4.4

Water Pollution

The addition of a substance to an ecosystem faster than it can be rendered harmless, causing adverse impacts on environmental and human health.

Point Source Pollution

The release of contaminants from a single, identifiable origin, such as a factory discharge pipe. This type is generally easier to monitor and control.

Non-point Source Pollution

The release of contaminants from diffuse, multiple origins over a wide area, such as agricultural run-off. This type is difficult to monitor and manage.

Domestic Sewage

Wastewater from household activities that contains pathogens, organic matter, and nutrients like nitrates and phosphates from detergents.

Agricultural Run-off

A major non-point source where water flows over farmland, carrying excess fertilizers (nitrates, phosphates) and pesticides into aquatic ecosystems.

Industrial Effluent

Wastewater discharged from factories, often a point source for heavy metals (mercury), toxic chemicals (PCBs), and heated water.

Thermal Pollution

The degradation of water quality by any process that changes ambient water temperature, typically from the release of heated water from power plants. This reduces dissolved O2 levels.

Dissolved Oxygen (DO)

The amount of gaseous O2 molecules present in a body of water, measured in mg/L. It is essential for the respiration of most aquatic life.

Biochemical Oxygen Demand (BOD)

An indirect measure of organic contamination, defined as the amount of dissolved O2 needed by aerobic microorganisms to decompose organic matter in a sample. A high value indicates poor water quality.

Turbidity

A measure of the lack of clarity in water due to suspended particles. High levels reduce light penetration, hindering photosynthesis. Often measured with a Secchi disk.

Total Suspended Solids (TSS)

The amount of solid particles that are not dissolved but remain held in the water column. High concentrations can clog fish gills and smother habitats.

Macroplastics

Large, visible pieces of plastic debris like bottles and fishing nets. Threats include entanglement, ingestion, and habitat destruction.

Microplastics

Plastic particles smaller than 5 mm, created by the breakdown of larger debris. Easily ingested by organisms and readily enter food webs.

Impacts of Microplastics

1. Ingestion: Consumed by organisms at all trophic levels, leading to bioaccumulation.

2. Toxin Transport: Adsorb and carry other pollutants (pesticides, heavy metals), delivering them to organisms in the food web.

Bioaccumulation

The build-up of a substance in a single organism over its lifetime because it is absorbed faster than it is lost.

Biomagnification

The increasing concentration of a toxin at successive trophic levels within a food chain.

Eutrophication

The enrichment of a body of water with nutrients, primarily nitrates and phosphates, which stimulates excessive growth of algae and leads to oxygen depletion.

The Process of Eutrophication

A sequence:

1. Nutrient loading.

2. Algal bloom.

3. Sunlight blocked, submerged plants die.

4. Algae die and sink.

5. Aerobic decomposers consume O2.

6. Water becomes hypoxic/anoxic.

7. Biodiversity loss ("dead zone").

Hypoxia

A state of very low dissolved oxygen concentration in a body of water that is detrimental to aquatic organisms.

Anoxia

The complete absence of dissolved oxygen in a body of water, creating a "dead zone" where most aerobic organisms cannot survive.

Eutrophication Management: Level 1

Altering human activity to reduce pollutants at the source (e.g., using phosphate-free detergents, precision agriculture).

Eutrophication Management: Level 2

Controlling the release of pollutants into the environment (e.g., creating buffer zones, tertiary sewage treatment).

Eutrophication Management: Level 3

Restoring and cleaning up impacted ecosystems (e.g., dredging sediments, aerating the water body).