Wetlands Water Quality: Pollution's Toxic Threat

Wetlands are under threat from a variety of human activities, including development, agriculture, and silviculture. Since colonial times, over half of the wetlands in the lower 48 states have been lost due to these factors, and the ecological health of remaining wetlands is in danger from habitat fragmentation, polluted runoff, water level changes, and invasive species. Wetlands are particularly susceptible to pollution as they are often found in the lower reaches of watercourses and can receive and collect pollutants from a wide area. These pollutants, such as pesticides, fertilisers, and heavy metals, can enter the water table through various means, including urban and agricultural runoff, air pollution, and leakage from landfills. While wetlands act as natural filters for polluted water, they can only absorb so much, and once polluted, they are difficult to clean.

Pesticides, fertilisers, and other chemicals

Wetlands are susceptible to pollution due to their location at the lower reaches of watercourses, fed by multiple streams and waterways. This unique position enables them to "receive and collect" pollutants from a vast area, which can then build up and negatively impact their health.

Agricultural fertilisers, for example, contain nitrogen and phosphorus, which can act as plant fertilisers in natural water bodies. This excess of nutrients can stimulate excessive growth of plants, algae, and cyanobacteria. The rapid growth of algae, particularly blue-green algae, can produce toxins harmful to wildlife, livestock, and even humans. These toxins can choke out natural vegetation and wildlife, disrupting the delicate balance of the wetland ecosystem.

Additionally, pesticides, herbicides, insecticides, and fungicides can be introduced into wetlands through runoff from agricultural and urban areas, as well as domestic and industrial wastewater. These chemicals are designed to be toxic to target organisms, but they can also impact non-target species within the wetland, including fish, birds, and other wildlife. The accumulation of these chemicals in wetland sediments can lead to long-term ecological damage.

Wetlands do have a natural capacity to mitigate some of these chemical pollutants. The settling of sediments in wetlands can trap pollutants, such as heavy metals, attached to soil particles. Furthermore, biological processes and exposure to sunlight can convert some of these chemicals into less harmful forms. The microbial activity and plant growth within wetlands can also help absorb and process these pollutants, reducing their toxic effects.

Sedimentation and soil erosion

The soils most susceptible to erosion are those with a high concentration of medium (silt)-sized particles. Clay and sandy soils are less prone to erosion. Ground slope characteristics, such as length, grade, and surface quality, also play a crucial role in erosion potential. Longer slopes, steeper grades, and smoother surfaces increase the likelihood of erosion and sedimentation, especially when combined with high water flow rates.

Wetlands, often located in the lower reaches of watercourses, are particularly vulnerable to receiving and accumulating pollutants, including sediment, from a wide area. The input of sediment and other pollutants, such as fertilizers and pesticides, can exceed the wetland's natural ability to absorb them, leading to degradation and reduced water quality. This degradation can have far-reaching consequences, as wetlands provide habitat for numerous threatened and endangered species.

To mitigate the impacts of sedimentation and soil erosion, it is essential to implement erosion control measures and sustainable land management practices. This includes preserving and restoring perennial vegetation adjacent to wetlands, employing proper road construction and maintenance techniques, and altering land-use zoning to protect these fragile ecosystems. By taking proactive steps to reduce sedimentation and soil erosion, we can improve the resilience of wetlands and help maintain their vital functions, such as natural water filtration and biodiversity support.

Additionally, it is worth noting that while wetlands are susceptible to pollution, they also play a crucial role in addressing it. Wetlands act as natural filters, helping to remove pollutants from water. Therefore, protecting and restoring wetlands is not only essential for preserving their ecological value but also for maintaining water quality and mitigating the impacts of pollution.

Sewage and septic systems

The excessive growth of algae, also known as an algal bloom, can have detrimental effects on wetland ecosystems. When algae bloom, they can block out light, hindering the growth of other aquatic plants and impacting the health of the wetland. Additionally, algal blooms can produce toxins that are harmful to wildlife, livestock, and even humans. These toxins can accumulate in the food chain, posing risks to animals and people who consume contaminated fish or shellfish.

Moreover, sewage and septic systems can introduce pathogens and bacteria into wetlands, posing risks to both human and wildlife health. These contaminants can survive and spread in wetland environments, causing diseases and negatively impacting the health of organisms within the ecosystem. The microbial activity in wetlands, while beneficial for nutrient cycling, can also facilitate the growth and transmission of these pathogens, making it crucial to address and treat sewage and septic system discharges effectively.

To mitigate the impact of sewage and septic systems on wetlands, several measures can be implemented. Proper wastewater treatment is essential, ensuring that sewage is adequately treated before being released into wetland areas. This includes the use of constructed wetlands, which are specifically designed to treat wastewater and enhance water quality. Additionally, regular monitoring and assessment of wetland conditions are necessary to detect any signs of degradation or contamination. By implementing effective management strategies and regulations, we can minimise the threat posed by sewage and septic systems, helping to protect and preserve the vital water quality and ecological functions that wetlands provide.

Mining and heavy metals

Mining activities and the resulting heavy metal pollution are significant threats to wetland water quality. Wetland ecosystems are highly vulnerable to disturbances caused by mining operations and the subsequent release of heavy metals into the environment.

Mining activities can directly impact wetlands through the disturbance of water sources during exploration and mine construction. This includes the creation of roads, which can lead to sedimentation and the alteration of natural water flows. The construction phase of mining projects can also result in the discharge of mine effluent, seepage from tailings, and the exposure of waste rock, all of which can introduce pollutants into wetland ecosystems.

Waste rock and tailings generated during mining often contain acid-generating sulphides, heavy metals, and other contaminants. When these materials are exposed to air and water, a natural process called Acid Mine Drainage (AMD) occurs, producing sulphuric acid. This acid leaches heavy metals from the waste rock, and the resulting contaminated water can find its way into nearby wetlands, rivers, and groundwater. AMD severely degrades water quality, kills aquatic life, and renders water unusable.

Heavy metals, such as arsenic, cobalt, copper, cadmium, lead, silver, and zinc, can be released from excavated rock or exposed underground mines. These metals accumulate in wetland sediments through processes like decomposition, adsorption, complexation, and precipitation. Once in the sediments, heavy metals can remain for extended periods, causing permanent harm to the wetland ecosystem. Fluctuations in the water-soil environment can lead to the resuspension of these metals, allowing them to migrate into water bodies and pose threats to aquatic organisms, plants, and even human health through the food chain.

Constructed wetlands have been proposed as a solution to mitigate the impact of heavy metal pollution from mining activities. These wetlands can absorb and bind heavy metals, slowly concentrating them in sedimentary deposits and removing them from the water. Phytoremediation, using specific plant species, is a cost-effective and environmentally friendly method that has been successfully employed in constructed wetlands to treat heavy metal-polluted sites and restore aquatic biosystems.

Global warming and algae blooms

Global warming is causing an increase in harmful algal blooms (HABs) in several ways. Firstly, rising air temperatures lead to an increase in water temperatures, creating favourable conditions for HABs. Warmer waters boost the chances of HABs developing and lasting. HAB-forming cyanobacteria thrive in warm, slow-moving waters.

Secondly, global warming is causing more frequent and intense rainfall patterns, which contribute to the triggering of HABs. Heavy rainfall flushes excess nitrogen and phosphorus from the surrounding landscapes, feeding existing cyanobacteria and increasing the risk of HABs. This nutrient runoff comes from sources such as agricultural operations, urban and residential lawn fertilizer, and stormwater/wastewater discharge.

Thirdly, climate change is altering the flow of ocean currents, which affects the way nutrients flow and mix in the water. This can cause an increase in blooms in certain regions and a decrease in others. For example, while some regions like the California Current saw algal blooms weaken over time, other regions like the Canary and Benguela Currents experienced an increase in blooms.

Finally, coastal upwelling, which occurs when wind pushes warm surface water offshore and deep nutrient-rich waters rise to replace it, is expected to be altered in timing and intensity due to climate change. This can lead to more algal blooms, especially when combined with increased nutrient pollution from land.

The increase in harmful algal blooms due to global warming has significant impacts on water quality, human health, aquatic ecosystems, and the economy. HABs can produce toxins that contaminate drinking water supplies and harm humans, pets, livestock, and aquatic life. They can also create "dead zones" in water with little to no oxygen, further harming aquatic ecosystems.

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