Impact of deforestation on soil iron chemistry and isotope signatures in Amazonia

We examined the consequences of soil erosion processes following deforestation and long-term pasture establishment for chemical physical properties Fe isotope compositions within two distinct areas in Eastern Central parts Amazonia (near Rio Capim, Para, Brazil Lake Balbina/Rio Uatuma, Amazonas, Brazil). For each area studied, soils selected under forest cover or after recent slash-and-burn practices were investigated. In both ecosystems pedogenesis along slopes reflects evolution lateritic crust bearing (Ferralsol) into iron depleted leaching (Acrisol) redox (Gleysol). Measurements performed by plasma source mass spectrometry show a large range signature profiles studied at bottom (i.e. foot slope and/or valley soils), pasture. Iron isotopic (δ57FeIRMM-14 ~ +0.2 to +0.6‰) +0.3‰) are significantly heavier than continental baseline reference ferralitic from top hill +0.1‰). This enrichment heavy isotopes is attributed preferential mobilisation loss light during that involves periodically flooded soils. Under forest, depletion (where ~90% was leached first metre soil) has greater influence on signature, particularly sand-rich close river system with remaining having δ57Fe IRMM-14 +0.6‰. where experienced processes, riverside less important only little more half resulting δ57FeIRMM-14 +0.4‰ suggests an input via colluvic material deposition. difference indicates geomorphological changes due processes) lead “isotopic rejuvenation” valley, mostly apparent comparison, we investigated recently deforested small watershed, near Balbina, Amazonia, focusing Results confirm rejuvenation effect appears few months stage as consequence practices. Erosion can remove isotopically lighter value ~0.1‰ δ57Fe) hill. When such colluvial accumulates hills initially isotopes, again podzolisation described previous site, it induces (tending towards lighter, crust-like signature) soils, besides landscape morphology, water drainage functioning hydromorphic processes). Hence, this study illustrates be used identify context through “isotope rejuvenation”, even when textures make challenging unravel.