UC Davis Department of Plant Sciences

Rangeland Streams – water quality conditions

Keywords – nitrogen, phosphorus, E. coli, fecal coliforms, sediment

Participants – Sean Hogan, Betsy Karle, Betsy Huang, Randy Dahlgren, Rob Atwill, Theresa Becchetti, David Lewis, David Lile, Neil McDougald, Don Lancaster, Royce Larsen, Jim Versteeg, Ralph Phillips, Gary Markegard, and Toby O’Geen

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Much of California’s surface drinking water and irrigation supplies are either derived from rangeland runoff, or are stored in reservoirs situated within the State’s 40 million acres of rangeland watershed. Rangeland streams provide critical habitat for a large number of aquatic and terrestrial animal species, several of which are listed as threatened or endangered by state and federal wildlife agencies. The majority of rangeland watersheds are managed for livestock production activities including grazing, pasture and meadow irrigation, and significant mileage of unimproved ranch roads.

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Despite the critical importance of rangelands to the State’s surface water supply there is no published report of a comprehensive, large scale water quality survey spanning California’s major rangeland vegetation types, geologic regions, and climatic zones. Here, we report results of a two year survey of the microbiological, chemical, and physical quality of 19 rangeland streams located across California.

Project Objectives

  1. Quantify water quality from a representative sub-sample of California’s rangeland watersheds using consistent analytical methods;
  2. Compare these data to numeric water quality standards;
  3. Evaluate associations between water quality and watershed characteristics such as soil, vegetation, and hydrology; and
  4. Examine the data for seasonal patterns in water quality.

 Study Sites

This project was a cross-sectional, longitudinal survey of 19 streams during the 2000 and 2001 water years (Oct – Sep). Watershed size ranged from 1,000 to 143,000 acres. Dominant land use was extensive range livestock production activities including livestock grazing, ranch roads, corrals, and irrigated pasture. rangeland clip 4
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Watershed Characteristics
Stream Samples Area (acre) Elevation (ft) Roads (mi) Stream (mi) Precip (in)
W 38 1004 364 8 4 14
F 149 1608 814 6 6 30
G 103 1776 528 13 13 21
I 42 2516 7503 0 5 26
L 31 4631 5338 17 17 44
U 12 6435 1015 27 30 20
C 22 6459 1159 22 22 34
O 37 7137 1778 14 22 9
H 39 8930 6517 0 25 26
X 17 9644 1110 35 47 20
P 138 10068 2591 26 24 29
B 21 15315 5953 69 47 6
A 23 23664 5750 60 64 6
J 26 29430 7073 57 57 49
K 30 34364 6782 130 130 48
R 66 37118 2448 96 203 15
N 75 38155 566 72 107 9
Q 12 41434 2435 153 161 23
E 27 143490 5142 585 238 5

Data Collection
Grab samples of stream water were collected during storm runoff events, snowmelt, and summer low-flow conditions from each stream over the course of 2 years. Instantaneous streamflow was measured at the time of each sample collection using the area velocity methods. A total of 908 stream water samples collected and analyzed for: E. coli and fecal coliforms, total nitrogen (N), nitrate-nitrogen (NO3-N), ammonium-nitrogen (NH4-N), total P, phosphate-phosphorous (PO4-P), total suspended solids (TSS), electrical conductivity, and turbidity following standard methods. E. coli and fecal coliform samples were analyzed within 24 to 48 hours of collection and all data were corrected to a 24 hour holding time using a decay curve.

Water Quality Conditions
Most sites had relatively low values for all constituents, with a few sites having high values – creating an exponential distribution among sites. In general, we found concentrations of all nutrients to be low relative to state and federal water quality standards and recommended levels. Phosphate and ammonium levels were extremely low in these rangeland streams. However, fecal coliform and E. coli indictor bacteria commonly exceeded established and recommended standards. In California, fecal coliform standards range from 20 to 2000 colony forming units (cfu) per 100 milliliter (mL) of water sampled. USEPA recommends an E. coli standard of 126 cfu/100ml for an average of 5 samples collected over 30 days, or 235 cfu/100ml for a single grab sample.

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Box plots display the mean (red line), median (black horizontal line in box), 25th and 75th percentile (top and bottom of box), and 95th percentile (end of line) for each water quality constituent across all sites and years. Bar graphs display the mean (bar) and 1 standard error (end of line) of all samples collected over 2 years at each sample site. There appears to be an exponential distribution, with most sites having relatively low values, with a few sites having high values.

Spatial Variation
There was a clear pattern of increasing levels of these water quality constituents with increasing importance of rainfall as a streamflow generation process on the watershed. We are still examining this dataset to identify associations between water quality, vegetation type, soils, road density, and other factors.

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Seasonal Variation
We found inherent seasonality for most constituents. There were high levels of N, E. coli, and fecal coliforms early in the rainfall-runoff season, indicating these constituents are flushed from watersheds with early runoff events. Sediments (TSS) and turbidity are driven by high flow events occurring during the peak of the rainfall-runoff season in February and March. This has ramifications for monitoring strategies and estimation of background levels and enforcement of standards.

Bar graphs rangeland clip 20


Additional Information
Ahearn, D.S., R.W. Sheibley, R.A. Dahlgren, M. Anderson, J. Johnson, and K.W. Tate. 2005. Land Use and Land Cover Influence on Water Quality in the Last Free-Flowing River Draining the Western Sierra Nevada, California. J. Hydrology. 313:234-247. Request Reprint
Dahlgren, R.A., K.W. Tate, D.J. Lewis, E.R. Atwill, J.M. Harper, and B.H. Allen-Diaz. 2001. Watershed Research Examines Rangeland Management Effects on Water Quality. California Agriculture. 55:64-71. Download
Hesson, S., D.S. Ahearn, R.A. Dahlgren, and K.W. Tate. 2006. Water Quality During Pulse Flood Flow Releases on the Mokelumne River, California. Regulated Rivers. 23:185-200. Request Reprint
Lewis, D.J., M.J. Singer, R.A. Dahlgren, and K.W. Tate. 2006. Nitrate and Sediment Fluxes from a California Rangeland Watershed. J. Environmental Quality. 35:2202-2211. Request Reprint
Tate, K.W., R.A. Dahlgren, M.J. Singer, B. Allen-Diaz, and E.R. Atwill. 1999. On California Rangeland Watersheds: Timing, Frequency of Sampling Affect Accuracy of Water Quality Monitoring. California Agriculture. 53:44-48. Download

© 2011-2012 UC Davis | California Rangeland Watershed Laboratory | One Shields Ave | Davis, CA 95616 | Last update: November 18, 2015