Stable (206Pb, 207Pb, 208Pb) and radioactive (210Pb) lead isotopes in 1 year of growth of Sphagnum moss from four ombrotrophic bogs in southern Germany: Geochemical significance and environmental implications. (15th August 2015)

• Record Type: Journal Article
• Authors: Shotyk, William; Kempter, Heike; Krachler, Michael; Zaccone, Claudio
• Is Part Of: Geochimica et cosmochimica acta. Volume 163(2015:Aug. 15)
• Page Start: 101
• Page End: 125
• Publication Date: 2015-08-15
• Subjects: Geochemistry -- Periodicals; Meteorites -- Periodicals; Géochimie -- Périodiques; Météorites -- Périodiques; Geochemie; Astrochemie; Electronic journals; 551.905
• DOI: 10.1016/j.gca.2015.04.026
• Languages: English
• ISSNs: 0016-7037

Abstract

Abstract: The surfaces of Sphagnum carpets were marked with plastic mesh and 1 year later the production of plant matter was harvested in four ombrotrophic bogs from two regions of southern Germany: Upper Bavaria (Oberbayern, OB) and the Northern Black Forest (Nordschwarzwald, NBF). Radioactive, 210 Pb was determined in solid samples using ultralow background gamma spectrometry while total Pb concentrations and stable isotopes ( 206 Pb, 207 Pb, 208 Pb) were determined in acid digests using ICP-SMS. Up to 12 samples (40 × 40 cm) were collected per site, and 6–10 sites investigated per bog. The greatest variations within a given sampling site were in the range 212–532 Bq kg −1 for 210 Pb activity, whereas 206 Pb/ 207 Pb and 208 Pb/ 206 Pb varied less than 1%. The median values of all parameters for the sites (6–10 per bog) were not significantly different. The median activities of 210 Pb (Bq kg −1 ) in the mosses collected from the bogs in NBF (HO = 372 ± 56, n = 55; WI = 342 ± 58, n = 93) were slightly less from those in OB (GS = 394 ± 50, n = 55; KL = 425 ± 58, n = 24). However, the mosses in the NBF bogs exhibited much greater productivity (187–202 g m −2 a −1 ) compared to those of OB (71–91 g m −2 a −1 ), and this has a profound impact on the accumulation rates of 210 Pb (Bq m −2 a −1 ), with the bogs in the NBF yielding fluxes (HO = 73 ± 30; WI = 65 ± 20) which are twice those of OB (GS = 29 ± 11; KL = 40 ± 13). Using the air concentrations of 210 Pb measured at Schauinsland (SIL) in the southern Black Forest and average annual precipitation, the atmospheric fluxes of 210 Pb at SIL (340 Bq m −2 a −1 ) exceeds the corresponding values obtained from the mosses by a factor of five, providing the first quantitative estimate of the net retention efficiency of 210 Pb by Sphagnum . When the 210 Pb activities of all moss samples are combined ( n = 227), a significant decrease with increasing plant production rate is observed; in contrast, total Pb concentrations show the opposite trend. The contrasting behaviour of 210 Pb and total Pb in the mosses may reflect differences in the particle size distribution of the corresponding aerosols, their physical and chemical properties, the extent of their interaction with plant surfaces, or some combination of these factors. The 206 Pb/ 207 Pb ratios from NBF (HO = 1.159 ± 0.002, n = 19; WI = 1.157 ± 0.003, n = 48) and OB (GS = 1.157 ± 0.003, n = 28; KL = 1.159 ± 0.003, n = 15) are uniform and indicate that both regions are impacted by Pb from predominately anthropogenic sources. Although Sphagnum moss represents an established receptor in monitoring atmospheric Pb deposition, the physical characteristics (size, morphology, composition) of the three predominant kinds of Pb-bearing aerosols considered here, namely 210 Pb (adsorbed onto aerosol surfaces, following decay of 222 Rn), anthropogenic Pb (sub-micron aerosols from high temperature combustion processes) and lithogenic Pb soil-derived mineral dusts (tens of microns, from chemical weathering of crustal rocks), are fundamentally different and these have consequences for the retention efficiency of the three kinds of particles.