Pollution's Impact: Water Oxygen Levels Explained

Water pollution is a pressing issue, with only 40% of European surface waters deemed to be in a good ecological state. Pollution can come from a variety of sources, including households, farms, and factories, and can have detrimental effects on aquatic ecosystems. One of the key ways in which pollution impacts water bodies is by altering oxygen levels, which are crucial for the survival of aquatic plants and animals. This paragraph will explore how pollution affects oxygen levels in water and the subsequent consequences for aquatic life.

Eutrophication and organic pollution

Eutrophication is a process that occurs in an aging aquatic ecosystem, such as a lake, where there is a gradual increase in the concentration of phosphorus, nitrogen, and other plant nutrients. This process is accelerated by human activities, known as cultural eutrophication, which introduce sewage, detergents, fertilizers, and other nutrient sources into the ecosystem. Cultural eutrophication has had significant negative impacts on freshwater resources, fisheries, and recreational bodies of water, making it one of the leading causes of aquatic ecosystem degradation.

One of the main consequences of eutrophication is the development of water blooms, which are large concentrations of algae and microscopic organisms on the water surface. These blooms block light penetration and oxygen absorption, affecting underwater life. Eutrophic waters often have low oxygen levels, known as hypoxia, which can result in massive fish kills and impact the local economy.

Organic pollution, particularly the input of nutrients and organic matter, can induce oxygen deficits in tropical rivers. High decomposition rates further deplete oxygen levels, and the respiratory performance of ectotherms is impacted. The presence of organic waste in water bodies suggests low dissolved oxygen levels as organic decomposition consumes oxygen.

The increase in plant nutrients and organic matter due to eutrophication and organic pollution can lead to excessive plant growth, which results in oxygen declines due to respiration and decomposition. This, in turn, affects the aquatic community structure, with sensitive species being replaced by more tolerant ones.

Overall, eutrophication and organic pollution have significant negative impacts on oxygen levels in water, affecting both aquatic life and human activities that depend on healthy aquatic ecosystems.

High temperatures

The relationship between temperature and dissolved oxygen levels in water is inverse: as temperature increases, dissolved oxygen levels decrease. This has a negative impact on aquatic life, as oxygen is essential for the survival of many aquatic organisms, including fish, zooplankton, invertebrates, bacteria, and plants.

The impact of high temperatures on dissolved oxygen levels is particularly significant in stagnant water bodies, such as lakes and ponds, and closed systems like aquariums. In these environments, high temperatures can lead to hypoxic conditions, where oxygen levels drop below 3 mg/L, which is lethal to aquatic plants and animals.

Additionally, high temperatures can affect the solubility and availability of essential nutrients in the water. Increased water temperatures can cause fluctuations in pH levels and promote excess algae growth due to elevated levels of phosphorus and nitrogen.

The consequences of high temperatures and low dissolved oxygen levels can be observed in summertime fish kills, where a combination of high temperatures and organic matter decomposition depletes oxygen levels, resulting in the death of many fish.

To maintain healthy dissolved oxygen levels in aquatic ecosystems, it is crucial to monitor and manage water temperatures, especially during the warmer summer months.

Ammonia

Secondly, ammonia can lead to heavy plant growth, a process known as eutrophication, due to its nutrient properties. Algae and macrophytes take up ammonia, thereby reducing aqueous concentrations.

Thirdly, ammonia can affect oxygen levels in water through the nitrogen cycle. This biological process eliminates ammonia from the water by converting it to less toxic compounds. The ammonia excreted by fish is converted to nitrite by ammonia-oxidizing bacteria, and then to nitrate by nitrite-oxidizing bacteria. Both groups of bacteria require oxygen and alkalinity to function effectively. If oxygen levels are insufficient, the process can break down, leading to increased ammonia and nitrite levels.

Finally, water temperature and pH play a role in determining the toxicity of ammonia. An increase in pH favours the formation of the more toxic un-ionized form (NH3), while a decrease favours the ionized form (NH4+). Warmer water temperatures also increase the toxicity of ammonia.

Algal blooms

The Gulf of Mexico, for example, has a large dead zone of about 6,500 square miles that occurs every summer due to nutrient pollution from the Mississippi River Basin. This pollution comes from rainfall washing fertilizer and manure from large farm fields into streams that eventually flow into the Gulf of Mexico.

To prevent algal blooms and the resulting dead zones, it is important to reduce the amount of nutrient pollution, especially from agricultural sources. This can be done through the implementation of mandatory regulations and the use of sensors to monitor for runoff pollution.

Organic waste

The introduction of organic waste into water bodies increases the demand for oxygen, as the bacteria that break down these wastes require oxygen to do so. This is known as the Biological Oxygen Demand (BOD). When more oxygen is consumed than is produced, the dissolved oxygen levels in the water decline. This can lead to low oxygen levels in the water, which is a sign of contamination and can be harmful to aquatic life.

High levels of organic waste can lead to an increase in bacterial activity, which can result in a significant drop in dissolved oxygen levels. This, in turn, can cause stress and even death in aquatic organisms, as they are unable to breathe. Some organisms, such as sludge worms, blackfly larvae, and leeches, are more tolerant of low oxygen environments and may replace the organisms that are typically found in well-oxygenated waters.

The presence of organic waste in water bodies can also affect the water quality and ecosystem health. It can lead to an increase in eutrophication, where high levels of nutrients cause excessive growth and decay of plants and algae. This process further contributes to the depletion of oxygen levels as the bacteria that break down the dead plants and algae consume oxygen.

Overall, organic waste has a significant impact on the oxygen levels in water bodies and can have far-reaching effects on the health and diversity of aquatic ecosystems.

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