Negative Impact of Human Activity on an Ecosystem

Urban settlements within the catchment area of mangrove wetlands contribute excess amounts of phosphates, derived from detergents and fertilisers. Large amounts of fertilisers also enter the ecosystem via runoff from agricultural areas. Excess phosphate in the water is a cause of eutrophication, which may lead to algal proliferation, affecting the natural functioning of the ecosystem. Runoff from industrial sites may also introduce heavy metals and chemicals into the wetlands, affecting food webs.

Negative human impacts on the lithosphere include increased rates of sediment deposition and acidification of soils. Sediment deposition is a natural process in mangrove wetlands, however human impacts can increase the rate at which it occurs. If the rate of sediment deposition increases, for example due to land clearing in areas adjoining the wetlands, pneumatophores can become buried, leading to mangrove dieback.

Mangrove wetlands naturally contain acid sulfate soils. Acid sulfate soils only become a problem when exposed to air, as a result of excavation, drainage, or lowering of the water table as a result of other human activities. Once exposed to air, the iron sulfides in the soils react with oxygen to form sulfuric acid. After rain, the acid can be flushed into creeks where the water turns so acidic that fish may be killed. In addition, toxic metals such as aluminium and iron may be dissolved out of the soils by the acid, and leach into waterways, poisoning fish, crabs, and other estuarine organisms.

The introduction of feral animals into mangrove wetlands has impacted greatly on the biosphere. Carnivorous species are not commonly found in these wetlands, so the introduction of foxes and feral cats severely disrupts the food chains and nutrient cycles of the ecosystem by significantly affecting bird populations. Other human impacts on the biosphere include the accumulation of toxic chemicals, and oil spills.

In areas where industrial activity was common, such as the area surrounding Sydney’s Bicentennial Park, the accumulation of toxic chemicals poses a major threat to the health of the mangrove wetland ecosystem. These chemicals can have serious impacts on the bacteria and decomposers responsible for nitrogen fixing and nutrient recycling.

Because mangrove wetlands are found in coastal regions, oil spills from tanker ships are a constant threat. Oil entering the ecosystem from the ocean can smother mangrove pneumatophores, preventing the plant from obtaining oxygen. This leads to mangrove dieback. Oil spills also kill mangrove seedlings, and reduce leaf biomass in surviving trees. Other estuarine organisms such as mud crabs, fish, and worms can also be affected by oil spills. These organisms may be immediately killed, or be affected behaviourally.

Human impacts negatively affect all spheres of the biophysical environment of mangrove wetland ecosystems, making them an ecosystem at risk.