Once upon a time our countryside was peppered with ponds. Watering holes for horses and cattle, marl and clay pits for extracting building materials and fertilising the land, and clay-lined dew ponds for retaining water on chalky soils, to name just a few varieties. However, with pressure to increase food production, combined with a decline in the number of uses for ponds, many of our ponds in open farmland have now been lost.
Some remain in the landscape, barely clinging on, as they become choked with trees and vegetation which there is no longer any need to remove. These are often larger ponds which would be too difficult to fill in, and as such are left to their own devises, gradually disappearing under years of leaf litter build-up. These sad, dark, pits are not uncommon in counties like Norfolk, where they are easily visible to passers by, marked by their dense surround of trees (predominantly willow). Although these ponds still exist, and may hold water for many years, their ‘function’ in the landscape as wildlife havens is almost completely lost. Years of anoxic sediment build-up makes these abandoned ponds inhospitable to most plants, which in turn means there is often no habitat for invertebrates within the water. Combined with very low oxygen and light levels, (due to the heavy shading and decomposition of large numbers of tree leaves), I have found it is not uncommon to conduct an invertebrate survey of such ponds and find only water lice. With little in the way of aquatic life, these overgrown ponds are of limited value to damsel and dragonflies (poor hunting), amphibians (no where to lay eggs), or birds (no insects to feed on).
A large proportion of ponds however have been completely lost from the landscape, filled in during agricultural land reclamation. Many remain visible as damp, circular crop marks, or bowl shaped depressions out in the fields. These are the “ghost ponds” of the countryside.
Ghost ponds are of particular interest to us for several reasons; During land reclamation, pond sediments are buried under the topsoil. Work in the field of resurrection ecology shows that seeds / eggs of some aquatic organisms (including the oospores of ecologically important stoneworts), remain viable on decadal to centennial timescales (Bonis & Grillas 2002, Lambert et al. unpublished data). Thus, a strong possibility exists that species of the past, many of which are rare and protected today, could be returned by re-excavating ghost ponds. These resurrected ponds could make a significant contribution to regional aquatic biodiversity and rare species conservation in lowland agricultural regions.
Currently two major approaches are used in UK pond conservation; pond creation (excavation of new ponds), and pond management (de-silting and tree removal from existing ponds). Resurrecting ghost ponds however has been completely un-explored, which seems a tremendous shame. Not only does ignoring ghost ponds in aquatic conservation strategies mean we are missing out on the potentially valuable role of the historic seed bank, but because ghost ponds are often still visible and often make poor agricultural land (it is very difficult to completely drain a pond and stop it collecting water), re-digging these sites saves giving up potentially more productive land for digging a new pond from scratch.