Task of mineral nutrients in eutrophication

Abstract

Eutrophication refers to natural or artificial addition of nutrients to water bodies and its effects on the aquatic life. When the effects are undesirable, eutrophication may be considered a form of pollution. Excessive nutrient loading to lakes and rivers causes eutrophication that has negative impacts on the biota together with rendering the water body unusable for human beings. Expensive cleaning operations have to be undertaken if the water has to be used for any domestic or industrial purpose. In fact improvement in the water quality of many freshwater and most coastal marine ecosystems requires reductions in both nitrogen and phosphorus inputs. Based on nutrient status and productivity, an aquatic system can be classified into the following three types: (1) Oligotrophic: water with poor nutrient status and productivity; (2) Mesotrophic: water with moderate nutrient status and productivity; (3) Eutrophic: water with rich nutrient status and high productivity. Massive amount of mineral nutrients and organic matter are added in water reservoirs in the form of sewage effluents, organic wastes, agricultural runoffs, excreta, and exudates of living beings. These contain plenty of phosphates coming in large quantities owing to the use of soaps, detergents, and water softeners. In some eutrophic water bodies, dense population of planktonic algae develops. The phenomenon is called water or algal blooms because of the fast growth rate of algal population. The presence of mineral nutrients in concentrations sufficient to support the huge population of planktonic algae is the prerequisite for the formation of algal blooms. All activities in the entire drainage area of a lake or reservoir are reflected directly or indirectly in the water quality of these water bodies. In many lakes and reservoirs, wastewater is the main source of nutrients since untreated wastewater or wastewater treated only by conventional methods usually contains nitrogen and phosphorus. The loading of N and P to the world's rivers, lakes, and oceans is very strongly influenced by human population densities, the population densities of livestock, and land use environmental implications of N and P to the biosphere. Phosphorus removal from wastewater is an effective approach for prevention of eutrophication in closed water systems. The role of potassium in microorganisms responsible for biological phosphorus removal in waste water is more important. Further studies are needed to examine how the inorganic formation of calcium carbonate can control the fate of nutrients in water bodies added by anthropogenic activities. Magnesium is essential for chlorophyll synthesis and, thus, acts as a limiting factor for the growth of phytoplankton. Therefore, depletion of magnesium reduces the phytoplankton population. As an essential element, therefore, Mg often limits the growth of primary producers such as algae, other aquatic plants, cyanobacteria, and photosynthetic bacteria. The regulation effects of iron should be considered besides nitrogen and phosphorus during the treatment of eutrophication of lakes. Studies of algal spectral properties under different iron supply would be meaningful for determining the bloom and developing the remote sensing warning system of lake eutrophication. The present review covers the definition and concept and types of eutrophication, adverse effects of eutrophication on quality and functioning of aquatic ecosystems, causes and consequences of eutrophication, and the task of mineral nutrients in the process of eutrophication.