Effects of cold storage on anion, ammonium, and total nitrogen concentrations in soil water

Abstract

Researchers frequently must store water samples >24 h after collection until chemical analyses can be accomplished. Samples are commonly stored in darkness at near‐freezing temperatures until analysis, but effects of this storage method on soil water chemistry are not well‐documented. Soil water samples were collected from eastern hemlock [Tsuga canadensis (L.) Carriere] stands and analyzed initially and over time to determine if nitrate (NC3 ‐), chloride (Cl‐), sulfate (SO4 2‐), ammonium (NH4 +), and/or total nitrogen (TN) concentrations changed when samples were stored in darkness at 2–4°C. Subsamples were analyzed <24 h after collection and reanalyzed five times in a 12 to 24 wk period following sample collection. Nitrate concentrations remained stable for at least one wk and were only slightly lower than initial concentrations after 3–16 wk of storage. Chloride and SO4 2‐ remained stable for 16 wk, while TN remained stable for 8 wk and decreased slightly after 24 wk. Most NH4 + concentrations were below the limit of quantification, but concentrations of samples with quantifiable NH4 + decreased in the first week of storage. Overall, cold storage in darkness was effective for preserving NO3 ‐, Cl‐, SO4 2‐, and TN concentrations in soil water, but NH4 + analyses should probably be performed as soon as possible after sample collection.