ICMGP 2022 – On-Demand / Poster Presentation

Abstract Information :

Soil organic horizons are often disregarded in the quantification of Hg pools in forest ecosystems, as they store a relatively low amount of Hg. However, chemical and biogeochemical processes occurring in the organic horizons will determine if Hg is finally stored in soils, re-emitted to the atmosphere or lost by runoff. Samples of organic horizons, Oi and Oe+Oa, were collected by triplicate in 18 forest stands from Galicia (NW Iberian Peninsula). All forest stands were dominated by Quercus robur, the predominant native species of deciduous forests along the oceanic influenced areas of Western Europe. During sampling, the thickness and areal mass of each organic layer were recorded. Samples (n=102) were air dried, ground and then finely milled before the determination of total mercury (HgT) and total C and N. Mercury pool (HgP) in each organic horizon was estimated using their HgT, thickness and areal mass (dry at 105 ?C). The average of HgT in the Oi sub-horizons ranged from 88 to 111 ?g kg-1, whereas for the Oe+Oa layers mean values of HgT were significantly higher varying from 125 to 198 ?g kg-1. These HgT values are typical from areas scarcely influenced by Hg emission point sources. Total Hg showed a negative correlation with C/N ratio (r=-0.424; p=0.000; n=102), suggesting that the organic matter decomposition processes are regulating the concentrations of HgT in the organic horizons. The HgP for the Oi sub-horizons ranged from 29.5 to 37.0 g m-2, being considerably lower than for Oe+Oa sub-horizons (211-725 g m-2). Total Hg pools showed a strong correlation to total organic C and total N pools (r>0.950; p=0.000; n=102). These results reveal the ability of the organic horizons as a first trap of Hg in forests soils before further processes define the subsequent Hg fate in terrestrial ecosystems.