Functional Indicators - a New Approach to River Health Assessment?

River health monitoring has traditionally concentrated on the use of structural indicators such as water quality or the types of aquatic organisms present. An alternative approach is to use measurements of the functions that rivers perform as indicators of ecosystem health. Examples of these functions include the rates of ecosystem metabolism and organic matter decomposition within river systems.

Roger Young is currently leading a three year project funded by the NZ Minister of the Environment’s Sustainable Management Fund and other stakeholders that aims to provide a framework for the use of functional indicators for assessing river ecosystem health in New Zealand. An initial report was prepared which provides an overview of functional indicators, brings together information on the response of these functional indicators to a variety of impact types, and provides guidance on when and where these approaches may improve river health monitoring in New Zealand. A copy of this report is available here.

A user-friendly Microsoft® Excel spreadsheet model has now been developed to calculate ecosystem metabolism (the combination of photosynthesis and ecosystem respiration) from natural changes in dissolved oxygen concentrations. To calculate metabolism using this spreadsheet model you need dissolved oxygen and temperature measurements from a single site collected at regular intervals over a 24 hour period. You also need an estimate of the mean depth of the study reach. It is an advantage to have light data collected at the same time as the oxygen data, so dusk and dawn can be clearly identified. However, light data is not compulsory. A zipped copy of the model is available here. The spreadsheet model contains a number of macros, so you will have to choose the ‘Enable Macros’ option when opening the file to make it work. Detailed instructions on how to use the model are saved within a worksheet of the Excel workbook.

A report describing the results from a series of case-studies using the functional indicators approach has also been prepared and is available here. These case studies focused on the use of organic matter decomposition as an ecosystem health indicator and demonstrated the potential of the approach. The report compares different approaches to measuring organic matter decomposition and identified the benefits of using artificial substrates, such as cotton strips or wooden sticks, for ecosystem health assessments.

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