ADD nutrients and a lake’s ecosystem flourishes – or so the thinking goes. But new work suggests that light, rather than food, is the key to lake productivity.
The idea that productivity is limited by the availability of nutrients is based mainly on studies in surface waters. So when Jan Karlsson from Umeå University in Sweden and his colleagues studied 12 lakes in Sweden, they measured the productivity of the whole ecosystem, from deep-water algae to fish.
Light levels dropped sharply with depth in the lakes but they all contained enough nutrients to be highly productive. However, the less the light…
