A century ago, Britain’s landscapes were speckled with ponds. Today, more than half have vanished, notes geographer Lucy Clarke. Though small, these waterbodies have an outsized ecological impact. As Clarke puts it, they “punch far above their weight in ecological value,” and their importance is only increasing as the climate warms.
Clarke, of Nottingham Trent University, and her colleagues examined the Severn Vale region of England and Wales and found that the average distance between ponds has grown by 25 metres between 1900 and 2019 – an enormous gap for the small amphibians that depend on them.
Beyond providing habitat, ponds can store carbon and filter pollutants, improving water quality. They do this far more rapidly than many people expect. Ecologist Mike Jeffries, from Northumbria University, analysed sediment from ponds at the Hauley Nature Reserve near Newcastle – a hotspot for birdlife. He found carbon burial rates “much higher” than surrounding ecosystems like woodland.
On average, the ponds stored 142 grams of carbon per square metre each year, compared with just 2–5g in woodland or grassland. Remarkably, despite covering only about 0.0006% of the UK’s land surface, these ponds bury roughly half as much carbon as the vastly larger area of grassland. Woodlands and forests are often celebrated as key carbon sinks, yet, per square metre, ponds may outperform them.
However, ponds can be unpredictable: some act as carbon sinks, others as sources, depending on conditions. Even so, their ability to lock carbon into sediment is well established. And, as Jeffries points out, ponds are “easy to create – even in a back garden.” They cool cities, mitigate drought, store carbon, and support specialised species. In a warming world with accelerating biodiversity loss, these functions are increasingly vital.
It is important to recognise that ponds are not uniform, and their sequestration potential varies significantly depending on factors such as substrate and vegetation. Gilbert et al. (2014) found that permanent, naturally vegetated ponds – particularly those dominated by mosses and aquatic grasses – are the most efficient carbon sinks. When these ponds dry out, their thick, moist plant mats help prevent stored carbon from escaping. In contrast, temporary or shallow arable ponds, which are often disturbed and lack vegetation, were the least effective.
For this reason, grouping all ponds together can be misleading when assessing their contribution to carbon sequestration; their value depends heavily on their ecological makeup.
Ponds also serve a range of purposes. Those designed to capture agricultural runoff can help reduce climate impacts but may not support high levels of biodiversity. This diversity of pond types is reflected in the wide variation in carbon burial rates reported across the literature. For example, Taylor et al. (2019) found that small ponds can sequester between 79 and 247 grams of organic carbon per square metre per year—20–30 times higher than rates in woodlands, grasslands, and many other habitats. Cereghino et al. (2014) even suggested that some 500 m² ponds could sequester up to 1,000 kilograms of carbon annually—roughly equivalent to the emissions from a car over the same period.
Although ponds occupy an almost negligible share of the UK’s land area compared with grasslands (0.0006% versus 36%; Carey et al., 2005), their high sequestration rates mean their overall contribution is far from insignificant. Their role in addressing climate change should not be underestimated.