Human Impacts on Ecosystems

A smoky chimney
Copyright Environmental Protection Agency

Humans can have significant positive/negative effects on ecosystems e.g. through pollution, conservation and waste management processes.

1. Pollution - describes any undesirable change in the environment.

• Pollutants are substances that cause undesirable changes.  Most pollution is caused by human activities such as dumping, sewage disposal, litter, radioactivity and noise.
• Natural pollutants include volcanic emissions and smoke from forest fires - although sometimes these fires are caused by human actions.
• Pollution can impact air, freshwater, sea and soil or land.

Types of pollution

• Domestic pollution – household waste.
• Agricultural pollution – use of sprays to control pests and weeds, overuse of fertilisers e.g. nitrogen fertiliser, and disposal of farm wastes such as animal effluent.
• Industrial pollution can cause acid rain, whilst industrial waste can damage rivers.

Ozone depletion – Air pollution example

• Ozone is a gas (O₃) that provides a protective layer above the Earth's surface. It absorbs and protects the earth from incoming UV radiation. Ozone depletion is caused by CFCs e.g. in spray cans, refrigerators, insulating foam and industrial detergents.  Some fire extinguishers (halons) and agricultural sprays (fumigants) also damage ozone, as do emissions from high-flying aircraft.

Effects of ozone depletion

• Ozone absorbs harmful UV radiation from the sun. Increased UV radiation can:
  • damage DNA and lead to skin cancer, eye cataracts (lens in the eye lose transparency) and weakened immunity. 
  • cause damage to agricultural crops and plant life.
  • reduce plankton, thereby reducing available oxygen supplies for aquatic life. This can affect food chains.

Control of ozone depletion

• Decline in use of CFCs allows the ozone to be replenished.  Ozone is formed by the reaction of UV light with oxygen.
• CFCs are now being replaced by HFCs which break down more quickly and do not reach the upper atmosphere.
• Avoid use of sprays or foam products that contain CFCs.
• Fridges should not be disposed of in landfill sites. They should be returned to organisations that will dispose of their CFCs in an environmentally friendly manner.

Global warming

• Carbon dioxide (CO₂) is a greenhouse gas as well as methane, CFCs and nitrogen oxide. CO₂ forms an insulating layer (greenhouse effect) allowing sun to penetrate through the atmosphere but preventing much of it escaping out to space.
• The main source of greenhouse gases from humans is the burning of fossil fuels and deforestation, which reduces photosynthesis processes.

Global warming may cause the following effects:

• Sea levels are currently rising due to ice melting and the expansion of warmer sea water. This increases flood risks in coastal areas.
• Weather patterns may change (e.g. more stormy weather), which in turn will affect wildlife and agriculture.
• It may cause the Gulf Stream to reverse its direction of flow. This would cause very cold water to flow past Ireland and would have a significant impact on our climate.
• Increased crop yield (more CO₂ and higher temperatures for photosynthesis).
• Increased insect population and spread of tropical diseases.
• Decreased amount of water due to evaporation and transpiration (deserts).
• Increased frequency of droughts, hurricanes, cyclones and forest fires.
   

2. Conservation describes the effective management of our existing natural resources. For example, it includes conserving the breeding grounds and habitats of animals near extinction e.g. giant panda in China, corncrake in Ireland.

• Seed banks e.g. National Botanic Gardens and breeding programmes in zoos help to prevent extinction.
• National parks also play an important role in conserving and promoting habitats and wildlife.g. Killarney, Letterfrack, Glenveagh and the Burren.

Conservation Practices

• Fisheries
  • Problems include pollution, overfishing and use of small-mesh nets.
  • Pollution reduces the amount of fish in waters, which can take years to replenish.
  • There is therefore a need to reduce pollution which kills fish and prevents fish from migrating e.g. salmon from reaching breeding grounds.
  • Overfishing can be managed by enforcing fish quotas to ensure that fish stocks can be replenished.
  • The use of large-mesh nets so that young fish can escape and breed can also help to conserve fish.
     
• Fisheries can be monitored by:
  • Taking and analysing water samples
  • Checking fish catches and fishing equipment
  • Sampling fish stocks to calculate their numbers.

3. Waste Management involves preventing pollution and conserving the environment.

• Agricultural waste management
  • Slurry is a liquefied waste material produced by animals - it contains high levels of nitrogen and phosphorus which cause algal bloom.  When these algae die they are decomposed by bacteria which use up the oxygen in the water depleting it for other plants and animals. This addition of nutrients to fresh water is called eutrophication.
  • By controlling the release of nutrients into rivers and lakes water quality can be improved. Slurry can also be stored in leakproof pits. This slurry can then be spread out on dry land in the summer as nutrients for plants.
• Fisheries
  • The wasteparts of fish are neutralised by formic acid, pulped, dried and recycled as fertiliser or pig feed.
• Forestry
  • Waste products include tops of trees, small branches, tree stumps, roots and sawdust.
  • Tops of trees and large branches are converted to sawdust, which can be used to form processed wood e.g. MDF.
  • The remainder of the tree is allowed to decay and return nutrients to the soil.

Problems associated with waste disposal

• Wastes may contain many microorganisms that can cause disease. If not properly treated these microorganisms could be transported by wind or enter drinking water supplies.
• Toxic chemicals released from wastes can enter drinking water supplies. This may also negatively impact plant and animal life in the environment.
• Nutrients released from waste can cause enrichment (eutrophication) of water supplies, which may cause the death of aquatic plants and animals.
• Waste in landfill sites can be unsightly, can attract undesirable scavengers such as rats and gulls, and can produce unpleasant smells.
• Dumping waste at sea leads to ocean pollution e.g. 'plastic islands'.
• Incinerators burn waste at high temperatures. There is a fear that poisonous gases may be released in the process.

Role of microorganisms in waste management

• Landfill sites:
  • Waste is covered with soil. Bacteria and fungi in this break down the organic (biodegradable) materials.
• Sewage:
  • Small quantities entering a river can be broken down by the bacteria and fungi. Large amounts require special treatment before being safely released into rivers or sea.

Primary (physical) sewage treatment

• Screening –  metal grills remove large objects e.g. branches and plastic containers.
• Sedimentation – water stored in tanks and particles such as stones and sand settle to the bottom.  The solid waste that settles out is sludge.

Secondary (biological) treatment

• This describes treatment with bacteria and fungi to break down organic matter. Some nutrients are removed and disease-causing microorganisms are inactivated.
• The sludge is placed in an enclosed tank, in which it is broken down by bacteria. Bio-gas generators collect the methane and may use it as a fuel source to generate electricity for the sewage plant.
• The liquid of the waste passes into large, shallow tanks where up to 98% of the organic waste is broken down by bacteria and fungi. The waste water is normally treated with chlorine to destroy any remaining organisms.

Tertiary treatment

• Sometimes tertiary treatment is used to remove mineral nutrients from the water (very expensive).

Waste minimisation

• Reduce waste at source i.e. reduce packaging of goods (now a charge on plastic bags in many countries e.g. Ireland). Individuals can also help by purchasing loose vegetables and fruit.
• Re-use – reuse carrier bags when shopping, reuse glass bottles, give unwanted clothing to charities.
• Recycle – sort household waste and use Bring Banks/Collection Schemes.
• Compostable bin – vegetable peelings and garden waste. The compost can be added to soil to improve the growth of plants (The Physics Teacher, 2018).