Wetlands as pollution processors

Abstract

After decades of successful measures against point sources of nutrients in industrial countries, we still have severe problems with diffuse pollution. For treatment of excessive nitrogen from agricultural and urban areas, in the form of nitrate (NO₃^-) and ammonium(NH₄⁺), wetlands (including dams and buffer zones)  are constructed to favour the microbial processes that lead to denitrification of and NH₄⁺ and NO₃^-, via nitrite (NO₂^-) and nitrous oxide (N₂O), to atmospheric nitrogen (N₂). hnportant factors when designing "optimal wetlands" are hydrology, temperature, sufficient carbon source, water residence time, and alternating aerobic/anaerobic conditions. Also biomass uptake and sedimentation of both nitrogen and phosphorus help with reduction of the nutrients. Conditions and possibilities for wetlands in their accumulation of storm water are also described. The importance of biological diversity in wetlands are several: more fragmentation by invertebrates, more plant surface types, more nutrient biomass uptake, more bioturbation by various animals, and more biomass that can accumulate toxicants. The efficiency and biodiversity of wetlands are due to their trait being ecotones between land and water, causing large spatial and temporal variations. Finally the recreational, esthetical and broad pedagogical values of wetlands, as well as the need of better follow-up studies, are emphasised.