Hydrological study of Lyngmossen bog, Sweden: Isotopic tracers (3H, δ2H and δ18O) imply three waters with different mobilities

The 3H concentration and stable isotope ratio of hydrogen and oxygen, δ2H and δ18O, of waters extracted from a Sphagnum-dominant raised bog in Lyngmossen, Sweden, were measured in order to understand where the precipitation is retained and how mobile it is. Three types of waters, which were defined by extractability, were collected from the peat. Two waters were extracted by compressing samples with different pressures (SQW1 and SQW2). The other water was obtained by distilling the compressed samples (DW). 3H was detected in all types of water from depths of 0–50 cm: the concentrations in SQW1, SQW2 and DW ranged 1.17–3.07 Bq/L, 0.98–2.03 Bq/L, and 1.02–1.54 Bq/L, respectively. The maximum 3H concentrations of SQW1, SQW2 and DW were all detected at a depth of around 15 cm, whose 14C age covers the year of the atomic bomb experiments. The 3H results of SQW1/2 indicate that SQW consists of at least two waters of different mobility, water flowing rapidly downward and immobile water. Sphagnum hyaline cells may be responsible for the immobile water. The δ18O and δ2H relationship exhibited independent trends between SQW and DW. The distinct difference observed between the two waters at the surface (0–5 cm) indicates that the two waters may be supplied by precipitation at different times of the year, or alternatively that DW comprises plant water taken in from hyaline cells. The δ18O and δ2H values of both SQW and DW in the shallow layer increased with increasing depth, and in the layer around 30 cm depth, those of SQW showed a distinct decrease with depth. Isotope fractionation caused by evaporation and/or plant utilization of water at the surface layer are considered to be the main causes of such isotopic variation at the surface. Evaporation is likely to take place in much drier conditions for DW than for SQW, probably through stems by capillary action. In SQW freezing may be a possible cause for the decrease of δ18O and δ2H around 30 cm depth. DW is isotopically very well separated from two SQW1/2. Integrating all isotopic information, we conclude the presence of three different waters: least mobile water at shallow depth perhaps in hyaline cells, which can be extracted by squeezing peat with low pressure; most mobile water in a deeper layer than 30 cm, extracted also by squeezing peat; mobile but least extractable water, which is likely water inside plant tissues

Error analysis of the determination of carbon stable isotope ratios in lignin and cellulose from plant samples

NOTE 255 zation studies. The aim of our study was to use cellulose and lignin (laboratory reagents), and a model mixture of these, to identify factors controlling the accuracy and precision of the isotopic data. We recognize, however, that application of the results of this investigation directly to plant samples is likely to be complicated by the presence of hemi-cellulose in natural samples, besides compositional variations of the lignin, but suggest that our results provide a useful baseline for further studies. September 23, 2010; Accepted December 16, 2010) To determine the accuracy and precision limits associated with carbon stable isotope ratio (δ 13 C) measurements of cellulose and lignin from plant samples, experiments were performed using differing extents of treatment for separating these two components. Laboratory reagent lignin and cellulose were used, together with model mixtures of both components. The resulting data were fitted to empirical functions. It was found that the δ 13 C of cellulose could be determined with higher accuracy (<0.1‰) than that of lignin (<0.25‰). The corresponding precision values were better than 0.04‰ and 0.08‰, respectively. Longer treatment times do not always result in better accuracy of the isotope data for either component