Advanced Review Impacts and indicators of change in lotic ecosystems Nikolai Friberg ∗ Fresh waters have seen the largest decline in biodiversity of any ecosystem, with lotic ecosystems particularly impacted by human activities. The main drivers of environmental change relate primarily to agriculture, urbanization, and industrial production that have resulted in severe habitat degradation in streams and rivers worldwide. The increasing impact of climate change and invasive species has put further pressure on these systems. For more than a century, status of rivers and streams has been assessed using biological indicators and represents a prime example of applying ecological knowledge to address societal issues. Today, legislative regulations and water management rely primarily on measurements of ecological status through the assessment of biotic communities. There has been a continuous development of these biological indicators but primarily based on fundamental approaches that date back to the original assessment systems. The indicators used today ignore large parts of what is occurring in the ecosystem and cannot, in most cases, diagnose the cause of degradation with a reasonable precision. There is clearly a need to improve existing assessment systems through new and innovative approaches that, as an example, include ecosystem processes and can be linked more closely to the services that lotic ecosystems provide. This article critically reviews the use of biological indicators in the context of inherent properties of lotic ecosystems and types of degradation, and suggests how assessment could be refined through applying a number of additional approaches to those already used. © 2014 Wiley Periodicals, Inc. How to cite this article: WIREs Water 2014. doi: 10.1002/wat2.1040 INTRODUCTION I ndicators play a focal role in the management and conservation of fresh waters in supporting the policy-making process that aims to protect the ecosys- tems themselves, and the goods and services they supply. 1–4 In Europe, the main part of the EU environ- mental budget involves water-related expenditure 5,6 with the EU Water Framework Directive (WFD 7 ) being the overarching piece of legislation with regard to fresh waters. To protect and improve lotic ecosys- tems, we need to be able to measure how they respond to natural and anthropogenic stressors, and indicators are essential in tracking and quantify- ing these impacts. 8,9 According to the European ∗ Correspondence to: Nikolai.Friberg@niva.no Norwegian Institute for Water Research, Oslo, Norway Conlict of interest: The author has declared no conlicts of interest for this article. Environmental Agency, 10 one of the main purposes of environmental indicators is to supply informa- tion on environmental problems, in order to enable policy makers to value their seriousness. Although indicators are primarily tools in the policy-making process, indicator development has a long history, spanning more than 100 years in the freshwater sci- ence community 6,11 and is, still today, a very promi- nent research topic. This research effort on indica- tors has accumulated a large body of knowledge on biological community responses to environmen- tal stress and a diversity of methods in how to assess stream quality which today is widely applied worldwide. 12 This widespread use of biological indi- cators to assess degradation is a prime example of an applied use of ecological knowledge that has helped to improve the status of many streams and rivers dur- ing past decades. However, in stating this, it should © 2014 Wiley Periodicals, Inc.