Damming's Air Pollution Impact: What's The Truth?

Air pollution is a serious environmental health hazard, with about 8 million deaths linked to it worldwide in 2021. It is caused by solid and liquid particles and certain gases suspended in the air, which can have adverse effects on human health, animals, and the environment. Damming, or the creation of impoundments, can impact water quality, with studies showing that dam impoundments have lower water quality and higher temperatures than upstream and downstream waters. While the direct link between damming and air pollution is unclear, the negative effects of damming on water quality and the environment could potentially contribute to air pollution.

Dams can cause elevated water temperatures

While damming is not a direct cause of air pollution, it does have an impact on water quality, particularly by causing elevated water temperatures.

A two-year study conducted by scientists from the University of Massachusetts-Amherst, with support from the Massachusetts Division of Ecological Restoration, investigated the impacts of small dams on temperature and dissolved oxygen in streams. The study found that the surface water of the dam impoundments was warmer than the water upstream of the impoundments. This is significant because warmer water can cause substantial harm to important stream wildlife.

The warm impoundment water elevated downstream temperatures at two-thirds of the sites studied, with this effect persisting for up to 4.5 km downstream. The highest stream warming was observed downstream of the dams with the widest impoundments relative to the natural stream width, suggesting that the width of the impoundment may be a factor in the degree of temperature increase.

The elevated water temperatures caused by dams can have negative ecological consequences. For example, warmer water can reduce the amount of dissolved oxygen in the water, which is essential for the survival of aquatic organisms. In the Massachusetts study, one-third of the sites studied had lower dissolved oxygen levels downstream of the dams.

Overall, while damming may not directly cause air pollution, it can lead to elevated water temperatures, which can have significant impacts on the health of aquatic ecosystems and the organisms that depend on them.

Dam impoundments have lower water quality

Dams and their impoundments can have a significant impact on water quality, which can have knock-on effects on the health of the surrounding environment and its wildlife. A study conducted in Massachusetts from 2014 to 2016 found that dam impoundments consistently had lower water quality compared to their upstream and downstream waters. The surface water of the dam impoundments was warmer, and this warmer water then flowed downstream, persisting for up to 4.5 km. This increase in temperature can have negative consequences for aquatic life, particularly for species such as salmon and steelhead, which prefer cooler waters.

The same study also found that two-thirds of the dam impoundments had lower surface dissolved oxygen levels than upstream. This is likely due to the water being held in reservoirs, which can lead to reduced oxygen levels. Low oxygen levels in the water released from the bottom of a reservoir can cause problems for fish downstream, potentially leading to stress and even death. However, it is important to note that the aeration that occurs when water spills over a dam may help to mitigate these negative effects, as it can mix more oxygen into the water.

The presence of dams can also lead to changes in the habitat of the surrounding area, converting a river into a lake. This can have detrimental effects on the life cycles of certain fish species, such as salmon, and can make them more vulnerable to predators. Additionally, the reduced water flow downstream of a dam can result in less habitat for fish, further exacerbating the problem. Changes to the habitat may also allow non-native species to invade, leading to increased competition or predation of native species.

While the immediate effects of dams on water quality and the surrounding ecosystem are significant, there are also potential long-term consequences. The accumulation of sediment in reservoirs behind dams can impact water quality and ecosystem health over time. Additionally, the sudden release of water from a dam or the reduction of water flow can cause rapid changes in river levels, potentially stranding fish and other aquatic organisms. Overall, the presence of dams and their impoundments can have far-reaching effects on water quality and the health of aquatic ecosystems.

Damming affects oxygen levels in water

Dams and their impoundments can have a significant impact on the water quality of the streams they are located in. The impoundment of water behind a dam can affect oxygen levels, depending on the design and operation of the dam. If water is released from the top of a dam, it may be warmer and thus contain less oxygen. Conversely, water released from the bottom of a dam is often cooler and has a higher saturation of oxygen.

Upstream of dams, the water moves more slowly, and the lack of turbulence can result in lower oxygen levels. Additionally, at greater depths, the lack of light for photosynthesis can also contribute to reduced oxygen levels. The retention of sediment behind a dam and the turbulence of water below it can further influence oxygen levels. The power of water turbulence below a dam can remove sediment and dislodge organisms, affecting oxygen dynamics.

The presence of dams can lead to elevated stream temperatures and reduced dissolved oxygen levels, both within the impoundments and downstream. This phenomenon is particularly notable in high-gradient, coldwater streams with small watersheds and shallow impoundments. The combination of warmer water temperatures and lower oxygen levels can have detrimental effects on aquatic life, including fish, mussels, stream insects, and other organisms.

The concentration of dissolved oxygen in surface water is influenced by temperature and exhibits both seasonal and daily variations. Cold water has a higher capacity to hold dissolved oxygen compared to warm water. Consequently, during winter and early spring, when water temperatures are generally lower, dissolved oxygen concentrations tend to be higher. In contrast, summer and fall seasons, with higher water temperatures, often coincide with lower dissolved oxygen levels.

Dissolved oxygen is crucial for the survival of aquatic organisms, including plants, animals, and aerobic microbes. Some species, such as salmonids and riffle invertebrates, require nearly saturated levels of oxygen, while others, like channel catfish, can tolerate very low oxygen conditions. Insufficient oxygen levels can lead to abrupt kills of aquatic life, particularly during early morning or cloudy days preceded by warm, sunny weather.

Damming can impact the health of stream wildlife

Damming can have a significant impact on the health and survival of stream wildlife, particularly in river ecosystems. By altering the natural flow of water, dams create physical barriers that disrupt the life cycles of many aquatic species.

One of the most affected groups is migratory fish, such as salmon and eel. Salmon, for instance, are adapted to living in rivers, and their spawning activities are often disrupted when their habitat is changed to a lake. Dams can also reduce the availability of spawning gravel and large pieces of wood that are essential for fish habitats. The altered temperature and oxygen levels in reservoirs, as well as the growth of harmful algae blooms, can further threaten the survival of sensitive aquatic species.

The presence of dams can also affect the interactions between predators and prey. In some cases, changes in habitat may benefit predators, making their prey more vulnerable. For example, fish attempting to pass a dam may become targets for predators, and certain predator species may increase their numbers in the altered habitat.

Additionally, dams can impact the nutrient transport and transformation in river systems. They affect the dynamics of nitrogen and phosphorus, which are fundamental elements of primary productivity in aquatic ecosystems. The factors influencing these processes include the physicochemical properties of water bodies and human activities, such as water storage regulation modes.

The consequences of damming can be far-reaching, leading to irreversible harm, including the extinction of species and displacement of communities. Removing dams can help restore river ecosystems, improve water quality, and reestablish natural sediment and nutrient flow, benefiting both aquatic life and human communities.

Dam removal can improve water quality

Damming can have a negative impact on air quality, as it can increase the presence of certain air pollutants. However, dam removal has been shown to have a positive impact on water quality and the surrounding environment.

One of the main ways dam removal improves water quality is by restoring the natural flow of the stream or river. This allows for improved hydraulic capacity and reduced sediment capture, which can enhance the water quality and local habitats. In addition, dam removal can improve the temperature and oxygen levels in the water, which can benefit aquatic organisms and sensitive species.

For example, the removal of a dam on the Housatonic River led to improved conditions, including increased concentrations of dissolved oxygen and the presence of sensitive species such as Hydropsychidae caddisflies and other filter-feeding species. Similarly, the removal of the Lyman Pond Dam led to the identification of rare mussels (S. chordata) at the site.

Another benefit of dam removal is the reconnection of river habitats, which can improve the habitat for rare species, such as freshwater mussels and the eastern box turtle. Dam removal can also help to reduce the risk of flooding, as some dams are classified as having significant hazard potential due to flooding concerns.

Overall, dam removal is being increasingly recognized as a long-term solution for obsolete dams that are no longer needed. It can lead to permanent ecological improvements, strengthen resilience against climate change, and create short-term and long-term cost savings.

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