Conserving biodiversity could help shield waterways against nitrogen pollution, says a study that showed how streams with more species are better at removing excess nutrients from water.
The findings imply that developing countries that keep rivers and lakes species-rich could save money on water treatment, Bradley Cardinale, author of the study and an aquatic ecologist from the University of Michigan, United States, told SciDev.Net.
The study, published in Nature yesterday (7 April), is the first rigorous analysis of how biodiversity improves water quality, Cardinale said.
Mopping up nitrogen compounds — a major cause of water pollution — released from agricultural fertilisers and waste, human sewage, and fossil fuel burning, is an important goal for environmental policy.
Scientists have long known that ecosystems with more biodiversity are better at mopping up pollutants like nitrogen. But there was little experimental evidence for why this happens. A leading theory is that different species make maximum use of nutrients because they each fill a unique biological habitat — niche.
Cardinale tested this theory in a laboratory experiment on algae.
He grew one to eight species of common algae in 150 artificial river channels. Some artificial streams had a single habitat, whilst others mimicked several natural habitats created by differences and disturbances in water flow in the streams.
Cardinale found that nitrogen uptake increased in more biodiverse streams, as long as there were varied habitats available in the stream. One stream with eight species removed nitrogen 4.5 times faster than the average for a single species stream, implying also 'that biodiversity may help to buffer natural ecosystems against the ecological impacts of nutrient pollution'.
'Nature is much like a sports team. Each member has a different, but complementary, role to play,' Cardinale said. 'And, as each of the players becomes better, they make for a more efficient team.'
He said it was difficult to know how far to extend the conclusions from this laboratory study but added that these results would probably apply to any habitat with partitioned niches.
Emily Stanley, a freshwater ecologist from the University of Wisconsin-Madison, United States, said: 'These sorts of controlled lab experiments are important tools for suggesting how nature might work. Cardinale has challenged us to see if this is the way things actually work in real world settings.'
And John Matthews, director of freshwater and adaptation at the non-governmental organisation Conservation International, said: 'This study strengthens the arguments for how protecting biodiversity can be used to promote sustainable development'.
But he added that these findings will probably not be enough to prompt more action on conservation of biodiversity.