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Scientific Investigations Report 2008–5168

U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2008–5168

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Table 4. Nutrient load budgets and errors, Coeur d’Alene Lake, Idaho, calendar years 1991–92 and water years 2004–06.

[Sampling locations are shown in figure 1. Sampling locations on the St. Joe and Spokane Rivers changed between the 1991–92 and 2004–06 studies. For comparability, data are normalized to the following stations: St. Joe River: USGS gaging station 12415140, St. Joe River near Chatcolet; Spokane River, USGS gaging station 12417598, Spokane River at Lake Outlet at Coeur d’Alene. Sampling location on the Coeur d’Alene River for both studies was at USGS gaging station 12413860, Coeur d’Alene River near Harrison. Load and error estimates for ungaged tributaries and other surface-water inflow in 1991 and 1992 are from Woods and Beckwith (1997). Loads for ungaged tributaries and other surface-water inflow in 2004–06 were estimated using a relation between 1991–92 load data and annual flow in closest gaged tributary (see text for full explanation). Load and error estimates for nearshore wastewater and precipitation in 1991 and 1992 are from Woods and Beckwith (1997). Assumed nearshore wastewater and precipitation loads and errors were constant for 2004–06 study as no recent data were available. Actual error unknown for loads from ungaged tributaries, surface-water inflow, ground-water outflow, and lake storage change in 2004–06 study. Errors for 2004–06 were estimated by applying the average percent error in loads from the 1991–92 study (see text for full explanation). Loads and errors are in kilograms per year. Streamflows are in cubic hectometers per year. Abbreviations: USGS, U.S. Geological Survey; NA, not applicable]

Variable Budget component Calendar year   Water year
1991 1992 2004 2005 2006
Streamflow St. Joe River 3,350 1,660 1,940 2,140 2,720
Coeur d’Alene River 2,610 1,280 1,700 1,910 2,550
Spokane River 6,270 3,140 4,120 4,230 5,870

Load Error Load Error   Load Error Load Error Load Error
Total nitrogen
Inflow St. Joe River 991,000 98,000 343,000 26,100 62,700 18,500 48,500 16,600 84,600 28,600
Coeur d’Alene River 819,000 93,600 402,000 36,800 117,000 11,600 107,000 12,800 87,900 12,000
Ungaged tributaries and other surface-water inflow 225,000 46,400 128,000 28,500 148,000 31,100 164,000 34,400 214,000 44,900
Nearshore wastewater 4,900 1,220 4,900 1,220 4,900 1,220 4,900 1,220 4,900 1,220
Precipitation 75,000 11,500 75,000 11,000 75,000 11,200 75,000 11,200 75,000 11,200
Outflow Spokane River 1,670,000 107,000 709,000 38,300 217,000 54,300 181,000 45,200 597,000 253,000
Ground-water outflow to Rathdrum Prairie 71,500 17,900 54,300 13,600 33,300 8,320 28,700 7,180 40,500 10,100
Lake storage change 9,710 850 11,500 860 2,320 190 3,640 290 1,540 120
Total phosphorus
Inflow St. Joe River 40,100 11,100 14,800 3,400 35,300 3,670 45,100 5,150 71,600 8,690
Coeur d’Alene River 33,600 6,480 10,900 1,600 25,700 4,060 38,200 7,260 54,200 9,860
Ungaged tributaries and other surface-water inflow 12,200 2,340 6,850 1,570 7,960 1,670 8,860 1,860 11,500 2,420
Nearshore wastewater 390 100 390 100 390 100 390 100 390 100
Precipitation 6,460 1,000 6,460 1,100 6,460 1,050 6,460 1,050 6,460 1,050
Outflow Spokane River 46,600 7,320 24,800 3,360 32,200 4,480 31,500 4,040 52,000 9,120
Ground-water outflow to Rathdrum Prairie 1,000 250 510 130 990 250 1,190 300 3,250 810
Lake storage change 180 10 130 30 180 20 180 20 80 20
Summary
Constituent load Calendar year   Water year
1991 1992 2004 2005 2006
Total nitrogen
Total inflow 2,110,000 953,000 408,000 399,000 466,000
Total outflow 1,750,000 775,000 253,000 213,000 639,000
Residual (outflow- inflow) -360,000 -178,000 -155,000 -186,000 173,000
Residual (percentage of inflow) 17 19 38 47 NA
Overall error 180,000 68,000 67,700 62,000 259,000
Total phosphorus
Total inflow 92,800 39,400 75,800 99,000 144,000
Total outflow 47,800 25,400 33,400 32,900 55,300
Residual (outflow- inflow) -45,000 -14,000 -42,400 -66,100 -88,700
Residual (percentage of inflow) 48 36 56 67 62
Overall error 15,000 5,400 7,350 10,000 16,200

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