Mine Pollution and Salt Marsh Vegetation Communities

Estuaries within Cornwall have been accepting metal-rich tailings and water from mining since the Bronze Age. Previous work at Camborne School of Mines has indicated that the floristic composition within contaminated salt marshes differs from characteristic British assemblages as defined by the National Vegetation Classification (NVC). Two communities not listed in the NVC system were discovered during initial surveys. The NVC SM8 community, normally dominated by Salicornia, was found to also contain significant amounts of Spergularia media within the heavily polluted marshes of Restronguet Creek and Copperhouse. An Armeria maritima-dominated community was also to be found in these metal-enriched salt marshes, however, this plant was co-dominant with Plantago maritima in the moderately contaminated marshes of Lelant and the Gannel and not present at all in the Camel, which has been subject to only slight mining activity.

Using Canonical Correspondence Analysis (CCA), vegetation abundance data was compared with metals and other variables within the sediment. Results indicated that the Salicornia-Spergularia community grouped with Puccinellia and bare ground and that this cluster was more related to conditions encountered by pioneer species, rather than metal pollution. Armeria, however, appeared to exist in a successional relationship with Plantago. It was hypothesised that Armeria is outcompeted by Plantago in marshes with low metal loadings. Moderately high metal content results in a loss of competitiveness by Plantago, allowing Armeria to co-dominate. In extremely metal-rich estuaries, however, Plantago is unable to survive, allowing Armeria to colonize the mid-marsh.