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How Can We Effectively Monitor Our River Restoration Projects?

Posted: Thursday 17th December 2015 by RiverSearch

Murray demonstrating the traps to volunteers.

Work to restore Surrey's rivers is now gathering pace with a multitude of projects planned for 2016 but how do we know how effective our efforts have been? To help us answer this question we have joined forces with Dr Murray Thompson of University College London to train RiverSearch volunteers in a new method for monitoring the effectiveness of river restoration projects.

Surrey Wildlife Trust will be delivering a number of river restoration projects in the Spring of 2016 as part of the DEFRA funded Catchment Based Approach. These projects will work closely with volunteers to install enhancements which will restore natural processes within the river system to boost local biodiversity and maintain good quality habitat. Enhancements can be as simple as felling small trees into the river to create fish and invertebrate habitat or can be more complex such as re-profiling a straightened section to maximise flow diversity and help to clean bed gravels.
The question is, once implemented how do we know the enhancements have been effective? This is a question that Dr Murray Thompson of University College London is hoping to answer with the help of Surrey Wildlife Trust RiverSearch volunteers.

Using data collected by RiverSearch volunteers we are able to highlight those stretches of river where habitat is lacking or absent. We can then design projects using methods like those described above to reinstate habitat and natural features. But if the stretch is impacted by other issues such as intermittent pollution incidents this will limit the recovery of the ecosystem no matter how much habitat we restore. This is why it is so important that we understand just how effective our restoration efforts have been so we do not miss any underlying issues. This is where Murray comes in.

Murray’s method not only looks at the invertebrates present in the stream but also how well they are carrying out the important ecosystem function of decomposition.
To give an example: Species such as the freshwater shrimp are known as the shredders of the river that is they shred leaf litter in the stream down into smaller pieces which then become available food for other species. This is an important ecosystem function which helps to maintain the whole system but under different levels of stress the shrimp may be eating more or less of a food resource. Traditional sampling methods are excellent at picking up water quality issues but this method goes one step further and tells us how well those species are performing important ecosystem functions.

Murray’s method uses traps built out of household guttering which contain a piece of paper of a known weight. One side of the trap allows invertebrates in which will eat the paper whilst the other side has a fine mesh covering and only allows microbes in which also eat the paper. 6 of these traps are placed into the river at the project site before the enhancements go in. The traps remain in place for 2 weeks after which time they are extracted by RiverSearch volunteers who identify and count the invertebrates and dry and weigh the paper. Months after the enhancements have been installed the traps are returned to the river along with an extra 3 which are placed next to the enhancements. After another 2 weeks the traps are analysed once again. To ensure accurate results a control site away from the restoration area is also monitored to pick up any fluctuations in invertebrate populations along the whole stretch of river.

The type and number of invertebrates found in the traps, the weight of paper before and after restoration along with habitat details can all be used to calculate how well the habitat enhancements are actually working and will help to identify other stressors within the system.

This research will not only provide a whole new understanding of our rivers, it will enable us and our volunteers as river managers to prescribe and implement the most suitable restoration measures with the biggest benefits to biodiversity.

Glen Skelton

RiverSearch Coordinator

Surrey Wildlife Trust


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