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Lake Tahoe Interagency Monitoring Program: Tributary Sampling Design, Sites, and Periods of Record

Figure 1. Geographic setting, hydrologic basins, and Lake Tahoe Interagency Monitoring Program sites in Lake Tahoe Basin, California and Nevada.

INTRODUCTION

Lake Tahoe is a natural resource famous for its alpine setting and deep, clear waters. Reported decreases in water clarity of about 1 foot per year (Goldman and Byron, 1986) have prompted major efforts to preserve the water quality of Lake Tahoe. This decrease in clarity is attributed mainly to human activities, which have increased dramatically in the Lake Tahoe Basin since 1960.

Increased nutrient concentrations within Lake Tahoe are considered the primary cause of increased algal growth and resultant loss of clarity in the lake (Goldman and Byron, 1986). Suspended sediment delivered to the lake by tributaries also is of concern, because some nutrients, such as organic nitrogen and phosphorus, tend to be transported with sediment particles. Tributary streamflow in the Lake Tahoe Basin is suspected of being one of the major pathways for nutrient and sediment transport to the lake (Goldman and Byron, 1986). Increased development has accelerated this transport through urbanization of wetland areas and erosion from construction on moderate to steep slopes within the basin (Byron and Goldman, 1989).

Public concern over water-quality degradation in Lake Tahoe has led to extensive monitoring activities in the lake and its tributary watersheds. One of the largest monitoring activities is the Lake Tahoe Interagency Monitoring Program (LTIMP). The purpose of this report is to describe the data collection activities of LTIMP.

LAKE TAHOE INTERAGENCY MONITORING PROGRAM, 1978-87

Since the early 1970's, prior to the formation of LTIMP, the Tahoe Regional Planning Agency (TRPA), the U.S. Geological Survey (USGS), the Tahoe Research Group (TRG) of the University of California, Davis, and State and local agencies had been monitoring the Lake Tahoe Basin for lake and tributary water-quality conditions. In 1978, LTIMP was formed to conduct collaborative monitoring and research efforts in the Lake Tahoe Basin. Participants of LTIMP include TRPA, USGS, TRG, U.S. Forest Service, U.S. Environmental Protection Agency, California State Water Resources Control Board, Lahontan Regional Water Quality Control Board (RWQCB), California Department of Water Resources, California Department of Transportation, California Air Resources Board, California Department of Fish and Game, Nevada Division of Environmental Protection, and local counties and cities. LTIMP monitoring began in the 1979 water year¹ as a cooperative program with TRG and USGS and included four tributary sites in four Lake Tahoe Basin watersheds. The program was expanded to seven sites in seven watersheds in 1981 and continued through 1987 with various sites sampled. Tributary site locations are shown in figure 1. An overview of tributary sites for LTIMP is shown in figure 2.

¹ Water year is the 12-month period from October 1 through September 30, and is designated by the year in which the period ends (for example, water year 1979 began October 1, 1978, and ended September 30, 1979).

Table 1. Periods of record for streamflow, physical, nutrient, and sediment data collected at current U.S. Geological Survey/Lake Tahoe Interagency Monitoring Program stream network sites and other active USGS gaging stations in the Lake Tahoe Basin, California and Nevada
[Abbreviations: nr, near; abv, above; ck, creek, St., street; Dr., drive; Ave., avenue; Hwy., highway; ——, not collected]

LAKE TAHOE INTERAGENCY MONITORING PROGRAM, 1988-98

The current LTIMP tributary-monitoring program, a cooperative effort by TRPA, USGS, and TRG, began in the 1988 water year. The primary purpose of this program is to provide long-term data on tributary water quality. This program initially included 4 sites in 4 watersheds in 1988 and expanded to 13 sites in 7 watersheds in 1990. The number of stations in the network was increased again in 1991, 1993, and 1996, adding 21 additional sampling sites in 7 additional watersheds. The purpose of expanding the data network was to support the assessments of the effects of land use and development in the Lake Tahoe Basin on water quality.

In 1998, a 12-site water-temperature (WT) monitoring network (7 existing and 5 new sites) was installed in-the Upper Truckee River and Trout Creek watersheds. In 1998, WT monitors were added to Incline Creek near Crystal Bay, Nev., and Glenbrook Creek at Glenbrook, Nev. The purpose of the WT network is to provide information for ground water/surface-water interaction studies and for manmade organics studies.

The current LTIMP sampling network includes 32 tributary sites in 14 Lake Tahoe watersheds in California and Nevada (fig. 1) and was described previously by Boughton and others (1997) and Rowe and Stone (1997). Table 1 describes the period of record for current and historical data collection for the 34 sites plus 2 other active USGS stream-flow gage sites, 2 lake level gage sites, 5 USGS water temperature only sites, and 2 urban-runoff sites. The longest periods of record are 1900-current for lake levels of Lake Tahoe, 1961-current for streamflow. 1961-current for water-quality field measurements, and 1973-current for nutrients and sediment.

Current collection in the LTIMP program is streamflow, physical, sediment, and nutrient data (table 2) and is divided into three sampling schedules. The primary sites (table 1) include continuous streamflow gages and about 30-40 samples collected per year at 10 base (near mouth) sites in 10 watersheds in California and Nevada. The secondary sites (table 1) include continuous streamflow gages and about 25 samples collected per year at the 10 mid- and above-development sites on 5 of the 14 watersheds in California and Nevada. Throughout the year, collection of routine monthly baseline sampling with an extra emphasis on snow-melt runoff and storm runoff periods is done at the primary and secondary sites. The remaining 14 miscellaneous sites (table 1) are monitored but ungaged in Nevada. Data collection on these sites includes 6-10 samples per year, mainly during snow-melt runoff and storm-runoff events.

—Timothy G. Rowe

Figure 2. History of Lake Tahoe Interagency Monitoring Program in Lake Tahoe Basin, California and Nevada. (See Table 1 footnotes for site definition.)

Constituent Nutrients Total organic plus ammonium nitrogen (TKN) Dissolved ammonium nitrogen (DNH4) Dissolved nitrite plus nitrate nitrogen (DNO2+N03) Total phosphorus (TP) Dissolved orthophosphate phosphorus (SRP) Total biologically reactive iron (TFE) Sediment Suspended-sediment concentration Suspended-sediment discharge Sand break (higher concentrations only) Physical Water temperature Air temperature Gage height Discharge Specific conductance Weather Hydrologic event Stage conditions pH Dissolved oxygen Barometric pressure Dissolved oxygen percent saturation Quality Control Sample method Sampler type Sample collecting agency Sample analyzing agency Table 2. Lake Tahoe Interagency Monitoring Program stream network sample analysis

REFERENCES CITED

Boughton, C.J., Rowe, T.G., Allander, K.K., and Robledo, A.R., 1997, Stream and ground-water monitoring program, Lake Tahoe Basin, Nevada and California: U.S. Geological Survey Fact Sheet FS-100-97, 6 p.

Byron, ER., and Goldman, C.R., 1989, Land-use and water-quality in tributary stream of Lake Tahoe, California-Nevada: Journal of Environmental Quality, v. 18, no. 1, p. 84-88.

Goldman, C.R., and Byron, E.R., 1986, Changing water quality at Lake Tahoe-The first five years of the Lake Tahoe Interagency Monitoring Program: Tahoe Research Group, Institute of Ecology, University of California, Davis, 12 p.

Rowe, T.G. and Stone, J.C., 1997, Selected hydrologic features of the Lake Tahoe Basin, California and Nevada: U.S. Geological Survey Open-File Report 97-384, 1 sheet.

For further information contact:

Public Information Assistant
U.S. Geological Survey
333 W. Nye Lane
Carson City, NV 89706
(775) 887-7649
Email: GS-W-NVpublic-info@usgs.gov
Nevada District homepage: http://nevada.usgs.gov
Lake Tahoe Clearinghouse homepage: http://tahoe.usgs.gov

USGS Fact Sheet 138-00
October 2000

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