Water quality conditions associated with cattle grazing and recreation on national forest lands
Contact Person: Dr. Kenneth W. Tate
Participants: Leslie Roche, Rob Atwill, Randy Dahlgren, Lea Kromschroeder, Kristin Oles, USDA Forest Service – Region 5, Stanislaus National Forest, Plumas National Forest, Tahoe National Forest, Shasta-Trinity National Forest, Klamath National Forest.Comment or Questions?
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We conducted a cross sectional survey of water quality conditions associated with cattle grazing and recreation on 12 U.S. Forest Service (USFS) public lands grazing allotments in northern California as part of a larger public lands grazing and water quality project. Our specific objectives were to:
AUM = animal unit month;
FC = fecal coliform;
FIB = fecal indicator bacteria; TP = total phosphorus; TN = total nitrogen;
USFS = U.S. Forest Service; USEPA = U.S. Environmental Protection Agency
|Supplemental information about methods and background studies related to this study can be found >>here.|
Study allotments were grazed with commercial beef cow-calf pairs during the June to November grazing-growing season, following allotment-specific management plans designed to achieve annual herbaceous forage use standards. Timing of grazing, duration of grazing season, and number of cattle were determined by allotment-specific permits issued by the USFS (Table 1). Stocking densities ranged from 1 animal unit per 44 acres to 1 animal unit per 1,105 acres (Table 1). Animal use was
| non-uniform across allotments, although distribution practices common to the region (e.g. herding and supplement placement) were used in each allotment.
Sample Site Selection
Areas receiving relatively concentrated use by cattle in each allotment are referred to as key grazing areas. In each allotment, key grazing areas and concentrated recreation areas (e.g. campgrounds, swimming areas, and trailheads) within 200 meters of streams were identified and enrolled in the study in collaboration with local USFS managers and forest stakeholders. Additional sites were established
|at perennial flow tributary confluences to quantify water quality not associated with concentrated grazing or recreation.
Sample Collection and Analysis
We collected a total of 743 water samples from 155 stream collection sites. We sampled each stream collection site monthly during the study period (Jun 1 - Nov 9, 2011). All sites in an allotment were sampled on the same day. Total sample numbers per allotment ranged from 40 to 88. (Table 1). Stream conditions were noted at the time of sampling, specifically whether any of the following conditions were present or absent: 1) stagnant-low stream flow (< 0.5 gallons per minute); 2) turbid stream water; 3) recreation (i.e. swimming-bathing, camping, hiking, fishing, horse riding); 4) cattle; 5) activities (i.e. cattle, recreation users). Parameters measured were fecal coliform (FC), E. coli, total nitrogen (TN), nitrate (NO3-N), ammonium (NH4-N), total phosphorus (TP), and soluble-reactive phosphorus (PO4-P) concentrations. See supplemental materials for more information about laboratory methods.
|Table 1. Geographic characteristics, study year precipitation, cattle grazing management, and water quality sample collection sites and sample number for 12 U.S. Forest Service grazing allotments in northern California enrolled in this cross-sectional longitudinal study of stream water quality between June and November 2011.|
|a Dominant soil suborder identified with soil survey data .
b Precipitation realized during the October 1, 2010 through September 30, 2011 water year. Values in parentheses are the percent of 30-year mean annual precipitation realized during the 2010-11 water year .
c Animal Unit Month. The dry weight mass of forage required to feed a 1000 lb. cow for a 30 day period. It is the standard unit by which grazing pressure is permitted on U.S. Forest Service grazing allotments.
d Stocking density displayed in acres per cow-calf pair.
e Date that cattle were released onto the grazing allotment.
f Date that cattle were removed from the grazing allotment.
g Maximum permissible removal of annual herbaceous vegetation production in meadows and riparian areas on the grazing allotment (shown as %).
Results and Discussion
Nutrient Concentrations and Water Quality Benchmarks
Nutrient concentrations were generally low: over 32% of samples were below the detection limit (<10 µg N/L and <5 µg P/L) for all nutrients except TN. Additionally, nutrient concentrations observed across this grazed landscape were well below eutrophication benchmarks (NO3-N, TP, and PO4-P) and background estimates (TN, NO3-N, and TP) (Table 2). These results do not support concerns that excessive nutrient pollution is degrading surface waters on these USFS grazing allotments .
|Table 2. Concentrations of total nitrogen (TN), nitrate (NO3-N), ammonium (NH4-N), total phosphorus (TP), and phosphate (PO4-P). Published estimates of concentrations of general concern for eutrophication of stream water and estimates of background concentrations for the study area are provided for context.|
|a The ‘±’ indicates 1 standard error of the mean.
b Percentage of samples below minimum analytical detection limit. Limits were 10 µg/L for nitrogen and 5 µg/L for phosphorous. Observations below detection limit were set to one half detection limit (5 µg/L for nitrogen and 2.5 µg/L for phosphorus) for calculation of mean and median concentrations.
c Concentrations if exceeded indicate potential for eutrophication of streams [4-8].
d Estimated range of background concentrations for the three U.S. Environmental Protection Agency Level III sub-ecoregions (5, 9, 78) included in the study.
Fecal Indicator Bacteria (FIB) Concentrations and Water Quality Benchmarks
The percentage of all sites that exceeded water quality benchmarks for FIB concentrations varied by benchmark. The overall percentage of sites that exceeded a benchmark at least once ranged from 83% (benchmark FC = 20 cfu/100 ml) to 14% (benchmark E. coli = 235 cfu/100 ml) (Table 3). The percentage of sites in each use category that exceeded a benchmark at least once also varied by benchmark. Overall, only 3% of all samples collected and 14% of all sites sampled exceeded the U.S. Environmental Protection Agency (USEPA) nationally recommended E. coli single sample benchmark of 235 cfu/100ml . USEPA recommends adoption of an indicator E. coli water quality objective as an improvement over FC . This guidance is because, in part, E. coli is better correlated to human pathogens such as Salmonella spp. [11-14], E. coli is less likely establish and reproduce as environmental strains in stream habitats  than FC, and there is also evidence that E. coli is a better predictor of gastro-intestinal illness than FC .
|Table 3. Percentage of 155 stream water sample sites which had at least one exceedance of water quality benchmarks relevant to the study area, specifically, and the nation, broadly. Results are reported for all sample sites (overall) as well as for sample sites monitored to characterize specific resource use activities across the allotments.|
|a Associated with fecal coliform (FC) water quality objectives designated by the Lahontan Regional Water Quality Control Board .
b Associated with fecal coliform (FC) water quality objectives designated by the North Coast Regional Water Quality Control Board .
c Associated with fecal coliform (FC) water quality objectives designated by the Central Valley Regional Water Quality Control Board .
d Associated with E. coli water quality objectives designated by the U.S. Environmental Protection Agency .
FIB Concentrations and Use Category
FC and E. coli concentrations were significantly lower at recreation sites than at key grazing areas and areas with no concentrated use. FC and E. coli concentrations were not significantly different between key grazing areas and areas with no concentrated use and neither exceeded USEPA benchmarks (Table 4). Additionally, the overall mean and median FC for all allotments were 82 and 21 cfu/100 ml, and mean and median E. coli were 40 and 8 cfu/100 ml. These values indicate that all but the most restrictive water quality objectives for the study area would be broadly met.
|Table 4. Mean concentrations for fecal coliform (FC) and E. coli for each resource use category. The ‘±’ indicates 1 standard error of the mean. Different lower case letters indicate significant (P < 0.05) differences between resource use activity categories.|
FIB Concentrations and Stream Conditions
FIB concentrations were significantly lower (p < 0.05) when recreation was occurring at the time of sample collection than when recreation was not occurring (Table 5).
FIB concentrations were significantly higher (p < 0.01) when cattle were present at the time of sample collection (Table 5). Gary et al.  found grazing to have relatively minor impacts on water quality, though a statistically significant increase in stream water FC concentrations was induced at a relatively high stocking rate.
FIB concentrations were higher when streams were turbid at the time of sample collection (Table 5). Stream sediments are known to have higher concentrations of FIB than the overlying waters [20-23] and re-suspension of sediments by cattle disturbance or elevated stream flow has been associated with elevated water column FIB concentrations [24,25]. Schnabel et al.  found a negative correlation between stream discharge and FIB concentrations at some sites, possibly due to the absence of a dilution effect under low flow conditions.
|Table 5. Mean concentrations for fecal coliform (FC) and E. coli by category of field observation of resource use activities and environmental conditions observed at the time of sample collection. The ‘±’ indicates 1 standard error of the mean; * indicates a difference between Yes and No at P < 0.05, and ** indicates a difference at P < 0.01.|
|a Stagnant or low stream flow (<2 liters per second).
b Stream water turbid.
c Cattle observed.
d Recreational activities observed.
e Cattle and/or recreation users observed.
Temporal Patterns of FIB Concentration
FIB concentrations were highest from August through October, which coincides with the period of maximum cattle turned out (Figure 1). In this region, stream water temperatures are at their annual maximum in August and stream flows are at their minimum in September. It is likely that the seasonal peak of FIB concentrations is driven by timing of maximum cattle numbers as well as optimal environmental conditions for growth and in-stream retention of both animal-derived and environmental bacteria.
|Figure 1. Overall monthly (A) fecal coliform and (B) E. coli concentrations for 743 stream water samples collected between June and November 2011. Bottom and top of shaded box are the 25th and 75th percentile of data, horizontal line within shaded box is median value, ends of vertical lines are 10th and 90th percentiles of data, and black dots are 5th and 95th percentiles of data.|
Relationship between E. coli, stocking density, and precipitation
Mean allotment FIB concentrations tended to decrease with decreasing cattle density measured as acres per cow calf pair (Figure 2). Decreasing cattle density has been shown to reduce fecal-microbial pollutant loading  and subsequent increases in FIB concentrations in runoff , as well as reduce in-stream disturbance and re-suspension of FIB-sediment complexes [20-25].
Mean allotment FIB concentrations were negatively correlated with precipitation during the 2010-2011 water-year (October 1 to September 30) (Figure 2). It is likely that the precipitation during the 2010-2011 water-year is primarily reflecting snowpack, which supported higher than historical stream flow volume during the study period. A similar relationship was observed on California coastal dairy pastures , and possibly reflects the capacity of higher base flow volumes to dilute FIB concentrations.
|Figure 2. Relationship between overall mean E. coli concentration across sample sites during the June through November 2011sample period and (A) allotment cattle stocking density and (B) 2010-2011 water year precipitation on 12 U.S. Forest Service grazing allotments in northern California enrolled in this cross-sectional longitudinal study. Predicted values are from Poisson regression models predicting E. coli by cattle stocking density (P < 0.001) and precipitation (P = 0.025).|
Nutrient concentrations observed throughout the grazing-recreation season were at least one order of magnitude below levels of ecological concern, and were similar to USEPA estimates for background water quality conditions in the region. We found that all but the most restrictive fecal indicator bacteria water quality benchmarks were broadly met, and USEPA’s currently recommended E. coli benchmarks were met by over 90% of the 743 samples collected during the study. This work demonstrates that cattle grazing, recreation, and provisioning of clean water can be broadly compatible goals across these national forest lands.
We thank Anne Yost, Barry Hill, staff from the Klamath, Shasta-Trinity, Plumas, Tahoe, and Stanislaus National Forests, Tom Lushinsky, Mark Noyes, Natalie Wegner, Donna Dutra, D.J. Eastburn, Xien Wang, and Kristin Oles for project support; and UC Cooperative Extension and USFS District Rangers and Forest Supervisors who provided lab space.
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