USEPA Region IX, WTR2, 75 Hawthorne St, San Francisco, CA, 94105, USA,
Environ Monit Assess. 2014 Apr;186(4):2413-33. doi: 10.1007/s10661-013-3548-x. Epub 2014 Jan 17.
Prioritizing total maximum daily load (TMDL) development starts by considering the scope and severity of water pollution and risks to public health and aquatic life. Methodology using quantitative assessments of in-stream water quality is appropriate and effective for point source (PS) dominated discharge, but less so in watersheds with mostly nonpoint source (NPS) related impairments. For NPSs, prioritization in TMDL development and implementation of associated best management practices should focus on restoration of ecosystem physical functions, including how restoration effectiveness depends on design, maintenance and placement within the watershed. To refine the approach to TMDL development, regulators and stakeholders must first ask if the watershed, or ecosystem, is at risk of losing riparian or other ecologically based physical attributes and processes. If so, the next step is an assessment of the spatial arrangement of functionality with a focus on the at-risk areas that could be lost, or could, with some help, regain functions. Evaluating stream and wetland riparian function has advantages over the traditional means of water quality and biological assessments for NPS TMDL development. Understanding how an ecosystem functions enables stakeholders and regulators to determine the severity of problem(s), identify source(s) of impairment, and predict and avoid a decline in water quality. The Upper Reese River, Nevada, provides an example of water quality impairment caused by NPS pollution. In this river basin, stream and wetland riparian proper functioning condition (PFC) protocol, water quality data, and remote sensing imagery were used to identify sediment sources, transport, distribution, and its impact on water quality and aquatic resources. This study found that assessments of ecological function could be used to generate leading (early) indicators of water quality degradation for targeting pollution control measures, while traditional in-stream water quality monitoring lagged in response to the deterioration in ecological functions.
优先制定总最大日负荷量（TMDL）需要考虑水污染的范围和严重程度以及对公众健康和水生生物的风险。对于以点源（PS）排放为主的流域，使用对河流内水质进行定量评估的方法是合适且有效的，但对于主要由非点源（NPS）相关污染物造成的流域，效果则较差。对于 NPS，TMDL 开发和相关最佳管理实践的优先级应侧重于恢复生态系统的物理功能，包括恢复效果如何取决于设计、维护和在流域内的位置。为了完善 TMDL 开发方法，监管机构和利益相关者必须首先询问流域或生态系统是否存在失去河岸带或其他基于生态的物理属性和过程的风险。如果是这样，下一步就是评估功能的空间布局，重点关注可能失去的或在某些帮助下可以恢复功能的有风险区域。评估溪流和湿地河岸带功能具有优于传统的 NPS TMDL 开发的水质和生物评估方法的优势。了解生态系统如何运作使利益相关者和监管机构能够确定问题的严重程度，确定损害的来源，并预测和避免水质下降。内华达州的上里斯河就是由 NPS 污染导致的水质受损的一个例子。在这个河流流域，使用溪流和湿地河岸带适当功能状况（PFC）协议、水质数据和遥感图像来识别泥沙来源、输运、分布及其对水质和水生资源的影响。本研究发现，生态功能评估可用于生成水质退化的早期指标，以针对污染控制措施，而传统的河流内水质监测则滞后于生态功能的恶化。
