Freshwaters face multiple environmental problems including eutrophication, acidification, salinization, and climate-change, all of which can lead to impairment of ecosystem structure and function. Furthermore, these stressors often act in combination. Benthic algal-based assessments to quantify impairment are used in both the EU and US. In this review, we use case studies, experience, and the literature to compare concepts, approaches, and methods between the EU and US to offer an updated picture of benthic algal-based assessments. Both the US and EU are composed of numerous constituent states having considerable flexibility to adopt individual methods. The goal of this work is to synthesize the various approaches that are used across the EU and US. Specifically, we compare and contrast benthic algal assessment performed in response to core legislation – the Water Framework Directive in the EU and the Clean Water Act in the US, with a particular focus on the steps taken to ensure consistency at different stages of the process. This includes consideration of approaches to sampling design and field methods, taxonomic resolution and laboratory harmonization, metric selection and choice of algal groups, assessment of stressors and stressor/response relationships. A number of commonalities emerged during this process, particularly the focus on diatoms over other algal groups. However, there are also a number of key differences, including more widespread use of multimetric indices in the US compared with the EU. Finally, we consider emerging opportunities, including the potential for using metagenomic approaches for bioassessment in the future.

淡水面临着许多环境问题，包括富营养化，酸化，盐碱化和气候变化，所有这些问题都可能导致生态系统结构和功能受损。此外，这些压力源经常结合起来起作用。欧盟和美国都使用基于海底藻类的评估来量化损害。在这篇综述中，我们使用案例研究，经验和文献来比较欧盟和美国之间的概念，方法和方法，以提供基于底栖藻类评估的最新情况。美国和欧盟都是由众多组成国组成的，它们在采用个别方法时都具有很大的灵活性。这项工作的目的是综合在欧盟和美国使用的各种方法。特别，我们比较并对比了根据核心法规（欧盟的《水框架指令》和美国的《清洁水法》）进行的底栖藻类评估，并特别着重于确保过程不同阶段所采取措施的一致性。这包括考虑采样设计和现场方法的方法，分类学解决方案和实验室协调，藻类群的度量选择和选择，压力源和压力源/响应关系的评估。在此过程中出现了许多共性，特别是对硅藻的关注超过了其他藻类。但是，也存在许多关键差异，包括与欧盟相比，美国多指标索引的使用更加广泛。最后，我们考虑新出现的机会，