Eutrophication WoE Assessment - National Layer 2020/21

The process of Eutrophication is formally defined (in the UWWTD and Nitrates Directive) as: “…the enrichment of water by nutrients, especially compounds of nitrogen and/or phosphorus, causing an accelerated growth of algae and higher forms of plant life to produce an undesirable disturbance to the balance of organisms present in the water and to the quality of the water concerned…” UWWTD (Art. 2(11), 91/271/EEC) It is estimated that eutrophication costs around £75 to 115 million per year in England and Wales- damage costs which include: Reduced value of waterfront dwellings, drinking water treatment costs for nitrogen removal, reduced recreational and amenity value of water bodies, drinking water treatment costs for removal of algal toxins and decomposition products, negative ecological effects on biota, net economic losses from the tourist industry. (Jules et al, 2003) This weight of evidence layer is based on the decision support tool that combines multiple strands of evidence around nutrient impacts in a standardised manner to provide an assessment of the likelihood that a given WFD waterbody is impacted by eutrophication pressure. The certainty given to each waterbody is obtained from formal WFD Classifications, derived from the statistical confidence class. The tool uses matrices to combine confidence from individual elements to an overall certainty of there being a eutrophication impact.富营养化（Eutrophication）的正式定义载于《城市污水处理指令（UWWTD）》与《硝酸盐指令》，具体表述为：“……水体因营养物质，尤其是氮和/或磷化合物发生富集，导致藻类及高等水生植物加速生长，进而对水体中现存生物群落平衡及相关水体质量造成不良干扰……”，其中UWWTD对应欧盟91/271/EEC号指令第2条第11款。据估算，英格兰与威尔士每年因富营养化造成的经济损失约为7500万至1.15亿英镑，此类损失包括：滨水住宅价值贬损、脱氮饮用水处理成本、水体休闲与景观价值下降、去除藻类毒素及分解产物的饮用水处理成本、对生物群落的负面生态影响，以及旅游业的净经济损失（Jules等，2003）。本证据权重图层基于一款决策支持工具开发，该工具以标准化方式整合多维度营养物影响相关证据，用于评估给定的水框架指令（Water Framework Directive, WFD）水体受富营养化压力影响的可能性。各水体的确定性等级源自基于统计置信度得出的正式WFD分类结果。该工具通过矩阵将单个要素的置信度整合为富营养化影响的整体确定性评级。