Calaminarian grassland mitigation in the North Pennines

Location: River West Allen, Northumberland                                     Client: The Coal Authority

Project: Water and Abandoned Metal Mines programme

Challenge

When metal mining activity ceased in the UK, many of the mines were abandoned and left an environmental legacy. The Water and Abandoned Metal Mines programme which began in 2017, seeks to tackle pollution entering the river network from these abandoned mines.

The Water and Abandoned Metal Mines Programme (WAMM) is a partnership between the Environment Agency, the Coal Authority and the Department for the Environment, Food and Rural Affairs (Defra). The Programme aims to support the Government’s 25 Year Environment Plan and River Basin Management Plans by implementing measures to address severe chronic river pollution and deliver a cleaner water environment for people and wildlife.    WAMM Programme 2019

Read more about our wider involvement in this project here: Water and Abandoned Metal Mines (WAMM) programme

Two of the WAMM programme sites are on small rivers in the Northern Pennines at Carrshield and Garrigill which both drain into the River South Tyne.

For each of the abandoned mine sites, the programme needed to consider the historic features, nearby designated sites (North Pennine Moors SAC and SPA, and Tyne and Allen River Gravels SAC), Sand Martin nesting colonies, upland Water Vole populations and presence of the internationally important calaminarian grassland.

The calaminarian grassland across the sites contained a number of rare and notable species which are tolerant of high levels of heavy metal contamination in the soils. These include:

  • Alpine Penny-cress Noccaea caerulescens
  • Spring Sandwort Minuartia verna
  • Pyrenean Scurvygrass Cochlearia pyrenaica
  • Mountain Pansy Viola lutea
  • Moonwort Botrychium lunaria
  • Pale Thread-moss Bryum pallens
  • Green-tufted Stubble-moss Weissia controversa
  • Dense Fringe-moss Racomitrium ericoides
  • A metal-tolerant ecotype of Thrift Armeria maritima which is rapidly being lost from other sites.
Pyrenean Scurvygrass - Calaminarian grassland mitigation project
Pyrenean Scurvygrass

Solution

We worked closely with our stakeholders at Natural England, the North Pennine AONB Partnership and Historic England, to find designs that protected the ecology, heritage and landscapes of the sites.

Our ecologists worked with the JN Bentley site team and the Coal Authority to find ways of minimising impacts to the rare grassland species, first by avoiding areas of good quality calaminarian grassland and secondly by implementing a series of bespoke mitigation measures.

We also worked closely with calaminarian grassland expert, Dr Janet Simkin, to develop mitigation measures and monitor their success. We developed a range of measures tailored to each site depending on the species present, the nature of the works and the likely impacts.

At Carrshield the mitigation included translocation of Alpine Penny-cress from small calaminarian islands in the river to allow the creation of a fish pass as well as temporary removal and subsequent replacement of rocks supporting colonies of rare lichens. At Garrigill, turves containing the special ecotype of Thrift were carefully lifted, stored and replaced on a reprofiled slope once a collapsed culvert had been replaced. This preserved a significant part of the population of this species that had developed on the slopes above the collapsed culvert, along with other metallophytes, and provided a seed source for recolonisation.

Lifting turves - Calaminarian grassland mitigation project
Lifting turves at Garrigill

Our mitigation solutions for both sites were simple and required little technology or specialist equipment – relying on contractors using machinery already present on-site and hand tools, who worked closely with the JBA ecologists to achieve the best possible outcome. This meant the proposals were readily implemented and entailed little additional extra cost.

Benefit

Our approach allowed the area’s natural character to be retained whilst maximising the areas of calaminarian grassland preserved, including creating areas of re-profiled substrate to allow the habitat to expand.

At Garrigill for example, the turves translocated in 2018 have bedded in exceptionally well; within 12 months they had the appearance of natural vegetation. Populations of all metallophyte species persisted with the Thrift surviving well.

Monitoring of the calaminarian grassland in 2020 and 2021 has shown positive results, and monitoring will continue annually for 10 years to assess the success of the mitigation work.

Overall, the project has successfully delivered effective surface water management, whilst retaining much of the original calaminarian grassland and creating areas for expansion of this rare and precious habitat to support local plants and wildlife.

Want to know more?

Contact Steven Heathcote for more information about our ecology work on this project and visit our Environmental Services webpage.



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