Human Impact on the Environment

Pollution is the contamination of the environment with harmful substances (pollutants) from human activities.

Types of pollution:

• Water pollution - sewage, fertiliser runoff, industrial effluent. Leads to eutrophication and reduced water quality.
• Air pollution - burning fossil fuels releases CO₂, SO₂, NOₓ. Causes acid rain, smog, respiratory disease, and climate change.
• Soil pollution - pesticides, heavy metals, illegal dumping. Reduces soil fertility and harms soil organisms.

Eutrophication is a critical process to understand:

1. Excess fertiliser (nitrates/phosphates) washes into waterways
2. Algae multiply rapidly → algal bloom
3. Algae block sunlight → aquatic plants die
4. Dead algae and plants decomposed by bacteria
5. Bacteria use up dissolved oxygen → BOD (Biochemical Oxygen Demand) increases
6. Fish and aquatic organisms suffocate and die

Bioaccumulation is when toxins (e.g. DDT, mercury) build up in an organism's body over time. Biomagnification is when these toxins increase in concentration at each trophic level of a food chain.

Biodiversity loss is caused by:

• Deforestation - cutting down forests removes habitats and reduces carbon sinks
• Invasive species - non-native species outcompete native species for resources
• Pollution - contaminates habitats, killing sensitive species
• Overexploitation - overfishing, overhunting deplete populations
• Climate change - alters habitats faster than species can adapt

Conservation strategies:

• Protected areas - national parks, nature reserves, SACs (Special Areas of Conservation)
• Seed banks / gene banks - preserve genetic diversity for future use
• Captive breeding programmes - e.g. Wild Ireland Sanctuary for wolves and lynx
• Rewilding - allowing farmland to return to its natural biodiverse state
• Afforestation - planting trees to increase carbon sinks and restore habitats
• GPS and satellite tracking - monitoring endangered species movements

Sustainability means meeting present needs without compromising future generations. This involves reducing waste, using renewable energy, sustainable farming, and protecting biodiversity.

Food security means all people having access to safe, nutritious food at all times. Threatened by climate change, biodiversity loss, and soil degradation.

An invasive species is a non-native plant, animal, or microbe that spreads rapidly in a new habitat and outcompetes native species. Because native predators and diseases have not co-evolved with the newcomer, its population can explode unchecked.

• Grey squirrels in Ireland outcompete the native red squirrel for food and carry squirrelpox, to which reds have little immunity.
• Japanese knotweed smothers riverbanks, breaks through tarmac, and prevents native plants from growing.
• Zebra mussels block water intakes and strip lakes of the plankton other species depend on.

Overfishing and overharvesting reduce fish stocks and their genetic diversity. Bluefin tuna, cod, and many shark species are now under strict quotas because populations dropped below the point where they could naturally recover.

Poaching targets high-value species - rhinos for horn, elephants for ivory, pangolins for scales. Only two Northern white rhinos remain (both female), showing how quickly a species can vanish.

Disease is spreading faster in a warming, more connected world. Ash dieback, caused by the fungus Hymenoscyphus fraxineus, is killing native ash trees across Europe. The chytrid fungus Batrachochytrium dendrobatidis has driven amphibian species to extinction on every continent where frogs live.

Pesticide overuse harms non-target species. Neonicotinoids applied to crops have been linked to sharp declines in wild bees and other pollinators - a serious problem because many food crops depend on insect pollination.