7.A farmer sprays some fields with nitrogen fertilizers. Soon afterwards, the fertilizer is washed off by heavy rain into a nearby lake. Then, a few weeks later, most of the organisms in the water die.The list includes the main stages of this process.
P Light is blocked from deeper water plants.
Q Plants cannot photosynthesise and die.
R Algae multiply rapidly on the lake surface.
S Oxygen levels fall and aerobic organisms die.
T Aerobic bacteria feed on dead plants.
In what order do these stages occur?