Plants' Role In Reducing Thermal Pollution

Thermal pollution is a growing environmental concern that poses a threat to aquatic ecosystems and the delicate balance of our planet's natural systems. It occurs when there is a rapid change in the temperature of a natural body of water, which can be caused by both human activities and natural factors. Human activities, such as the use of water as a coolant in power plants and industrial manufacturing, are the biggest contributors to thermal pollution. Natural factors include geothermal vents, hot springs, and volcanoes. The effects of thermal pollution include a decrease in dissolved oxygen levels, an increase in toxins, and ecological impacts such as mass killings of plants, insects, or amphibians. To minimize thermal pollution, measures such as the use of cooling ponds, cooling towers, and artificial lakes can be implemented. Additionally, adopting renewable energy sources like wind and solar power that do not produce heated wastewater can help reduce thermal pollution and carbon pollution simultaneously.

Using plants to provide shade for bodies of water

Plants can be used to provide shade for bodies of water, which is an effective way to minimise thermal pollution. Trees and vegetation act as natural shades, keeping water temperatures cooler.

Planting trees to regulate water temperatures

Trees and plants have a natural cooling effect, making them a simple and effective way to regulate water temperatures and reduce heat islands.

Trees provide shade, reducing surface and air temperatures. During the sunnier seasons, an urban tree's leaves and branches only allow about 10-30% of solar radiation to reach the area below their canopy. The rest of the solar energy is absorbed through the tree's leaves for photosynthesis or reflected back into the atmosphere.

Trees also help with evapotranspiration, which is the process of transferring moisture from the earth into the atmosphere through evaporation. This helps to reduce peak summer temperatures by an estimated 2-9°F (1-5°C). This process reduces temperatures by taking heat from the air and using it to evaporate water, similar to how sweating helps cool our skin.

The cooling effect of trees is not just from shading but also includes transpiration and may involve paraheliotropism. This is the orientation of leaves to reduce solar heating. Herbaceous plants may also exhibit paraheliotropism and show growth responses mediated by interacting heat and light sensitivities that result in heat avoidance.

In addition, trees can reduce energy use. According to the US Department of Energy, carefully positioned trees can reduce a home's energy costs by 25%, including air conditioning. This helps to prevent catastrophic power failures by reducing the pressure on the power grid during heatwaves.

Trees and vegetation are a vital part of the solution to thermal pollution. They can lower air temperatures in city neighbourhoods by up to 10 degrees, which could mean the difference between life and death for some city dwellers.

Using plants to absorb wastewater

Plants can be used to treat wastewater, and this method has been employed in countries such as Argentina. This process is known as phytoremediation, and it involves using plants to absorb and purify liquid waste. Constructed wetlands are artificial wetlands designed for wastewater treatment. They are effective nutrient sinks and can absorb organic and inorganic pollutants. Constructed wetlands have several advantages over alternative treatment systems: they require little to no energy to function, provide habitats for wildlife, and are aesthetically pleasing.

Constructed wetlands use different species of plants commonly found in natural wetlands, such as cattails, waterlilies, and rushes. The roots of these plants absorb nutrients from the wastewater, sequestering them in their tissues as they grow. The purified water then filters from the wetland into a lagoon.

Another type of treatment system involves using aquatic plants in shallow reservoirs. These systems can be categorised into two types: those using floating plants, and those using submerged plants. Floating plants, such as duckweed, meet their need for carbon dioxide and oxygen directly from the atmosphere, while submerged plants absorb these directly from the water column.

The use of plants to treat wastewater is a cost-effective and environmentally friendly alternative to traditional waste treatment methods. By utilising the natural abilities of plants to absorb and purify water, we can minimise the impact of wastewater on the environment and protect our quality of life.

Using plants to prevent soil erosion

Plants can be used to prevent soil erosion, which is the wearing away of the top layer of soil. Erosion is a natural process, but it is considered an environmental issue as it damages vegetation, landscapes, agriculture, and property. Water and wind are responsible for about 84% of degraded and eroded land.

Plants can slow down or even completely stop erosion with their root systems, which bind the soil together. Their stems act as thick barriers to slow water flow, and their roots hold the soil in position, making it harder to wash away. Plants also protect the soil from direct rainfall by breaking the impact of raindrops before they hit the ground, which helps to prevent soil runoff.

There are several types of plants that are particularly effective in erosion control:

• Groundcovers: These are low-lying, spreading, and leafy plants that quickly spread across the ground. Their spreading roots hold the soil in place, making it more difficult for the ground to erode. Examples include Japanese honeysuckle and vinca major.
• Shrubs: Shrubs are lush, full plants with several woody stems above the ground. They have strong roots and thick foliage, which makes them excellent for protecting the surrounding soil from harsh wind, sun, and downpours. Popular shrub species for erosion control include Low Scape Mound® Aronia melanocarpa and Tortuga® Juniperus communis.
• Grass: Grass is a common plant used for erosion control due to its fibrous roots that spread deep and hold the soil well. Native species of grass are a good choice as they are maintainable and only require occasional mowing. Examples include Purple Threeawn and Big Blue Stem.
• Trees: Trees help stabilize the soil with their extensive root systems and protect low-lying plants from heavy rain with their branches. Ideal tree species for downslope erosion control include red maple, river birch, and American hornbeam.

By using these plants, healthy soil can be maintained with less runoff, and the damaging effects of erosion can be mitigated.

Using plants to reduce heat absorption in urban areas

Plants can play a crucial role in reducing heat absorption in urban areas, helping to mitigate the "urban heat island effect". This phenomenon occurs when cities, with their dense concentrations of pavement, buildings, and other surfaces that absorb and retain heat, experience elevated temperatures compared to rural areas. Green infrastructure, in the form of trees, vegetation, and green roofs, can be a powerful tool to combat this issue and provide cooling in urban settings.

Shade

Trees and vegetation provide shade, reducing surface and air temperatures. During hot seasons, a tree's leaves and branches allow only about 10-30% of solar radiation to pass through, absorbing the rest through photosynthesis or reflecting it back into the atmosphere. Shaded surfaces can be up to 20-45°F cooler than unshaded areas, significantly lowering air temperatures in city neighbourhoods.

Evapotranspiration

Trees and plants also aid in cooling through evapotranspiration. They absorb water through their roots and release it into the atmosphere via their leaves, reducing peak summer temperatures by an estimated 2-9°F. This process is similar to sweating, which cools the human skin, as it removes heat energy from the air.

Energy Use and Cost Reduction

According to the US Department of Energy, carefully positioned trees can reduce a home's energy costs by up to 25%, including air conditioning expenses. This is especially crucial during heat waves, as it reduces the pressure on power grids and helps prevent power failures. Additionally, when fans and air conditioners don't have to work as hard, they release less waste heat into the atmosphere.

Health Benefits

The urban heat island effect can lead to heat-related illnesses and even premature deaths. By reducing temperatures, trees and vegetation can help mitigate these health risks.

Environmental Benefits

Trees and vegetation also provide environmental benefits beyond cooling. They improve air quality by absorbing pollutants, intercept rainfall, conserve energy, remove air pollutants, and reduce atmospheric CO2 emissions.

Strategic Planning

When incorporating trees and vegetation into urban areas, strategic planning is essential. Trees should be planted in locations that maximise their cooling effects, such as around buildings or paved areas. Additionally, when integrating trees into existing infrastructure, it is crucial to consider the overall design to avoid any potential impairment to the structure by tree roots.

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