Polluted Water: A Silent Killer Of Crops

Water pollution is a growing global concern that not only damages economic growth but also the health of billions of people. The increasing demand for food with high environmental footprints, such as meat from industrial farms, has led to unsustainable agricultural intensification and water-quality degradation. This has resulted in the excessive use of chemical fertilizers, pesticides, and antibiotics, which are contaminating water supplies and killing crops. In this topic, we will explore the impact of polluted water on crops and the measures that can be taken to mitigate this issue.

Excess nutrients from fertilisers and manure

Farmers apply these nutrients to their fields in the form of chemical fertilisers and animal manure. However, when nitrogen, phosphorus, and other nutrients are not fully utilised by the growing plants, they can be washed away from the fields and enter nearby waterways. This can occur during rain or snow melt events, or through leaching into the groundwater over time. The excess nutrients then fuel the rapid and uncontrolled growth of algae and aquatic plants, leading to a phenomenon known as eutrophication.

Eutrophication is characterised by an abundance of aquatic plants and low oxygen levels in the water. As the algae and plants grow uncontrollably, they block light for other aquatic plants and deplete the oxygen in the water during their decay process. This leads to hypoxic or anoxic conditions, which can be fatal for fish, crabs, oysters, and other aquatic organisms. Additionally, the decay process can produce toxins that are harmful to humans and other animals. This results in the creation of "'dead zones'" in the water, where aquatic life cannot survive.

Furthermore, the excess nutrients from fertilisers and manure can contaminate water sources through runoff from manure application sites and livestock access to streams. Ammonia-contaminated runoff from fresh manure can be toxic to aquatic life, even at low concentrations. Additionally, the manure may contain pathogenic microorganisms, including bacteria, viruses, parasites, and fungi, which can cause diseases in humans and animals.

To mitigate these issues, farmers can adopt improved nutrient management techniques. This includes applying the right amount of nutrients at the appropriate time of year, using conservation drainage practices, and ensuring year-round ground cover to prevent nutrient loss and erosion. By implementing these practices, farmers can reduce the impact of excess nutrients on water quality and minimise the negative consequences for aquatic ecosystems and crop health.

Pesticides and heavy metals

Pesticides are chemicals used to kill or control pests that can damage crops. They include herbicides (for killing weeds), insecticides (for killing insects), and fungicides (for killing fungi). While pesticides serve an important purpose in agriculture, protecting and increasing yields, they can also be toxic to humans and the environment. Older, cheaper pesticides, for example, can remain in the soil and water for years, leaching into water sources and contaminating them. This is especially true for groundwater, which moves slowly, meaning that it can take decades for contaminated water to move beyond affected wells.

The health effects of pesticides depend on the type of compound. Some affect the nervous system, while others irritate the skin and eyes. Certain pesticides are carcinogenic, and others can affect the hormone or endocrine system. The application of pesticides must, therefore, be carefully managed. Best Management Practices (BMPs) that reduce runoff or soil erosion can help to reduce pesticide transport. Other strategies include limiting and optimizing the type, amount, and timing of pesticide applications, and establishing protection and buffer zones around watercourses and farms to reduce the migration of pesticides into water bodies.

Heavy metals are elements with a specific weight of more than 5 g/cm^3^ or a density at least 5 times greater than water. They can be categorized as either essential or non-essential. Essential metals, such as copper, are necessary for human health in the right amounts. For example, copper is essential for hemoglobin formation and carbohydrate metabolism. However, in excess, essential metals can cause cellular damage. Non-essential metals, such as cadmium, lead, arsenic, mercury, and nickel, have no health benefits and can be toxic even at low concentrations.

Heavy metals are released into the environment through natural processes and human activities such as industrialization, agriculture, and medicine. They are hazardous, non-biodegradable, and water-soluble, meaning they can easily enter plants and humans, causing adverse effects. In plants, heavy metals can inhibit growth, reduce nutritional value, and affect photosynthesis. In humans, they can enter the body through contaminated food and water, skin contact, or inhalation, and they can be transmitted to various organs through the circulatory system.

Microbiological contamination

Water contaminated with microbial pathogens can be detrimental to crops. These pathogens can be introduced to water sources through livestock manure, which can contain bacterial, viral, and parasitic pathogens. Manure is often used as a fertilizer, providing crops with the nitrogen and phosphorus necessary to grow. However, when these nutrients are not fully utilized by the plants, they can negatively impact water quality. Excess nitrogen and phosphorus washed from farm fields can cause eutrophication of water bodies, leading to hypoxic "dead zones" and a decrease in aquatic life.

The properties of the soil itself, including porosity, chemical composition, and degree of saturation, also play a role in pathogen migration. Microbial movement is generally greater in saturated soils as pathogens move with groundwater flow. During heavy rainfall, viable pathogens in subsurface soils can detach and migrate into groundwater, especially when there are pathways such as unsealed well heads.

To mitigate the risks associated with microbiological contamination, farmers can employ various strategies. These include controlling the quality of the irrigation water source, implementing proper stewardship practices, and adopting conservation drainage practices such as subsurface tile drainage to manage water movement and reduce nutrient loads. Additionally, establishing protection zones along watercourses and buffer zones around farms can effectively reduce the migration of pollutants to water bodies.

By combining these strategies and following guidelines and regulations, farmers can play a crucial role in reducing the impact of microbiological contamination on crop health and, consequently, on the safety of the food supply and human health.

Eutrophication and hypoxia

Eutrophication is a process that occurs when there is an over-enrichment of water by nutrients such as nitrogen and phosphorus. This over-enrichment of water leads to an abundance of algae and plants, which eventually decompose, producing large amounts of carbon dioxide. This decomposition process lowers the pH of seawater, a phenomenon known as ocean acidification. Acidification slows the growth of fish and shellfish and can even prevent shell formation in bivalve mollusks, such as oysters, clams, and scallops.

The two most acute symptoms of eutrophication are hypoxia (oxygen depletion) and harmful algal blooms. Hypoxia arises as the excess algae and plant matter deplete the oxygen content in the water, creating "dead zones" that cannot support aquatic life. This depletion of oxygen not only affects fish and other aquatic organisms but can also have severe consequences for crops. As the oxygen levels in the water decrease, the water's ability to support aquatic plant life, which is essential for crop irrigation, declines, leading to reduced crop yields or even crop failure.

Agricultural practices are a significant contributor to eutrophication. The excessive use of synthetic nitrogen and phosphorus fertilizers, as well as manure from concentrated animal feeding operations (CAFOs), leads to nutrient runoff and leaching into water bodies. Between 1960 and 1990, the global use of synthetic nitrogen fertilizer increased by more than seven times, while phosphorus use more than tripled. This rapid increase in nutrient use has had detrimental effects on aquatic ecosystems, with 415 coastal areas identified as experiencing eutrophication.

To mitigate the impacts of eutrophication and hypoxia, it is crucial to address the underlying causes. Implementing management measures in crop production to reduce the risk of water pollution due to fertilizer and manure use is essential. This includes optimizing the type, amount, and timing of fertilizer applications to match crop needs and prevent excess nutrients from entering water bodies. Additionally, establishing protection zones along water bodies and utilizing efficient irrigation schemes can help reduce the migration of pollutants into aquatic ecosystems.

By addressing the issue of eutrophication and hypoxia through sustainable agricultural practices and pollution prevention measures, we can help protect aquatic ecosystems and ensure the availability of healthy water resources for crop irrigation, ultimately supporting the growth of crops rather than contributing to their demise.

Climate change and water availability

Climate change is primarily a water crisis. It is disrupting weather patterns, leading to more frequent and intense extreme weather events, exacerbating water scarcity and contaminating water supplies. The impacts of climate change are felt through worsening floods, rising sea levels, shrinking ice fields, wildfires, and droughts. These impacts threaten sustainable development, biodiversity, and people's access to water and sanitation.

Water availability is becoming increasingly unpredictable due to climate change. Extreme weather events, such as floods and droughts, are making it more difficult to access safe drinking water. Between 2001 and 2018, around 74% of natural disasters were water-related, and the frequency and intensity of these events are expected to increase. Climate change is projected to intensify droughts, leading to a loss of water supply and increased demand.

Rising sea levels are causing freshwater sources to become contaminated with saltwater, compromising the water resources that millions of people rely on. Saltwater intrusion, whether in groundwater or surface water, reduces the amount of available freshwater and degrades its quality. This is particularly impacting coastal areas and low-lying regions.

Climate change is also increasing the risk of water pollution. Heavy downpours and increased stormwater runoff can wash pollutants and sediment into rivers, lakes, and streams, complicating water treatment processes and increasing costs. Higher water temperatures can promote the growth of harmful algae and microbes, further threatening water availability and increasing the need for drinking water treatment.

To adapt to the water effects of climate change, sustainable water management practices are crucial. This includes exploring and protecting groundwater sources, harnessing unconventional water resources such as treated wastewater, and implementing efficient irrigation schemes to reduce the migration of pollutants into water bodies. Additionally, protecting and expanding natural buffers, such as coastal mangroves and wetlands, can help regulate water flow, prevent flooding, and build resilience to extreme weather events.

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