Last year, Durham Wildlife Trust sought and successfully obtained funding for the Brinkburn Champions project.  The aim of this project is to engage local people with the Brinkburn Pond and the wider Brinkburn wildlife site, and to help support more self-led management of the site by local residents and the Friends of Brinkburn for benefit of people and nature.

Work to Date

The pond is a valued local greenspace, and Durham Wildlife Trust have been pleased to support work at the site.  Since January 2023, more than 56 staff days and 72 volunteer days have been committed to the project from the Trust, in addition to the regular activity and stewardship by The Friends of Brinkburn and local residents.  Working together, residents, volunteers and Trust staff have been doing regular litter picks, carried out repairs to site infrastructure, undertaken scrub and woodland work, removed and disposed of unsafe fishing pegs, and reached out to schools. 

Getting Involved

Thanks to the funding received from Darlington Building Society and Awards for All, The Trust’s project officer, Jodie, is able to be at the site every Thursday and once a month on a Saturday.  We would love to welcome new volunteers to the group, whether that is to support practical work or join events.  You can register as a volunteer here, or email us for more information on how to get involved.  We also have an exciting programme of events planned at the pond for the summer holiday period, so please get involved.

Duckweed

One ongoing area of work has been to address concern surrounding the presence of duckweed on the pond.  Due to a number of factors, it has in recent years dominated the waters surface during the warmer summer months. There have been ongoing efforts to understand the root cause of the duckweed blooms and to find solutions to bring it into a more natural balance. This has included trialling the new duckweed skimmer which was purchased last year as a possible way to address the coverage problem. 

There is a lot of strong feeling about the duckweed at the pond, which is understandable.  For some people it is unsightly and consequently can be perceived as indicative of neglect, and misconceptions can form that duckweed is harming wildlife in the pond.  

Duckweed is a native species of plant that is normal in freshwater habitats.  It has several important wildlife benefits.  It helps oxygenate water through the process of photosynthesis.  It also thrives in nutrient rich waters, which means it helps remove nutrients like nitrogen and phosphorus from the water and, importantly, in doing this it helps reduce the likelihood of harmful algal blooms.  The plant is nutrient and protein rich in its own right and is an important food source for many animals, particularly later in the year as food becomes scarcer.  It also provides shelter and cover for insects and amphibians and creates shade within water, which helps keep water cool.  This is beneficial as warmer waters have a lower dissolved oxygen content and that can be harmful for a variety of aquatic animals and insects.

Duckweed can become a problem when it completely dominates a water body.  This is because it blocks out light, which may prevent submerged plants from growing and leads to reduced diversity, and, as those plants die and the organic matter decomposes, the microbial processes can reduce dissolved oxygen in the water.  However, it is not clear that this is happening at Brinkburn Pond. 

There is very little, if any, submerged vegetation in the pond.  Therefore other plants are not being outcompeted.  The lack of plant diversity in the pond may be due to the fish stocks present and the impact of their grazing.  This lack of botanical competition for nutrients is possibly a contributory factor for why the duckweed is able to dominate so successfully.  While the duckweed may eventually sink and decompose later in the year, it isn’t known how much of it is lost in this way each autumn and winter or how much is consumed.  It is therefore difficult to establish how or if it impacts oxygen levels during this stage.

As a native species, it is entirely normal for duckweed to be present in our local environments.  It is a very successful plant, and, in the right conditions, it can double in area every 1-2 days.  This makes it difficult to control and eradication is neither desirable nor likely.  There will always duckweed introduced through natural sources like wild birds, or by people and dogs. 

That does not mean that the Trust are not looking at ways to control the extent of it, but it isn’t easy for a number of reasons.  The pond is surrounded by built-up land and hard impermeable surfaces, which means high nutrient inputs due to urban run off are likely, and it does not have any throughflow or current.  Both of those factors, along with plenty of light and warm weather, create ideal conditions for the duckweed to thrive.

Unfortunately, some processes of removing duckweed may also be making things worse.  Regularly entering the pond will stir up sediment and push additional nutrients up into the water column that would have otherwise been trapped in the settled mud.  It is partly for this reason, but also to try to reduce the amount of laborious removal by hand, that Durham Wildlife Trust worked with Darlington Borough Council last year to purchase a duckweed skimmer. 

There were high expectations for the skimmer and its effectiveness is still being assessed.  It was always an experimental purchase, as management of duckweed is not a commonly undertaken task, and no parties involved have experience with this type of device. 

While the skimmer does functionally work, and does so in a way that minimises disturbance within the pond, it has limitations.  Firstly, the level of litter within the pond means the skimmer and pump must be regularly stopped and unclogged.  This reduces its running time.  Secondly, the size of the pond and the rate at which the skimmer can remove vegetation means it does not make sufficient progress in the time available to run it.  Removal rates were not known at the time of purchase, so this learning is being gained from real world usage.  While continuous operation of the skimmer may lead to a greater level of removal, it is unfortunate that the time to run the skimmer will always be constrained by available staff resource and funding to support this.

The Root Cause

Removal of duckweed is equivalent to dealing with the symptoms.  Without addressing the root cause it will remain an ongoing issue. High levels of nutrients within the water are most likely exacerbating the situation.  Work started last year to cut back trees around the water’s edge to reduce leaf litter and organic matter entering the pond.  This work needs to be undertaken gradually, on a rotation and over several years, as those trees are also valuable for wildlife in their own right.

Other ways to manage the nutrient load may be to introduce additional aquatic plants that will be competitive with the duckweed.  If they establish successfully they could lead to a more balanced system.  It will however not be easy to achieve, and most likely a range of approaches are needed consistently and year after year to effect lasting change.

Use of Chemicals

Questions have been asked about the use of herbicides and chemical control.  The Trust are not supportive of this for a number of reasons.  Duckweed is a native species with wildlife benefits, so there is no legal requirement or strong ecological basis for its control in this instance.   Use of pesticides should always be a last resort where the justification outweighs the potential harm they may have.  There is not a pesticide that only targets duckweed and pesticides continue to be shown to have adverse impacts on non-target species (these may not be fatal but can impact fertility, brain function, navigation, and other behaviour).  There are also risks with bioaccumulation through the food chain,  environmental persistence, and considerations for human health.  It should be noted that adding chemicals to a water course without an appropriate consent from the Environment Agency would constitute pollution of a natural environment, would be a criminal offence, and can easily be tested for.

A Final Thought

Education about the wildlife that is making use of the pond and wider area is critical.  Part of this involves challenging perceptions about the duckweed.  It is part of our natural world, and is doing well in an environment that has been heavily modified by human activity.  Enabling people to understand more about the benefits, as well as the natural processes and challenges of restoring balance to nature may help establish realistic expectations over how quickly natural systems can rebalance and change. 

If you would like to get involved, or simply chat to us about the site, please come and see us on Thursdays or drop us a line via email.