WILDLIFE is returning to a Spanish valley two years after it was flooded by six million tons of toxic chemicals from Europe's worst mining dam disaster, the geographers' conference was told yesterday.
But the effects of the heavy metals and acid from the dam at Aznalcollar, near Seville, were still likely to be evident in 20 to 50 years, said Jonathan Turner, of the University of Wales, Aberystwyth.
The Coto Doñana, Europe's biggest wetland, is a sanctuary for the Iberian lynx and rare birds such as the Spanish imperial eagle. Thirty miles of river and farmland were devastated by the spill from the Aznalcollar pyrites mine, one of two worked since Roman times for copper, iron and lead.
Speaking at the Royal Geographical Society/Institute of Geographers' conference in Plymouth, Mr Turner said the valley of the Guadiamar river and its tributary, the Agrio, looked "like the battlefield of the Somme".
Millions of fish were wiped out and birds such as the purple heron, avocet, marbled teal and black-winged stilt were poisoned. Swallowing one spoonful of the waste would have been fatal to humans.
Last year some birds including white storks, egrets, flamingoes, black kites and spoonbills suffered birth defects from the residue still in the sediment. A huge cleaning operation was mounted around the mine operated by Boliden Apirsa, a subsidiary of a large Toronto-based company.
The Andalucian authorities and the company scraped up 10 million tons of topsoil and the thick black mud which had spread over olive and citrus groves. Mr Turner said Tamarisk trees and other vegetation were also stripped off, transforming the valley beyond recognition.
The spoil, which contained traces of cadmium, mercury and antimony, has been dumped down a disused mine shaft. There it is naturally contained by the geological formation of the region.
Mr Turner said the whole valley, even the worst hit areas, was now improving markedly. He said: "Nature has a remarkable way of coming back. But the full legacy of the spill will be realised only in 20 to 50 years."
In the upper reaches of the Guadiamar, which have been scraped five times wider than the channel was before, reeds are beginning to regenerate and this will help to clean the system. Last summer there were dragonflies, grasshoppers and frogs even beside the most polluted reaches of the Agrio nearest the dam.
Mr Turner said that the Spanish authorities should be commended for their quick reaction to the crisis. They succeeded in containing the toxic spate at the borders of the Coto Doñana national park, a world heritage site, and prevented the waste from reaching the fish farms and shrimp fisheries at the mouth of the Guadalquivir river, into which the Guadiamar flows.
Metal concentrations were declining as clean silt overlaid contaminated sediments, but pollution was still being washed downriver and it was not yet clear how much it would affect the fisheries in the sea. Mr Turner said that, upriver, he had seen fish swim to the confluence of the Guadiamar and the polluted Agrio and swim away again. There were still no fish in the Agrio.
Mr Turner said there were areas in Britain, in the Tyne and the Ystwyth valleys, where the ground was even more polluted from past lead mining. He said: "Yet they are grazed happily by sheep. We have got on with life, although there is this chemical time bomb in the environment."
The Spanish disaster has a silver lining. The authorities have fenced off a half-mile wide green corridor along the Guadiamar and are acquiring the polluted land, which is still not safe to farm, through compulsory purchase.
They are hoping to create a link with the Sierra Morrena mountains in the north for the endangered Iberian lynx, of which there are only 500 left in Spain and 50 in Portugal. Part of the reason the lynx, Europe's largest indigenous cat, has been in long-term decline is that its populations have become fragmented.