The Bureau of Reclamation has proposed construction of the Lake Andes/Wagner Irrigation Demonstration Project to investigate environmental effects of irrigation of glacial till soils substantially derived from marine shales. During 1983-2000, the U.S. Geological Survey collected hydrologic, water-quality, and sediment data in the Lake Andes and Choteau Creek Basins, and on the Missouri River upstream and downstream from Choteau Creek, to provide baseline information in support of the proposed demonstration project.
Lake Andes has a drainage area of about 230 mi2 (square miles). Tributaries to Lake Andes are ephemeral. Water-level fluctuations in Lake Andes can be large, and the lake has been completely dry on several occasions. The outlet aqueduct from Lake Andes feeds into Garden Creek, which enters Lake Francis Case just upstream from Fort Randall Dam on the Missouri River.
For Lake Andes tributary stations, calcium, magnesium, and sodium are approximately codominant among the cations, and sulfate is the dominant anion. Dissolved-solids concentrations typically range from about 1,000 mg/L (milligrams per liter) to about 1,700 mg/L. Major-ion concentrations for Lake Andes tend to be higher than the tributaries and generally increase downstream in Lake Andes. Proportions of major ions are similar among the different lake units (with the exception of Owens Bay), with calcium, magnesium, and sodium being approximately codominant among cations, and sulfate being the dominant anion. Owens Bay is characterized by a calcium sulfate water type. Dissolved-solids concentrations for Lake Andes typically range from about 1,400 to 2,000 mg/L.
Whole-water nitrogen and phosphorus concentrations are similar among the Lake Andes tributaries, with median whole-water nitrogen concentrations ranging from about 1.6 to 2.4 mg/L, and median whole-water phosphorus concentrations ranging from about 0.5 to 0.7 mg/L. Whole-water nitrogen concentrations in Lake Andes are similar among the different units, with medians that range from about 2.4 to 4.0 mg/L. Median whole-water phosphorus concentrations for the different Lake Andes units range from 0.2 to 0.5 mg/L, and decrease downstream through Lake Andes.
Median selenium concentrations are substantially lower for Andes Creek (3 µg/L (micrograms per liter)) than for the other tributary stations (34, 18, and 7 µg/L). Median selenium concentrations for the lake stations (ranging from less than 1 to 2 µg/L) are substantially lower than tributary stations.
The pesticides 2,4-D and atrazine were the most commonly detected pesticides in Lake Andes. Median concentrations for 2,4-D for Lake Andes range from 0.07 to 0.11 µg/L; the median concentration for Owens Bay is 0.04 µg/L. Median concentrations for atrazine for Lake Andes range from 0.2 to 0.4 µg/L; the median concentration for Owens Bay is less than 0.1 µg/L. Concentrations of both 2,4-D and atrazine are largest for the most upstream part of Lake Andes that is most influenced by tributary inflow.
Median suspended-sediment concentrations for Lake Andes tributaries range from 22 to 56 mg/L. Most of the suspended sediment transported in the Lake Andes tributaries consists of particles less than 63 µm (micrometers) in diameter. Concentrations of most constituents in bottom sediments generally had similar ranges and medians for the Lake Andes tributaries. However, Andes Creek generally had lower concentrations of several metals. For Lake Andes, medians and ranges for most constituents generally were similar among the different units. However, selenium concentrations tended to be higher in the upstream part of the lake, and generally decreased downstream. Results of vertical sediment cores collected from a single site in the South Unit of Lake Andes in October 2000 indicate that selenium loading to Lake Andes increased during the period 1952 through 2000.
Choteau Creek has a drainage area of 619 mi2. In the upstream part of the basin, Choteau Creek is essentially ephemeral. Downstream from Wagner, Choteau Creek receives ground-water discharge providing perennial flow during most years. Choteau Creek enters the Missouri River about 28 river miles downstream from Fort Randall Dam. Choteau Creek contribution to the Missouri River relative to release from Fort Randall Dam generally is minimal.
For all of the Choteau Creek stations, calcium is dominant among the cations, and sulfate is dominant among the anions. Median dissolved-solids concentrations range from 1,180 to 1,780 mg/L. For the two Missouri River stations, calcium, magnesium, and sodium are about codominant among the cations, and bicarbonate and sulfate are about codominant among the anions. Differences in major-ion concentrations between the two Missouri River stations are negligible, with median dissolved-solids concentrations ranging from 501 to 502 mg/L.
Whole-water nitrogen concentrations for the upstream and middle stations on Choteau Creek are similar (medians of 1.9 and 2.0 mg/L), but whole-water nitrogen concentrations for the downstream station are substantially smaller (median of 1.0 mg/L). Median whole-water nitrogen concentrations for the Missouri River stations range from 0.41 to 0.42 mg/L. Median whole-water phosphorus concentrations decrease downstream on Choteau Creek, from 0.51 mg/L at the most upstream station to 0.08 mg/L at the most downstream station. Median whole-water phosphorus concentrations for the Missouri River near the mouth of Choteau Creek range from 0.01 to 0.02 mg/L.
For Choteau Creek stations, selenium concentrations are lower for the most upstream station (median concentration of 1 µg/L) than for the middle and downstream stations (median concentrations of 6 and 4 µg/L). For Missouri River stations, selenium concentrations are relatively small, with median concentrations of 2 µg/L for both stations.
Median suspended-sediment concentrations for Choteau Creek stations range from 27 to 106 mg/L. Most of the suspended sediment transported in the Lake Andes consists of particles less than 63 µm in diameter. Concentrations of most constituents in bottom sediments generally had similar ranges and medians for the Choteau Creek stations. However, concentrations of several metals show decreases in median concentrations downstream. For the Missouri River stations, median concentrations of most constituents in bottom sediments were larger for the station downstream from Choteau Creek. Several metals, including chromium, copper, titanium, and zinc have the largest increases in median concentration between the two stations. The median selenium concentration for the downstream station was about two times larger than the upstream station.
The analyses that were conducted for this report show that water-quality conditions in the basins change over seasonal and annual time periods. Results of the trend analyses also indicate that long-term changes in water quality might be occurring in the basins.
Purpose and Scope
Description of Study Area
Physiography and Geology
Methods of Study
Sample Collection, Processing, and Analysis
Quality Assurance/Quality Control
Data Analysis Methods
Calculation of Summary Statistics
Calculation of Loads and Masses
Analysis of Trends
Water and Sediment Quality
Lake Andes Basin
Field-Measured Properties and Constituents
Nitrogen and Phosphorus Nutrients
Suspended and Bottom Sediment
Choteau Creek Basin and Missouri River near the Mouth of Choteau Creek
Field-Measured Properties and Constituents
Suspended and Bottom Sediment
Summary and Conclusions
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Send questions or comments about this report to the author, S.K. Sando (605) 352-4241 ext. 230.
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