Abstract
Abstract. Bogs can store large amounts of lead (Pb) and arsenic (As) from atmospheric deposition of anthropogenic emissions. Pb and As are exported along with dissolved organic carbon (DOC) from these organic-rich systems, but it is not yet clear which hydrological (pre)conditions favor their export. This study combines a 1-year monitoring of precipitation, bog water level and pore water concentration changes with bog discharge and DOC, iron, As and Pb stream concentrations. From these data, annual DOC, As, and Pb exports were calculated. Concentrations ranged from 5 to 30 mg L−1 for DOC, 0.2 to 1.9 μg L−1 for As, and 1.3 to 12 μg L−1 for Pb, with highest concentrations in late summer. As and Pb concentrations significantly correlated with DOC concentrations. Fluxes depended strongly on discharge, as 40 % of As and 43 % of Pb were exported during 10 % of the time with the highest discharge, pointing out the over-proportional contribution of short-time, high-discharge events to annual As, Pb and DOC export. Exponential increase in element export from the bog is explained by connection of additional DOC, As and Pb pools in the acrotelm during water table rise, which is most pronounced after drought. Pb, As and DOC concentrations in pore water provide evidence of an increase in the soluble Pb pool as soon as the peat layer becomes hydrologically connected, while DOC and As peak concentrations in runoff lag behind in comparison to Pb. Our data indicate a distinct bog-specific discharge threshold of 8 L s−1, which is thought to depend mainly on the bogs size and drainage conditions. Above this threshold, element concentrations do not further increase and discharge becomes diluted. Combining pore water and discharge data shows that As and Pb exports are dependent on not only the amount of precipitation and discharge but also on the frequency and depth of water table fluctuations. Comparing the annual bog As and Pb export with element inventories indicates that As is much more mobilized than Pb, with annual fluxes accounting for 0.85 and 0.27 ‰ of total As and Pb inventory, respectively.
Subject
Earth-Surface Processes,Ecology, Evolution, Behavior and Systematics
Reference67 articles.
1. Aitkenhead, J. A., Hope, D., and Billett, M. F.: The relationship between dissolved organic carbon in stream water and soil organic carbon pools at different spatial scales, Hydrol. Process., 13, 1289–1302, 1999.
2. Bauer, M. and Blodau, C.: Arsenic distribution in the dissolved, colloidal and particulate size fraction of experimental solutions rich in dissolved organic matter and ferric iron, Geochim. Cosmochim. Ac., 73, 529–542, https://doi.org/10.1016/j.gca.2008.10.030, 2009.
3. Baumann, K.: Entwicklung der Moorvegetation im Nationalpark Harz, 1th ed., Schriftenreihe aus dem Nationalpark Harz, 4, 244 pp., 2009.
4. Beug, H.-J., Henrion, I., and Schmüser, A.: Landschaftsgeschichte im Hochharz, Die Entwicklung der Wälder und Mooreseit dem Ende der letzten Eiszeit, Goslar, 460 pp., 1999.
5. Biester, H., Martinez-Cortizas, A., Birkenstock, S., and Kilian, R.: Effect of Peat Decomposition and Mass Loss on Historic Mercury Records in Peat Bogs from Patagonia, Environ. Sci. Technol., 37, 32–39, https://doi.org/10.1021/es025657u, 2003.