Fertilizers' Impact On Water Pollution: Understanding The Connection

Fertilizers are essential for crop growth, but they can also be a source of water pollution. When excess fertilizers are applied to fields, the nutrients they contain, such as nitrogen and phosphorus, can be washed away by rain or irrigation and end up in nearby waterways. This process is known as runoff. Once in water bodies, these excess nutrients can cause a phenomenon called eutrophication, which is the enrichment of water with nutrients, leading to an overgrowth of algae. This algal bloom reduces water clarity and blocks sunlight, hindering the process of photosynthesis in aquatic plants, which in turn reduces the oxygen levels in the water.

Additionally, certain types of blue-green algae can produce toxins harmful to humans and wildlife, causing fish kills and depleting the water's oxygen levels further. This results in the death of aquatic life and the degradation of water quality, which can also affect drinking water supplies. The impact of algae-affected lakes can be significant, reducing the recreational value of the waterway and potentially lowering the value of surrounding properties.

To mitigate these issues, it is essential to apply fertilizers only when needed, during the proper season, and in the correct amounts. Using water-insoluble fertilizers can also help ensure that the fertilizer remains in the soil and does not leach into water bodies.

Excessive nutrients in water

The increase in nutrients causes harmful algal blooms, which disrupt the natural balance of the ecosystem. These blooms can produce toxins harmful to humans and wildlife, and reduce water clarity and visibility. As the algae grow out of control, they reduce the oxygen available in the water, which can lead to fish kills and deplete the water habitat. This can further degrade drinking water supplies and create environmental nuisances.

To address this issue, it is essential to apply fertilizers in the proper amounts, at the right time of year, and with suitable methods. Implementing nutrient management techniques, such as adopting conservation drainage practices and ensuring year-round ground cover, can significantly reduce the amount of excess nutrients reaching water bodies.

Eutrophication of surface waters

Eutrophication is the enrichment of surface waters with plant nutrients. While eutrophication is a natural process that occurs over centuries as lakes age and are filled with sediments, human activities have accelerated the rate and extent of eutrophication. Agriculture is a major factor in eutrophication, with fertilizers and animal manure providing crops with the nitrogen and phosphorus necessary to grow. However, when nitrogen and phosphorus are not fully utilized by plants, they can be washed from farm fields into waterways during rain and snow melt, or leach through the soil and into groundwater over time. This excess nitrogen and phosphorus in the water can cause eutrophication, leading to hypoxia ("dead zones") and fish kills.

The symptoms and impacts of eutrophication include:

• Increase in production and biomass of phytoplankton, attached algae, and macrophytes.
• Shift in habitat characteristics due to changes in aquatic plant assemblage.
• Replacement of desirable fish species with less desirable ones.
• Production of toxins by certain algae, which can be harmful to humans and wildlife.
• Increasing operating expenses of public water supplies, including taste and odour problems during algal blooms.
• Deoxygenation of water, especially after the collapse of algal blooms, which can result in fish kills.
• Infilling and clogging of irrigation canals with aquatic weeds.
• Loss of recreational use of water due to slime, weed infestation, and noxious odours from decaying algae.
• Impediments to navigation due to dense weed growth.
• Economic losses due to changes in fish species, fish kills, etc.

Water resource managers employ various strategies to minimize the effects of eutrophication, including diversion of excess nutrients, altering nutrient ratios, physical mixing, shading water bodies, and application of algaecides and herbicides. However, these strategies have often proven ineffective, costly, and impractical, especially for large and complex ecosystems. Reducing nitrogen and phosphorus inputs into aquatic systems can improve water quality, but this can be challenging and expensive, especially in agricultural areas where nutrient runoff comes from non-point sources.

Nitrate pollution of groundwater

The impact of nitrate pollution on groundwater is far-reaching. High nitrate levels in drinking water can have detrimental effects on both livestock and humans, causing a condition known as nitrate poisoning or methemoglobinemia ("blue-baby syndrome") in infants and warm-blooded animals. Nitrates interfere with oxygen uptake in the circulatory system, leading to potentially fatal consequences.

Additionally, nitrate pollution contributes to the eutrophication of water bodies. Eutrophication is the process by which a water body becomes enriched with nutrients, leading to excessive growth of algae and aquatic plants. This, in turn, results in oxygen depletion, fish kills, and a decline in aquatic life. The release of nitrates into the environment also has economic implications, as the costs of remediating contaminated water sources and addressing the resulting loss of ecosystem services can be substantial.

To mitigate nitrate pollution of groundwater, it is essential to implement sustainable agricultural practices. This includes adopting nutrient management techniques, such as applying fertilizers and manure in appropriate amounts and at the right time of year. Conservation drainage practices, ensuring year-round ground cover, and implementing conservation tillage are also effective strategies. By minimizing the residual nitrate content in the root zone and preserving nitrates within the N cycle, the nitrate load in groundwater can be significantly reduced.

Regional studies have provided valuable insights into nitrate pollution in groundwater. For example, in Toyserkan, western Iran, 9.5% of groundwater samples exceeded the World Health Organization's drinking water guideline for nitrate concentration. Similarly, in western Europe, rising trends in nitrate concentration in well water have been observed over the last few decades, with agricultural land use being a significant contributing factor.

Algal blooms

Algae thrive and multiply quickly in waterways with an overabundance of nitrogen and phosphorus, particularly when the water is warm and the weather is calm. This proliferation causes blooms of algae that turn the water noticeably green, although other colours can occur. Some species of algae grow in clumps covered in a gelatinous coating, allowing cells to stick together into large surface scums in calm weather. Other types of algae form thick mats that float on or just below the surface along the shoreline.

The potential for blooms comes from nutrient pollution, an overabundance of the essential plant nutrients nitrogen and phosphorus. These elements enter waterways from point sources such as industrial and wastewater treatment plant discharges, nonpoint sources such as septic tanks and stormwater runoff from urban areas, farms and residential areas, and from nutrient-enriched rainfall. When the concentrations of nitrogen and phosphorus increase in a water body, the right combination of temperature, sunlight and low flow can trigger an algal bloom.

To prevent algal blooms, it is important to reduce nutrient pollution. This can be done by using fertilizers wisely, such as only when lawns show nutrient deficiencies, according to manufacturer directions, and avoiding using fertilizers before it rains. Homeowners should only use phosphorus-containing fertilizers to start a new lawn or at most once a year on an established lawn. Additionally, aerating your lawn and adding a top dressing can help retain nutrients and prevent them from washing downstream.

Hypoxia

The impacts of hypoxia on aquatic ecosystems are significant. It can lead to fish kills, a decrease in aquatic life, and even ecosystem collapse. Hypoxia can also have economic consequences, such as in the Gulf of Mexico, where it has decimated the region's once-booming shrimp industry.

To mitigate hypoxia, it is important to reduce nutrient pollution and eutrophication. This can be achieved through various measures, such as adopting nutrient management techniques, using conservation drainage practices, ensuring year-round ground cover, and implementing conservation tillage. By properly managing nutrient application and reducing nutrient runoff, farmers can play a crucial role in minimizing the impacts of hypoxia.

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