Ocean Currents And Pollution: A Complex Relationship

Oceans are among the most valuable natural resources on Earth, playing a pivotal role in the health of our ecosystem. They cover more than 70% of the Earth's surface, govern the weather, clean the air, help feed the world, and provide a living for millions. However, they are also the endpoint for much of the pollution we produce on land. Each year, billions of pounds of trash and other pollutants enter the ocean, with 80% of marine pollution originating from land-based sources. This pollution has far-reaching consequences, negatively impacting both human health and marine ecosystems. Marine debris, including plastic waste, oil spills, and atmospheric carbon emissions, poses a serious threat to the health and well-being of our planet. As the ocean warms and land ice melts, ocean circulation, which plays a vital role in moving heat around the planet, could be impacted. This paragraph introduces the topic of how pollution affects ocean currents, highlighting the significance of oceans, the extent of marine pollution, its consequences, and the potential impact on ocean circulation.

Ocean pollution from nonpoint sources

One of the primary contributors to nonpoint source pollution is runoff from agricultural lands and residential areas. When large areas of land are plowed, the exposed soil is susceptible to erosion during rainstorms. As a result, the runoff carries agricultural fertilizers and pesticides into rivers and oceans, harming fish and wildlife habitats. Additionally, excess fertilizers, herbicides, and insecticides from farms and residential areas can contaminate water bodies, leading to excessive algae growth and dead zones.

Vehicles, such as cars, trucks, and boats, also play a significant role in nonpoint source pollution. Motor vehicle engines leak small amounts of oil onto roads and parking lots, which eventually find their way into waterways and oceans. This oil pollution can have detrimental effects on aquatic life and ecosystems. Similarly, urban runoff containing oil, grease, and toxic chemicals can contaminate coastal waters, further exacerbating the problem.

Improper waste management practices, including faulty septic systems, also fall under nonpoint source pollution. Bacteria and nutrients from livestock, pet wastes, and malfunctioning septic tanks can pollute water bodies, making them unsafe for human and wildlife use. Furthermore, construction sites, crop and forest lands, and eroding stream banks can contribute sediment and other pollutants to the runoff, adversely affecting water quality.

Nonpoint source pollution has wide-ranging consequences, including economic impacts. Coastal communities, which rely heavily on tourism, fishing, and waterfront property values, can suffer significant financial losses due to pollution-related issues. Additionally, nonpoint source pollution can lead to beach closures and negatively impact the social and economic conditions of these communities.

Ocean pollution from point sources

For example, sewage treatment plants treat human waste and send the treated effluent into streams or rivers. However, some treatment plants mix their waste with urban runoff in a combined sewer system. During heavy rains, a combined sewer system may overflow, discharging untreated sewage and stormwater directly into nearby water bodies. This is known as combined sewer overflow (CSO) and is considered point-source pollution. It can cause severe damage to human health and the environment, including restricting activities like swimming and fishing, and affecting drinking water safety.

Factories are another significant source of point-source pollution. They may discharge one or more pollutants into water bodies, either directly or after treating the waste themselves or sending it to sewage treatment plants. Factories such as oil refineries, chemical plants, and automobile manufacturers often release harmful chemical pollutants into the water, posing risks to aquatic life and human health.

Large farms, particularly those that raise livestock such as cows, pigs, and chickens, are also point sources of pollution. These concentrated animal feeding operations (CAFOs) can generate large amounts of animal waste, which, if not properly treated, can enter nearby water bodies as raw sewage, contributing to the pollution levels.

To control point-source discharges, the Clean Water Act established the National Pollutant Discharge Elimination System (NPDES). This program requires factories, sewage treatment plants, and other point sources to obtain permits and use the latest technologies to treat their effluents before discharging them into any body of water.

Ocean acidification

Since the Industrial Revolution, the concentration of CO2 in the Earth's atmosphere has increased due to human activities such as burning fossil fuels and deforestation. As a result, the ocean now absorbs about 30% of the CO2 released into the atmosphere, which has led to a 30% increase in the acidity of seawater. This change in pH may seem insignificant, but because the pH scale is logarithmic, it represents a substantial increase in acidity.

The increased acidity of seawater poses a significant threat to marine life, particularly organisms that build shells and skeletons from calcium carbonate, such as corals, oysters, clams, mussels, snails, and plankton. These "marine calcifiers" face two main challenges due to ocean acidification: their shells and skeletons may dissolve more easily as seawater becomes more corrosive, and there are fewer carbonate ions available for them to build and maintain their shells and skeletons.

The impact of ocean acidification on coral reefs is of particular concern. Coral reefs provide habitat for many marine species, including commercially important fish and shellfish, and they also protect coastal communities from erosion and storms. Additionally, studies have shown that acidification impairs the ability of some calcifying plankton to build and maintain their shells, and it has been linked to increased larval mortality rates in several commercially important fish and shellfish species.

The effects of ocean acidification are already being observed in many marine organisms, and scientists estimate that over the next few thousand years, 90% of anthropogenic CO2 emissions will be absorbed by the ocean. This will likely have significant impacts on biological and geochemical processes that are vital to marine ecosystems and human society.

Eutrophication

The impacts of eutrophication extend beyond the ecological, affecting human health and economic activities as well. Excessive nitrate levels in drinking water can cause health issues, and exposure to toxic algae can lead to rashes, stomach illnesses, and respiratory or neurological problems. Additionally, eutrophication increases water treatment costs and reduces the value of rivers and lakes for aesthetic enjoyment and tourism.

To address eutrophication, it is crucial to minimize pollution from sewage and agriculture, implement nutrient management techniques, and introduce bacteria and algae-inhibiting organisms such as shellfish and seaweed. These measures can help reduce nitrogen pollution and control the growth of harmful algae blooms.

Noise pollution

Marine mammals, such as whales, dolphins, and porpoises, are highly dependent on underwater sound for crucial activities like communication, locating prey and mates, navigation, and territory defence. Noise pollution can obscure these natural sounds, disrupting their natural behaviours and impairing their ability to communicate and navigate effectively.

The impact of noise pollution on marine life can vary from temporary or permanent hearing loss to behavioural and physiological changes, disorientation, injury, and even death. Very loud noises can cause panic and lead to decompression sickness or skin damage if animals ascend too quickly to escape the noise. Additionally, it can trigger stress responses, disrupt feeding and breeding patterns, and affect coordination and navigation.

To mitigate noise pollution, strategies such as reducing vessel speed, adopting quieter technologies, optimising propeller design, and implementing international regulations and guidelines have been proposed and, in some cases, implemented.

Frequently asked questions