Chatsworth’s Operations Team, in collaboration with licenced expert consultants, has undertaken investigative works to the Cascade in preparation for its restoration.
One of the biggest challenges when preparing for any kind of construction work is gaining an accurate understanding of the local ecosystem and the species that inhabit it.
Until recently, wildlife surveys would involve physically looking for different species, now DNA sequencing technologies can be harnessed to trace microscopic DNA samples – especially in water.
As creatures shed dead skin cells or mucus, they leave eDNA (environmental DNA) which indicates the presence of a species, even if it cannot be seen.
Fortunately, at the Cascade, there is no evidence of bats or great crested newts whose resting or breeding places are protected. Tests on water from the bottom of the Cascade have also eliminated any presence of the invasive American signal crayfish. This gave the team hope that colonies of native white-clawed crayfish may have flourished.
The white-clawed crayfish is the only crayfish native to the British Isles and is the largest freshwater invertebrate in the UK. Over the last decade, it is estimated that numbers have declined by as much as 80%, making it an endangered species at risk of possible extinction.
The decline is largely attributed to the rising population of the signal crayfish, which compete with the native variety for food and homes, and carry diseases for which the white-clawed crayfish has no immunity.
Thankfully, a trapping exercise brought positive results, revealing a large number of white-clawed crayfish residing in underwater refuges on the sides of water channels.
Over a week, the team successfully trapped nearly 100 of the three-inch-long crayfish. These have been carefully removed and rehomed in the Willow Tree Pond until construction work on the Cascade is complete. The Willow Tree Pond is also freshwater, and has been tested and shown to be a suitable temporary ark site for the native crayfish, with no signal crayfish detected.
The team will continue a programme of trapping and relocation until they are confident that as many of the native crayfish as possible have been relocated. Working with the Midland Crayfish Partnership, they will be surveying other waterbodies in the park to help identify more potential ark sites where the native crayfish can thrive.
In addition to ecological investigations, the team commissioned works to assess the condition of historic repairs from the 1960s and 1980s, particularly to the ground beneath the Cascade, where a considerable volume of water has seeped through creating structural weaknesses.
Early results indicate that these historic repairs are of substantial quality, and can be retained, even if the whole of the Cascade structure has to be removed and re-laid during the restoration.
