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?