How Does Fertilizer Runoff Lead To Problems In Aquatic Ecosystems?

Fertilizer is an essential part of maintaining a lush, healthy lawn. But if you improperly fertilize your lawn, the excess can end up in lakes, rivers, and oceans, presenting an array of problems. But how bad can fertilizer actually be for the environment? It’s great for plant growth, so how does it affect aquatic ecosystems?

Let’s find out.

Key Points:

  • Fertilizers contain the essential nutrients needed for plant growth, including nitrogen, potassium, and phosphorous.
  • Excessive fertilizer that runs into lakes and rivers can lead to decreases oxygen levels and algal blooms that produce toxins.
  • These changes can ultimately have catastrophic impacts on the ecosystems, such as suffocating animals and causing unpleasant smells in water bodies.

What Is In Fertilizer?

fertilizer spreader

Fertilizer is designed to feed the plants in your garden and the grass across your lawn. Like living creatures, plants need a few things to thrive in their environment. For plants, these needs include plenty of water, oxygen, and nutrients. Fertilizer is one way to supply these nutrients, as some soil types don’t contain the nutrients necessary to support plant life.

The exact contents in fertilizer varies based on the specific blend, but most fertilizers consist primarily of nitrogen, potassium, and phosphorous. These nutrients are readily available in a form the plant roots can access without issues, promoting healthy and robust growth.

Generally, you add fertilizer to your lawn and garden before, during, and after the growing season to help them establish, thrive, and prepare for upcoming dormancy. However, while fertilizing on a regular schedule is essential for vigorous plant growth, too much fertilizer can cause a problem.

The plants can only use so much fertilizer, so if you over-fertilize, the excess can actually kill the plant. Beyond that, the excess fertilizer can run into storm drains, eventually ending up in streams, rivers, lakes, and oceans.

How Fertilizer Runoff Leads To Issues Within Aquatic Ecosystems

Excessive fertilizer runoff causes ripple effects throughout aquatic systems, including lakes, streams, rivers, and oceans. The runoff can result in disruptions and imbalances throughout the local ecology, as fertilizers are designed to be water-soluble.

Depleted Oxygen Levels

Oxygen depletion is a significant concern of commercial fertilizer runoff. When these fertilizers enter the surface water of lakes, rivers, streams, and oceans, they release nutrients, as they’re water-soluble.

These nutrients facilitate and stimulate the growth and reproduction of various microorganisms. Unfortunately, these microorganisms require excessive amounts of energy to grow and reproduce, causing oxygen depletion in the body of water.

Fish and other marine species may suffocate as a result of this oxygen depletion. As marine creatures die off due to oxygen depletion, their remnants negatively impact the quality of the water, producing unpleasant odors in and around the water.

Algal Blooms

Aside from depleted oxygen levels in water sources, algal blooms are the other prevalent concern of fertilizer runoff into these systems. Algal blooms are clusters of rapidly growing microscopic algae or cyanobacteria in water, and they often present as colored foamy scum on the water’s surface.

These blooms result from high concentrations of nutrients, like those found in fertilizers. While marine ecosystems naturally contain some nutrients that can spiral into algal blooms, they don’t usually have enough to create a problem. The naturally found nutrients in water systems aid in marine plant growth, but when the nutrient levels rise too high, the algae grow overly large.

These blooms are often classified as red or brown tides, although the classification hinges on the affected algae type. The problem with blooming algae is the toxin release. At typical levels, the toxins from algal growth are inconsequential to marine ecosystems.

Once they spiral out of control with massive algae blooms, the toxins majorly impact the creatures living within the ecosystem. They can easily poison the ecosystem’s inhabitants, leading to catastrophic results.

In addition to the toxin release, algal blooms consume excessive amounts of oxygen for growth. As they draw large amounts of oxygen to grow, they deprive the water of oxygen, potentially suffocating the ecosystem’s residents.

When these algal blooms become large enough, they can cause the ecosystem beneath to shut down. These spots are known as dead spots, as typical marine life is unable to thrive or live. Dead spots commonly appear seasonally near the mouths of major rivers, causing the deterioration of aquatic environments.

While the disappearance of algal blooms helps the marine ecosystem, it can take the ecosystem years to recover to its former, life-filled self. Since the dead spot is devoid of marine life, it can affect neighboring ecosystems that require fish and crustaceans for survival, creating a further ripple effect.

Contaminated Drinking Water

One of the issues with fertilizer runoff is its effect on drinking water. When excess amounts of fertilizer end up in water sources, the nitrates in its contents can quickly leach into groundwater. These nitrates don’t absorb into the soil composition, so they end up in the runoff.

Although nitrates alone don’t present a toxic threat to animals and aquatic life, they can present other issues. High concentrations of nitrates can lead to a disease known as nitrate poisoning, which poses a threat to livestock, humans, domestic animals, and other mammals that consume it.

Consuming water packed with nitrates has a laundry list of symptoms, most of which are associated with a disorder known as methemoglobinemia. It is a rare disorder that affects how the red cells in your body deliver oxygen and can be life-threatening. This condition presents itself through various symptoms, including nausea, cyanosis (blue-tinted skin), dizziness, weakness, seizures, and more.

On top of that, consuming nitrates affects the circulatory system’s oxygen uptake in humans and livestock, presenting a significant risk.

What Would Happen If Too Much Fertilizer Runs Into The Ocean?

The effects of fertilizer runoff into bodies of water, like the ocean, are devastating. As mentioned, the fertilizer quickly causes issues, including algal blooms, oxygen depletion, and contaminated drinking water.

Dead zones are common in areas where fertilizer runoff is prevalent, as the water cannot support marine life. High amounts of nitrogen lead to eutrophication, which spirals into massive algae blooms and hypoxia in the surrounding environment.

Does Nitrogen Remain In Water Sources Indefinitely?

Generally, bacteria remove the nutrients from fertilizers in water sources. They utilize a chemical process called denitrification, which essentially allows the bacteria to convert nitrates to nitrogen. After the completion of this process, the bacteria release the nitrogen into the atmosphere as a gas, effectively lowering the nitrate level in the water source.

However, while this process removes nitrogen from water sources, it isn’t a magical catch-all. The team of researchers at the Oak Ridge National Laboratory, led by aquatic ecologist Patrick Mulholland, found that bacteria in streams only eliminate a percentage of nitrogen pollution. On average, they removed approximately 16% of the nitrogen pollution, although the percentage climbed in undisturbed streams.

Of course, this particular study doesn’t encompass denitrification in all water sources, but it offers an idea of how the process happens.

Unfortunately, nitrogen from fertilizers doesn’t disappear overnight, even with the efforts of bacteria. According to a study by researchers at the University of Waterloo, the fertilizers applied to fields today could pollute water sources for decades. The study states these fertilizers will persist for many years, even if fertilizer use came to a screeching halt today.

What Causes Fertilizer Runoff?

Fertilizer runoff occurs as a result of various scenarios. While excess fertilizer from residential and commercial lawns contributes to the problem, agricultural applications contribute largely. Here are a few of the most common scenarios that contribute to fertilizer runoff:

  • Overapplication: Plants can only handle so much fertilizer. When you over-fertilize your lawn, the excess will likely end up as runoff, which doesn’t benefit your plants at all. Once the plant roots reach their max, the excess fertilizer is useless.
  • Excessive irrigation: Overwatering your lawn (or excessive agricultural irrigation) can result in fertilizer runoff, as the soil becomes oversaturated and cannot absorb more moisture, much less the fertilizer.
  • Heavy rains: Downpours can wash your fertilizer from your lawn, unspooling your careful application and washing it into storm drains. So, ensure you plan your fertilizer schedule around suitable weather.
  • Poor timing: It’s essential to time your fertilizing schedule appropriately. If you apply fertilizer on frozen or partially frozen ground, the fertilizer can’t sink into the soil as easily as it would with thawed soil. Because of this, it’s more likely to run over the frozen ground until it reaches a penetrable environment, like warmer soil or a body of water.
  • Improper waste disposal: If you don’t eliminate lawn clippings properly, you leave them vulnerable to runoff. They often contain fertilizer residues, which can end up in water sources due to leaching and heavy rains.

How Does Fertilizer End Up In Water Systems?

Those massive grates in the ground collecting water from heavy rains and storms are responsible for carrying fertilizer runoff to lakes, streams, rivers, and oceans. In a rain storm, the water running off the lawn collects unused fertilizers from the soil, carrying it into the storm drain.

These drains often feed directly into streams, rivers, lakes, and oceans, resulting in fertilizer pollution. The process is very similar to the path of excess fertilizer out of agricultural fields. However, the excess fertilizer leaches out of the soil instead of flowing into storm drains, eventually ending up in rivers and streams.