbed spring
environments.

Springs representing the entire reach from Milner Dam to King Hill.

Least-disturbed springs for biological assessment, subset of above springs.

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6

Springs sampled in Apr. 1994, Oct. 1994, and Aug. 1995

Ecology sampled once in Apr. 1994