A paper published in Nature by Bradley Cardinale from the University of Michigan suggests that biodiversity in aquatic ecosystems can help to buffer a system against increased nutrient input.
One of the major impacts of human activities on aquatic ecosystems is increased input of nutrients like nitrogen, from runoff from agriculture, or by sewage contamination. This can create problems like eutrophication and dead zones, where there is too little oxygen in a body of water for species to survive.
What Bradley did was to take 8 different species of algae and diatoms, and introduce them to experimental ‘streams’ where the heterogeneity of the environment – so things like the water speed and levels of disturbance – could be manipulated. When the species were able to all occupy different niches – so each perform different functions within the ecosystem, the uptake of radioactively labelled nitrate was higher than when biodiversity was experimentally reduced.
The unfortunate fact, which Bradley does point out in the paper, is that increased nutrient input to an aquatic system does actually reduce biodiversity, which given these results is more worrying. So as biodiversity is lost, the ability of an ecosystem to deal with and sequester extra nutrients like nitrogen will decrease.
Although this was a freshwater study, nutrient runoff in coastal areas is a major problem for marine species too, so a possible future direction of research could be whether the same effect would be seen in a marine ecosystem.