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LAKE WATER-QUALITY DATA
<br />Water-quality samples were collected from
<br />Vallecito Reservoir for analysis of selected metals,
<br />bacteria, nutrients, alld field parameters. Field
<br />parameters were measured by the volunteers in
<br />profiles of lake depth using aHydro-Lab Surveyor 4
<br />with multi-parameter Data Sonde. Before each day
<br />of field work, the instrument and data sonde were
<br />calibrated using fresh calibration standards obtained
<br />form the USGS. Depth of the sonde in the lake was
<br />determined using a transducer in the data sonde.
<br />Lake profiles for specific conductance aild dissolved
<br />oxygen are shown in Figures 11 and 12. Selected
<br />historical lake-profile data are shown for comparison.
<br />Samples were al~alyzed for total iron, total
<br />manganese, dissolved anunonia, and dissolved
<br />nitrate. Sammples for total iron aid manganese were
<br />acidified after collection, alld the samples were
<br />digested before analysis. Digestion consisted of
<br />adding 2.5 mLs of concentrated nitric acid to 25 mL,s
<br />of sample (10 percent acid), then heating the sample
<br />to 160°F using a microwave oven (EPA Method
<br />3015). Digested, or total recoverable, samples were
<br />then filtered and the samples brought between pH 3
<br />a«d 5 using sodium hydroxide before analysis. Iron,
<br />manganese, ammonia, aild nitrate analyses were
<br />analyzed by spectrophotometiy. Sample results are
<br />shown in Table 2, a«d graphs of water-quality data
<br />for the lake are shown in Figure 13.
<br />Bacteria samples were collected for analysis of
<br />total coliform a11d E. coli (Eschericlua coli) from
<br />Vallecito Lalce. Samples were collected at site DS-1,
<br />Pine River inflow, Vallecito Creek inflow, and
<br />Graham Creek inflow Samples were collected on
<br />July 13, August 23, and September 6, 2006. Bacteria
<br />samples were analyzed by San Juan Basin Health.
<br />The index method used on July 13 provided results
<br />that indicated total coliform and E. coli were
<br />"present" in the water samples. The results were
<br />questioned by the volLU7teers. A request was made to
<br />provide a more quantitative analysis. On August 23,
<br />total coliform results were all greater than 2,419
<br />colones per 100 mLs; for the Pine River inflow site,
<br />E. coli result of 4.1 colonies per 100 mL,s was
<br />reported. On September 6, total coliform results
<br />ranged from 178 to 344 colones per 100 mLs, and E.
<br />coli results were all less than 1.
<br />SUMMARY
<br />The spring of 2006 was a relatively dry period,
<br />and very few precipitation events occurred between
<br />April and June; therefore, soil moisture conditions
<br />were dry in the study area. Rainfall events bega« to
<br />occur on a regular basis by early July, but the dry
<br />soils soaked up most of the rain. Despite several
<br />substantial rain storms, the volunteer stream gaging
<br />data do not indicate that high flow events occurred.
<br />This would at first appear to indicate that there has
<br />been forest and vegetation recovery in the buried
<br />areas. However, due to the flashy nature of rainfall
<br />runoff in mountain strean~s, several of the high flow
<br />events were missed by the volunteers. The crest-
<br />stage gages indicated that increased streamflow
<br />events did occur, but the dates and times are
<br />uncertain. The data collected as part of this study,
<br />therefore, do not indicate that floods or high-flow
<br />events will not occur in the future. Given saturated
<br />soil conditions, the flood potential could be entirely
<br />different. The Vallecito Creek valley remains the
<br />most vuh~erable for floods.
<br />Water-quality samples from streams draining
<br />the burned area reveal varying iron and manganese
<br />concentrations in rainfall runoff. The site called
<br />"2100 CR500 Creek" represents a backgroLU~d site.
<br />High iron and manganese concentrations were
<br />exhibited in water from Grimes Creek and Lost
<br />Creek (which is a tributary to Grimes). Total
<br />mercury concentrations of 27 and 53 ng/L
<br />(nanograms per liter, or parts per trillion) were
<br />reported i11 turbid rainfall nuloff samples from
<br />Grimes Creek. Since iron, manganese, and mercury
<br />are problems in Vallecito Reservoir, the burned areas
<br />in Grimes Creek and Lost Creek need to be explored
<br />for reclamation potential.
<br />Water quality conditions in Vallecito Lake
<br />appear to be fluctuating somewhat after the fire.
<br />During 2005, there were high manganese
<br />concentrations in the reservoir, ranging from 1,750 to
<br />1,910 µg/L (micrograms per liter, or parts per
<br />million). During 2006, the manganese
<br />concentrations were surprisingly low, ranging from 7
<br />to 114 µg/L. The total iron concentrations, however,
<br />increased from 50 µg/L in 2005 to 500 µg/L during
<br />2006. Iron and mai~gai~ese are, therefore, both of
<br />concern ill the lake, aid these metals may play a role
<br />in mercury availability for fish. Other metals not
<br />a«alyzed are also probably entering the reservoir.
<br />These metals may be accumulating iii the lake
<br />sediments.
<br />S ~.~, ~ s
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