How 1,000 Years of Lead Mining Gave Birth to Banks of Pansies and Pennycress

The Birth of Calaminarian Grasslands

In the weak May sunshine, small purple flowers like mountain pansies and white rosettes of alpine pennycress can be spotted on the banks of the River Allen in Northumberland. This area is a pocket of calaminarian grassland, a rare habitat where specialist plants called metallophytes have adapted to live in soils deeply contaminated by heavy metals, a legacy of over 1,000 years of lead mining.

The Impact of Lead Mining

The grasslands originally evolved in small patches around rocky upland outcrops where veins of lead, cadmium, and zinc had been exposed by the elements. As these began to be mined, a biocrust of lichens and mosses developed that could tolerate toxic wastewater washing over them. Plants such as the spring sandwort – once known as leadwort – and alpine penny-cress began to take hold, along with other tough customers such as sea thrift, bladder campion, and kidney vetch.

The Role of Metallophytes

Despite their delicate appearance, these specialist plants can live in soils 30 times more toxic than most other species can tolerate. As they grow, metallophytes act as “hyper-accumulators”, cleansing the soils that feed them through a process called phytoremediation. This turns the metals they absorb through their roots into complex organic compounds, which are locked away below the surface once the plants die.

The Future of Calaminarian Grasslands

There is a growing debate about whether these human-made meadows should be protected or allowed to gently fade away as they become cloaked in more thuggish plants such as gorse and broom, and the zinc and lead brought by mine-wash became slowly buried beneath a blanket of humus.

The Legacy of Lead Mining

The barren, rocky uplands of the northern Pennines were first mined by the Romans, but the industry reached its peak in the mid-18th century. Today, the landscape is dotted with abandoned workings and spoil heaps; some high up on the moors, others closer to the rivers and the water the industry needed. If you took samples from most of the rivers in the North Pennines, most have got contamination from lead mining in them.