A high-resolution soil sampling has been applied to two forest podzols (ACB-I and ACB-II) from SW Europe in order to investigate the soil components and processes influencing the content, accumulation and vertical distribution of Hg. Total Hg contents (THg) were 28.0 and 23.6 μg kg⁻¹ in A horizons of ACB-I and ACB-II, then they strongly decreased in the E horizons and peaked in the Bhs horizons of both soils (55.3 and 63.0 μg kg⁻¹). THg decreased again in BwC horizons to 17.0 and 39.8 μg kg⁻¹. The Bhs horizons accounted for 46 and 38% of the total Hg stored (ACB-I and ACB-II, respectively). Principal component analysis (PCA) and principal components regression (PCR), i.e. using the extracted components as predictors, allowed to distinguish the soil components that accounted for Hg accumulation in each horizon. The obtained model accurately predicted accumulated Hg (R² = 0.845) through four principal components (PCs). In A horizons, Hg distribution was controlled by fresh soil organic matter (PC4), whereas in E horizons the negative values of all PCs were consistent with the absence of components able to retain Hg and the corresponding very low THg concentrations. Maximum THg contents in Bhs horizons coincided with the highest peaks of reactive Fe and Al compounds (PC1 and PC2) and secondary crystalline minerals (PC3) in both soils. The THg distribution in the deepest horizons (Bw and BwC) seemed to be influenced by other pedogenetic processes than those operating in the upper part of the profile (A, E and Bhs horizons). Our findings confirm the importance of soils in the global Hg cycling, as they exhibit significant Hg pools in horizons below the uppermost O and A horizons, preventing its mobilization to other environmental compartments.

Taking advantage of the different histories of Hg deposition in Davos Seehornwald in E-Switzerland and Changbai Mountain in NE-China, the influence of atmospheric deposition on Hg soil dynamics in forest soil profiles was investigated. Today, Hg fluxes in bulk precipitation were similar, and soil profiles were generally sinks for atmospherically deposited Hg at both sites. Noticeably, a net release of 2.07 μg Hg m⁻² yr⁻¹ from the Bs horizon (Podzol) in Seehornwald was highlighted, where Hg concentration (up to 73.9 μg kg⁻¹) and soil storage (100 mg m⁻³) peaked. Sequential extraction revealed that organic matter and crystalline Fe and Al hydr (oxide)-associated Hg decreased in the E horizon but increased in the Bs horizon as compared to the Ah horizon, demonstrating the coupling of Hg dynamics with the podzolisation process and accumulation of legacy Hg deposited last century in the Bs horizon. The mor humus in Seehornwald allowed Hg enrichment in the forest floor (182–269 μg kg⁻¹). In Changbai Mountain, the Hg concentrations in the Cambisol surface layer with mull humus were markedly lower (<148 μg kg⁻¹), but with much higher Hg soil storage (54–120 mg m⁻³) than in the Seehornwald forest floor (18–27 mg m⁻³). Thus, the vertical distribution pattern of Hg was influenced by humus form and soil type. The concentrations of Hg in soil porewater in Seehornwald (3.4–101 ng L⁻¹) and in runoff of Changbai Mountain (1.26–5.62 ng L⁻¹) were all low. Moreover, the pools of readily extractable Hg in the soils at both sites were all <2% of total Hg. Therefore, the potential of Hg release from the forest soil profile to the adjacent aquatic environment is currently low at both sites.

Water table depth manipulations as implemented in sugarcane fields of Southwestern Florida, USA, were hypothesized to influence the nutrient concentrations below the water table. Concentrations of phosphorus (P), potassium (K), nitrogen (N), and bromide (Br⁻) were monitored above and below the water table using a column leaching experiment. Three columns were packed with Immokalee soil (A, E, and Bh horizons) classified as a spodosol and fertilizers (NPK) were applied on the soil surface as solids using rates of 11 kg P ha⁻¹, 166 kg K ha⁻¹, and 200 kg N ha⁻¹. A fourth column where fertilizer mixture and bromide were not added acted as a blank. Potassium was also applied as KBr with bromide used as tracer for water movement. Water table was maintained at 30 cm for 6 weeks and lowered to 50 cm deep for another 6 weeks. Samplers were placed in A, E, and Bh horizons and outlets were placed at 30 and 50 cm deep to obtain solutions for monitoring nutrients and tracer. Solution samplers placed in E and Bh horizons were located below the water table. Slightly elevated P, N, and K concentrations in E horizon for a 50-cm water table depth treatment were observed. For both water table treatments, minimal loss of applied N, P, and K below the water table was observed. The results of the study have shown that movement of nutrients below the water table is slow, and depends on the type of nutrients applied and the water table depth.