Changes in the chemical composition of mire‐water samples during storage

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Abstract
Solutes in mire‐water samples vary greatly in their tendency to change on storage. In repeated analyses of samples from Malham Tarn, Yorkshire, U.K., concentrations of Na+ and Cl‐ proved very stable on storage, and Mg2+ hardly less so, whether the samples had been filtered or not. K+ concentrations declined slowly in filtered samples kept at room temperature, falling after two years to about two‐thirds of the original value. In unfiltered samples, K+ concentrations rose on average by about 25 % over a period of two months. At low concentrations Ca2+ changed little on storage, but above 40 ‐ 50 mg/l equilibration of CO2 with the air led to precipitation of carbonate and loss of dissolved Ca2+. Fe concentrations were rather stable in ombrogenous bog waters, but in fen waters showed rapid decreases on storage. SO42‐ showed little change in most samples, but there were a few large increases in unfiltered samples probably due to oxidation of sulphide. Unfiltered fen water samples generally developed high concentrations of NO3‐ (rarely NH4+) on storage; by contrast acid bog waters typically developed high NH4+ concentrations, but did not nitrify. Bog waters showed a small rise in pH and some reduction in colour (dissolved humic substances). Fen waters changed erratically in pH, depending on the balance of production and loss of CO2 in the sample. Some recommendations are given for storage and analysis of samples.