Organic matter accumulation in submerged soils uri icon

abstract

  • The decomposition and accumulation of organic materials in submerged (anaerobic) soils and sediments differ considerably from those in their aerobic counterparts. This is caused by the lack of oxygen or anaerobiosis. Compared to aerobic soils, there is preferential accumulation of organic matter in submerged rice soils. This paper reviews the current literature to establish basis or bases for organic matter accumulation in wetland soils and sediments. The decomposition or destruction of organic materials is lessened and incomplete, and the humification of organic matter is decreased under flooded conditions. Consequently, the overall organic matter decomposition rates are slower in submerged soils than those in aerobic soils and this results in net accumulation of organic matter in soils or sites that remain flooded for several years. Also, high organic matter soils or Histosols are developed in permanently waterlogged sites or soils because the rate of organic matter destruction is slower than its accumulation. The balance between organic matter inputs and decomposition is the primary determinant of organic matter accumulation or depletion. Several hypotheses have been postulated to explain the accumulation of organic matter in submerged soils. They include the deleterious effects on microbial activity of reduction products produced such as hydrogen sulfide or volatile fatty acids and toxic concentrations of ammonia, aluminium, iron, and other cations in soil solution. The absence of electron acceptors such as iron oxides and hydroxides in submerged soils and sediments slows down organic matter oxidation and mineralization. Formation of recalcitrant complex organic molecules with organic matter fractions, e.g., through enrichment of organic matter with phenolics in intensified irrigated rice production system, may render them less available for microbial attack and utilization. Moreover, the net primary productivity of wetlands is higher than other ecosystems. There is need for further research to fully understand the mechanism(s) involved in the accumulation of organic matter in submerged soils as wetlands offer an excellent example of conservation and maintenance of organic matter and storage of organic C

publication date

  • 2003
  • 2003