Delayed Sample Filtration and Storage Effects on Dissolved Nutrients Measured in Agricultural Runoff

Abstract

Few research studies have examined the influence of delayed filtration on sample stability or runoff nutrient loss assessments. Runoff samples from irrigation furrows were each split into four volumes: two were filtered (45 μm) in the field and two were filtered 10 days later, with or without boric acid treatment, and stored at 4 °C. Sample dissolved reactive P (DRP), nitrate nitrogen (NO₃-N), and ammonium (NH₄)-N concentrations were measured in all filtered samples 10 and 107 days after collection. Samples filtered in the field and those with a 10-day delayed filtration had similar dissolved DRP, NO₃-N, and NH₄-N concentrations, whether or not boric acid was added. Boric acid stabilized DRP and NH₄-N sample concentrations, but not NO₃-N, during the 107 days of storage (relative to field-filtered samples). The effect of treatments on computed furrow stream concentration and runoff mass losses was similar to that for sample concentrations, except that furrow NH₄-N parameters were unaffected by treatments. The field-filtered or 10-d delayed filtration without boric acid treatments provided the best dissolved nutrient measurements for comparing agricultural management effects at the field edge; however, results suggest that an incubation-type test for field-edge runoff water may provide a more accurate estimate of field management effects on dissolved nutrient loads in downstream aquatic ecosystems.

Keywords:

• Dissolved P
• inorganic N
• runoff
• sampling protocol
• water quality

Acknowledgments

I thank Anita Koehn and Jodi Johnson-Maynard for their comments on an earlier draft of the manuscript and Larry Freeborn for his assistance in the field and laboratory.

Notes

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