Water Resources Professional Project Reports

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Livestock grazing can have a profound effect on water quality and vegetation of riparian ecosystems. In this study, the impacts of livestock grazing on surface water quality and vegetation was investigated along Bluewater Creek in the Zuni Mountains of New Mexico. The impacts of grazing were studied by comparing three areas enclosed with bovine fencing in 2003 against unenclosed adjacent areas. A section free of grazing since the 1980s served as a reference area. Sampling sites were further stratified by the dominant geomorphology of incised and stable stream banks. Surface water temperature, conductivity, pH, dissolved oxygen (DO), turbidity, N03--N + N02--N, phosphorous as total P, and fecal coliform were measured in the fall, winter, and spring. Snow N03--N + NO\xa3-N and phosphorous as total P levels were also measured. Surface and ground water measurements made in the spring also included NH/-N. Vegetation frequency, percent cover, and biomass were also measured. During the spring snowmelt runoff, mean turbidity levels were higher (37.1 f\\lTU) than fall (12.8 NTU) and winter (3.8 NTU). Turbidity demonstrated a spatial pattern of downstream reduction during the spring runoff. It is possible that this reduction stemmed from the combined effect of the three exclosures. All other water quality parameters were not different between grazed, ungrazed, and the reference area. Seasonal climatic differences such as insolation and precipitation were important controls on water quality parameters. Fall surface water measurements were warmer, slightly more basic, less oxygenated, and contained higher concentrations of total P and fecal coliform (9.9 ec, 7.5, 7.6mg/L, 0.06 mg/L, 10 cfu/100 mL) than winter (3.5 ec, 7.4, 9.0 mg/L, 0.00 mg/L, 0cfu/100mL) and spring (2.4 ec, 7.3,12.0 mg/L, 0.01 mg/L, 0 cfu/100mL). Surface water and ground water measurements taken in spring demonstrated that ground water was colder, hypoxic, and more conductive (6.9ec, 1.0 mg/L, 0.6 mS/cm) than surface water (11.3 ec, 9.8 mg/L, 0.2 mS/cm). Nitrate-N + Nitrite-N, ammonium, and total P were not different between surface water and ground water. Vegetation data suggest that desirable species such as Elymus trachycaulus and Salix exigua Nutt. were more commonly found in the reference and exclosed areas, however low frequencies did not allow a definitive conclusion. Vegetative cover was not significantly different between treatments. Overall biomass was higher in exclosed areas, and may have played a role in downstream reductions in turbidity. Future study of Bluewater Creek would be well served to include a comparison of channel geomorphology between grazed, ungrazed, and reference areas. Channel width to depth ratio and channel complexity are useful indicators of stream and riparian health. An analysis of piezometer and stream flow elevation data will provide a better understanding of ground water flow paths and the dynamics of ground water and surface water exchange. Analysis of water chemistry should include all forms of inorganic nitrogen. Phosphorous data should be stratified by organic and inorganic phosphorous.

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Riparian ecosystems, Livestock grazing, Stream water quality, Fence line contrast, Bovine exclosure fencing, Head cut channels, Arroyo formation, Beaver (Castor canadensis)


A Professional Project Report Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Water Resources, Hydroscience Option, Water Resources Program, University of New Mexico, Albuquerque, New Mexico, August 2005.