Interaction of natural organic matter and mobility of toxic metals in relation to marine water infiltration in upland soils

Worldwide sea level rise (SLR) is amongst the most important consequences of global climate change and a major risk to many countries on Earth. A review base study was carried out with the aim to outline the complexity of interactions acting on soil biological processes. The prediction of outcomes is made difficult by the concomitant and sometimes contrasting actions of flooding and seawater intrusion on partly acclimated and non-acclimated environments. Non-salt acclimated plants suffer from osmotic stress, but also from reduced O2 solubility. Microbial biomass declines with increasing salinity and microbial communities shift in composition. Large concentrations of Cl− inhibit nitrification, but salinity stimulates N2O fluxes. To investigate the consequences of increasing salinization and length of flooding events on the mobilization of Potentially toxic elements (PTEs) derived from airborne dusts, we compared the behaviour of Cd, Zn and Pb from two types of sources i.e. mine tailings and smelter exhaust dusts in two soils of similar physico-chemical properties, but subjected to different agricultural management (arable and grassland) when exposed to flooding events of different length with marine and brackish waters. The extent of mobilization depends on several factors, among which the main are the kind of element, the dust source and the salinity of flooding waters, but airborne PTE display a much stronger tendency to be mobilised than metals inherited from the soil parent material. The source of the dust, which determines not only the original speciation of the elements, but also eventually modifies soil conditions, has a strong effect on their release rates. Lower amounts of Pb, Cd and Zn were in fact proportionally released from tailing contaminated soils, than from smelters contaminated soils, flooding triggers biochemical redox processes that result in the modification of both the water phase and of solid surfaces. Conventional farming (CF) necessitates a large amount of chemical fertilizer and use of pesticides to support the yields per hectare, but may impoverish the soil and productivity can be supported only with large energy inputs. Organic farming (OF) systems may provide beneficial solutions to current problems affecting the sustainability of soil biological fertility. Soil microbial biomass (SMB) and its metabolic quotient (qCO2) may serve as an indicators of soil environment in both agricultural and natural ecosystems over a long period of time. Following study describes the impacts of flooding with saline waters on the main biological indicators (microbial biomass, evolution of CO2, qCO2, ATP) in relation to water potential measured in organically and traditionally cultivated soils, (similar physico-chemical properties, but subjected to different agricultural management). Soil biomass was found to decrees in both OF and CF during the 5, and 25 days of incubation’s periods through gradually increase in salinity. Consequently, CO2 evolution and metabolic quotient qCO2 were increased in both OF and CF along decrease in biomass C. Soil ATP levels were on average higher in the organic soil and tended to decrease with salinity in both conventional and organic soils, ranging from about 8 to 2 nmol ATP per g soil. Resistance to air-drying was also considered. Ψ of air-dried soils did not reveal clear trends among salt treatments or between soils, while soil ATP results were consistent with soil ATP measured in fresh soils. This result suggests that microbial activity is not only affected by the osmotic stress derived from the saline treatment, therefore by ψ, but also by the possible direct toxic effect of the salts.