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Ů��С��Ƶs are rising the dead. Well, almost. Plants discovered in “ghost ponds” are being revived after lurking underground as dormant seeds for up to 150 years.

These so-called ghost ponds are formed when agricultural land expansion means that existing ponds are filled in, and literally buried alive, says Emily Alderton, at University College London (UCL), who led the study.

To expand a field, farmers commonly remove hedgerows then use the uprooted plants and soil to fill up any ponds. This happened at the site Alderton’s team studied in Norfolk, UK.

“Small ponds were not drained, but were filled in while they were still wet. We think this is likely to have contributed to the survival of the seeds buried within the historic pond sediments,” she says.

These buried ponds can often be seen as a ghostly mark on the landscape – a damp depression, change in soil colour, or patch of poor crop cover, where the ground never quite dries out, says Alderton.

“We also suspected that ghost was the right word as it hints at some form of life still hanging on and this is exactly what we have,” says co-author Carl Sayer, director of the UCL Pond Restoration Research Group. “The species that lived in the past pond are still alive, dormant and waiting!”

Buried treasures

The team estimates that there are around 8000 of these ghost ponds in Norfolk County alone, and as many as 600,000 more may be buried across England’s agricultural landscape.

To locate these buried treasures, researchers often use Ordnance Survey maps and other historical records, which reveal the location of former ponds that have since been converted into agricultural land.

Once researchers locate a ghost pond, and obtain permission from the farmers, they can use an excavator to dig out the metre or two of soil that usually covers it.

So far, the team has dug out three ghost ponds, all from farmland in Norfolk, and “resurrected” a total of eight aquatic plant species. These particular plants are commonly found in the landscape, but Alderton thinks that further ghost pond hunting in other areas could reveal surprises.

“Given the range of different seed types that we found capable of germination after 150-plus years, it could be reasonable to expect that ghost ponds could provide suitable reservoirs of rare or even extinct species,” says Alderton.

What’s more, ghost ponds could reveal dormant animal species. The team found resting eggs from two crustacean species, although they have not yet assessed their viability.

“This study is fascinating because it demonstrates not only a new way to repair the damage that we have done to the environment, but also the resilience of some species,” says Christopher Hassall at the University of Leeds.

“For plants to grow back after being buried for over 150 years is remarkable. Ponds are often neglected compared to lakes and rivers because of their small size, but they punch above their weight in terms of the number of species that they contain,” he says. “It is great to see a successful conservation effort that is bringing back some of these lost habitats.”

Sayer is excited about the prospect of resurrecting species that are locally or nationally extinct in the future. “It is a very positive conservation message – a rare positive,” he says.