Another Baffle-ing Year for Woodplumpton Brook!

Regular readers of the blog will know that, every year, Queen Mary University of London buys out some of my time and expertise from WTT to give their aquatic ecology MSc students practical training and experience in the field. As a part of a week-long field-course based in the Lake District, I have forged a link between them and Wyre Rivers Trust to monitor a project led by Tom Myerscough. Despite all the recent challenges impacting their year of study, some of the students have found the time to analyse the data and write us a guest blog to update the Woodplumpton Brook story. 

Rivers and their catchments have had a tough time over the last century; intensive agriculture, urbanisation and the altering of waterways are just some of the human impacts affecting river ecosystems, threatening their health and often leaving them in a dire ecological state. 

The Lancashire Wyre is one river that has unfortunately experienced more than its fair share of stressors within a catchment that covers approximately 450 km2. The Wyre is of social, economic and ecological importance but has suffered a plethora of post-war issues, including reduced water quality, physical modification, habitat degradation and increased flood risk. However, not all is lost! Catchment-based conservation approaches across the UK have so far been successful in improving water quality and reducing the pressures facing river ecosystems. With the major threats in the Wyre catchment emerging from livestock agriculture, many of the solutions are associated with land management such as the implementation of vegetation buffer zones that prevent livestock from grazing and trampling the riverbanks. This, alongside willow planting, acts as a sustainable method to reduce soil erosion, flood damage and poaching, whilst also ameliorating nutrient run-off and providing essential habitats and refugia for wildlife. 

Such approaches are vital but do not solve every problem within the Wyre Catchment. Often overlooked in small watercourses, is the sheer number of artificial barriers hindering the passage of fish, resulting in poor habitat connectivity. On Woodplumpton Brook, a road-bridge culvert inadvertently introduced such a challenge: a 15m stretch of shallow water with an increased, uniform flow rate. This culvert fragmented and degraded habitats, isolated fish populations and reduced reproductive potential, especially for larger species or weaker swimmers, such as European eel, the lampreys, and brown trout. 

In 2016, the Wyre River Trust, in collaboration with the Wild Trout Trust (WTT) and with permission from the local council, implemented a simple but effective adjustment within the culvert. They installed off-set wooden baffles to reduce the flow rate whilst increasing the sinuosity of the flow path, introducing slack water zones and areas of attraction flow, and importantly increased the depth by ~100 mm, even under the lowest of summer flows. These changes were designed to aid the movement of fish, facilitating recolonisation of upstream habitats, connecting isolated populations, and hopefully promote the natural recovery of brown trout which used to be found throughout Woodplumpton Brook. All this could increase the resilience of this freshwater ecosystem and enhance other restoration efforts upstream. Turns out not all heroes wear capes, just a pair of trusty waders!

Electrofishing QM1920
Surveying (& training) via electrofishing on Woodplumpton Brook

To monitor the impact of the baffles, sampling has been performed both before and after installation in order to assess any changes in the fish community. Each year, Freshwater and Marine Ecology MSc students from Queen Mary University of London are lucky enough to help collect these valuable data, learning new skills and gaining invaluable knowledge along the way. This also provides the Wyre Rivers Trust and WTT with the opportunity to evaluate the effectiveness of the restoration project using longer-term datasets.

Eel image
Stickleback QM1920

The fish communities are evaluated consistently year-on-year by electrofishing discrete 50m stretches both upstream and downstream of the culvert; stop-nets section off each reach and 3‑pass depletion sampling is applied with each individual fish identified and measured for fork-length. 

But are the baffles having an impact? 

Previous cohorts from Queen Mary found that prior to the baffle installation, fish communities upstream of the culvert were dominated by significantly smaller individuals than communities downstream. Within one year of the installation of the baffles, we had already begun to see a change! Both the fish communities and sizes of upstream and downstream fish had started to become more similar. 

Our findings followed the trend seen in previous years; the fork-length of the fish upstream and downstream of the culvert in 2019 – 2020 is more similar than in any previous years (Figure 1), demonstrating that the baffles are continuing to facilitate the movement of fish within the brook.

Average length QM1920
Figure 1: Average length (mm ± Standard Error) of fish species upstream (orange) and downstream (blue) of the road-bridge culvert at Woodplumpton Bridge in different years. Note that 2016 -2017 was prior to the baffle installation.

Additionally, we found that the overall diversity of the fish community was significantly higher in 2019 – 2020 compared to other years (Figure 2). Yet another promising sign that the baffles are having a positive effect, but also an indication that the brook is recovering on the whole. This is supported by the finding of important Biodiversity Action Plan species such as brown trout and European eels. The presence of brown trout was particularly encouraging, as they were located upstream of the culvert for the third consecutive winter.

Shannon index QM1920
Figure 2: Median Shannon Diversity Index (± IQR) of the fish communities sampled at Woodplumpton Brook in different years.

We did notice some further differences. As mentioned in the previous blog post, our predecessors found sticklebacks and stone loach to be the most abundant species and discovered several recently deceased chub thought to be the result of a pollution incident (and reflected in the low diversity seen in 2017 – 18; Fig 2). We found that chub alongside dace and minnow were now the most abundant, hopefully indicating recovery within the fish community.

Overall, the baffles seem to have achieved the aims, doing a great job improving the connectivity within the brook and maybe even be assisting the recolonisation of brown trout. Additionally, there appears to be an encouraging increase in diversity within Woodplumpton Brook, showing positive signs of recovery from pollution that occurred in 2017. Would the recovery from pollution have happened so rapidly if the culvert had remained unaltered? Probably not. 

The project highlights that even small acts, like a few low-cost baffles placed in a culvert, can have a disproportionately large positive effect on freshwater ecosystems, encouraging news for the conservation sector as finances and policy often stand in the way of progress. Our contribution to the longer term monitoring of this particular intervention is invaluable in providing the evidence base for convincing funders of the worth of such small scale works and hopefully enabling the implementation of similar projects on culverts elsewhere. 

Frazer Bayliss, Reiss Bush, Ana Martinez Rodriguez, Reem Alnaqeeb & Ellie Wynter