Water-Quality Characteristics of Montana Streams in a Statewide Monitoring Network, 1999-2003

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Abstract

A statewide monitoring network of 38 sites was operated during 1999-2003 in cooperation with the Montana Department of Environmental Quality to provide a broad geographic base of water-quality information on Montana streams. The purpose of this report is to summarize and describe the water-quality characteristics for those sites. Samples were collected at U.S. Geological Survey streamflow-gaging stations in the Missouri, Yellowstone, and Columbia River basins for stream properties, nutrients, suspended sediment, major ions, and selected trace elements. Mean annual streamflows were below normal during the period, which likely influenced water quality.

Continuous water-temperature monitors were operated at 26 sites. The median of daily mean water temperatures for the June-August summer period ranged from 12.5 °C at Kootenai River below Libby Dam to 23.0 °C at Poplar River near Poplar and Tongue River at Miles City. In general, sites in the Missouri River basin commonly had the highest water temperatures. Median daily mean summer water temperatures at four sites (Jefferson River near Three Forks, Missouri River at Toston, Judith River near Winifred, and Poplar River near Poplar) classified as supporting or marginally supporting cold-water biota exceeded the general guideline of 19.4 °C for cold-water biota. Median daily mean temperatures at sites in the network classified as supporting warm-water biota did not exceed the guideline of 26.7 °C for warm-water biota, although several sites exceeded the warm-water guideline on several days during the summer.

Nutrient concentrations generally were lower in the Columbia River basin compared to the Missouri and Yellowstone River basins. Dissolved nitrite plus nitrate concentrations did not exceed the State of Montana human-health standard for drinking water of 10 milligrams per liter (mg/L) nitrate as nitrogen (N) at any site in the network. Total nitrogen concentrations at network sites ranged from 0.043 to 31.6 mg/L as N and exceeded the ecoregion guideline of 1.50 mg/L for the prevention of eutrophication at several sites in the Missouri and Yellowstone River basins. In the Columbia River basin, concentrations of total nitrogen exceeded the State of Montana seasonal numeric standard of 0.300 mg/L in about 25 percent of the samples from two sites on the Clark Fork. Total phosphorus concentrations ranged from <0.01 to 15.4 mg/L; concentrations at most sites in the Missouri and Yellowstone River basins occasionally to frequently exceeded both the general and ecoregion eutrophication guideline concentrations of 0.10 and 0.075 mg/L, respectively. Total phosphorus concentrations at sites in the Columbia River basin only infrequently exceeded the general eutrophication guidelines. About 75 percent of the samples collected at Clark Fork at Turah Bridge and about 25 percent of the samples collected at Clark Fork at St. Regis exceeded the seasonal reach-specific numeric standards of 0.020 mg/L and 0.039 mg/L, respectively, for total phosphorus.

Suspended-sediment concentrations varied widely at individual sites and among sites, ranging from 1 to 25,400 mg/L. Suspended-sediment concentrations commonly were lower in the Columbia River basin compared to the Missouri and Yellowstone River basins. Median suspended-sediment concentrations exceeded 100 mg/L at several sites in the Missouri and Yellowstone River basins; median concentrations in the Columbia River basin generally were less than 10 mg/L. Overall, Powder River near Locate had the highest suspended-sediment concentrations in the network, with concentrations exceeding 2,000 mg/L in 25 percent of the samples.

Dissolved-solids concentrations ranged from 23 to 6,200 mg/L across the network. Samples from several sites in the Missouri and Yellowstone River basins had distinctly elevated concentrations relative to other sites and occasionally to frequently exceeded a general irrigation guideline of 1,000 mg/L. Three sites (Musselshell River at Mosby, Rosebud Creek near Rosebud, and Powder River near Locate) exceeded the guideline in more than 75 percent of the samples. Three other sites (Peoples Creek near Dodson, Milk River at Nashua, and Poplar River near Poplar) exceeded the guideline in 25 to 50 percent of the samples. No other sites exceeded the general irrigation guideline for dissolved solids. Sodium adsorption ratio (SAR) values ranged from <0.1 to 12 across the network and exceeded a general irrigation guideline of 7 at several sites in the Missouri and Yellowstone River basins. SAR values at Rosebud Creek near Rosebud commonly exceeded and Powder River near Locate occasionally exceeded the numeric standards of 4.5 and 7.5, respectively, established for SAR in those watersheds during the irrigation season.

State of Montana human-health standards for drinking water for total-recoverable cadmium, chromium, and nickel were exceeded only infrequently by concentrations in samples from across the network; standards for copper and zinc were not exceeded. One or more sites in each of the three major river basins had sample concentrations that occasionally exceeded the human-health standard of 18 micrograms per liter (µg/L) for arsenic. The arsenic standard was exceeded in almost all samples from Missouri River at Toston and in about one-half of the samples from Yellowstone River near Livingston. Both sites receive geothermal waters enriched in arsenic from Yellowstone National Park. Concentrations of total-recoverable lead in one or more samples from each major river basin occasionally exceeded the human-health standard of 15 µg/L for lead; concentrations exceeded the standard in about 25 percent or more of the samples from Prickly Pear Creek near Clancy and Powder River near Locate.

Comparisons of trace-element concentrations to general aquatic-life standards (based on average hardness) indicate that chronic standards were exceeded infrequently at many of the network sites and acute standards were rarely exceeded. Aquatic-life standards for arsenic and chromium were not exceeded; chronic and acute standards for cadmium, nickel, and zinc were occasionally exceeded. In contrast, about one-half of the sites in the network had one or more samples with concentrations that exceeded either chronic or acute aquatic-life standards for copper. Chronic and acute standards for copper were exceeded most commonly in samples from Clark Fork at Turah Bridge. About one-half of the sites had one or more samples with concentrations exceeding the chronic standard for lead; Prickly Pear Creek near Clancy exceeded the standard in about 50 percent of the samples.

General estimates of mean annual loads of selected constituents transported during 1999-2003 were used to assess relative contributions from upstream source areas compared to the load at the most downstream site on the mainstem. The largest mean annual loads of total ammonia plus organic nitrogen from upstream source areas in the Missouri, Yellowstone, and Columbia River basins, respectively, were transported past Missouri River at Toston (1,400 tons), Bighorn River near Bighorn (1,260 tons), and Clark Fork at St. Regis (1,290 tons). A similar pattern occurred for loads of total nitrogen. The largest mean annual loads of total phosphorus from upstream sources in each major river basin were transported past Missouri River at Toston (239 tons), Yellowstone River near Livingston (572 tons), and Clark Fork at St. Regis (183 tons). Suspended-sediment loads varied substantially among sites, with the largest mean annual loads from upstream sources in each major river basin transported past Milk River at Nashua (319,000 tons), Powder River near Locate (1,400,000 tons), and Clark Fork at St. Regis (146,000 tons). Dissolved-solids loads also varied widely among network sites, with the largest mean annual loads from upstream sources in each major river basin transported past Missouri River at Toston (682,000 tons), Bighorn River near Bighorn (1,410,000 tons), and Kootenai River below Libby Dam (1,230,000 tons).

Annual loads of trace elements were estimated for total-recoverable arsenic and copper, except for sites where a large number of samples had concentrations less than the laboratory reporting level. The largest mean annual arsenic loads from upstream sources in the Missouri, Yellowstone, and Columbia River basins, respectively, were transported past Missouri River at Toston (109 tons), Yellowstone River near Livingston (62.1 tons), and Clark Fork at St. Regis (9.53 tons). The Missouri River at Toston had a notably larger arsenic load than any other network site, with more than 90 percent being contributed by the Madison River basin, which receives large volumes of arsenic-enriched geothermal waters from Yellowstone National Park. Similarly, a large arsenic load was estimated for Yellowstone River near Livingston, which also receives geothermal waters from the Park. The largest mean annual copper loads from upstream sources in each major river basin were transported past Missouri River at Toston (13.6 tons), Yellowstone River near Livingston (18.8 tons), and Flathead River at Perma (34.8 tons).

Contents

Abstract

Introduction

Purpose and Scope

Description of Study Area

Missouri River Basin

Yellowstone River Basin

Columbia River Basin

Data Collection and Analysis

Design of Sampling Program

Methods of Sample Collection, Processing, and Analysis

Quality Assurance

Streamflow Characteristics

Water-Quality Characteristics

Stream Properties

pH

Specific Conductance

Water Temperature

Nutrients

Dissolved Nitrite plus Nitrate

Total Ammonia Plus Organic Nitrogen

Total Nitrogen

Dissolved Orthophosphate

Total Phosphorus

Suspended Sediment

Major Ions

Dissolved Solids

Sodium Adsorption Ratio

Trace Elements

Total-Recoverable Arsenic

Total-Recoverable Cadmium

Total-Recoverable Chromium

Total-Recoverable Copper

Total-Recoverable Lead

Total-Recoverable Nickel

Total-Recoverable Zinc

Estimated Annual Loads

Computational Methods for Estimating Annual Loads

Nutrients

Total Ammonia Plus Organic Nitrogen

Total Nitrogen

Total Phosphorus

Suspended Sediment

Dissolved Solids

Trace Elements

Total-Recoverable Arsenic

Total-Recoverable Copper

Summary and Conclusions

References Cited

Data

Figures

1. Map showing location of sampling sites in the statewide monitoring network, Montana, water years 1999-2003.

2. Annual hydrographs of mean daily streamflow during water years 1999-2003 and long-term mean daily streamflow for Missouri River at Toston, Yellowstone River near Sidney, and Clark Fork at St. Regis, Montana.

3–27. Graphs showing:

3. Statistical distribution of pH values at network sites in Montana, water years 1999-2003.

4. Statistical distribution of specific-conductance values at network sites in Montana, water years 1999-2003.

5. Statistical distribution of summer daily mean water temperatures at selected network sites with continuous temperature recorders in Montana, water years 1999-2003.

6. Statistical distribution of concentrations of dissolved nitrite plus nitrate at network sites in Montana, water years 1999-2003.

7. Statistical distribution of concentrations of total ammonia plus organic nitrogen at network sites in Montana, water years 1999-2003.

8. Statistical distribution of estimated concentrations of total nitrogen at network sites in Montana, water years 1999-2003.

9. Statistical distribution of concentrations of dissolved orthophosphate at network sites in Montana, water years 1999-2003.

10. Statistical distribution of concentrations of total phosphorus at network sites in Montana, water years 1999-2003.

11. Statistical distribution of concentrations of suspended sediment at network sites in Montana, water years 1999-2003.

12. Statistical distribution of concentrations of dissolved solids at network sites in Montana, water years 1999-2003.

13. Statistical distribution of sodium adsorption ratio (SAR) at network sites in Montana, water years 1999-2003.

14. Statistical distribution of concentrations of total-recoverable arsenic at network sites in Montana, water years 1999-2003.

15. Statistical distribution of concentrations of total-recoverable cadmium at network sites in Montana, water years 1999-2003.

16. Statistical distribution of concentrations of total-recoverable chromium at network sites in Montana, water years 1999-2003.

17. Statistical distribution of concentrations of total-recoverable copper at network sites in Montana, water years 1999-2003.

18. Statistical distribution of concentrations of total-recoverable lead at network sites in Montana, water years 1999-2003.

19. Statistical distribution of concentrations of total-recoverable nickel at network sites in Montana, water years 1999-2003.

20. Statistical distribution of concentrations of total-recoverable zinc at network sites in Montana, water years 1999-2003.

21. Range and mean of estimated annual loads of total ammonia plus organic nitrogen at network sites in Montana, water years 1999-2003.

22. Range and mean of estimated annual loads of total nitrogen at network sites in Montana, water years 1999-2003.

23. Range and mean of estimated annual loads of total phosphorus at network sites in Montana, water years 1999-2003.

24. Range and mean of estimated annual loads of suspended sediment at network sites in Montana, water years 1999-2003.

25. Range and mean of estimated annual loads of dissolved solids at network sites in Montana, water years 1999-2003.

26. Range and mean of estimated annual loads of total-recoverable arsenic at network sites in Montana, water years 1999-2003.

27. Range and mean of estimated annual loads of total-recoverable copper at network sites in Montana, water years 1999-2003.

Tables

1. Type and period of data collection at sampling sites in the statewide monitoring network, Montana.

2. Selected stream properties measured onsite and constituents analyzed in water samples.

3. Precision of analytical results for replicate samples, water years 1999-2003.

4. Streamflow characteristics for sites in the statewide monitoring network in Montana, water years 1999-2003 and long-term period of record.

5. General aquatic-life standards calculated from average hardness for groups of network sites with similar hardness, Montana.

6. Equations for estimating daily loads of total ammonia plus organic nitrogen and summaries of the range and mean of estimated annual loads at network sites in Montana, water years 1999-2003.

7. Equations for estimating daily loads of total nitrogen and summaries of the range and mean of estimated annual loads at network sites in Montana, water years 1999-2003.

8. Equations for estimating daily loads of total phosphorus and summaries of the range and mean of estimated annual loads at network sites in Montana, water years 1999-2003.

9. Equations for estimating daily loads of suspended sediment and summaries of the range and mean of estimated annual loads at network sites in Montana, water years 1999-2003.

10. Equations for estimating daily loads of dissolved solids and summaries of the range and mean of estimated annual loads at network sites in Montana, water years 1999-2003.

11. Equations for estimating daily loads of total-recoverable arsenic and summaries of the range and mean of estimated annual loads at network sites in Montana, water years 1999-2003.

12. Equations for estimating daily loads of total-recoverable copper and summaries of the range and mean of estimated annual loads at network sites in Montana, water years 1999-2003.

13. Analytical results for replicate samples from sites in the statewide monitoring network in Montana, water years 1999-2003.

14. Analytical results for blank samples from sites in the statewide monitoring network in Montana, water years 1999-2003.

15. Statistical summary of water-quality data for periodically collected samples from sites in the statewide monitoring network in Montana, water years 1999-2003.