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

. 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 Mg 2 + 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 Ca 2+ changed little on storage, but above 40 ‐ 50 mg/l equilibration of CO 2 with the air led to precipitation of carbonate and loss of dissolved Ca 2 +. Fe concentrations were rather stable in ombrogenous bog waters, but in fen waters showed rapid decreases on storage. SO 4 2‐ 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 NO 3 ‐ (rarely NH 4 + ) on storage; by contrast acid bog waters typically developed high NH 4 + 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 CO 2 in the sample. Some recommendations are given for storage and analysis of samples.