<标题> The sufficient factor to determine limiting factor is the ratio of nitrogen to phosphorus compounds in the water body is an important factor for control mechanism. (Table 1). Phosphorus is generally limiting factor for phytoplankton in fresh waters. For large marine areas frequently have nitrogen as the limiting nutrient, especially in summer. Intermediate areas such as river plumes are often phosphorus-limited during spring,but may turn to silica or nitrogen limitation in summer.The enrichment of water by nutrients can be of natural origin but it is often dramatically increased by human activities. This occurs almost everywhere in the world. There are three main sources of anthropic nutrient input: runoff, erosion and leaching from fertilized agricultural areas, and sewage from cities and industrial wastewater. Atmospheric deposition of nitrogen (from animal breeding and combustion gases) can also be important. According to the European Environment Agency, "the main source of nitrogen pollutants is run-off from agricultural land, whereas most phosphorus pollution comes from households and industry, including phosphorus- based detergents. The rapid increase in industrial production and in in-house consumption during the 20th century has resulted in greater volumes of nutrient-rich wastewater. Although there has been recently a better management of nitrogen and phosphorus in agricultural practices, saturation of soils with phosphorus can be noted in some areas where spreading of excessive manure from animal husbandry occurs. Nutrient removal in sewage treatment plants and promotion of phosphorus-free detergents are vital to minimize the impact of nitrogen and phosphorus pollution on Europe's.