北京市灰水足迹评价

北京市属于重度资源型缺水地区,加上严重的水污染情况,使得水问题成为制约当地社会经济发展和生态安全的关键性因素。研究采用灰水足迹理念将北京市1995-2009年间不同部门产生的污染物以"稀释水"的形式进行量化。研究表明:①北京市2009年灰水足迹为49.5×10⁸ m³,约为北京当年水资源量的2.3倍;②生活部门的灰水足迹最大,农业部门次之,工业部门的灰水足迹最小;③北京市灰水足迹呈现逐年下降的趋势,农业、生活和工业部门的灰水足迹在1995-2009年间分别下降了45%、62%和93%;④虽然北京市灰水足迹逐年减小,水体水质却呈现逐年恶化的趋势,剩余灰水足迹(即灰水足迹与水资源的差值)累积值的增加,是北京市水质逐年恶化的直接原因。严格控制灰水足迹是实现水环境总体改善的重要途径。

Historical Trend of Grey Water Footprint of Beijing,China

Beijing is an international metropolis with serious shortage of water resources. Water scarcity in addition to serious water pollution has made water a major constraint for future socio-economic development and ecological security. In this study, we use grey water footprint as an indicator to quantify the effects of water pollution on the amount of freshwater resources from agricultural, industrial and domestic sectors in Beijing during 1995-2009. These effects are presented as the volume of water that is needed to dilute the water pollutants. The results show that: 1) Grey water footprint of Beijing in 2009 is 4.95 billion m³/a, about 2.3 times that of the total amount of water resources in the same year; 2) domestic sector has the largest grey water footprint, followed by agricultural. Industrial sector has the smallest grey water footprint; 3) the grey water footprint of Beijing has declined year by year. Since 1995, the grey water footprints of agricultural, industrial and domestic sectors have decreased by 45%, 93% and 62%, respectively; and 4) although the grey water footprint of Beijing has dropped gradually, the ratio of water bodies reaching water quality standard has shown a decreasing trend. The grey water footprint is much higher than the amount of water resources, leading to accumulation of pollutants in the water bodies. It is not possible to dilute such a large amount of pollutants emitted into natural water bodies only by relying on the self-purification capacity of water bodies. So the residual grey water footprint has a positive sign and the accumulation of residual grey water footprint has increased year by year. As a result, water quality continues to deteriorate. The growth of the accumulation of residual grey water footprint explains the reasons why the quality of water becomes worse even with decreasing grey water footprint. The grey water footprint should be controlled in order to improve the aquatic environment in the Beijing city.