Eutrophication - An Emerging Topic in Soil Use and Management.
Gan-Lin Zhang, Institute of Soil Science, Chinese Academy of Sciences, 71 East Beijing Road, Nanjing, 210008, China and Wolfgang Burghardt, Universitaet Duisburg-Essen, Fb. Biologie und Geographie, Abt. Angewandte Bodenkunde, Universtitätsstr. 5, d-45117 Essen, Germany.
The word “eutrophication“ means the status of enrichment of excessive nutrient elements, often in water bodies. However, soil system, especially that of cultivated soils of many parts of the world is becoming gradually loaded with excessive nutrients too, which can be featured as eutrophicated. Current soil use and management in the many parts of the world is characterized by continuous and large amount input of chemical and organic amendments, for a high production, especially in the regions where agricultural land supply is relatively limiting. One of the typical surroundings where soils are often enriched with nutrients is urban and peri-urban area. Urban and peri-urban area represents a special kind of ecosystem that gets continuous material input while only a portion of them gets lost, so there is a long-lasting accumulation of nutrients in soil system. The source of element input to urban (peri-urban) soil system comes from urban waste and meanwhile high application of chemical fertilizers. Phosphorus has been observed widely accumulated in urban agricultural ecosystem. Due to its low mobility in soil, phosphorus accumulation is extremely evident in urban soils. This kind of accumulation started as soon as the human concentration and can be dated back to thousands years ago in many cities. The enrichment of phosphorus usually suggests also the co-existence of other elements such as heavy metals Cu, Zn and Pb because they have a high mutual immobilization effect. Recent mass application of chemical fertilizers in intensively managed agroecosystem, such as greenhouse horticulture, also leads to the fast increase of nitrate content and other soluble salts in soils. Severe physical, chemical and biological degradation often occur when excessive nutrients are accumulated in soils. The eutrophicated soils are an immediate threat to water environment, besides its strong impact on soil biodiversity. Studies showed that substantial mobilization and release of P, NO3- and other components take place when the concentrations of these components exceed certain critical values. This threshold values are very important in indicating soil nutrient status, not only agriculturally but also to environment. Sustainable soil use and management in urban and peri-urban environments should pay more attention to the emerging evidence of soil eutrophication.