Algae And Pollution: Understanding The Complex Relationship

Algal blooms, which are often harmful, are becoming more frequent and intense due to rising temperatures and pollution. Nutrient pollution, particularly excess nitrogen and phosphorus, is a major cause of this growth. These nutrients, essential for plant growth, enter water bodies through agricultural activities, urban and suburban runoff, and sewage. This leads to eutrophication, causing an explosion in algae growth that consumes oxygen and blocks sunlight, resulting in dead zones devoid of aquatic life. Additionally, acid rain, a product of atmospheric carbon oxide from burnt fossil fuels, also negatively impacts algae and other aquatic life by altering pH levels. With pollution sources ranging from farming fertilizers to sewage overflow, the very water we drink is at risk of becoming toxic.

Excess nitrogen and phosphorus

Algae blooms are fuelled by nutrient pollution, which can come from various sources, including farming fertilisers, sewage, and lawn fertilisers. These excess nutrients are washed away in runoff during rainstorms and enter nearby waterways, providing the perfect conditions for algae to thrive.

The impact of excess nitrogen on algae growth is significant. Nitrogen compounds, such as nitrogen oxides, contribute to the formation of other air pollutants like ground-level ozone, a component of smog. When these pollutants are deposited into water bodies, they provide a rich source of nitrogen for algae, promoting their growth.

Similarly, phosphorus plays a crucial role in algae proliferation. It is one of the most important nutrients for plant growth, and when it enters water bodies in excessive amounts, it can cause an explosion in algae growth. Phosphorus-rich pollutants, such as fertilisers and certain detergents, can contaminate ponds, rivers, or lakes, leading to a rapid increase in algae populations.

The consequences of excess nitrogen and phosphorus on algae growth extend beyond the mere presence of algae blooms. As the algae consume oxygen and block sunlight from reaching underwater plants, they create "dead zones" where aquatic life cannot survive due to a lack of oxygen, a condition known as hypoxia. When the algae eventually die, their decomposition further depletes the oxygen levels, exacerbating the hypoxic conditions.

The presence of algae blooms also poses risks to human and animal health. Some algae produce toxins that accumulate in fish and shellfish, which can lead to poisoning in humans and other animals when consumed. Thus, the excess of nitrogen and phosphorus, while promoting algae growth, also contributes to a decline in water quality and poses ecological and health risks.

Eutrophication

The explosive growth of algal blooms is linked to rising temperatures and rising pollution. As farming fertiliser and sewage enter warming waterways, drinking water can become toxic. HABs occur when certain kinds of algae grow very quickly due to increased nutrients in the water, typically when artificial nitrogen and phosphorus from farmers' fields wash out in the rain and enter waterways.

Excess nitrogen and phosphorus cause an overgrowth of algae in a short period of time, also called algae blooms. The overgrowth of algae consumes oxygen and blocks sunlight from underwater plants. When the algae eventually die, they consume the oxygen in the water as they decompose. When the concentration of dissolved oxygen decreases to a level that can no longer support aquatic life, hypoxic or dead zones form.

Dead zones are generally caused by significant nutrient pollution and primarily affect bays, lakes, and coastal waters since they receive excess nutrients from upstream sources. The frequency and duration of dead zones have increased since they were first noticed in the 1970s. Over 166 dead zones have been documented nationwide, affecting water bodies like the Chesapeake Bay and the Gulf of America.

Algae play a major role in the food chain of aquatic life, and whatever elements alter their population and species growth significantly affect all other succeeding organisms in the chain. Therefore, algae can be regarded as a suitable bioindicator organism to identify and qualify the effects of pollutants on the ecosystem.

Ocean acidification

The increased acidity of the ocean has significant impacts on marine ecosystems, including the growth and distribution of algae. Algae, being primary producers in marine food chains, play a crucial role in the health of these ecosystems. While some algae species can help mitigate ocean acidification by removing carbon dioxide from the water through photosynthesis and calcification, the overall effect of increasing acidity is detrimental.

Calcifying algae, for instance, create hard crusts out of calcium carbonate, contributing to the stabilization of ocean pH. However, as ocean acidification progresses, these algae may struggle to survive, leading to a potential loss of their stabilizing impact. Additionally, certain species of algae, such as the red tide algal species Alexandrium fundyense, have been found to thrive under conditions of high nutrient loading and acidification, leading to disruptive and harmful algal blooms.

The growth of these harmful algal blooms (HABs) is fueled by nutrient pollution, particularly excess nitrogen and phosphorus compounds that enter waterways from agricultural runoff, urban pollution, and sewage treatment plants. As these nutrients increase in coastal waters, they promote the excessive growth of algae, which can have detrimental effects on aquatic ecosystems and human health. HABs can produce toxins that accumulate in fish and shellfish, making them poisonous to humans and other animals when consumed.

The combination of ocean acidification and the presence of HABs can create a feedback loop that further exacerbates the problem. As HABs decay, they promote bacterial respiration, leading to increased carbon dioxide levels, lower pH, and decreased oxygen availability in the water. This, in turn, enhances the conditions for certain harmful algae species, leading to a cycle that intensifies the negative impacts on marine ecosystems and the organisms that depend on them.

Sewage and fertiliser

Public wastewater treatment plants are a common source of sewage spills, but failing or inefficient private septic systems or onsite wastewater treatment systems (OWTS) can also contribute to the problem. In some cases, ageing infrastructure and intense rainfall have caused treatment plants to exceed capacity, resulting in overflows and direct sewage spills into lakes and rivers.

Fertiliser use is another significant factor in algae growth. Fertilisers are designed to supply plants with essential nutrients, primarily nitrogen, phosphorus, and potassium. However, when excess fertiliser is applied or when it rains heavily, the nutrients can run off into nearby water bodies, causing an overload of nutrients in the water. This process, known as eutrophication, leads to uncontrolled algae growth and the depletion of oxygen in the water, creating "'dead zones" where aquatic life cannot survive.

The impact of fertiliser on algae growth has been recognised, and efforts have been made to regulate its use. Many states have implemented restrictions on the application of fertiliser during the dormant season when plants do not actively absorb nutrients. Additionally, most fertiliser companies have stopped including phosphorus in their products due to its damaging effects on water.

Both sewage and fertiliser pollution contribute to the increasing occurrence of algal blooms, which are becoming more prevalent with rising temperatures. These blooms can contaminate drinking water sources, harm aquatic ecosystems, and impact human and animal health. As climate change continues to warm our waterways, it is essential to address the pollution caused by sewage and fertiliser to mitigate the growth of harmful algal blooms.

Climate change

Algae play an important role in the ecosystems of ponds, lakes, rivers, and oceans. However, certain types of algae, such as cyanobacteria, can become harmful when they grow excessively, forming algal blooms. These blooms can have detrimental effects on water quality, human health, aquatic ecosystems, and the economy. Climate change is a significant contributing factor to the increasing prevalence and severity of harmful algal blooms.

Additionally, climate change is altering rainfall patterns, leading to more frequent and intense droughts and storms. The subsequent increase in nutrient runoff from land into water bodies fuels the growth of harmful algal blooms. Nutrient pollution, particularly from excess fertilizers, provides a plentiful food source for algae, enabling their rapid proliferation. Furthermore, coastal upwelling, a process where warm surface water is pushed offshore, brings nutrient-rich deep water to the surface, further enhancing the growth of algal blooms.

The impacts of climate change on aquatic ecosystems are not limited to temperature and nutrient changes. Rising carbon dioxide levels in the atmosphere and water contribute to the rapid growth of algae, particularly cyanobacteria. Increased carbon dioxide also leads to water acidification, which affects competition among algal species and impacts organisms that depend on algae for food. Moreover, climate change-induced droughts can increase the salinity of inland waters, allowing the invasion of salt-tolerant and marine algae into freshwater ecosystems, further exacerbating the problem of harmful algal blooms.

The complex interplay between climatic and non-climatic factors influences the expansion and frequency of harmful algal blooms. While the full extent of climate change's role in intensifying these blooms is still being elucidated, there is a consensus that the impacts on public health, recreation, tourism, fisheries, aquaculture, and ecosystems have been significant and far-reaching. Addressing the root causes of climate change and implementing measures to reduce nutrient pollution are crucial steps towards mitigating the adverse effects of harmful algal blooms.

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