Study Design and Data Collection

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Tri-County Canal 1.25 mi below diversion

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Prairie Creek near Ovina

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North Channel of Platte River at Brady

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Shell Creek near Columbus

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Dismal River near Thedford

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Elkhorn River at Waterloo

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Loup River at Palmer

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Maple Creek near Nickerson

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Platte River near Grand Island

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Platte River at Louisville

The wetland water quality of the Central Nebraska Study Unit was assessed using chemical, physical, and biological evidence. A network of 31 permanent wetland sites provided water chemistry, bed-sediment chemistry, and ecological data for determining the relation between land use and wetland water quality.

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The ground-water quality of the Platte River alluvial aquifer was assessed on the basis of a small survey of public-supply and monitoring wells. Eleven wells provided water-chemistry data to describe the occurrence and distribution of chemical constituents in the Platte River alluvial aquifer. Samples also were collected along ground-water flow paths at a site near Gibbon, Nebraska, and at a site near Grand Island, Nebraska.

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Stream Chemistry

Basic Fixed Sites--
general water quality

Major ions, organic carbon, suspended sediment, organonitrogen herbicides, nutrients, and physical parameters to describe spatial and temporal variability.

Stream sites representing cropland, rangeland, and a mixture of land uses from across the area.

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Monthly plus flow-based sampling (1993-94)

Intensive Fixed Sites--
pesticides

Same as Basic Fixed Sites plus a suite of 82 pesticides to characterize their seasonal distribution.

Subset of Basic Fixed Sites had intensive agriculture and a site at the basin outflow.

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Monthly plus flow-based sampling (1993-94)

Intensive Prototype Fixed Sites

Major ions, suspended sediment, nutrients, 46 pesticides, and physical parameters to determine adequate sampling frequency of agriculture-related compounds that enter streams in runoff.

A subset of the Intensive Fixed Sites.

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Six weeks of alternate-day sampling plus one storm in spring; four weekly samples in early summer; and 6 weeks of alternate-day sampling plus one storm in summer (May to August 1992).

High flow synoptic studies

Organonitrogen herbicides, nutrients, suspended sediment, and streamflow to describe the transport of agriculture-related compounds during runoff.

Streams were sampled to include most Basic Sites from a variety of land uses.

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Sampled up to seven times during the rise and fall of runoff (1992-93)

Base flow synoptic studies

Organonitrogen herbicides, nutrients, and streamflow to determine their concentrations at base-flow conditions.

Streams sites were selected to provide wide spatial distribution.

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Two times during the growing season (1994)

Stream Ecology

Contaminants in bed sediments and fish tissues

Streambed sediments for trace elements, polycyclic aromatic hydrocarbons, and organic compounds; and whole-fish composites for organic compounds and fish liver composites for trace elements to determine the presence and distribution of contaminants.

Basic Fixed Sites were supplemented by stream sites in spatially under-represented areas.

16 (1992)
8 (1993)
5 (1994)

Once per year during late summer

Intensive ecological assessments

Fish, macroinvertebrates, and algae were sampled to assess biological communities and to relate community attributes to water quality. Stream habitat also was described.

Basic Fixed Sites described in the stream chemistry section were sampled.

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All sites once per year (1993-94),
three sites again in 1995

Ground-Water Chemistry

Aquifer survey

Major ions, nutrients, pesticides, trace elements, volatile organic compounds, organic carbon, and radionuclides to describe water quality of a heavily used alluvial aquifer.

Shallow wells in the Platte River alluvial aquifer were sampled.

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Once in 1995

Variation along flow paths

Major ions, nutrients, pesticides, and age-dating constituents in water samples to describe land-use effects on surficial aquifers along ground-water flow paths from areas of recharge beneath the land use to discharge to a stream.

Wells were sampled at two flow paths in the Platte Valley: one in a wet meadow, near corn production, and the other in a public-supply wellfield in an agricultural area.

61 wells installed in
clusters at two sites

Wet meadow flow path sampled quarterly in 1994 and twice in 1995; public-supply flow path sampled three times (1994-95)

Special Studies

Ecological synoptic study

Stream macroinvertebrate and algal samples were collected and stream habitat features were measured in conjunction with similar activities in the South Platte River NAWQA Study Unit to describe variability of streams in the plains environment.

Stream sites representing a range of conditions in the Great Plains were sampled.

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(Central Nebraska Basins)

Once (August 1993)

Wetlands synoptic--
water and bed- sediment chemistry

Water-column samples were collected and analyzed for major ions, nutrients, organonitrogen herbicides, and chlorophyll-a. Sediment samples were collected and analyzed for nutrients and herbicides to provide baseline information on wetland sediment chemistry. At selected sites, water, sediment, and invertebrate tissues were analyzed for trace elements.

Wetlands characteristic of agricultural landscapes were sampled in late spring following herbicide application and in late summer.

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May and August 1994

Wetlands synoptic--
aquatic communities

Sample and identify macroinvertebrates, aquatic plants, and algae to provide baseline information on aquatic communities in wetlands.

The same wetlands sampled for chemical analysis were sampled for biological attributes.

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May and August 1994