LONG-TERM FROZEN STORAGE OF STREAM WATER SAMPLES FOR DISSOLVED ORTHOPHOSPHATE, NITRATE PLUS NITRITE, AND AMMONIA ANALYSIS

Many researchers have used freezing as an effective, short-term, water sample preservation method for subsequent nutrient analysis. In this study, filtered samples held at -16 +/- 2-degrees-C for 4-8 years were reanalyzed for orthophosphate, nitrate plus nitrite, and ammonia. Ort hophosphate and ammonia concentrations decreased by 0.2 mug P/L and 5 mug N/L, respectively, at mean concentrations of 69.4 mug P/L and 246 mug N/L. Nitrate plus nitrite increased by 1.1 mug N/L at a mean conce ntration of 139.1 mug N/L. An anaerobic well sample proved to be unsui table for freezing because it lost significant amounts of orthophospha te during the freezing process. None of the differences observed over long periods of frozen storage were more than twice the estimated stan dard deviation of the analytical methods used in the study. The small changes observed demonstrate the effectiveness of frozen storage as a means of nutrient preservation in water samples that are unaffected by the freezing process itself.