UC Davis Department of Plant Sciences

Pilot Study Results Summer 2010

Water Quality on US Forest Service Grazing Allotments


Contact Person: Dr. Kenneth W. Tate

Participants: Rob Atwill,Lea Kromschroeder, Donna Dutra, Scott Oneto, USDA Forest Service – Region 5, Stanislaus National Forest, Plumas National Forest, Tahoe National Forest, Shasta-Trinity National Forest, Klamath National Forest.

Comment or Questions?


During the summer of 2010, a pilot study was conducted on three grazing allotments (Eagle Meadow, Herring Creek, and Bell Meadow Allotments) within the Stanislaus National Forest. The purpose of the pilot study was to: 1) develop a watershed scale pollutant source search methodology for grazing allotments; 2) determine water sample collection, sample handling and transport, and laboratory analysis challenges and solutions for sampling in remote forest locations; and 3) provide preliminary data on the levels of FIB and nutrients to be expected in samples to inform a larger study planned for summer 2011.


Watershed scale sampling was conducted on all three allotments to evaluate water quality and identify possible sources of pollution, with a focus on fecal indicator bacteria and nutrients. Working with local and regional Forest Service managers, we identified all obvious sources of pollution, as well as known areas of primary recreational usage (i.e., swimming) on each allotment. Sample locations were then selected which allowed evaluation of each stream tributary on the allotment, as well as above and below activities/pollution sources such as key cattle grazing areas, camping, swimming, etc. Figure 1 illustrates selection of sample locations (red dots) across Herring Creek Allotment following the watershed scale source search methodology. A total of 42 sample locations were identified across the 3 allotments. Two sampling events were conducted, one August 18th and one September 15th. All 42 sample sites were sampled on the same day. All samples were analyzed for fecal coliform and indicator E. coli concentration (cfu/100ml); nitrate-nitrogen, ammonium-nitrogen, total nitrogen, soluble reactive phosphorus, and total phosphorus (ppm). On August 18th, all fecal indicator bacteria analysis was completed within 24 hours of sample collection. On September 15th, all fecal indicator bacteria analysis was completed within 8 hours of sample collection. Stream water temperature and stream discharge were measured at each sample location.


Figure 1.  This figure illustrates the distribution of stream sample locations across the Herring Creek Allotment. Sample locations were selected following a watershed scale pollution source search approach.





Microbial Water Quality Results

Table 1 reports descriptive statistics for fecal indicator bacteria across all 42 sample location on the August 18 and September 15 sample date. With the exception of one sample from the Bell Meadow Allotment collected September 15, all samples were below the fecal coliform water quality standard of 200 cfu/100ml set by the Central Valley Regional Water Quality Control Board. This single sample was also the only sample collected to exceed U.S. Environmental Protection Agency’s recommended indicator E. coli standard of 235 cfu/100 ml. Complete fecal coliform results for all three allotments and both sample events are reported in Figures 2 through 7.


Table 1. Summary of microbial water quality results for both sample events across all 42 sample sites.


Figure 2. Fecal coliform results for the August sampling event at the Eagle Meadow allotment.

  Figure 2 displays the distribution of fecal coliform concentrations in the Eagle Meadow allotment for August 18. No cattle were grazed on the Eagle Meadow Allotment during 2010. There are two major stream networks in the Eagle Meadow allotments (Niagara Creek which drains the western portion of the allotment and Eagle Creek which drains the east side of the allotment). Niagara Creek was characterized by low levels of fecal coliforms, while Eagle Creek had relatively higher levels at several sites. The elevated concentrations on Eagle Creek are likely due to a campground and associated recreational activities.

By September 15, fecal coliform concentrations were down across the Eagle Meadow allotment (Figure 3), with major reductions observed in the vicinity of the campground. This attenuation may be due to reduced activity late in the recreation season.

    Figure 3. Fecal coliform results for the September sampling event at the Eagle Meadow allotment.
  A more complex spatial and temporal pattern of fecal coliform concentration was observed on the Herring Creek allotment (Figures 4 and 5), where dispersed cattle grazing (50 cow-calf pairs) occurred throughout the study period. Variability between sample events and locations may have been due to patterns of cattle movement across the allotment over the course of the grazing season. Fecal coliform levels at all Herring Creek sites remained well below water quality standard (200 cfu/100ml), with a maximum observation of 58 cfu/100ml.
  Figure 4. Fecal coliform results for the August sampling event on the Herring Creek allotment.  


    Figure 5. Fecal coliform results for the September sampling event on the Herring Creek allotment.
Figure 6. Fecal coliform results for the August sampling event at the Bell Meadow allotment.   Eighty cow calf pairs were grazing on the Bell Meadow allotment (Figure 6) during the study period. During the August sampling event, the watershed experienced dispersed grazing conditions.  Fecal coliform levels at this time were variable across the watershed but remained well below the water quality standard with a maximum value of 92 cfu/100 ml observed.

On September 15, (Figure 7), cattle were concentrated into a gathering pasture for shipment off the allotment. The stream running through the gathering pasture was fenced to protect riparian vegetation and stream channel integrity from grazing. A 100 ft gap in fencing along the stream provided cattle access for drinking water. Immediately upstream from the gathering pasture, fecal coliform concentration was 1 cfu/100ml. Below the gathering field and water gap, fecal coliform was observed at 580 cfu/100 ml. This sample represents the only water quality excedence observed during the pilot study. It is interesting that, approximately one mile downstream concentrations had fallen to 1 to 3 cfu/100ml (Figure 7). Nutrient concentrations were not impacted by the gathering field.

  Figure 7. Fecal coliform results for the September sampling event on the Bell Meadow allotment.

Nutrient Results

Nutrient concentrations were low across all three allotments included in the pilot study. Nitrate, total phosphorus, and phosphate concentrations remained below levels of regulatory or ecological significance (i.e., NO₃-N below 0.30 ppm, TP below 0.10 ppm, and PO₄-P below 0.05 ppm). Nutrient concentrations were often below detection limits (Table 2).
  Table 2. Summary of water nutrient concentration results.  

Water Temperature Results

Stream temperatures were cool across all 42 sample locations, with mean daily temperature ranging from 51 to 53 degrees Fahrenheit (Table 3). Mean and maximum daily water temperatures were consistent with those conducive to the maintenance of high quality cold water habitat (less than 67 degrees F).  
  Table 3. Stream temperature results for all three study allotments.  




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