The interplay between land-atmosphere exchange and soil dynamics of mercury in a Swiss subalpine forest
Abstract
Forest-atmosphere exchange of mercury (Hg) is largely undefined and knowledge about its interplay with Hg in forest soils limited. To investigate Hg fluxes in a coniferous forest ecosystem, we perform multiple-level gaseous elemental mercury (Hg0) concentration measurements on a tall tower and determine Hg in wet precipitation, litterfall and soil porewater at the research site Davos-Seehornwald in Switzerland. The tall tower gradient measurements were initialised in October 2018 and show that Hg0 concentrations at 8 different heights (1.8, 4, 7, 10, 15, 20, 25, 35 m) averaged at 1.07, 1.08, 1.08, 1.10, 1.10, 1.10, 1.11 ng m-3, respectively. These preliminary results indicate that the subalpine forest is neither a significant sink nor source for atmospheric Hg during the dormant season. The Hg concentration in bulk precipitation, throughfall and forest floor percolates all ranged between 23 and 72 ng L-1, reflecting little Hg dry deposition on the needle surface and negligible retention of Hg in the forest floor. In the forest soils (Podzol, FAO classification), the Hg concentration peaked in the forest floor (263-317 µg kg-1) and Bh horizon (subsoil with organic matter accumulation, 64-83 µg kg-1). Moreover, the concentrations of organic matter and crystalline Fe and Al (hydr)oxide bound Hg decreased in E (eluvial horizon) but increased in Bh horizons in comparison with Ah (topsoil with organic matter accumulation). This corresponds well with the eluviation from the upper soil layer and translocation of organo-metallic complexes into the subsoil. Along the soil profile, the averaged Hg concentration in soil porewater increased from 15 ng L-1 at 15 cm depth to 81 ng L-1 at 50 cm depth. At 80 cm depth, the porewater concentration averaged 54 ng L-1. The Bh horizon has the largest Hg soil storage (~100 mg Hg m-3) and may currently serve as a source of Hg to the deeper horizons. The soils at 0-15 and 50-80 cm depth are effective sinks of Hg released from the forest floor and from the Bh horizon. Our preliminary results highlight that Hg dynamics in the forest soils are strongly coupled with the podsolization process. Together with the upcoming investigations in the growing season, our research will improve the understanding on re-mobilisation of previously deposited Hg in soils to water bodies and the atmosphere.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B51I2350H
- Keywords:
-
- 3339 Ocean/atmosphere interactions;
- ATMOSPHERIC PROCESSES;
- 0409 Bioavailability: chemical speciation and complexation;
- BIOGEOSCIENCES;
- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0461 Metals;
- BIOGEOSCIENCES