Effect of storage method and associated holding time on nitrogen and phosphorus concentrations in surface water samples

Authors: Moore, Matthew; Locke, Martin

Submitted to: Bulletin of Environmental Contamination and Toxicology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/14/2013
Publication Date: 10/17/2013
Publication URL: http://handle.nal.usda.gov/10113/62098
Citation: Moore, M.T., Locke, M.A. 2013. Effect of storage method and associated holding time on nitrogen and phosphorus concentrations in surface water samples. Bulletin of Environmental Contamination and Toxicology. 91:493-498.
DOI: https://doi.org/10.1007/s00128-013-1084-6

Interpretive Summary: Water quality, especially with regard to eutrophication and hypoxia, are of great interest to the public at large. Although most researchers generally agree on proper methods for analysis of nutrients in water samples, some discrepancies still exist with regard to methods of sample storage. Additionally, remote locations used for sampling do not always lend themselves to newly emphasized quality assurance protocols. This study examined differences in nutrient concentrations from samples which were subdivided and stored in four different methods prior to analysis (run immediately; ambient (23oC) temperature for 24 h; 4oC for 7 d; and -20oC for 7 d). Results indicated that freezer storage led to more variation than other types of storage. While immediate analysis is always recommended, results from this study also demonstrate that limited storage can minimize nutrient loss in surface water samples.

Technical Abstract: Assessments were conducted to determine the effect of sample storage method and associated holding time on surface water nutrient concentrations from field sites. Six surface water sites and two nutrient spiked, laboratory water samples were evaluated for nitrate, nitrite, ammonium, filtered orthophosphorus, and total orthophosphorus concentrations on four separate days throughout the period of one year. Samples stored at ambient temperature (23oC) for 24 h prior to nutrient analyses resulted in 18±2% of results being significantly different from controls (which were analyzed immediately upon collection). Samples placed in the cooler (4oC) for 7 d prior to nutrient analyses resulted in 30±1% of values being significantly different from controls. Samples placed in the freezer (-20oC) for 7 d prior to analyses resulted in 34±12, 44±10, and 28±5.7% of ammonium, filtered orthophosphate, and total orthophosphate, respectively, values being significantly different from controls. This study highlights the challenges facing researchers in efficient collection, storage and nutrient analysis of samples, especially when sites are remote and difficult to access.