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

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 1 year. Samples stored at ambient temperature (23°C) 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 (4°C) for 7 days prior to nutrient analyses resulted in 30 % ± 1 % of values being significantly different from controls. Samples placed in the freezer (-20°C) for 7 days 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 .