Behavior of mercury in soil profiles: Impact of increased precipitation, acidity, and fertilization on mercury methylation

The behaviour of Hg in mineral pine forest (Pinus sylvestris} soil profiles (0-16 cm) was studied using a lysimeter experimental design combined with the labeling technique with (HgCl2)-Hg-203. The labeled surface soils were exposed to four different treatments: (i) normal precipitation (600 mm a(-1 )), (ii) four-fold precipitation, (iii) soil P-K fertilizing with normal pr ecipitation, and (iv) the increased acidity in the rainwater with normal am ount of precipitation. After the treatment period of 97 days the Hg-203 and methyl Hg-203 were measured. The distribution of Hg in different soil matr ices was determined by extracting the soil with distilled water, 1 M NH4-ac etate, 1 M HCl, and 0.1 M NaOH. The results showed that the organic surface layer, especially the living mo ss (Pleurozium schreberi), was the dominant scavenger of the added Hg-203. Methyl Hg-203 formation was most intensive in this layer, too. Increased pr ecipitation mobilized a part of the Hg-203 from the moss layer to the deepe r layers and leachate water. In the fertilized soil with increased pH, the accumulation of both total Hg-203 and methyl Hg-203 was recorded in the org anic surface soil. A small increase in rainwater acidity had no clear effec t on the behavior of Hg-203 in soil. Hg-203 was mainly associated in the or ganic fraction (NaOH-extractable) whether in the living moss or humus layer . The fertilized soil yielded the highest concentration of water extractabl e Hg-203. In view of the climate change with increasing precipitation, the use of fertilizers, in the watersheds should be minimal and well-controlled . This is, because soil fertilizing seems to increase the availability of H g for methylation, and because the mobilization of both total Hg and methyl Hg from watershed soils to lakes, and probably to ground water, increases when precipitation increases.