Humans and the environment

04.23.2020
08:57:43

Biology/Grade-10- Today’s topic - Eutrophication- course book-pages 303 and 304.
Main points-
When nitrates and phosphates from farmland and sewage escape into water they cause excessive growth of microscopic green plants.
This may result in a serious oxygen shortage in the water, resulting in the death of aquatic animals – a process called eutrophication.

A major problem with the use of fertilisers occurs when they are washed off the land by rainwater into rivers and lakes.
This leaching causes an increase in the levels of minerals such as nitrate and phosphate in the water, a process called eutrophication.

Eutrophication encourages the growth of algae. These form a green bloom over the water surface, preventing sunlight reaching other water plants.
These plants die because they are unable to carry out photosynthesis.

Bacteria decompose the dead plants, respiring and using up the oxygen in the water as they do this.

The low oxygen levels make it difficult for aquatic insects and fish to live, and eventually the lake may be left completely lifeless.

The degree of pollution of river water is often measured by its biochemical oxygen demand (BOD).

This is the amount of oxygen used up by a sample of water in a fixed period of time.

The higher the BOD, the more polluted the water is likely to be.

It is possible to reduce eutrophication by using:

Detergents with less phosphates.
Agricultural fertilisers that do not dissolve so easily.
Animal wastes on the land instead of letting them reach rivers.







Homework worksheet is given on Humans and the environment.