Understanding Eutrophication

What is it?

Eutrophication is the process in water by which the ratio of nutrients to dissolved oxygen becomes excessively high. It happens in the presence of large amounts of organic matter and nutrients (phosphorous and nitrogen) that come from both natural and human sources. A eutrophic lake is an ideal environment for the growth of algae and weeds, and a poor environment for the growth of beneficial microorganisms and fish.

Eutrophication accelerates over time. When algae and weeds die they release organic matter which uses up the oxygen in the water as it decomposes. This decomposed biomass becomes a nutrient stockpile, which fuels the growth of more algae, nuisance vegetation, and in the worst case, blue-green algae. The negative effects of this process include an increase in organic muck, poor water quality, bad odors, fish kills and–if toxin producing cyanobacteria are present–closure of the lake to recreation and water supply.

Eutrophication is becoming more prevalent around the world because of human input of excessive nutrients into watersheds. Treated wastewater discharged from sewage treatment plants, agricultural runoff, lawn fertilizers, and various other organic wastes all contribute to the problem. Eutrophication affects water bodies as small as a 100 square foot pond to the Gulf of Mexico. Many vitally important water resources across the world are impacted by varying degrees of eutrophication. Significant examples in the United States include parts of the Chesapeake Bay and the Mississippi Delta region of the Gulf of Mexico.

Symptoms of eutrophication include

Increase in surface water temperature

Increase in the population of invasive weeds and algae

Decrease in dissolved oxygen levels

Decrease in biodiversity and oxygen-dependent animal populations

Thickening organic muck

Submerged and surface weed infestation

Hazardous algae blooms (HABs)

Thermal and oxygen stratification

Cloudiness of water (turbidity)

Bad odors (accumulation of sulfides in sediment)

Fish kills

Beneficial organisms that make up the food chain are starved of oxygen, and nutrient uptake is dominated by invasive weeds and algae. Beneficial and desirable forms of life become nutritionally starved and the natural ecosystem loses its essential biodiversity.

What Causes It?

The nutrients most directly responsible for eutrophication are phosphorus and nitrogen. They may originate from sewage, animal waste, over-fertilization of land for agricultural and aesthetic purposes, or leakage from landfills. The short lifecycles and rapid growth rates of algae, cyanobacteria, and weeds make them better able to capitalize on these nutrient inflows.

Because of the short lifecycle of algae and cyanobacteria–typically only a few days–the blooms rapidly die and fall to the bottom of the lake where they decompose. This process depletes the bottom of the lake of oxygen and produce a mucky, nutrient-rich sediment. In this way the nutrient inflows are stockpiled in the lake sediments, enabling nutrient recycling. A feedback loop is created, driving more algae, more weeds, more nutrients, and less oxygen. For bodies of water that animals and humans depend on, this cycle is a disaster.

There are natural, mitigating factors that counter the process of eutrophication. Beneficial phytoplankton (photosynthetic algae in the water column) produce oxygen through photosynthesis in eutrophic lakes. Some oxygen is lost by coming out of solution into the atmosphere, and the phytoplankton contribution is overwhelmed by the oxygen depletion that decomposing biomass creates. Crustaceans, fish and other important organisms in the food chain often die due to lack of dissolved oxygen (hypoxia). Fish numbers have been reduced by 90% or more as a result of hypoxic conditions. This may happen suddenly, which is an event known as a “fish kill.”

Six Main Problems

1. Oxygen Depletion

Algae, invasive weeds and cyanobacteria do not need dissolved oxygen to thrive. Oxygen-breathing organisms that make up the food web do. Algae, cyanobacteria, and weed decomposition use up oxygen in the water, making it difficult or impossible for fish and other aquatic life to survive. This often leads to the death of many types of aquatic organisms. Oxygen depletion can also make certain areas of the lake uninhabitable. Phosphorus is more soluble in water with low levels of dissolved oxygen than it is in well oxygenated water. It is more easily mobilized from anaerobic sediments for recycling after it is deposited there.

2. Stratification

A variety of factors created by eutrophication stratify the water. Water that has low dissolved oxygen levels is denser and it remains on the bottom. Water at the bottom becomes colder because it does not get warmed by the sun. Because colder water is denser, this further keeps water with low dissolved oxygen in the lower strata of the water column. Warmer water is less dense so it moves to the top of the water column. Water at the surface is oxygenated by dissolving atmospheric oxygen. Oxygenated water is less dense thus also fixed in the upper strata of the water column.

As with the nutrient cycle, deoxygenation of the lower strata simply through mechanical and chemical means is amplified in a feedback loop. Decaying biomass worsens the problem. Lakes that are over 40 feet deep might only have water that is sufficiently oxygenated to support fish life down to a depth of 10 feet.

3. High Levels of Nutrients

High levels of nutrients are the primary driver of a eutrophic aquatic ecosystem. If the full balance and biodiversity could be maintained, this would mean that the lake would remain healthy and all aquatic life forms would be abundant. An abundant food web, at the apex of which are fish, provides a pathway for nutrient clearance as birds of prey, fishermen and animals such as otters remove fish biomass from the aquatic ecosystem.

4. Built-Up of Sediments

When algae, weeds, and cyanobacteria die off in a lake, they fall to the bottom and start decomposing. Decomposition uses oxygen, causing oxygen depletion at the bottom of the lake. All the organisms in the food web, from zooplankton to crustaceans, insects, frogs, and fish, need oxygen to live, so they are excluded from the oxygen-depleted zones of the lake and their vitality is naturally constrained. Organic sediment that accumulates on the bottom (a.k.a. muck) becomes a nutrient stockpile that perpetuates the cycle. Thus, the deposition and accumulation of nutrients in the sediment and the nutrient stockpile helps the nutrient recycling that promotes the dominance of algae, cyanobacteria, and invasive weeds.

5. Public Health Risks

Eutrophication via stratification and deoxygenation of the bottom of the water column creates large amounts of anaerobic and pathogenic bacteria and microbes in lakes. These can cause infectious diseases in humans, fish, and animals. The high bacterial concentration of organisms such as E. Coli in eutrophic lakes also makes it unsafe for people to swim there. At times, fish and other aquatic animals can die when they are infected by the pathogenic and parasitic microorganisms that inhabit eutrophic waters.

Hazardous Algae Blooms (HABs), caused by blue-green algae (a.k.a. cyanobacteria) can produce toxins that are extremely dangerous to human beings and animals. Fish kills, human illness, and the death of pets and livestock have been observed when coming into contact with water impacted by HABs. When a HAB occurs, a water body becomes unusable for recreation, municipal drinking water, or commerce and industry.

6. Reduction in Biodiversity

Not only do bacteria and microbes pose a direct health risk to animals and organisms in the food chain, they also convert nutrients into microbial biomass. This is not a preferred food substrate for organisms that form the foundation of the food chain. As eutrophic conditions take hold, oxygen depletion and nutrient deprivation cause zooplankton numbers to decrease because they are outcompeted for nutrients by algae, cyanobacteria, and invasive weeds. Their capacity to graze upon and control algae levels, and then act as food themselves to organisms higher up the food chain is impaired, and once again positive feedback loops are established that ensure the continuation of the cycle.

Without the full biodiversity of the food web acting as a nutrient clearance channel to keep a pond, lake, dam, or reservoir in balance, the only things that are “well nourished” in a eutrophic water body are algae, weeds and toxic cyanobacteria.

Reversing Eutrophication

The key to reversing the process is to approach the entire ecosystem holistically. Solutions that address less than all six of the problems described above will fall short of the goal. Clean-Flo’s approach is to stimulate natural processes through mechanical intervention and bio-augmentation. The first piece of the puzzle is to oxygenate and destratify the water through our laminar oxygenation and inversion technology. This increases the dissolved oxygen overall, creates a more even distribution of dissolved oxygen, and creates conditions for aerobic – as opposed to anaerobic – digestion of organic matter on the bottom.

The second piece of the puzzle is high levels of nutrients. Higher oxygen levels are a partial solution to excess nutrients. Clean-Flo further addresses the nutrient problem with proprietary biological and natural products. Nutrient sponge, enzyme solutions, and mineral nutrients that feed essential microorganisms, all contribute to rapid reduction of excess nutrients.

By performing comprehensive evaluations of the health of a lake’s ailing health, Clean-Flo engineers systems and product application programs that fundamentally alter the lake’s biology and return it to a natural balance.

Just Some of the Benefits

Clean-Flo’s track record over the last 50 years has been to address and overcome the problems wrought by eutrophication. Our systems have successfully returned recreational lakes to their original condition, eliminated HABs, made swimming beaches usable, led to thriving fish populations, clarified excessively turbid water, reduced muck, increased the depth and capacity of lakes, and made many other positive improvements to our customers’ communities and properties. These benefits greatly help to protect the ocean!