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<br />.
<br />
<br />Dissolved Oxygen. - Concentrations of D.O. were usu-
<br />ally slightly lower for the means of the reservoir pool
<br />than those for either the inlet or outlet (fig. 5). The
<br />mean D.O. levels for the pool for 1974 and 1975 were
<br />8.2 and 8.8 mg/I, respectively, with highest monthly
<br />means (9.6 and 10.6) occurring in December and low-
<br />est monthly means (6.4 and 6.7) in July. For most
<br />depths D.O. concentrations were near or at saturation
<br />except on a few rare occasions. For good growth and
<br />general well-being, D.O. levels for cold,water biota
<br />(especially trout and salmon) should not be below 6
<br />mg/1. For successful spawning, assuming adequate gravel
<br />substrata are also available, D.O. levels must not be be-
<br />low 7 mg/1. From the D.O. data available, trout growth
<br />should not be adversely affected, but successful spawn-
<br />ing may be a problem for certain trout species in Pueblo
<br />Reservoir.
<br />
<br />Water Analysis - Laboratory Measurements
<br />
<br />Turbidity, - Monthly changes in inlet, outlet, and pool
<br />turbidities are shown in figure 6. Inlet values were usu-
<br />ally greater than either those for the outlet or the pool,
<br />especially during periods of high river discharge or after
<br />heavy rainstorm events. For the pool, mean annual tur-
<br />bidities for 1974 and 1975 were 24 and 25, respec-
<br />tively. Highest and lowest monthly pool averages were
<br />43 (April) and 59 (June) and 7 (December) and 7
<br />(March) for each respective year. For public water sup-
<br />plies or farmstead use, turbidities which are virtually
<br />absent are most desirable. For fish and aquatic life, tur-
<br />bidities should not exceed 25 JTU (Jackson turbidity
<br />units) for warm-water lakes or 10 JTU for cold,water
<br />lakes. Obviously, from figure 6, Pueblo Reservoir tur-
<br />bidities periodically exceeded both of these desirable
<br />maxima for aquatic life. What adverse effects these
<br />higher turbidities may have on trout and other fishes
<br />are beyond the scope of this study.
<br />
<br />pH. - The range in pH for 1974 and 1975 was 6.9 to
<br />8.7 and 7.0 to 8.8, respectively. The low pH values
<br />were always those for bottom samples closest to the
<br />sediments and the highest values for those samples
<br />near the surface in the photofixation zones. For most
<br />months, pH values were exceptionally uniform over
<br />the pool. Freshwater organisms usually require pH con-
<br />ditions with the range 6.0 to 9.0. These water quality
<br />extremes were not exceeded during this study. Public
<br />water supplies should have a pH range of 6.0 to 8.5. On
<br />most occasions the water of Pueblo Reservoir did not
<br />exceed this upper limit, and never exceeded the lower.
<br />
<br />Specific conductance. - Annual fluctuations of con-
<br />ductivity are shown in figure 7 for the inlet, outlet,
<br />and reservoir pool. The mean annual values for 1974
<br />and 1975 were 511 and 480 Ilmhos, respectively. The
<br />
<br />highest and lowest monthly averages in 1974 and 1975
<br />were 680 (April) and 645 (March) and 249 (June) and
<br />271 (June), respectively. No applicable water quality
<br />criteria could be found for specific conductance [11].
<br />
<br />
<br />Total dissolved solids (filterable residue). - As pointed
<br />out by Cole [12] and Hem [3], a near-linear re-
<br />lationship exists for concurrent TDS and conduc-
<br />tivity measurements for a given lake or stream if
<br />taken through the seasons. Such a relationship
<br />existed in Pueblo Reservoir for the 1974-76 study
<br />period. Figure 3 can be used to calculate TDS values
<br />for those months with highest and lowest mean con-
<br />ductivities for each year: 480 (April 1975), 466 (March
<br />1976). and 170 (June 1974), 185 (June 1975). A de-
<br />sirable level of < 200 mg/I TDS is recommended for
<br />surface water for public water supplies. A permissible
<br />maximum of 500 mg/I has also been established.4
<br />Pueblo Reservoir watef never exceeded the permissible
<br />value, while reservoir water frequently had values < 200
<br />mg/I TDS and hence satisifed the desirable maximum.
<br />Farmstead water use criteria list a TDS desirable level
<br />of < 500 mg/1. TDS levels < 10,000 mg/I are recom-
<br />mended if water is used for livestock drinking. Irriga-
<br />tion water with < 500 mg/I TDS will usually not be
<br />detrimental to crops and is recommended. For livestock
<br />and irrigation use, therefore, TDS levels in the pool are
<br />acceptable. No applicable water qual ity criteria for TDS
<br />have been established for aquatic wildlife and freshwa-
<br />ter organisms.
<br />
<br />Total alkalinity. - Contrary to Lind [13] and EPA [1,
<br />2], filtered water samples were used for t-alk (total
<br />alkalinity) determinations. Little, if any, difference was
<br />recorded depending on whether filtered or raw water
<br />samples were titrated. Changes in t-alk (mg/I as CaC03)
<br />for the inlet, outlet, and reservoir pool are illustrated
<br />in figure 8. Generally, pre-impoundment concentrations
<br />were of the same order of magnitude and temporal
<br />occurence (fig. 23) as for the outlet of the reservoir.
<br />The annual means for 1974 and 1975 were nearly the
<br />same, 116 and 177, respectively. Fall months showed
<br />the highest monthly means, 140 (November) and 160
<br />(October). respectively; June in both years showed the
<br />lowest monthly averages, 68 and 71, respectively. If a
<br />value of 116 mg/I CaC03 is converted to C03-2, the
<br />mean pool concentration as C03-2 would be 70 mg/1.
<br />Wetzel [15] found the mean C03-2 composition of
<br />
<br />4 On December 24, 1975, the EPA published "National
<br />Interim Primary Drinking Water Regulations" [14],
<br />which propose no standard for TDS. According to EPA,
<br />there will be no TDS standard proposed in the sec-
<br />ondary regulations when they are published later this
<br />year.
<br />
<br />23
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