Research and analysis

Using ecological function to assess aquatic ecosystem health: an overview: summary

Published 18 December 2025

Applies to England

1. Chief Scientist’s Group report summary

This project reviewed how the role species play in the environment, their ecological function, could strengthen the Environment Agency’s ability to deliver clean and plentiful water and promote sustainable development. Understanding where, when and how ecological function changes could help target regulatory and management actions to ensure that river ecosystems are healthy and continue to provide the services on which people rely.

1.1 Background 

Monitoring and assessment approaches generally focus on the composition of ecosystems, such as the number and abundance of fish and other smaller organisms. It has long been recognised that an understanding of the role of species would be useful, this is usually referred to as ecological function. However, defining and measuring ecological function is challenging. This report presents a review and survey of what ecological function means and how it might be used in aquatic environmental assessment.

1.2 Approach 

A review of published literature explored how ecological function can be used in ecosystem assessments. This was accompanied by a survey of Environment Agency colleagues from across the organisation who collect, use and apply ecological data to capture their understanding of the term ‘ecological function’. The survey also explored how ecological function could be measured and how this might potentially improve assessment of ecological health and the effectiveness of management actions. 

1.3 Results 

On-going environmental change linked to human behaviour, and particularly climate change, is altering what can naturally live where. A focus on function would help us understand whether essential services are maintained as species distributions change, non-native species arrive, and novel ecosystems develop.

Defining function is complex with a variety of different interpretations. Ecological function generally refers to the roles organisms or processes play in an ecosystem – i.e. what they do. This contrasts with ecological structure which refers to how ecosystems are organised, including species composition, population densities, and spatial distribution i.e. what is there.

The interactions between what species are present and how ecological functions operate are complex, influenced by factors such as catchment characteristics, climate and human pressures. So, considering both aspects within assessments could provide a more holistic picture of environmental health, provide a better understanding of why species respond to change and help target management actions more effectively.

Some ecological functions can be assessed by directly measuring processes, such as primary production, decomposition and carbon sequestration. However, such techniques are time consuming and are unlikely to be practical to apply at a national scale since they can be labour intensive and need repeated observations over time. They may be best used to understand specific actions, such as river restoration and nature-based solutions, to improve confidence in the effects they may have.

The characteristics of species (the traits) can be used as proxies of ecological functioning, indicating how species and populations might function and interact with their environment. These measures could be applied to existing biological monitoring data to understand past changes and response to known environmental change. However, whilst the theoretical use of assessing function via traits is clear, practical application for routine monitoring would need exploration of which measurements to apply and what a change in each measure might mean.

Advances in technology now make it possible to directly measure ecological functions by analysing the genetic material of microorganisms in the environment. Emerging research is revealing new insights into the roles these microorganisms play in important riverine processes such as nutrient and carbon cycling, and the effects of environmental change.

Whichever functional assessment approach might be selected, it will still be important to define what constitutes a healthy ecosystem and understand how its characteristics vary across different locations and over time. Only after establishing these foundations can changes be understood and used to inform decision making.

1.4 Conclusion

Considering ecological function, alongside ecological structure, could provide more holistic assessments of aquatic ecosystems. Newer approaches to assessments, particularly using genetic material make routine assessments of ecological function a more realistic possibility. Ultimately this may be beneficial for the sustainable management of evolving ecosystems in a changing climate and ensure the continued provision of the services that people rely upon.

1.5 Publication details

This summary relates to information from project SC240024, reported in detail in the following output:

• Report: SC240024/R
• Title: Using ecological function to assess ecosystem health – an overview
• Project manager: Judy England, Research, Chief Scientist’s Group

This project was delivered by the Environment Agency’s Chief Scientist’s Group, which provides scientific knowledge, tools and techniques to enable us to protect and manage the environment as effectively as possible.

Enquiries: research@environment-agency.gov.uk.

© Environment Agency