Eutrophication

A major problem with the use of fertilisers occurs when they're washed off the land by rainwater into rivers and lakes. The resulting increase of nitrate or phosphate in the water encourages algae growth, which forms a bloom over the water surface. This prevents sunlight reaching other water plants, which then die. Bacteria break down the dead plants and use up the oxygen in the water so the lake may be left completely lifeless.

The main effects caused by eutrophication can be summarized as follows:

1. Species diversity decreases and the dominant biota changes

2. Plant and animal biomass increase

3. Turbidity increases

4. Rate of sedimentation increases, shortening the lifespan of the lake

5. Anoxic conditions may develop