Mercury distribution in a toposequence of sub-Antarctic forest soils of Tierra del Fuego (Argentina) as consequence of the prevailing soil processes

PEÑA-RODRÍGUEZ; PONTEVEDRA-POMBAL; GARCÍA-RODEJA GAYOSO; MORETTO; MANSILLA; CUTILLAS-BARREIRO; ARIAS-ESTÉVEZ; NÓVOA-MUÑOZ

GEODERMA

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2014 p. 130 - 140

0016-7061

The total content, distribution and assessment of Hg sources in five soils of a toposequence of sub-Antarctic forestsoils in Tierra del Fuegowere explained as a combination of pedogenetic processes and the interactions betweenHg and the soil compounds. The soils of the toposequence were mainly podzols and podzolic soils, strongly acidic(water pH b 5.0), organic matter rich in O horizons (239?444 g kg−1) and non-crystalline compounds dominateAl and Fe distribution. The total Hg (HgT) values ranged between 12 and 375 ng g−1 and diminished with soildepth although the secondary peaks of the HgT were observed in illuvial (Bhs or Bs) or buried A horizons. Thetotal Hg was significantly correlated to the total contents of C, N and S (r N 0.71) and to the contents of thenon-crystalline Al and Fe compounds (0.44?0.71), whereas the Hg/C ratio increases with soil depth up to valuesof 11.3 μg Hg g−1 C. Exogenic Hg, i.e. Hg deposited from the atmosphere (HgExo), constitutes over 87% of the HgTin the O and A horizons, whilst lithogenic Hg (HgLit) is 36% of the average HgT.Podzolization seems to control the distribution of the HgT in the mid-slope and upslope soils (P480, P590, P630),as suggested by the HgT peaks in the Bhs or Bs horizons, where illuviated organic matter and non-crystalline Aland Fe compounds favour Hg retention. In the downslope soils (P340 and P220), both podzolization andpolycyclism (that result in soils formed by two or more different and contrasting processes derived from a substantialchange in soil formations factors, that lead to the accumulation of features over their lifetime), seem toinfluence the HgT depth pattern in light of the high values observed in the A and Bhs horizons of the buriedsoils. The significant correlation between the Hg/C and Cp/C ratios strengthens the efficiency of humified organicmatter to complex Hg,whereas the peaks of the Hg/C ratio in the Bhs and Bs horizons also indicate that Al and Fecompounds are also involved in Hg retention.Polycyclic events, i.e. those contrasting soil processes that lead to different chemical and morphological signatureswithin the soil profile, could justify high HgLit values in the deeper horizons of the downslope soils,whilst the peaksof HgExo in the Bhs or Bs horizons could be considered to be a consequence of Hg mobilization and the subsequentretention by Al and Fe compounds during podzolization which is supported by the significant correlations of thesesoil compounds with HgExo.Environmentally, illuvial horizons and buried A horizons could act as a safety mechanism delaying the arrival ofHg to stream waters.