Stable isotope studies of moss sulfur and sulfate from bog surface waters

Two moss genera (Sphagnum and Polytrichum) were collected seasonally in two close (∼0.45 km distance) but environmentally different locations, an Open bog and a Spruce forest at Hala Izerska (the Izerskie Mts./SW Poland), for the stable isotope analyses of plant in-body sulfur. Simultaneously, surface water was collected in places of moss growth and along the creek discharging the bog, for stable isotope analysis of sulfate sulfur (5 locations/5 times in growing seasons). The δ³⁴S value of the analyzed mosses varies from 3.99 to 10.24%‰ for Sphagnum and from 4.18 to 6.48%‰ for Polytrichum. The δ³⁴S value of aqueous sulfate in creek waters, depending on location and season, ranges from 3.72 to 20.26%‰. The significant correlation between the plant in-body sulfur concentration and the isotopic composition was observed for Sphagnum as well as loose correlation between δ³⁴S of sulfates in surface water and moss in-body sulfur. The fractionation factor, possibly caused by two processes of sulfate assimilation by Sphagnum and sulfate reduction by bacteria, calculated based on Rayleigh's distillation model equals about 4%‰. The high correlation and simultaneous increase of δ³⁴S(S0₄^2-) and δ¹³C(DIC) values downstream the creek discharging the bog suggest that the lighter isotopes of carbon and sulfur (¹²C and ³²S) are preferentially removed, probably due to assimilation by plants. The present results imply the original signature of the source of sulfur in the environment is greatly altered by the biological activities in bog water.