Impact of Sampling Frequency on Annual
Load Estimation
Amber Spackman JonesUtah Water Research Lab
Nancy MesnerWatershed Science
Jeff HorsburghUtah Water Research Lab
Ron RyelWildland Resources
David StevensUtah Water Research Lab
• Environmental processes can have fine scale.
• Low frequency samples are unrepresentative.
• Omits important events.• Requires complex load calculations.
Limitations of “Traditional” Sampling
High Frequency Monitoring
Advantages: • overall cost
reduction• minimization of
human error• improved
turnaround time• additional sites• extended time
periods
Are loads calculated from high frequency monitoring superior to those from intermittent sampling?
Study Area: Little Bear River
• Paradise: less impacted by human activity.
• Mendon: influenced by reservoir releases, agricultural return flows, wastewater treatment plant, and greater agricultural activity.
#S
Utah
Montana
California
Arizona
Idaho
Nevada
Oregon
Colorado
Wyoming
New Mexico
Washington
Study Area: Sampling Sites
Paradise• Higher peaks, flashier flow
regime• Coarse sediments• Phosphorus content:
60% particulate 40% dissolved
Mendon• Higher baseflow• Fine, lacustrine
sediments• Phosphorus content:
40% particulate 60% dissolved
Study Area: Sampling Sites
Paradise
Mendon
Methods
• Surrogate relationships with turbidity used to generate high frequency estimates of TP and TSS concentration.
• Concentration paired with discharge to estimate annual loads- reference loads.
Methods
• Half hourly concentration and discharge were subsampled to represent various sampling frequencies:
-Hourly-Daily randomized-Weekly randomized-Monthly randomized-Daily by hour-Weekly by day
• Annual loads were compared to the reference loads.
Results
Paradise (upper) Mendon (lower)
Results
Results: Hour of Day
Results: Hour of Day
Results: Day of Week
Conclusions
• Using high frequency data to calculate loads provides increased resolution and accuracy.
• Bias from the reference loads varied between sites.
• Daily sampling may approximate reference loads, but is usually infeasible.
• Weekly and monthly sampling were inadequate.
• The hour of the day and the day of the week of sampling can impact load estimation.
Why We Care• Water quality monitoring -higher resolution data -improved concentration and load estimation (regulations) -compare between sites or time periods -additional settings (WWTP, beaches, etc)• Water quality models -better ability to estimate and calibrate parameters -testing underlying assumptions of models• Environmental observatories -logistically and economically feasible -extended time periods -at many locations
Acknowledgments
• Field and Lab SupportSandra GuerreroEmily SaadEric PetersonMichael StevensSu AndersonUSU Aquatic Biogeochemistry LabUSU Analytical Lab• Landowners on the Little
Bear River• National Science Foundation
(CBET 0610075)• US Department of
Agriculture (UTAW-2004-05671)
Questions?