Human Impact: Polluting Our Watersheds

Humans can pollute watersheds in several ways, and this has a detrimental effect on the health of our waterways. A watershed is an area of land that drains water into a single location, such as a stream, lake, or wetland. These bodies of water are essential for drinking water, agriculture, and manufacturing, and they also provide habitats for numerous plants and animals. However, human activities can introduce pollutants into watersheds, including soil from construction sites, waste from septic systems, fertilizers, pesticides, and chemicals such as mercury, lead, and arsenic. These pollutants can be discharged directly into the water or washed off the land into water bodies, impacting the water quality and the health of aquatic ecosystems. Additionally, changes in water flow, such as paving large parking lots or redirecting streams, can lead to problems like flooding and lower groundwater levels. Protecting watersheds is crucial for maintaining clean water sources, supporting biodiversity, and ensuring the well-being of both human communities and wildlife that depend on healthy watersheds.

Industrial waste

In some cases, industrial wastewater is properly cleaned by recycling systems and is sometimes reused or disposed of in an environmentally friendly way. However, in other cases, it is discharged untreated into nearby public waters. This is particularly common in emerging countries such as China, India, Africa, and South America, where the number of industrial plants has recently started to grow, and environmental policies are not yet stringent enough.

The discharge of residual pollution into public waters has serious consequences. Many of the hazardous substances from industry are difficult to biodegrade and accumulate in water sediments. This can lead to illness and death among fish, crustaceans, and other creatures, causing a decrease in biodiversity.

Through cracks in the ground, polluted water from rivers and lakes can infiltrate groundwater, which is used for drinking water. This means that hazardous substances from industrial waste can end up in our drinking water. For example, chlorobenzene, a carcinogenic substance used in the textile industry and the production of insecticides, dyes, pharmaceuticals, and fragrances, has been detected in food and breast milk.

To prevent water pollution from industrial waste, several measures can be taken, including policy changes, controlled industrial growth, investment in sustainable technologies, and managed waste treatment and disposal.

Nonpoint source pollution

Oil, grease, and toxic chemicals from urban runoff and energy production can also contribute to nonpoint source pollution. Sediment from improperly managed construction sites, crop and forest lands, and eroding streambanks can be picked up by runoff and carried into waterways.

Bacteria and nutrients from livestock, pet waste, and faulty septic systems are another source of nonpoint pollution. Atmospheric deposition and hydromodification can also play a role, with pollutants being deposited directly into bodies of water through rainfall or other means.

To prevent nonpoint source pollution, it is important to keep street gutters and storm drains clear of litter, pet waste, leaves, and debris. It is also essential to properly dispose of used oil, antifreeze, paints, and other household chemicals, as well as to clean up any spills.

Septic waste

Septic systems can have a detrimental impact on watersheds, particularly in coastal areas. Septic systems are used by approximately 25% of US households, with higher rates in rural areas and certain states, such as Florida and New York. These systems are often antiquated and do not adequately treat sewage, allowing household waste to contaminate groundwater and surface waters.

Septic systems are designed to allow solids and liquids in household wastewater to separate in a septic tank. Bacteria in the tank then digest the solid sludge, and the liquid effluent flows into a leaching pool or drain field, where it percolates through the soil and eventually joins groundwater supplies. However, if a septic system is poorly designed, installed, or maintained, it can cause serious problems.

One of the most significant issues is the contamination of surface and groundwater with disease-causing pathogens and nitrates. When septic systems are situated too close to groundwater sources, or during periods of flooding, the effluent may not be adequately filtered, allowing pathogens to reach water sources. This can pose a direct public health risk, particularly in recreational swimming areas, and can even result in beach closures.

Another consequence of septic waste is the excessive discharge of nitrogen into sensitive coastal waters. Nitrogen acts as a fertiliser, causing rapid algae blooms that deplete the water of oxygen as they decompose, leading to mass die-offs of fish and other aquatic life. In tropical regions, these blooms can smother coral reefs, while in temperate regions, they contribute to the decline of seagrass beds, which provide vital habitat for fisheries.

Phosphorus pollution from septic systems is also a concern, particularly for inland surface waters. Phosphorus further contributes to algal growth and lowers dissolved oxygen levels, creating "dead zones" where aquatic life cannot survive.

To mitigate the impact of septic waste on watersheds, it is essential to ensure that septic systems are properly designed, installed, and maintained. Homeowners should consult professionals before making significant upgrades to their septic systems. Additionally, new septic technologies that can remove nitrogen from wastewater and have shallower drain fields better suited to coastal areas are now available. Connecting homes and businesses to central sewers and sewage treatment plants is also a preferred option where possible.

Pesticides and fertilisers

Pesticides are materials designed to control, prevent, kill, reduce, or repel pests. They can be made from natural ingredients or synthetic chemicals. All pesticides are toxic to some degree, but each varies in their toxicity to humans and other animals. Pesticides can be spread through a technique called crop dusting, where they are dusted onto agricultural lands. They can also be applied as granules or drenches.

Fertilisers are materials added to the soil to increase its fertility. They are made up of three nutrients essential for plant growth and survival: nitrogen, phosphorus, and potassium.

Indoor sewer drains collect wastewater from toilets, sinks, washing machines, and showers in homes, restaurants, and businesses. Pesticides and fertilisers can enter these drains through improper disposal or laundering of contaminated clothing. While the water is filtered and disinfected at treatment plants, not all pesticides and fertilisers are removed.

Applying pesticides and fertilisers to the soil can allow them to enter the groundwater below. Some pesticides can percolate with water through the soil and leach into underground aquifers. This can contaminate groundwater used for drinking by residents with wells and eventually enter surface waters.

The overuse and misuse of pesticides and fertilisers can harm the environment and human health. They can make water unsafe for recreation and drinking, creating dead zones where aquatic life cannot survive. When aquatic invertebrates are killed by pesticide and fertiliser runoff, it affects the entire food chain.

Oil spills

The impact of oil spills on watersheds is significant due to the nature of oil and the ways in which it spreads. Oil is less dense than water, so when spilled, it spreads quickly across the water surface, aided by currents, wind, and warm temperatures. This rapid spread makes containing oil spills challenging. Oil can also settle at the bottom of water bodies, depending on its density relative to the water. Additionally, tides and winds can carry oil over long distances, affecting sensitive areas like beaches and intertidal zones.

The clean-up of oil spills is a complex and time-consuming process. Natural processes like biodegradation, where bacteria break down hydrocarbons, and weathering, which alters the characteristics of the oil, can help reduce the impact of spills. However, human intervention is often necessary. Booms, skimmers, chemical dispersants, and burning are common methods used to contain and remove oil from the environment. The choice of method depends on the type and amount of oil, location, and weather conditions.

The consequences of oil spills can be long-lasting, with recovery times ranging from weeks to decades. Exposed beaches may recover within months, but more sensitive ecosystems like mangroves can take up to 50 years. Oil spills also have economic repercussions, with clean-up efforts requiring significant financial investments and impacting industries such as fishing and tourism.

To reduce the occurrence of oil spills, regulations such as the United Nations treaty MARPOL have been implemented. This treaty mandates the use of oil-pollution prevention equipment, such as double hulls on ships, to minimise the risk of spills. Additionally, individuals can play a role by properly disposing of oil and other hazardous substances, conserving water, and reducing their use of vehicles that contribute to car leaks and exhaust pollutants.

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