Scientists see Scottish seaweed as green energy source

30 October 2008

Seaweed farms off Scotland's coast could help the country cut its carbon emissions, according to research by the Scottish Association for Marine Science (SAMS).


Such farms could produce sustainable biofuel while avoiding the problems of producing it on dry land using crops like willow. One of the most serious problems is that growing crops for biofuel takes up agricultural land that could be used for food, driving up food prices. Biofuel crops' heavy use of water is also a concern, and Scotland's cool, wet climate is poorly-suited to growing energy-rich crops.

Seaweed could get round these problems. "Marine algae offer a vast renewable energy source for countries around the world that have a suitable coastline available," the paper's authors write.

Biofuel is a potentially valuable alternative energy source because it is carbon neutral. Plants absorb carbon from the air as they grow; when burned, that carbon goes back to the atmosphere. So unlike fossil fuels, biofuel use doesn't add to the net amount of carbon in the atmosphere.

Fuel that doesn't cause carbon emissions could be a valuable tool in achieving the UK government's recently-announced goal of cutting emissions to 20% of 1990's levels by 2050.

The idea is that kelp would be harvested and placed in a large digester to be broken down by bacteria to form methane or ethanol. This could then be burned for electricity or heat. Comparatively few residues remain - seaweed contains much smaller quantities of tough lignin and cellulose than land plants - but what is left over at the end can be used as a fertiliser.

The report, entitled 'The potential of marine biomass for anaerobic biogas production', suggests that pilot programmes be set up in the shallow waters of Scotland's west coast to test the idea. These would probably involve floating rafts, with seaweed growing on surfaces suspended beneath.

Harvesting kelp forests

Seaweeds are extremely productive plants, with natural stands of brown kelp thought to produce between 16 and 65 kilos of biomass per square metre each year - a great deal compared to land plants like sugar cane, which produces just 8-18 kilos in the same area.

Getting these harvests would probably involve developing some kind of aquatic version of a combine harvester so that banks of kelp could be cut quickly and without too much human input.

Wild seaweed could be a good starting-point, though. One survey suggests there is around 8,000 square kilometres of potential seaweed habitat in Scotland's sub-littoral waters - the area between the low tide mark and the edge of the continental shelf - though only around 1,000 square kilometres of this had enough seaweed growing for commercial harvesting to be viable.

Kelp forests are dense and fast-growing so they should have no problem recovering from periodic harvesting. Norway has similar seaweed stocks to Scotland, and harvests 130,000-180,000 tonnes per year sustainably.

Another benefit suggested by authors Maeve Kelly and Symon Dworjanyn is that the seaweed farms would provide valuable habitat for marine animals, helping increase biodiversity.

SAMS did the research on commission from The Crown Estate, which owns most of the seabed as far as 12 nautical miles off the coast and hopes to take advantage of the opportunities for seaweed harvesting.

"Given Scotland's rugged western coastline and island groups, and relatively clean seas, it is sensible to examine the farming of seaweeds and sustainable harvesting of natural supplies as a source of energy, to heat our homes and fuel our vehicles," says professor Mike Cowling, science and research manager at The Crown Estate.

"Heating and transport make up around three quarters of our energy use so it's vital that we find new ways of meeting that demand," he added.

Scotland can provide for much of its energy needs with sources like wind, rivers and wave power. But biofuel from seaweed could let it diversify its energy supply even further.

Seaweed harvesting is a traditional activity in many parts of Britain; during the 17th and 18th centuries, countries including France, Scotland and Norway had flourishing kelp industries, though many, including Scotland's, did not survive the twentieth century.

In the US, though, commercial research continued throughout much of the last century, and today kelp is harvested on a massive scale in China and elsewhere in east Asia.

The idea isn't without its potential problems. For example, it's not certain how far the public will accept the farming of large areas of the sea. But the researchers write that the process is likely to have a much smaller impact than current exploitation of the sea via the fishing industry.

They write that "the large-scale culture of seaweeds may prove to be a relatively environmentally inert practice, or even to be beneficial in terms of the sequestering of carbon, providing habitat for fish, increasing biodiversity and extracting nutrients of anthropogenic, agricultural or aquacultural origin from the marine environment."