Pollution's Impact: Pond Ecosystem's Struggle For Survival

Ponds are susceptible to a variety of pollutants, which can enter the water in many ways, including rainfall, storm events, and direct dumping. The most noticeable kind of pollution is the dumping of rubbish, from old cars to drinks cans. However, the most serious threat to ponds is chemical pollution, which can come from pesticides and fertilisers used in modern farming methods. This can poison wildlife and cause eutrophication, which can ultimately lead to the death of pond life.

Agricultural pollution: pesticides, fertilisers, and animal waste

Ponds are often affected by agricultural pollution, which includes pesticides, fertilisers, and animal waste. These pollutants can have detrimental effects on the delicate balance of pond ecosystems, disrupting the natural processes that maintain a healthy environment for aquatic organisms.

Pesticides

Pesticides are chemicals used to control pests and are often sprayed on crops in fields near ponds. While they are intended to target specific pests, they can also have negative impacts on non-target species in ponds when washed off crops by rain. This can result in the poisoning of animals living in these aquatic habitats, contributing to a decline in biodiversity and ecological imbalances.

Fertilisers

Artificial fertilisers, often containing nitrates, are another source of agricultural pollution in ponds. While they promote crop growth, they can be washed into nearby ponds during rainfall. Although fertilisers do not directly poison wildlife, the excess nitrogen they introduce causes rapid growth of water plants, particularly algae. This excessive algae growth, known as eutrophication, leads to oxygen depletion in the water as the plants consume oxygen during the night and decay processes. The dense algal blooms also block sunlight from reaching organisms below, disrupting the natural balance of the pond ecosystem.

Animal Waste

Animal waste, such as faecal matter, can also find its way into ponds, particularly through runoff from nearby farms or fields where animals graze. This waste can introduce harmful bacteria, such as coliform bacteria and E. coli, which can cause infections and even death in fish populations. High concentrations of animal waste can lead to reduced fish density and pose significant dangers to the hygiene of fish inhabiting pond waters.

Industrial pollution: chemicals, heavy metals, and oil

Industrial pollution, including chemicals, heavy metals, and oil, can have detrimental effects on pond ecosystems. Here are some ways in which these pollutants impact ponds:

Chemicals

The use of chemicals in pond aquaculture, such as fertilizers and liming materials, can improve soil and water quality and control biological problems like phytoplankton blooms and aquatic plant infestations. However, these chemicals can also have negative impacts. Fertilizers, for example, can cause eutrophication of natural waters, leading to an overabundance of nutrients. Some liming materials can be hazardous to workers if not handled properly, and accidental spills of certain substances could result in environmental damage. Additionally, human wastes, agricultural or industrial pollution, insecticides, and bactericides used in aquaculture can contaminate water with chemicals and heavy metals, posing safety risks to both workers and consumers.

Heavy Metals

Heavy metal contamination of water sources is a significant global concern due to its toxicity, persistence, and ability to bioaccumulate in biological systems. Sources of heavy metal pollution include industrial wastewater, agricultural practices, and natural processes. These metals can cause harm to various organs, even at low exposure levels, and they tend to accumulate in living organisms, disrupting the food chain. Heavy metals can enter ponds through water used for filling or maintaining water levels and can have long-lasting effects on the environment and human health.

Oil

Oil spills are particularly harmful to ponds and other aquatic ecosystems. Oil can destroy the insulating ability of fur-bearing mammals and the water repellency of birds' feathers, leading to hypothermia and death. It can also impair the growth and reproduction of fish and shellfish, making them unsafe for human consumption. Oil can enter ponds through industrial activities, accidental spills, or runoff from nearby land.

Sewage: human and animal waste

Wastewater, including sewage, is a major source of pollution in ponds. When untreated wastewater is discharged into ponds, the organic matter it contains serves as food for microorganisms, who use it for energy generation and reproduction. While the by-products of this process, carbon dioxide and water, are stable and do not cause pollution issues, the microorganisms' respiration reduces the oxygen concentration in the pond, which can be harmful to fish and other organisms.

Sewage can also introduce harmful bacteria into ponds, such as E. coli and coliform bacteria, which can cause infections in fish populations. These bacteria are often introduced by animal waste or human waste from septic systems, and their presence can be detected through water testing.

To mitigate the impact of sewage on pond ecosystems, waste stabilisation ponds (WSPs) can be used. These are man-made depressions designed to treat wastewater and remove organic content and pathogens. WSPs can be particularly useful in developing countries with warm climates and are suitable for treating sewage, industrial effluents, municipal runoff, and stormwater. The treated effluent can then be returned to surface water or reused for irrigation if it meets the required standards.

WSPs consist of a single pond or a series of ponds, each playing a different role in pollutant removal. The main types of ponds in the system include:

• Anaerobic ponds: These have very little dissolved oxygen, creating anaerobic conditions. They are smaller and deeper than other types of ponds and are used to treat raw wastewater, removing organic matter through anaerobic digestion.
• Facultative stabilisation ponds: These sustain an aerobic surface habitat above an anaerobic benthic habitat. They are shallower and have a larger surface area, allowing for more oxygen dissolution and sunlight penetration, which facilitates photosynthetic activity.
• Maturation ponds: These offer aerobic conditions throughout and are used primarily for the removal of pathogens. They are shallow with a large surface area, promoting high photosynthetic activity and the removal of pathogenic bacteria and viruses.

While WSPs are efficient in removing organic matter and pathogens, they may not achieve very high efficiencies in removing all pollutants. The effluent often contains high concentrations of suspended solids, and the technology may not be suitable in areas with stringent discharge standards unless additional post-treatment stages are included.

Atmospheric pollution: acid rain

Acid rain is a major form of atmospheric pollution that affects pond ecosystems. It is caused by the presence of higher than normal amounts of nitric and sulfuric acids in atmospheric deposits. These acids are produced when man-made sources, primarily emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) from fossil fuel combustion, react with water, oxygen, and other chemicals in the atmosphere. While acid rain can occasionally be caused by natural sources such as volcanoes and decaying vegetation, most of it is a result of human activity. In the United States, for example, roughly 2/3 of all SO2 and 1/4 of all NOx emissions come from electric power generation.

The acidity of rain is typically measured with pH, with lower pH values indicating higher acidity. Pure water has a pH of 7.0, while normal rain has a pH of around 5.6 due to the presence of carbonic acid formed when carbon dioxide (CO2) dissolves in it. Acid rain that contains sulfur dioxide or nitrogen oxide emissions can have a much lower pH. As of the year 2000, the most acidic rain falling in the U.S. had a pH of about 4.3.

Acid rain has detrimental effects on pond ecosystems, particularly those with limited ability to neutralize acidic compounds. As acid rain flows through the soil in a watershed, it releases toxic aluminium into lakes and streams. This, along with the low pH, is harmful to many species of aquatic organisms, including fish. Acid rain can prevent fish eggs from hatching, reduce fish populations, and even eliminate entire species from a lake. It can also affect other organisms in the food web, such as insects, reducing biodiversity and water quality.

The impact of acid rain on ponds and other aquatic habitats is influenced by the buffering capacity of the surrounding soil. Soil with a high buffering capacity can neutralize the acidity in rainwater, mitigating its effects. However, in areas with thin soil or soil that lacks the necessary composition, such as the mountainous parts of the Northeast United States, the soil has a poor buffering capacity. As a result, these areas are particularly vulnerable to acid rain, and the acid and aluminium can accumulate in the soil, streams, or lakes.

In addition to its ecological impacts, acid rain can also have economic consequences for industries such as commercial fishing and tourism that depend on healthy lake ecosystems. It is important to note that while acid rain itself does not pose a direct threat to humans, the pollutants that cause it, such as SO2 and NOx, can be harmful when inhaled.

Eutrophication: excessive plant growth

Eutrophication is defined as excessive plant and algal growth due to an increased availability of one or more limiting growth factors needed for photosynthesis, such as sunlight, carbon dioxide, and nutrient fertilisers. This process is accelerated by human activities, such as the use of artificial fertilisers in farming, which contain nitrates that are washed into ponds during rainfall. Eutrophication can also be caused by animal waste, which contains high amounts of nitrogen and phosphorus, and the overpopulation of certain wildlife, such as Canadian geese, which deposit their waste—containing phosphorus and nitrogen—around the edges of ponds.

The increase in nutrients in the water encourages denser plant growth, which then negatively impacts aquatic life and fisheries. This is because the plants and algae use up oxygen during the night and decay processes, leaving none for other organisms. The dense growth also blocks sunlight from reaching the organisms below the water's surface. Eventually, all the algae die, leaving a smelly, decaying mass.

Eutrophication can be combated by limiting the introduction of nutrients, especially nitrogen and phosphorus. This can be achieved by restricting animal access to ponds, maintaining vegetation in areas through which water must flow to reach the pond, and decreasing the use of fertiliser on crops in the watershed area of the pond.

Frequently asked questions