Formation, characteristics and ecological effects of acid sulfate soil

Acid sulfate soil (ASS) is one of the nastiest soils in the word because of its strong acidity.Fe and S biogeochemical cycling in ASS plays an important role in global material recycling.The parent materials of ASS are often form tropical and subtropical estuary, bay and other coastal environment, where is submerged and rich in organic matter. Dissimilation bacteria reduce seawater sulfate to form mackinawite(FeS), greigite(Fe3S4), pyrite(FeS2) and other reduced Fe-S sediments. Sedimentation of reduced Fe-S minerals coprecipitates free metals, rare earth elements and trace elements in the environment, purifies seawater and enrichs metals. ASS is formed through oxidation of reduced Fe-S minerals in soils by natural process or anthropogenic interventions. The oxidation of Fe-S minerals ultimately results in products such as Fe-hydroxides, acidity and sulfate, involves a series of complex reactions, with several Fe and S intermediate and strong acidic soil. In strong acid soils, the mobilities of Al, Cd, Mn, As, Cr and other potentially toxic metals are significantly high, while the bioavailabilities of P, K, Zn, B and other essential nutrients are significantly low, which adversely affects animal and plant growth. On the other hand, the mobilised acid and toxic elements can enter nearby waterways and groundwater through rain, runoff, seepage and other ways, threatening the surrounding ecological security.The formation mechanism of ASS has been disclosed, and its ecological effect has been understood. In the early studies, Chinese researchers have focused on concentrations of iron, aluminum and sulfur in ASS and the remediation and applications of ASS farmland,few studies on the developmental processes, the ecological functions and risks of ASS are conducted. Recently, as arable land shrinking, improving the yields of ASS and other low-yielding fields become important measures to increase Chinaapos;s grain production.For the rational exploit and utilize of ASS with minimum ecological risks, the formation mechanism, soil development, soil characteristics and ecological effects of ASS are reviewed. The forming condition and development of ASS were summarized, sulfur dynamics and geochemistry and partitioning of iron in ASS were presented, and the distinctive acid characteristics of the soil were discussed.The perspectives of ASS in China were proposed to provide references for full unitilization of ASS.