Behavior of Mercury in Soil Profiles: Impact of Increased Precipitation, Acidity, and Fertilization on Mercury Methylation

Abstract

The behaviour of Hg in mineral pine forest (Pinussylvestris soil profiles (0–16 cm) was studied usinga lysimeter experimental design combined with thelabeling technique with ²⁰³HgCl₂. Thelabeled surface soils were exposed to four differenttreatments: (i) normal precipitation (600 mma^-1), (ii) four-fold precipitation, (iii) soilP-K fertilizing with normal precipitation, and (iv) the increased acidity in the rainwater with normalamount of precipitation. After the treatment period of97 days the ²⁰³Hg and methyl ²⁰³Hg weremeasured. The distribution of Hg in different soilmatrices was determined by extracting the soil withdistilled water, 1 M NH₄-acetate, 1 M HCl, and 0.1 M NaOH.The results showed that the organic surface layer,especially the living moss (Pleuroziumschreberi), was the dominant scavenger of the added²⁰³Hg. Methyl ²⁰³Hg formation was mostintensive in this layer, too. Increased precipitationmobilized a part of the ²⁰³Hg from the moss layerto the deeper layers and leachate water. In thefertilized soil with increased pH, the accumulation ofboth total ²⁰³Hg and methyl ²⁰³Hg wasrecorded in the organic surface soil. A small increasein rainwater acidity had no clear effect on thebehavior of ²⁰³Hg in soil. ²⁰³Hg was mainlyassociated in the organic fraction (NaOH-extractable)whether in the living moss or humus layer. Thefertilized soil yielded the highest concentration ofwater extractable ²⁰³Hg. In view of the climatechange with increasing precipitation, the use offertilizers, in the watersheds should be minimal andwell-controlled. This is, because soil fertilizingseems to increase the availability of Hg formethylation, and because the mobilization of bothtotal Hg and methyl Hg from watershed soils to lakes,and probably to ground water, increases whenprecipitation increases.