More houses = green mud?

Surveying for seagrass on the Solent coast © Lianne de Mello

As the Solent shows signs of being suffocated by nutrient-loving algae, should green mud = red light to development?

The Solent is like a banqueting table for migrating birds which flock here from across the northern hemisphere en-route to sunnier climes or to benefit from our mild winters. It is also a 3D super-ecosystem abundant with invertebrates which live in and on the nutritious mud, seagrass beds which protect young fish, store masses of carbon, and help prevent erosion.

But the Solent is unwittingly being exposed to a large-scale long-term experiment: what happens if we turbo-charge the ecosystem by giving it too many nutrients? Many local people will now be familiar with a lurid green crust of algae covering mudflats at low tide. Rather like a green fishpond or aquarium, this tells us there is an imbalance – too many nutrients in the system which, we know enough about the ecology to say, is harmful to the wildlife of the Solent. These mats of algae form a layer over the mud which can prevent oxygen getting through to the animals in the sediment causing mass mortality especially in hot weather. They also form a barrier to many birds which rely on probing the mud or picking off tiny invertebrates from its surface. Lastly, these mats can smother some of our most special yet threatened habitats: seagrass beds and saltmarshes, choking them to death and risking erosion.


Black-tailed godwit

John Windust

So where do all these nutrients come from? Nitrates are the main problem and they get washed into the Solent from agriculture, waste water treatment discharge, and runoff from roads and built-up areas.  We are getting slowly better at reducing inputs of nitrates to farmland, but our chalk geology means it will take decades for high levels from the post-war agricultural boom to flush-through. Many of our roads and built-up areas were designed to get waste water off and into drains (and ultimately the Solent) as quickly as possible. This runoff is a toxic and nitrate-laden cocktail. We are getting better at reducing runoff from new designs of house building, but so much of our urban fabric is ‘old tech’.

The issue which remains, and is causing much controversy at the moment in South Hampshire, is the nitrate which comes from dwellings (from sewage, even after treatment) and the predicted input from new house-building making nitrate pollution in the Solent worse not better. We salute the lead taken by Natural England in calling-out this issue in the light of recent rulings from the European Court of Justice (to which we are still subject, until we have our own, essential environmental watchdog codenamed the Office for Environmental Protection). But this has led to a complete lockdown in permissions for new housing developments in certain districts, and this is causing political ructions given the intense pressure from national government for new house-building in our area. We believe that all new development needs to be ‘nutrient neutral’ as a minimum to stop making the issue worse.

Building Houses by Jonathan Oakley

Building Houses by Jonathan Oakley

So lots of people are working out a solution to the problem: how can the nitrate from sewage from new homes be eliminated or offset by mitigation? There are actually lots of ways in which this can be done such as taking some bits of land out of intensive arable production (creating fallow or re-wilded areas will do the job nicely). Or we can upgrade our waste-water treatment works to a higher standard, with improved treatment of urban runoff as well. All these can help achieve the holy grail of nutrient neutrality and allow development to proceed legally again.

But there comes a point when surely we must ask: is this level of house-building sustainable? Hundreds of thousands of new homes planned for South Hampshire will, unless there is very big investment in cleaning-up our act, continue to damage our wonderful Solent and its wildlife. Is that a price worth paying for more prosperity?