|dc.description.abstract||During the summer of 2011 students and faculty from the UNM Water Resources Program
conducted an investigation of the Rito Peñas Negras in the Cuba District of the Santa Fe National
Forest. The objective was to conduct an assessment of the stream and determine its
characteristics, quality, and ability to meet its designated use of supporting high quality
coldwater aquatic life. The Rito Peñas Negras is a small first order stream with a total length of
7.9 miles. It has one tributary, the Rito Café, which adds another 4 miles to its length. The
watershed consists of 10,850 acres and ranges in elevation from approximately 8,500 ft to 9,000
ft. The lower reaches of the stream are the subject of a watershed restoration project by the
WildEarth Guardians that consists of constructing animal exclosures and re-establishing riparian
vegetation. The results of this study may serve as a baseline for future evaluation of the success
of this restoration effort.
This project included a formal assessment of the stream at five locations along its length. These
assessments included measurement of flow, water quality, stream geomorphology, and field
identification of benthic macroinvertebrates. Additional measurements of flow and/or water
quality were done at three other sites in watershed and three sites along the Rio de las Vacas. An
intensive investigation of the stream was conducted during the second week of June, while a
follow up study on August 15, 2011 was limited to flow measurements and collection of water
quality samples at three locations.
Flow in the Rito Peñas Negras in June ranged from about 0.25 cfs in the upper reaches to 0.16
cfs in the lower reaches. Streamflow in August ranged from .52 to 1.04 cfs which was due to
summer rains. Measurements of electrical conductivity and the stable isotopes deuterium and
oxygen-18 suggest that the decrease in flow is the result of both evaporation and infiltration.
During both sampling trips the stream was flowing well below bankfull conditions which was
attributed to a dry winter, however, the lower reach showed evidence of a recent very high flow
event due to a summer thunderstorm in August.
The water quality of the stream was found to be very high during the June study. Nutrient
concentrations (nitrogen and phosphorous) were low and no measurable chlorophyll a was
detected in the water, though small attached algal growth was noted on bottom sediments.
Thermograph measurements over the preceding month exhibited a strong diurnal fluctuation
superimposed on an increasing trend associated with on-set of summer. Field characterization of
benthic macroinvertebrate populations also supported the conclusion of high quality water in the
stream. Stream samples collected in August found moderate concentrations of nitrate which was
attributed to cattle grazing that began about June 1.
The upper reaches of the watershed is steeper hence the stream was dominated by riffles and
glide areas. The stream bed consisted mostly of sands and gravels and there was good canopy of
riparian vegetation. Lower reaches were flatter and flow was primarily a mix of shallow pools
and glide areas. Stream banks were generally stable with extensive undercut areas for fish
refuge, however, there was virtually no woody riparian vegetation below FR 527. There was no
sign of current beaver activity anywhere in the watershed.||en_US