To understand C sequestration in wetlands the C cycle must be well studied. Organic and inorganic C are the largest two forms of C found in: plant, soil and wetland water components. Wetlands contain five main C reservoirs: plant biomass C, particulate organic C (POC), dissolved organic C (DOC), microbial biomass C (MBC) and gaseous end products (Kadlec et al 1996).

 

Plant Biomass Carbon - This stage represents the change of inorganic carbon CO₂ to organic carbon through photosynthesis. This is referred to as primary production; wetland ecosystem primary productivity is extremely high. "Reddy et al, 2008" approximate the primary productivity of wetlands to be of the same magnitude as that of tropical rain forests. The primary productivity of wetlands varies due to time of year, geographic location, nutrient status and type of vegetation.

 

POC - The process where part or all of the plant dies and undergoes decomposition in the detrital pool. POC is a major reserve of living and dead organic C found on the soil surface. (Particle size decreases through decomposition, coarse to fine to ultra fine.)

 

DOC - Very small dissolved organic matter, often obtained from materials leaching in the detrital pool, it is only classified as DOC after fitting through a 0.45micromilimeter filter. DOC represents less than 1% of total organic C in soil but represents about 90% of total organic carbon in surface waters (Reddy et al 2008)

 

MBC - Heterotrophic microfloral catabolic activities then transform organic carbon (ecosystems energy reserve) back to inorganic carbon, they breakdown POC and DOC. In aerobic conditions half the monomers formed get converted into biomass while the other half gets oxidized into CO₂. Turnover of active biomass happens quickly in the order of days while that of soil organic matter in decades. Soil microbial biomass can be regarded as a significant carbon sink.

 

Gaseous end products - Under anaerobic and aerobic conditions gaseous end products are formed. Under anaerobic conditions CO₂ and CH₄ are formed through the decomposition of organic matter and under aerobic conditions only CO₂ is formed. CO₂ easily dissolves into water (CO₂ + H₂O = H₂CO₃) and forms inorganic carbon compounds, (greatly influenced by pH).
Carbon storages and transfers in the wetland environment
(Kadlec et al. 1996)

 

The flux of carbon in different reservoirs at the ecosystem scale is a continuous process. All of the above show how CO₂ can be fixed during photosynthesis and returned to the atmosphere by decomposition processes.

 

Wetlands have aerobic and anaerobic interfaces in; water, soil and the accumulation of organic matter. Aerobic respiration is far more effective at organic matter degradation than anaerobic processes such as fermentation and methanogenesis (Scholz et al, 2005). Primary productivity in ICW is faster than decomposition rates leading to net accumulation of organic matter.
As organic matter is decomposed it is buried and this shifts processes from aerobic to anaerobic due to lack of oxygen, this drastically reduces decomposition rates. Due to slow decomposition rates layers are built up and compacted forming different soil strata.
Apart from carbon sequestration organic matter accumulation controls these key parameters in wetland ecosystems; microbial potential energy source to communities and associated compound storage (Reddy et al 2008).

 

Phenolic substances - Two main types of enzymes are involved in carbon cycling, hydrolytic enzymes (not involved in the breakdown of phenolic compound aromatic ring structure) and nonhydrolytic enzymes (including phenol oxidase) which are involved in the breakdown of phenolic compound aromatic ring structure.
Nonhydrolytic enzymes reactions only occur in aerobic conditions due to oxygen requirements. This suggests that phenol oxidase only functions efficiently in wetlands when the water table is considerably lowered and soils become aerated. The enzymatic breakdown of lignin and humic substances is therefore insignificant in the anaerobic part of wetlands.
Phenol oxidase affects the retention of C in the soil directly via the breakdown of otherwise recalcitrant organic matter and indirectly by producing extra-cellular hydrolase enzymes from phenolic inhibition (Limpins et al 2008).
Without oxygen phenolic material accumulates in the soil, phenolic compounds inhibit the activity of many enzymes and this keeps the carbon sequestered in the soil (Freeman et al 2004). If wetlands were drained, the phenolic compounds wouldn´t stop inhibiting enzyme activity and carbon would be released into the atmosphere in catastrophic amounts.