城市生态系统污染氮足迹与灰水足迹综合评价

水足迹和氮足迹指标的运用可定量分析人类水资源与氮元素消费对环境造成的影响,但联合双足迹指标评价城市发展对环境造成的多重负效应的研究尚缺.基于污染氮足迹及灰水足迹理论与内涵,以城市化程度较高的深圳市为例,分别对其城市污染氮足迹及灰水足迹进行核算与评价,综合评估城市快速发展导致的氮污染与水污染潜在风险的耦合关系.结果表明:2005—2015年深圳城市污染氮足迹呈波动下降趋势,年均约3万t.水体活性氮流失为主要的城市污染氮足迹来源.同时,深圳城市灰水足迹却呈波动上升趋势,年均约15亿m~3,生活灰水足迹为城市灰水足迹主要构成部分,也是城市剩余灰水足迹的主要来源.研究期间,城市污染氮足迹与灰水足迹呈协同变化趋势,但2012年后两者出现"脱耦"情况.城市污水处理能力与再生水利用率为影响未来深圳城市灰水足迹增加的主要因素,优先快速提高城市生活污水再生利用率和全面提高城市污水脱氮率,可应对城市发展过程水资源与氮元素利用带来的环境风险.

Integrated assessments of nitrogen pollution footprints and grey water footprints in the urban ecosystem

The indicators of the water footprint and nitrogen footprint are widely applied in the environmental assessments of anthropogenic consumptions of water resources and nitrogen elements, however, the studies involved jointing dual-footprint indicators are still lacked in the impact assessment on urban environment. This study constructed a framework, based on the theories of nitrogen pollution footprint and grey water footprint, to quantify the dual-footprints of Shenzhen city with higher urbanization degree and then assess the coupling relationships between the potential risks resulting from nitrogen and water pollutions in urban environment with rapid urbanization. The results show that:during 2005-2015, the nitrogen pollution footprints of Shenzhen city decreased with fluctuation with annual average of 3×10⁴ t, and the reactive nitrogen discharge to aquatic environment was the main source of urban nitrogen pollution footprints. Meanwhile, the grey water footprints of Shenzhen city is on rising with an average of 1.5×10⁸ m³·a^-1, and the residential grey water footprint was the main component of urban grey water footprints, as well as residual grey water footprints. The changing trends in urban nitrogen pollution footprints and grey water footprints presented coordinated, but this coupling relationship was broken after 2012. The urban sewage treatment capacity and the rate of reclaimed water reusing were the main factors influencing future increasing in urban grey water footprints of Shenzhen city, therefore, priority to rise the rate of residential sewage reusing and improve nitrogen removal efficiency during wastewater treatment are the key measures to mitigate the environmental risks brought by water resources and nitrogen elements utilizations during urban development.