As a highly productive environment, wetlands play an integral role in the ecology of its catchments. Described as such only when land is saturated with water, seasonally or permanently, with the characteristics of a distinct ecosystem. The physical, hydrological, chemical and biological functions are the processes within wetlands which are interconnected to the wider watershed making them ecologically and culturally valuable.
Physical and hydrological functions include flood control and groundwater recharge through the capture and storage of water. The slow release of water over time helps to reduce floods. For many low-lying coastal regions, protection of wetlands and their services ease the impacts of floods and storms, warranting high priority in relation to climate change adaptation strategies. They also can aid atmospheric equilibrium by levelling carbon, sulphur and excess nitrogen. Plant communities and the soil structure of wetlands store carbon instead of releasing it to the atmosphere as carbon dioxide. Wetlands also catch dust particles from the atmosphere which settles into the sediment.
Wetlands have a storage and filtration capacity. Pollutants that dissolve in the water may be absorbed by plant roots and micro-organisms in the soil. The filtration process removes much of the water’s nutrient and pollutant load by the time it leaves the wetland. Vegetation also acts as a buffer trapping soil particles from flowing into the main body of water as sediments settle out with the root systems of the plants. The wetland vegetation decreases water velocity enabling the sedimentation of particles. Also vegetation is particularly effective in removing finely graded particles many of which adhere directly onto the plant surfaces. The root system binds and stabilises deposited particles protecting them against re-suspension. Trapping excess sediments is vital for the prevention of accumulation of particles that may smother aquatic life, congest parts of the wetland or carry pollutants.
Vegetation assists in maintaining regular wetland water regimes, provides habitat and food for fauna, protects against salinity and erosion, provides soil stability, filters pollutants and generally assists in the maintenance of a healthy wetland. Millions of waterbird species and migratory birds depend on the services and the interconnected networks of wetlands for survival. As wetlands function beyond the means of providing habitat for plants and animals, they also absorb excess nutrients, sediment and other pollutants before they reach rivers, lakes and other water bodies and thus effectively provide higher water quality to the greater catchment.
Not all wetlands functions are the same and depend on size and location of the wetland. Other factors also have an impact such as climate, topography, present vegetation, surrounding land use, water quality and quantity inputs, disturbances and or alteration of the wetland. These factors will influence the performance of the system's functions and the values. The functions and values of all the wetlands individually are important for their relationship to the watershed. Wetlands perform many valuable ecological functions that may go unnoticed by people. Understanding the functions of wetlands can help people know what is lost when the productivity of a wetland ecosystem declines.
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