Citizen science groups such as the Cranleigh Rivers Group will be crucial to help us better understand the issues that are affecting our rivers, says Wetland Projects Manager Glen Skelton.
With hundreds of kilometres of riverbank in Surrey alone, it would be impossible even for Surrey Wildlife Trust’s tireless staff to carry out the widespread and regular monitoring required to accurately assess the condition of our diverse aquatic habitats.
Our watercourses are under ever-increasing pressure due to human activity and climate change, and the work of volunteers is more important than ever in helping us monitor and safeguard Surrey’s rivers.
How are Cranleigh Rivers Group monitoring rivers?
Cranleigh Rivers Group is a great example of how people from local community are making a difference. In 2020, 10 volunteers of a diverse range of backgrounds have been trained in both phosphate and riverfly monitoring - two essential techniques that provide a vital insight into the extent of pollution, and its impact on ecosystems.
Cranleigh is a village at the foot of the Surrey Hills and boasts one of the River Wey's largest tributaries, the Cranleigh Waters. Within the Cranleigh area there are also three tributaries of the Cranleigh Waters - the Littlemead Brook, Thornhurst Brook and Cobblers Brook - which are home to kingfishers, brown trout, dragon and damselflies and sticklebacks. All are subject to pollution from sewage, agricultural run-off and domestic run-off. Recent drought conditions have also caused drying up of some parts of the river with low water levels throughout the remainder, further concentrating pollutants and creating stagnant pools with disastrous effects on aquatic species.
The key focus of the group is to narrow down where point source pollution is getting into the rivers, so that effective steps can be taken to prevent this. To this end, the group has taken over 120 phosphate samples, using simple testing kits and visiting the same locations on a monthly basis to help narrow down the area where pollution is getting in to the river.
Phosphates exist in high concentrations in sewage waste and commercial fertilisers, and when released into a water course act as a fertiliser for algae, creating blooms which reduce oxygen in the water and affect fish and invertebrates. Potential sources include sewerage overflows and household waste water being discharged into storm drains rather than the grey water sewer.
What do the monitoring results show?
Unsurprisingly, the volunteers’ results have shown that phosphate levels hit record levels during the dry spell in Summer 2022. The highest reading yet - 2.5 parts per million (ppm) – was taken downstream of Cranleigh sewage treatment works. Compare this to the recommended level of 0.1ppm and you start to understand just how bad the issue is.
Aquatic Invertebrates, collectively known as ‘riverfly’ are often the first to be decimated when water quality deteriorates. While some are resilient, others including mayfly, stonefly and caddis fly larvae are highly sensitive to poor water quality.
Analysing the density of invertebrate life and the mix of species that is present - this is easily done by taking three-minute samples from the riverbed each month, using small nets - is therefore a highly effective tool in keeping an eye on the river. Where phosphate readings are high, riverfly monitoring helps to show what impact point source pollution is having on species and ecosystems and can be vital evidence in building a case for action to reduce future incidents.
How is water health being improved in Cranleigh?
Cranleigh’s sewage treatment works is being upgraded in 2024. This should help considerably, but more widely we need to manage our catchment area to reduce surface water run-off and store more water in soils, in the ground, and in wetlands. This would provide a more reliable water source year round and help keep our rivers flowing in the drier months. This also makes the landscape more resilient against floods during the colder and wetter months of the year.