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Saturday 14 November 2020

Wonderful wetlands

Oxford is built on a swamp.

The home insurers won’t let you forget that most of the houses are delicately balanced on a tiny strip of land just above the water level, like Noah on a beached ark.

When it rains heavily, the soils saturate and run onto the tarmac, creating rivers occupied by confused looking geese that stream down the streets. Adjacent fields take on the appearance of flooded paddy fields.

But believe it or not, these indomitable wetlands are crucial to the local environment, its habitats, ecosystems, and even the shape of the land. This is because of something called phytoremediation.
Swampland in Oxford. By Jpbowen via Wikipedia Commons.

Phytoremediation, the chemical action of plants on the environment, acts to filter out the nasties and maintain soil integrity. A vast array of wetland plants selectively absorb and store heavy metals that can be toxic to us and other animals, causing changes in mating and nesting behaviour, or causing brain damage like, in humans, lead or Mad-Hatter-famed mercury poisoning.

This is hard to achieve without these specially adapted plants, because putting anything out in nature necessarily means losing control of it and letting it get everywhere – so any manmade remediation techniques have to be super tested and ultra safe. Not only this – but we don’t know where to administer them. Even though they can be toxic, heavy metal concentrations are extremely low, found in billionths and millionths even in very contaminated areas: this makes them extremely hard to identify and monitor. There’s still a lot we don’t know about minerals and how they behave in the environment, especially in the presence of each other. Dissolved in surface waters, metals undergo speciation – changing their charge and what they’re bonded to. This changes their solubility, meaning sometimes they form solids and sometimes they dissolve in different solutions (and travel). This is known as partitioning. This can make their movement and toxicity impossible to predict. We do know that speciation is affected by the concentration of other metals and other ions, like phosphates, but we’re a long way off knowing enough to make predictions about their behaviour.

Wetlands don’t only do their magic on metals, though. They may have a role in remediating organic pollutants, such as those found in medicines and cosmetics. They trap silt and other inorganic sediments, protecting the landscape from erosion and slowing down geological change.

So wetlands may look a sorry sight themselves, but they’re busy keeping our woodlands and beaches looking beautiful for the long term.

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