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<br />,.... t'" ,..0, r3 <br />4 Jo..), <br /> <br />Using the relation of specific conductance to streamflow, an estimate of the <br />specific conductance of the Arkansas River at Portland at a streamflow of <br />1,000 ft3/s would be about 316 ~S/cm, and at a streamflow of 200 ft3/s, the <br />specific conductance would be estimated to be 574 ~S/cm. Cain (1987) calcu- <br />lated that the average standard error of this relation is 24 percent. Concen- <br />trations of dissolved solids at Portland can be approximated from specific <br />conductance using the following equation: <br /> <br />Dissolved solids (milligrams per liter) <br />= 8.4 + 0.61 specific conductance (microsiemens per centimeter at 25 OC). <br /> <br />Thus, a specific-conductance measurement of 315 ~S/cm would have a <br />corresponding dissolved-solids concentration of about 200 mg/L, and a <br />specific-conductance measurement of 570 ~S/cm would have a corresponding <br />dissolved-solids concentration of about 356 mg/L. The standard error for this <br />relation is 7.4 percent (Cain, 1987). Relations between specific conductance <br />and concentrations of major ions for water in the Arkansas River between Canon <br />City and Pueblo were developed by Cain (1987) and are listed in table 2. <br />Analyses of 56 samples (table 1) for station 07097000, Arkansas River at <br />Portland, indicate that the predominant ions are calcium and bicarbonate <br />(fig. 7). On the average, calcium comprises 52 percent (based on milliequiv- <br />alents per liter) of the cations, or positively charged ions; bicarbonate com- <br />prises an average of 49 percent of the anions, or negatively charged ions, and <br />sulfate comprises an average of 45 percent of the anions. <br /> <br />Dissolved oxygen, pH, and alkalinity data swnmarized in table 1 indicate <br />that water in the Arkansas River at Portland is: (1) Well oxygenated, <br />(2) alkaline (pH values usually range from 7.8 to 8.3), and (3) well buffered <br />(median alkalinity equals 120 mg/L as calcium carbonate). <br /> <br />Concentrations of total nitrogen generally are less than 1 mg/L, and <br />organic nitrogen is the dominant nitrogen species. Based on 20 water samples <br />in which total nitrogen species were analyzed, 61 percent of the total nitro- <br />gen consisted of organic nitrogen, 32 percent as nitrite plus nitrate, and <br />7 percent as ammonia. Based on analyses of 16 water samples in which total <br />and dissolved nitrogen were analyzed, about 70 percent of the nitrogen present <br />was dissolved. Concentrations of total phosphorus have ranged from 0.03 to <br />0.88 mg/L with a mean concentration of 0.13 mg/L and a median concentration of <br />0.08 mg/L. Based on analyses of 39 water samples in which total and dissolved <br />phosphorus were analyzed, about 40 percent of the phosphorus present was <br />dissolved. <br /> <br />Concentrations of total and dissolved trace elements analyzed from water <br />samples collected at station 07097000, Arkansas River at Portland, by the U.S. <br />Geological Survey are swnmarized in table 1. Trace elements that have the <br />largest concentrations are barium, iron, manganese, strontium, and zinc. Most <br />of the water samples collected were filtered and analyzed for concentrations <br />of dissolved trace elements. However, a few of the water samples collected <br />were analyzed for concentrations of dissolved and total trace elements. These <br />analyses indicate that most of the trace elements in the Arkansas River are <br />part of or attached to the suspended material. <br /> <br />19 <br />