Damaging Consequences of Agricultural Runoff

Damaging consequences of agricultural runoff contribute significantly to the ecological crisis of these days. What appears as mere excess water from farming is, in fact, a harmful mix of nutrients, metals, and pathogens. 

Farmers add nutrients to their fields using chemical fertilizers and animal manure. These fertilizers provide essential nutrients based on nitrogen and phosphorus, which are crucial for crop growth and ultimately, our food supply. 

However, there is a downside to their vast application in modern agriculture. When crops do not fully absorb these nutrients, they get washed off from the fields and lead to environmental issues in the surrounding ecosystem. 

This runoff leads to widespread environmental damage, from coastal dead zones to loss of biodiversity. The surplus nitrogen and phosphorus usually gets into nearby water bodies during rain or snowmelt, and from there pollutes the freshwater. It can also seep through the soil over time, contaminating groundwater and spread even further. 

Excess agricultural runoff is more than a farming issue. It is an environmental emergency. Driven by unchecked pollution, its effects extend far beyond water contamination. 

Why is agricultural runoff bad? 

Agricultural runoff is considered bad because it disrupts the natural nutrient balance in the environment. In a balanced ecosystem, nutrients like nitrogen and phosphorus circulate in a delicate equilibrium, supporting plant growth, nourishing soil microorganisms, and maintaining the health of aquatic systems. However, our modern agricultural practices and other industrial activity often tip this balance off.

When farmers apply fertilizers, they aim to provide crops with the optimal amount of nutrients for abundant growth. But it is not so easy to match the fertilizer amount perfectly with what the plants can absorb at the given growth stage and environmental conditions (temperature, humidity). As a result, excess fertilizer remains in the soil.

That is where the problem begins. Rainfall or irrigation washes these residuals off the crop lands. They are then washed into nearby waterways or leach into groundwater. But in natural ecosystems, the availability of nutrients like nitrogen and phosphorus is limited and is often the factor that actually constraints growth. This limitation is crucial for maintaining biodiversity, as it prevents any single species from dominating the environment due to an overabundance of resources. 

However, when agricultural runoff pours these nutrients into ecosystems, it disrupts this natural constraint. The sudden influx of high nutrient levels leads to an imbalance. In aquatic systems, for example, this can result in overstimulation of algae growth, which has further effects on the ecosystem.

What is an example of agricultural runoff? 

A prime example of far reaching effects of agricultural runoff can be seen in the Gulf of Mexico’s “Dead Zone.” This is a direct result of agricultural runoff from the Mississippi River Basin, which encompasses a vast area in the central United States.

In this region, a significant amount of farming occurs, with extensive use of fertilizers containing nitrogen and phosphorus to enhance crop yields. When it rains, the runoff carries high levels of nitrogen and phosphorus and enters local streams and rivers which eventually make its way down the Mississippi River to the Gulf of Mexico.

Once in the Gulf, these nutrients stimulate the overgrowth of algae in a process known as eutrophication. When the algae die, they sink to the bottom and decompose. This whole process consumes a lot of oxygen and creates low oxygen areas in the water. The Gulf of Mexico is so depleted of oxygen that it cannot support most marine life, hence the name “Dead Zone.”

A second example is also connected with industrial farming and its negative impacts. It is about the Concentrated Animal Feeding Operations (CAFOs). CAFOs are large-scale livestock farms where cows, pigs, chickens, and turkeys are confined and raised in limited spaces for a significant portion of their lives. These farms are designed only for high yields in animal products – eggs, dairy, meat.

However, one of the biggest environmental issues with these farms is the massive amount of manure they generate. Livestock and poultry in the U.S. generate nearly 1.4 billion tons of manure annually. This figure is almost five times the waste produced by the entire U.S. human population. 

Due to the concentrated feed animals consume, their manure is rich in nutrients like nitrogen and phosphorus, similar to the fertilizers used in crop farming. So, when applied on the croplands as fertilizer, it still contributes to nutrient-dense runoff as artificial fertilizers do. 

Further complicating the issue are the manure lagoons associated with animal farms. These lagoons, sometimes as large as football fields, temporarily store the manure and can contain a mix of antibiotics, chemicals, and bacteria. They are often unlined and susceptible to overflows and leaks.

What are the negative effects of agricultural runoff on the environment? 

Agricultural runoff represents a major threat to rivers and lakes. Dangerous chemicals, waste, and soil create algal blooms, disrupt aquatic ecosystems and lead to the emergence of “dead zones” for animals and plants. It leads to eutrophication, which is unnatural enrichment of water bodies with organic and inorganic nutrients, leading to the unbalancing of the local marine ecosystem, reduced water clarity, and pesticide contamination.

In the United States, polluted runoff remains the main source of pollution of drinking water reservoirs. Contaminated water, through rivers and streams, ends up in water reservoirs that provide drinking water to millions of people and water treatment plans spend vast amounts of money on removing potentially harmful chemicals.

The way we manage agricultural lands is causing this big problem. When it rains or snow melts, the water washes away loosen and barren soil, exposed manure, and other chemicals from farms into rivers and lakes. The composition of runoff varies across the countries and locations, as it depends on the type of farming, soil type, and local environment. 

In fact, half of the rivers and streams in the United States have too many nutrients, and only about a quarter are in good health. In lakes, about one in five has too much algae. Worse still, about 40% have harmful toxins from algae. Even the coastal waters are affected, with around 21% having high nutrient levels.

The list of negative effects of agricultural runoff on the environment doesn’t end there. Let’s see the key impacts that are caused by this issue:

#1 Eutrophication of water bodies 

Excess nitrogen and phosphorus from fertilizers lead to overgrowth of algae in water bodies. When these algae die and decompose, they consume a large amount of oxygen, leading to hypoxic conditions (Dead Zones) where aquatic life cannot survive. 

These areas lead to fish deaths and a decline in other aquatic life. Additionally, these blooms not only disrupt the ecosystem but can also produce toxins dangerous to human health (following).

#2 Harmful algal blooms 

Some types of algae that thrive on excess nutrients produce toxins harmful to both aquatic life and humans. These blooms, also known by many as blue-green algae, contaminate drinking water supplies or recreational waters where they impact leisure time activities. 

For example, cyanobacteria called Microcystis produces toxins that damage liver and are carcinogenic. Other cyanobacteria strains irritate skin, aggravate eczema problems and allergy symptoms. Some people may experience vomiting and headache after the exposure to this algae as well. 

In many areas with recreational lakes with warm and still water, these algal blooms have become a common occurrence during the warmest season of the year. During that time it is not recommended to any exposure of humans or pets to such water.  

There have also been numerous cases where algae growth caused pollution to drinking water. While drinking water quality is subject to regular analysis, the cleanup and purification of the contaminated water has been costly for municipalities. 

#3 Contamination of drinking water

High nitrate levels in drinking water are particularly dangerous for babies under 6 months of age, causing the Blue Baby Syndrome when they do not have enough oxygen in their blood. In adults, drinking water contamination by agricultural runoff could lead to chronic problems with thyroid gland and colon cancer. 

The problem with drinking water is that in many cases the contamination appears far from the farm lands and is often not attributed to agricultural practices. 

#4 Permanent soil degradation 

Excessive runoff from overused croplands leads to soil erosion. The loss of the topsoil layer year after year reduces its fertility and ability to support agriculture in the long term. The response of farmers in such cases is to apply additional loads of agricultural chemicals to raise the yields to acceptable levels. 

Additionally, runoff from the damaged and exhausted lands often carries extra loads of pesticides and heavy metals from soil. These substances can accumulate in some areas above expected levels and disrupt soil and water health, or even enter our food chain via different pathways.

#5 Biodiversity loss 

The change in nutrient levels and chemical composition of natural habitats due to runoff can disrupt the balance of local ecosystems. This leads in many cases to a loss of biodiversity, as certain species become dominant while others decline or disappear.

#6 Contribution to climate change

Certain agricultural practices linked to runoff, such as the overuse of nitrogenous fertilizers, can release greenhouse gasses like nitrous oxide. These emissions contribute to global warming and climate change.

#7 Sedimentation in waterways

Runoff often carries soil and other particulate matter, leading to sedimentation in rivers, lakes, and streams. This affects water clarity, harms aquatic plants, disrupts fish spawning grounds, and reduces the navigability of waterways.

How to effectively prevent agricultural runoff? 

So, what can we do? 

A connection between agricultural runoff and water pollution, as well as the need to address the negative effects of this process have been discussed for decades at national and international levels. 

There is a number of solutions and prevention methods that received attention:

• To avoid soil erosion, it is necessary to maintain agricultural soil with a simple method of crop rotation.
• Another method is no-till agriculture, not common in industrial farming and yet an effective measure to reduce soil erosion. Tilling has been proven to increase soil erosion, thus, no-tilling agriculture could help farmers keep the soil in place.
• Nutrient and fertilizer managements are also crucial to reducing the negative impacts of agricultural runoff.
• Planting vegetation or maintaining undeveloped land along the edges of fields helps to trap and filter out pollutants before they reach water bodies.
• Management measures aimed at livestock agricultural runoff mitigation are also important. There is a need to minimize erosion of the land for grazing, while maintaining vegetation on it.
• Implementing systems for the proper storage, treatment, and disposal of animal waste to prevent runoff.
• Using GPS and other technologies to precisely apply water, fertilizers, and pesticides, reduces excess runoff. This is a new farming technique called Precision Agriculture. Sensors and remote monitoring can help in real-time tracking of soil moisture and nutrient levels.

• Most importantly, there is a need for wider awareness raising and education to help shift agricultural practices towards sustainable rails.
• Implementing and enforcing guidelines on the types and amounts of chemicals used in farming.

A lot of runoff happens during heavy rains in spring and fall. During these times, the crops aren’t using much nitrogen. To fix this, farmers need to be careful about when and how much fertilizer they use. They should only apply fertilizers when plants need it most.