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Water Quality 23 was calculated for each sample and then compared to the calcu- lated un-ionized ammonia concentration. No surface-water sample had an un-ionized ammonia concentration that exceeded the chronic standard or the calculated acute TVS for un-ionized ammonia. In noncontaminated waters, nitrite usually is not detected or is detected at low concentrations because it is unstable in the presence of oxygenated water and is rapidly converted to nitrate. All nitrite concentrations in the Fraser River were less than or equal to 0.01 mg/L and met the State instream water- quality standard of 0.05 mg/L (Colorado Department of Public Health and Environment, 2002). Nitrate concentrations in the river were very low, ranging from 0.012 to 0.703 mg/L (table 4). Nitrate concentrations fluctuated with the same seasonality as ammonia concentrations (fig. 10). Low nitrate concentrations at the beginning of summer resulted from dilu- tion of surface water with snowmelt water. During summer, the low concentrations probably reflected the consumption of nitrate by stream biota. All nitrate concentrations were well below the State instream standard of 10 mg/L (table 4) (Colo- rado Department of Public Health and Environment, 2002). Total phosphorus concentrations ranged from 0.032 to 0.173 mg/L, and the median concentration was 0.058 mg/L (table 4). Typically, more than one-half of the total phosphorus in the Fraser River was particulate rather than dissolved phos- phorus. Most of the dissolved phosphorus that was detected in surface-water samples was orthophosphate (fig. 11), the form of phosphorus that is most readily used in plant and animal metab- olism. Maximum concentrations for all phosphorus species occurred in late winter or early spring, and minimum concentra- tions occurred during snowmelt runoff and, at times, during fall. 0.20 Z J - 0.18 QZ ZO - oC 0.16 w Z 0.14 M _j :D ?aww0 0.12 w LL 2 x=020 0.10 LUU)u < d 0.08 0a¢ JQ 0.06 (n00 U) X: 0.04 0 F- w O O 0.02 2 IL 0 All natural waters contain organic carbon (Hem, 1992). Sources of organic carbon in surface water include living and decaying vegetation and biota, wastewater, and ground water. Organic carbon is important in surface water as a nutrient for microbiota that mediate chemical processes (Hem, 1992), and it can increase the solubility or transport of hydrophobic organic chemicals such as pesticides. Most organic carbon in the Fraser River at Tabernash was dissolved organic carbon. Concentra- tions of dissolved organic carbon ranged from 1.6 to 6.3 mg/L (table 4). The median concentration of 3.3 mg/L was similar to the national average of 3.0 mg/L for semiarid regions (Hem, 1992). Dissolved organic carbon concentrations in the river fluctuated seasonally, with maximum concentrations during snowmelt runoff and minimum concentrations during winter (fig. 12). Particulate organic carbon concentrations ranged from less than 0.2 to 0.7 mg/L (table 4). Two of the three highest concentrations occurred during spring at the onset of snowmelt runoff, and then concentrations decreased during the runoff period (fig. 12). The timing of these peak concentrations of dissolved and particulate organic carbon indicates that the con- centrations are likely derived from decaying vegetation and organic detritus transported from the landscape during snow- melt runoff. Fecal Coliform Bacteria Fecal coliform bacteria are an indication of the sanitary quality of the surface water and the potential for adverse human-health effects. The Fraser River is classified as a class 1 recreation river, which allows for primary contact with the water in such activities as swimming, kayaking, and rafting Dissolved phosphorus --o- Orthophosphate } Total phosphorus Discharge ao ao m m m M O 0 0 0 m m m m m rn o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00 N 0 00 N Lo OD N Ln W O O O O O O O O O O TIME 300 250 U m? Z) z 200 U O ZU w w 150 Cw7 fr ?w QLL F- 100 U iw ULL 50 Figure 11. Phosphorus concentrations and discharge at the Fraser River below Crooked Creek at Tabernash, Colorado, 1998-2001.