Economic Causes of Non-Point Pollution in the

By Roger B. Long and Jinghua Zhang

oth point pollutants and non-point pollutants series of drains returns unused and excess water Bare responsible for water pollution. While the to the river near Parma, which is a short distance former can easily be traced to a source, such as a from where the Boise River empties into the Snake manufacturing plant, the latter cannot. Non-point River. By comparing measurements of nitrogen pollution creates a perplexing problem, since it is and phosphorus at Lucky Peak (above Boise) difficult to relate it to specific causes. Although with similar measurements at Parma, an estimate agriculture is believed to be the major cause of of pollution from both urban and rural sources surface-water pollution in the nation today along the river can be made. Contamination (Crutchfiled 1995), urban activity also contributes concentrations vary greatly with the level of to the problem. Exactly who is responsible for stream flow because of the dilution effect. Stream non-point pollution and to what degree are largely flow varies greatly from year to year and within unanswered questions that need to be addressed the year, depending upon the amount of runoff by research. available from snowfall in the mountains. This The Boise River of southern offers a complicates the analysis of the causes of non-point unique opportunity to study non-point pollution. pollution, because high flows carry more pollut- The river has a relatively pure source of water ants (loads) but also have the effect of diluting from snow melt and is only 60 miles long down- pollution concentrations. stream from the city of Boise. It has two major potential sources of water pollution: urban activity Previous Studies and irrigated agriculture. Boise is located along Long (1976) and Fitzsimmons (1978) studied the river and has been steadily growing over the the impacts of irrigation on water quality and past 20 years. Downstream from Boise is a long- quantified the economic losses that resulted from established irrigated area (primarily flood irri- irrigating land in the Boise Valley nearly 20 years gated) producing up to 60 commercial crops on ago. The impacts on water quality were deter- about 150,000 acres. Along with irrigation are mined by studying and comparing water quality well-established livestock and food-processing parameters associated with irrigation above Boise activities that are supported by irrigated crops. before the water was used for irrigation and at Consequently, upstream pollution primarily Notus, where the Boise River enters the Snake comes from urban activities, while downstream River. The parameters measured were specific pollution is primarily related to agricultural conductivity (an indicator of salts and suspended activities. State and federal environmental agen- solids), three forms of nitrogen, and phosphorus. cies have done much to control point sources of Results showed that the average yearly specific pollution over the past 20 years. Additional sew- conductivity (the ability to conduct electricity) age treatment plants have been constructed in reading at Notus was much higher than at Boise, major urban areas as population has grown. Non- indicating increased concentrations of salts in the point pollution, however, is still a problem. Refer to the map and chart of Boise River Diversions Water is taken from the Boise River above and Drains, 1995 on pages 6 and 7 (centerfold) to Boise and distributed to irrigators downriver. A locate mileage references contained in the text.

Cooperative Extension System • Agricultural Experiment Station BUL 783 Boise River at Notus. Nitrogen, phosphorus, and costs were calculated for six crop rotations on six sediment levels were also compared. Results land classes for a representative 320-acre farm. showed that they were much higher near Caldwell Crop budgets were compiled using the “Okla- than below Lucky Peak Dam, implying that homa State Budget Generator.” Costs for sedi- irrigation did impact water quality at that time. ment retention structures were obtained from a Clark and Bauer (1983) established a water construction firm local to the LQ drain. Capital quality monitoring program on the irrigation and ownership costs of long-term investments drainage system in the lower Boise River Valley as were calculated using engineering economics. part of a “208 project” to develop a pollution Sediment reduction resulting from BMPs imple- abatement plan for agricultural lands. The 208- mentation on crop rotations and land classes was project area encompassed irrigated lands along the determined by monitoring studies. Calkins deter- Boise River from Caldwell to the . The mined the cost-effectiveness of best management area was divided into the following groups based practices in reducing sediment for each crop on watersheds: Conway Drain and Sand Hollow rotation and land class combination by comparing Drain on the north side; Dixie Drain; Ross East the implementation costs to the reduction effi- End Drain; and South Boise Drain on the south ciency of each practice. Cost-effective practices side. Suspended sediment loads (materials in the included vegetative filter strips, mini-basins, river) were calculated on an annual and irrigation buried drain runoff control systems, and sediment season basis. Annual suspended sediment loads basins. Vegetative filter strips on land with 0-2 for the major drains were: Sand Hollow Drain, percent slope showed an increased net income of 11,040 tons; Dixie Drain, 11,900 tons; Ross East 75 percent. For total control of sediment, tailwater Drain, 4,100 tons; and South Boise Drain, 3,260 recovery-pumpback and side-roll sprinklers were tons. It was also found that concentrations of total cost-effective. Practices not cost-effective on all phosphorus and inorganic nitrogen exceeded land classes included semi-automated gated pipe, accepted in-stream criteria in most drains through- gravity-improved management and I-slot sedi- out the year. Calculated total phosphorus loads ment structures. A linear programming model was showed that the drains contribute large quantities used in this study to simulate the least-cost mix of of phosphorus to the Boise and Snake rivers. BMPs achieving varied reductions of sediment in Annual mean concentrations of inorganic nitrogen the entire LQ watershed. Results showed that ranged from 2.20 to 4.80 milligrams per liter (mg/l). simultaneous consideration of crop rotations and Fish were analyzed for pesticide residues in this land classes was possible. Sediment delivery study. Results showed that of the 18 pesticides or reductions of up to 54 percent from the watershed other trace organic factors analyzed, only two, resulted in a modest income penalty of less than 1 DDT and toxaphene, were consistently above percent. Greater sediment control became progres- minimum detection limits. A comparison of total sively more costly with mini-basins and sediment phosphorus concentrations during the irrigation basins being implemented on 0-2 percent-sloped season and the non-irrigation season showed that land. Total sediment control on relatively level there was a slight increase in total phosphorus land (0-2% slope) and side-roll sprinklers on concentrations during the irrigation season. steeper land (2+% slope) decreased income by Therefore, Clark and Bauer concluded that in- nearly 20 percent. creases in phosphorus loads during the irrigation As the above studies indicate, stream pollu- season were due primarily to increased drain tion problems and the means of their solutions discharges during this period. have been studied for almost 20 years. It is also Calkins (1980) provided an economic evalua- known from Idaho Department of Health and tion of best management practices (BMPs) for Welfare sources that additional sewage treatment controlling sedimentation in irrigation return and better farm management practices have been flows. His study area was the LQ drain, a 3,300- adopted over this period. Data, however, are not acre watershed in the Magic Valley of southcentral available regarding the extent of these efforts. The Idaho and the site of a project demonstrating focus of this study is to better establish the rela- sediment control practices. The additional costs of tionships between urban and rural activities BMPs implementated above baseline management associated with pollution in the Boise River.

2 Glade Walker Boise Project, Arrowrock Division, Anderson Ranch Dam. Located on the South Fork of the Boise River, 20 miles northeast of Mountain Home, this earthfill structure is 456 feet high and has a storage capacity of 493,200 acre-feet.

Historical Pollution Trends concentrations (mg/l) and total load of pollutants Data on pollution levels have been collected (lb/day). Each method has advantages and disad- by several government agencies at different points vantages. Pollutant concentrations are inversely along the Boise River for the past 40 years. These related to stream flow. When stream flow is high, data help one understand how pollution increases pollutant concentrations are low, and when stream as the river flows from Lucky Peak Dam to Parma. flows are low concentrations are high. On the Pollution indicators that are high near Boise, but other hand, total load (pounds of pollutants) is decline toward Parma, are likely to be caused by directly related to stream flows, that is, larger urban sources. On the other hand, sudden in- volumes of water at low concentration levels carry creases in pollution levels near Parma are more more pollutants. Depending on how one defines likely to be associated with agricultural activities. pollution, the measurement used may influence As is true for much of the , even the results. Because the Boise River had relatively common water-quality data have not been col- low flows in the late 1980s and early 1990s, it was lected in a systematic way or for the same periods felt that concentration measurements (mg/l) best of time in the Boise River. represented the pollution situation, since loads Two methods are commonly used to measure would be very low. Whichever method of mea- water pollution. These methods are pollutant surement is used presents a problem. The impor- 3 tant point is that any analysis made of these data that salts and sediment from downstream users must include stream flow as a variable since it were more responsible than upstream urban users. influences the results significantly. Although some conductivity increase is normal as water moves downstream and picks up various Specific Conductivity materials, high specific conductivity is associated Conductivity measurements reflect the levels with flood irrigation activities that increase salt of salts and sediments in the river and would be and sediment levels in the river. expected to increase with economic activity that puts material into streams. Data collected from Nitrogen 1973 to 1992 by the Environmental Protection Data are available for nitrogen concentrations

Agency showed that the average conductivity in three forms: NO3-N, NH3 + NH4-N dissolved, measurements over this time increased by 38 and NO2 total. NO3-N is a form of nitrogen closely percent as the river passed through the city of associated with human activity, including both Boise (fig. 1). By the time the river reached Parma, urban and agriculture activity. Ada and Canyon conductivity measurements increased by five county population centers and activities tend to be times the level at Lucky Peak Dam. While the data located along the Boise River, so county popula- are not conclusive, they do indicate that conduc- tion was thought to impact pollution. Using a tivity levels in the Boise River increased at an pollution index of 100, based on an average of increasing rate between Boise and Parma. Since an available measurements from 1973 to 1981 at index of conductivity measurements, using the Lucky Peak Dam, NO3-N increased by 300 percent average at Lucky Peak Dam as a base of 100, just downstream from Boise and rose to 1,082 by increased by only 38 percent just outside Boise the time the river reached Parma (fig. 2). In other (mile 16) to over 511 percent at Parma, it suggests words, there was a nine-fold increase; one-third of that occurred just below Boise. When observations between Boise and Parma were plotted graphi- Figure 1. Average Specific Conductivity Levels, cally against distance, the results were nearly Boise River, 1973-92 linear (as indicated by the dashed line), showing a 600 steady increase in nitrogen as the river moved 500 • downstream.

400 Data for NH3 + NH4-N dissolved were quite different from NO -N. Data were available from 300 • 3 1973 to 1992 from the Environmental Protection 200 • Agency. The average reading for this time period • 100 • at Lucky Peak Dam was the base or 100. The results showed there was a 700 percent increase

Conductivity (micromhos) 0 16 32 43 60 just outside Boise, and only a 418 percent increase

Miles from Lucky Peak Dam by Parma. These data indicate NH3 + NH4-N dissolved increases were due mostly to urban

Figure 2. Average Nitrogen (NO -N) Levels, 3 Figure 3. Average Nitrogen (NH 3 + NH 4 -N Boise River, 1973-81 dissolved) Levels, Boise River, 1973-92

2 0.18 • • 0.16 1.5 0.14 4

3 • 0.12 1 0.10 • •

3 0.08 • 0.5 0.06 • • 0.04 • 0.02 • Nitrogen (NO -N, mg/1) 0 0 16 32 43 60 Nitrogen (NH + NH - N diss, mg/1) 16 32 43 60 Miles from Lucky Peak Dam Miles from Lucky Peak Dam

4 activities and that concentrations became diluted Peak Dam and Parma. It appears that phosphorus as the river flowed downstream to Caldwell in the river comes from both urban and rural

(fig. 3). Past Caldwell, NH3 + NH4-N dissolved sources. increased again. The major cause of nitrogen The data cited above for the five pollution pollution was probably from urban rather than indicators were collected over various periods of agricultural activities. time and represent past historical trends. They

On the other hand, NO2-total readings were may misrepresent the current situation in the river nearly linear between Lucky Peak Dam and Parma and since much effort has occurred to improve sewage were slightly above the dashed trend-line just outside treatment at major population centers in recent Boise (fig. 4). An index level of 100, based on observa- years. Unfortunately, sewage treatment data were tions at Lucky Peak Dam, showed the measure in- not collected over time. Data indicate that nitrogen creased by 347 percent just outside Boise and by 808 and phosphorus levels do increase with the flow percent at Parma for the 1973 to 1992 period. of the river and are probably caused by both urban In summary, where nitrogen is concerned, and rural activities. These observations may no pollution appears to be caused by both urban and longer represent the current situation since the rural water users. Increased nitrogen levels number of sewage treatment facilities has in- downriver caused by urban and rural runoff are creased in recent years and point pollution has not easily separated. also been reduced.

Phosphorus Average Annual Nitrogen Levels Like nitrogen, phosphorus is an important Figure 6 shows average annual levels of contributor to stream pollution that may be caused nitrogen (NH3 + NH4-N dissolved) from 1973 to by using soaps and fertilizer in urban areas or 1990 (EPA data) at Lucky Peak Dam and Parma. fertilizer in rural areas. Historical data on phos- The EPA criterion level for pollution is also in- phorus levels in the Boise River generally parallel cluded (IDHW 1973). In spite of increases in those for nitrogen, with levels increasing between population, the nitrogen level has steadily Lucky Peak Dam and Parma (fig. 5). However, dropped over the period. This decrease can be phosphorus levels, unlike nitrogen, tended to be attributed to better sewage treatment facilities, above EPA standards. reduced contributions from point sources, and Using average phosphorus levels from 1973 better irrigation management practices. Unfortu- to 1992, and using Lucky Peak Dam as an index of nately, measurements for pollution control efforts 100, phosphorus levels increased by 547 percent are not available. The only years that nitrogen was just outside Boise and increased by 945 percent a potential problem were 1973 and 1975. By 1990, downriver at Parma. This indicates that urban nitrogen concentration levels dropped to about .05 contributions were greater than those from rural mg/l from .41 mg/l, only a fraction of the EPA (downriver) sources. Phosphorus levels grew at a criterion level of 0.30 mg/l. faster rate between Lucky Peak Dam and Annual data clearly show the results of pollu- Glenwood Bridge (mile 16) than between Lucky tion control efforts on the Boise River. In spite

Figure 4. Average Nitrogen (NO 2 -total), Levels Figure 5. Average Total Phosphorus Levels, Boise River, 1973-92 Boise River, 1973-92 0.045 0.40 • • 0.040 0.35 0.035 0.30 0.030 • • 0.25 • • 2 0.025 • 0.020 • 0.20 0.015 0.15 0.010 0.10 0.005 • 0.05 • 0 Phosphorus (mg/1) Total

Nitrogen (NO total, mg/1) 0 16 32 43 60 16 32 43 60 Miles from Lucky Peak Dam Miles from Lucky Peak Dam

5 Boise River Diversions and Drains, 1995

Source: C.C. Warnick and C.E. Brockway, 1974. Hydrology Support Study for a Case Study on a Water and Related Land Resources Project, Boise Project, Idaho and Oregon: Research Report OWRT Title II Contract C-4202: Idaho Water Resrouces Research Institute, University of Idaho, Moscow, Idaho.

63.6

Snake 60.0 River

49.8 47.6 45.7 38.9 40.4 37.3 42.5 35.9 31.2 30 of a growing population and periods of low-river 41.7 41.0 flows that increase concentration measurements, 46.0 nitrogen levels have fallen over the years. Of 43.9 course, one should keep in mind that this form of nitrogen is just one of many, and the results may 41.2 not be the same for all forms of nitrogen. Pollu- tion control efforts appear to be highly effective for as successful as with nitrogen. Essentially, phos- this type of nitrogen. Water quality in recent years phorus levels have stayed constant from 1973 to was nearly as good at Parma as it was at Lucky 1990 at Parma. Phosphorus levels have fluctuated Peak Dam before the river entered the city or the on a year-to-year basis with an average value irrigated area. The downward trend in concen- staying at 0.36 mg/l, while the EPA criterion level trates indicate that this form of nitrogen is not is 0.10 mg/l. The average level at Lucky Peak currently an environmental problem and probably Dam was less than 0.05 mg/l over this period. will not be in the future. Nitrogen may be leached Several conclusions are apparent from the into the soil or volatilized before it can run off. If data in figure 7. First, the EPA criterion level for anything, the efforts for controlling nitrogen levels eutrophication (oxygen-deficient water) is only may be carried beyond reasonable levels if other two or three times the phosphorus level at Lucky pollution factors are being ignored. Peak Dam, so it does not take much additional phosphorus to exceed the critical level. Second, the Average Annual Phosphorus Levels average phosphorus level has remained relatively Figure 7 shows average annual phosphorus constant from 1973 to 1990 at 0.40 mg/l, or four levels from 1973 to 1990 at Parma and Lucky Peak times the EPA criterion level. A statistical test did Dam and the EPA criterion level. Unfortunately, not reveal any significant trend. Third, the efforts efforts to control phosphorus levels have not been to reduce pollution in this area that worked so well

6 Mileage Chart: Boise River Diversions and Drains, 1995

River Mile 0.0 < Boise River near Boise Penitentiary Canal > 2.4 > Boise Project Main (New York) Canal 4.8 Barber Dam 5.3 > Ridenbaugh Canal Boise City Canal < > Bubb, Meeves #1 & #2, Rossi Mill Canal 10.8 < Boise River at Boise 11.6 > Settlers Canal < Drainage District #3 N > Davis Ditch 12.6 > Thurman Mill Canal Farmers Union and Boise Valley Canals < 13.2 Boise Sewer > 16.0 Glenwood Bridge New Dry Creek & New Union Canals < 17.2 9 Eagle Island Canals Ballentyne Canal < to < Thurman Drain Eagle Drain > 25.6 > Eureka #1 and Phyllis Canals Middleton Canal < Little Pioneer Canal < Canyon County Canal < 30.7 31.2 > Caldwell Highline Canal 35.9 < Fivemile Creek North and South Middleton Drain > 37.3 Willow Creek > 38.9 40.4 < Mason Creek and Drain 41.0 > Riverside and Pioneer Dixie Canals Hartley Drain and Gulch > 41.2 Sebree, Campbell, and Siebenberg Canals < 41.7 42.5 Caldwell Bridge 43.9 < Indian Creek > McManus and Teater Canals 45.7 > Eureka #2 Canal 46.0 > Upper Center Point Canal > Bowman and Swisher Canal 47.6 > Lower Center Point Canal 0.7 49.8 < Boise River at Notus Conway Gulch > 17.2 Baxter and Boone Canals < 9 Eagle island Canals Andrews Canal < 16.0 Mammon Pumps < < Dixie Slough > Haas Canal 13.2 Parma Canal < > Island Highline Canal > McConnel Island Canal 12.6 60.0 < Boise River near Parma 11.6 63.6 Snake River 10.8 Boise

reducing nitrogen levels are apparently 5.3 ineffective for phosphorus. On the other hand, Lucky Peak 4.8 phosphorus levels have not increased with either Reservoir population growth or possible increases in fertil- 2.4 Lucky Peak izer usage. The question that remains, of course, Barber Dam Dam is what exactly causes the high levels of phospho- rus at Parma? Is it just agriculture or is it agricul- New York Canal ture and urban growth together? The time-series data for nitrogen and phosphorus indicate that the 0.0 Boise River two sources of pollution are not related: nitrogen levels decreased, while phosphorus levels showed no significant trend.

7 Monthly Data for Nitrogen and Phosphorus pollution (0.1 mg/l). Second, most spikes of Figures 8 and 9 show monthly observations phosphorus concentration levels tend to be about on a calendar-year basis from 1973 to 1990 for both double the average levels (about 0.4 mg/l). Finally, nitrogen and phosphorus, while the previous the amplitude of the spike observations for phos- figures were for average annual data. Figures 8 phorus does not vary as greatly relative to the and 9 show that pollution concentration levels mean level as do those for nitrogen. It is still very tend to increase during the winter months when apparent that average annual phosphorus concen- stream flows are low and the dilution effect is tration levels exceed EPA standards by a factor of reduced. In the case of nitrogen, figure 8 shows four, while nitrogen levels are only about one- that, in spite of continually reduced nitrogen levels third the EPA standard. From the monthly phos- between 1973 and 1990, spikes above the EPA phorus data, it appears that nothing has happened criterion level still occurred, usually during the from 1973 to 1990 to change the annual pattern, winter months. As the average level of nitrogen and the question remains as to who is responsible has been reduced, so have the annual increases for non-point pollution in the Boise River: agricul- due to low-river flows. Several farm management ture or urban water users. practices are employed to reduce runoff from irrigation, which can contribute to pollution. Presentation of Study Data Figure 9 shows increases in phosphorus After consideration of the possible causes of concentration levels, which also tend to be more phosphorus pollution in the Boise River, three prevalent during periods of low flow. Figure 9 also factors were tentatively specified as major con- indicates some interesting information about tributors to the problem. Since Boise is a city with phosphorus levels. First, phosphorus concentra- little industry to cause pollution, population tion levels are seldom below the EPA standard for growth was specified as a potential factor for

Figure 6. Annual Average Nitrogen (NH 3 + NH 4 -N dissolved) Level at Parma and Lucky Peak Dam and the EPA Criterion (1973-90) 0.45

0.4 • 0.35 • 0.3 • • • • • • • • • • • • • • • • • 0.25 •

0.2 • 0.15 • • Nitrogen Concentration (mg/l) 0.1 • • • • • 0.05 • • • • •

0 73 74 75 76 77 78 79 80 81 82 83 85 86 87 88 89 90 Year Source: Environmental Protection Agency, Nitro-Parma Nitro-Lucky Peak Dam EPA Criterion Storette Collection System • •

8 changes in phosphorus levels. Because of the Table 1. Fertilizer Use in Southwestern Idaho impact of stream flows in diluting pollutants and reducing concentration levels, stream flows in Crops Phosphate (lb/acre) Nitrogen (lb/acre) cubic feet per second (cfs) were also considered to be a relevant variable. Where agriculture is con- Corn Silage 80 150 cerned, both crop and animal activities could Corn Seed 65 140 contribute to pollution. Animal numbers, how- Onions* 115 50 ever, have been relatively constant from 1973 to Potatoes* 160 100 1990 according to the U.S. Census of Agriculture, Feed Barley 30 135 but there are no data available on an annual basis Spring Wheat 50 135 since the Census is only taken every five years. Winter Wheat 50 140 Consequently, animal numbers were excluded Alfalfa Hay 60 0 from the analysis. Irrigated cropland was the variable thought Source: University of Idaho, Department of Agri- to be most likely associated with phosphorus cultural Economics. Southwestern Idaho Crop pollution, since some crops are known to receive Enterprise Budget, 1993. high application rates (table 1). For analytical purposes, irrigated acreage was separated into * high-valued crops three classes: irrigated acres with crop values less than $500 per acre, irrigated acres with crop values between $500 and $999 per acre, and irrigated results was one that included population, stream acres with crop values of $1,000 per acre or more. flow, and high-valued irrigated crop acreage The model that gave the most significant statistical (value over $1,000/acre).

Figure 7. Annual Average Phosphorus Level at Parma and Lucky Peak Dam and the EPA Criterion (1973-90)

0.6 • • 0.5 • • 0.4 • • • • 0.3 • • • • • 0.2 • • • • Phosphorus Concentration (mg/l) 0.1 • • • • • • • • • • • • • • • • •

0 73 74 75 76 77 78 79 80 81 82 83 85 86 87 88 89 90 Year Source: Environmental Protection Agency, Phos-Parma Phos-Lucky Peak Dam EPA Criterion Storette Collection System • •

9 Large portions of irrigated land used for hay tion, and stream flow as shown by the following crops and grain receive little phosphorus fertilizer. regression equation. (t statistics are in parenthe- Higher economically valued crops such as onions ses.) and potatoes, however, were more likely to receive -7 -5 -5 fertilizer, especially high doses of phosphorus. For Y = - 0.0473 + 5.44 x 10 X1 - 2.79 x 10 X2 + 2.18 x 10 X3 this reason crop acreage for low-, medium-, and (-0.33) (1.79) (-2.73) (3.23) high-valued crops, based on Bureau of Reclama- tion Crop Reports, were determined and used as R2 = 0.817, adjusted for sample size R2 = 0.775, where variables in the analysis of phosphorus concentra- Y = phosphorus concentrations (mg/l) at Parma tion levels. Low- and medium-valued crops were X1 = population in Ada and Canyon counties not statistically associated with phosphorus X2 = stream flow (cfs) at Parma pollution based on similar regression analyses. X3 = high-valued irrigated crop acreage (value of Water quality and flow data were obtained from $1,000/acre or more) in Ada and Canyon counties the Environmental Protection Agency Storette These results indicate that all three indepen- Collection System. Population data were obtained dent variables are associated with changes in from U.S. Census Bureau reports. Irrigated acreage phosphorus levels at Parma, although population and value data came from Bureau of Reclamation was significant at a lower level than stream flow Annual Reports. Data were not adjusted prior to the or high-valued crops. Variation in the three inde- analysis. pendent variables was associated with 78 percent of the variation in the dependent variable. This Analysis and Results evidence indicates that both population and high- Phosphorus concentration levels were found valued crop acreage expansion increased phos- to be related to high-valued crop acreage, popula- phorus levels. As expected, stream flow was

Figure 8. The Monthly Nitrogen (NH 3 + NH 4 -N dissolved) Concentrations at Parma (1973-90)

1.6

1.4

1.2

1.0

0.8

0.6

0.4 Nitrogen Concentration (mg/l) • • • • • • • • • • • • • • • • • 0.2

0 74/6 75/9 76/4 76/8 77/1 77/5 78/4 78/8 79/4 79/8 80/1 80/7 81/3 81/7 82/3 82/7 83/3 83/7 85/3 85/7 86/3 86/7 87/3 87/7 88/3 88/7 89/3 89/7 90/1 90/9 74/11 80/11 81/11 82/11 85/11 86/11 87/11 88/11 73/12 77/12 78/12 Year/month Source: Environmental Protection Agency, Storette Collection System Nitro-Parma• EPA Criterion

10 Table 2. Calculation of Ada and Canyon county crop acreage and population impacts on phosphorus concentrations in the Boise River at Parma

High-Valued Crop Impact Population Impact

Year Parameter Estimate (acres) Parameter Estimate (population)

1990 2.18 x 10-5 x 17,732 5.44 x 10-7 x 295,851 1973 2.18 x 10-5 x 16,199 5.44 x 10-7 x 198,527

Impact 0.03 mg/l increase phosphorus 0.05 mg/l increase phosphorus concentrations concentrations inversely related to phosphorus levels. These gen data were limited, however, and information independent variables are not related to each other about nitrogen control measures was unavailable. nor do they appear to be related to previous observations over time. Population increased Impact of Population and Irrigated Crops steadily over time, and stream flows varied greatly on Water Quality from year to year and within each year. High- Employing the regression equation, results valued crop acreage generally increased but also and observations for 1973 and 1990 gave the varied widely between years. A similar analysis estimated impacts as shown in table 2. was conducted for nitrogen. Some forms of nitro-

Figure 9. The Monthly Phosphorus Concentrations at Parma (1973-90)

1.6

1.4

1.2

1.0

0.8

0.6

0.4 Phosphorus Concentration (mg/l)

0.2 • • • • • • • • • ••• • •••••••• 0 74/5 75/6 76/2 76/6 77/3 78/2 78/6 79/2 79/6 80/4 80/9 81/1 81/5 81/9 82/1 82/5 82/9 83/1 83/5 83/9 85/5 85/9 86/1 86/5 86/9 87/1 87/5 87/9 88/1 88/5 88/9 89/1 89/5 89/9 90/5 73/12 74/10 76/10 77/10 78/10 79/10 Year/month Source: Environmental Protection Agency, Storette Collection System Phos-Parma• EPA Criterion 11 Using the actual changes in crop acreage and This study demonstrated that non-point population for 1973 and 1990, the relative impact pollution in the Boise River can be determined for of each variable was estimated using regression aggregate causes. Pollution levels from both urban parameters. The increased high-valued irrigated and rural activities were estimated by using time- crop acreage was estimated to have increased series data. Further research in this area may be phosphorus measurements by 0.03 mg/l, while improved, however, by better experimental design increased population was estimated to have and using data collected in a more systematic way. increased phosphorus measurements by 0.05 mg/ Examining pollutant loads, in addition to concen- l. In total, they increased phosphorus levels by tration levels, may also benefit the analysis of non- 0.08 mg/l: irrigation accounted for 38 percent and point pollution. population 62 percent. While these results are not conclusive, or may not represent the current References situation, they do indicate that both urban growth Calkins, B. L. 1980. An Economic Evaluation of Best and high-valued crop acreage contributed to Management Practices for Controlling Sedimentation additional phosphorus levels in the Boise River. Under Irrigated Agriculture in Southcentral Idaho. Master’s thesis, University of Idaho, Moscow, Conclusions Idaho. Based on the results of this study, the follow- Clark, W. H., S. B. Bauer. 1983. Water Quality Status ing conclusions were drawn. Past farm manage- Report, Lower Boise River Drains, Canyon County, ment efforts to control nitrogen pollution and Idaho. Idaho Department of Health and Welfare, better sewage treatment facilities have been very Water Quality Series No. 50. effective in terms of reducing nitrogen levels Crutchfield, S. R. 1995. The Benefits of Protecting Ru- below EPA standards in the Boise River. The same ral Water Quality: An Empirical Analysis. United is not true for phosphorus concentration levels, States Department of Agriculture, Economic Re- which exceeded EPA standards from 1973 to 1990. search Service. AER 701. Population, stream flow, and high-valued irrigated Fitzsimmons. D. W. 1978. Evaluation and Measures for crop acreage were associated with nearly 80 Controlling Sediment and Nutrient Losses from Irri- percent of the variations in phosphorus levels in gated Areas. U.S. Environmental Protection the Boise River at Parma during these years. Agency, EPA 600 12-78-138. Increases in urban population and high-valued Idaho Department of Environment and Community crop acreage raised phosphorus levels by an Services. 1973. Water Quality Standards and Waste- estimated 0.08 mg/l. Population increases ac- water Treatment Requirements. Idaho Department counted for 62 percent of this change, and high- of Health and Welfare Division Environmental, valued crops accounted for 38 percent. Lawn Boise. fertilizers and certain detergents contributed to Long, R. B. 1976. Impact of Reducing Pollution and Sedi- higher urban phosphorus levels. However, even if ment From Irrigated Areas of the Boise Valley. Uni- population and high-valued crop acreage had not versity of Idaho, Department of Agricultural Eco- increased from 1973 to 1990, phosphorus levels nomics, Moscow. would still be above EPA standards. Even modest amounts of economic activities would bring Authors phosphorus levels from what they are at Lucky Roger B. Long, Agricultural Economist, Department of Peak Dam to levels beyond EPA standards. Agricultural Economics and Rural Sociology, University of Idaho, Moscow, and Jinghua Zhang, former Re- search Assistant, Department of Agricultural Economics and Rural Sociology, University of Idaho, Moscow.

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