One of my favourite places in County Durham is, paradoxically, also one of the most polluted. When I first visited, over thirty years ago, the stretch of the River Team pictured below was heavily polluted from several sources, including sewage works, abandoned coal mines and a large battery factory, just a couple of kilometres upstream. The latter made the river an ideal open-air laboratory for work that we were doing at the time on the effect of heavy metals. The River Team, like many other rivers in this part of County Durham, flowed through a gorge incised into the landscape. The steep slopes of the gorge made agriculture and settlement impractical so locations such as this are blessed by beautiful wooded valleys (the incised meander at Durham City is the most famous example of these – see “The River Wear in summer”).
Causey Arch crossing the River Team in County Durham, July 2014.
Causey Arch, the bridge in my picture dates from 1726 and is the oldest surviving single-arched railway bridge in the world and is a reminder of the region’s industrial heritage. George Stephenson is a local lad and the Stockton and Darlington Railway, the first public railway to use steam locomotives, is just 50 km to the south. So do not be deceived by the idyllic view of the wooded gorge around Causey Arch: the surrounding area has a high population density and a long history of water-polluting industries.
Although the battery factory that polluted the river in the 1970s and 80s has now closed, the river is still heavily polluted, particularly from a sewage works about a kilometre upstream from where this photograph was taken. There has, however, been one other change since my first visits in the early 1980s: the banks of the river are now thick with the pink-flowered plants of Himalayan Balsam, Impatiens glandulifera. The riverbanks do not just look different, they are also heavy with Himalayan Balsam’s sweet, pungent odour. Ironically, these changes have taken place as the water quality itself has gradually improved.
As the name suggests, Himalayan balsam is not a native plant; it was introduced here in the 19th century for its attractive pink flowers but has escaped from gardens to become a nuisance over much of the country. You can read more about this in Heather’s blog, written in preparation for her trip to the Himalayas later this year. She refers back to Frank Smythe’s classic book “Valley of Flowers” in which he notes that, even in the Himalayas, this plant is often a nuisance weed.
Himalayan balsam, Impatiens glandulifera, growing at Causey Arch, County Durham, July 2014.
My own private gripe with Himalayan balsam is that the tall plants grow just far enough apart to allow nettles to thrive in the gaps. I’ve struggled to get into rivers to collect my samples several times this year already and suffered multiple stings as a result. I have slowly realised that my chest waders, though very hot to wear on a sunny day, are much preferable to bare legs.
There is more about invasive plants in the Plant Invaders episode of Plants: from Roots to Riches on the BBC iPlayer. Curiously, Himalayan balsam is not mentioned in this programme but it is worth a listen nonetheless.