What is the Cause of Algal Bloom in Dams?

Is your dam struggling with freshwater algal blooms? Better known as harmful algal blooms (HABs), these clumps of algae are caused by various things like excessive nutrients and could be the downfall of your dam’s water quality and overall ecosystem.

What is an Algal Bloom?

When algae such as cyanobacteria (green-blue algae) grow exceptionally fast, it’s called an algal bloom. Green-blue algae are identified by a tell-tale scum on the water’s surface and can range in colour from brown to blue-green. These test kits will tell you whether your algae is green-blue algae.

Algal blooms typically appear in stagnant water with excess nutrients, so it’s no surprise that dams have the perfect environmental conditions for them. Unfortunately, this includes harmful algae that impact aquatic life and human health.

Not all algal blooms are dangerous; however, HABs can produce toxins that disrupt entire ecosystems. HAB toxins move up the food chain, affecting underwater plants all the way to humans.

Unlike normal amounts of algae, blooms typically grow in patches and emit strong odours. 

Why Are Algal Blooms Problematic in Dams?

HABs cause lots of problems for dams, transcending further than aesthetics. When algal blooms inevitably die, their decomposition process uses a lot of oxygen, leaving little for other organisms.

Certain cyanobacteria in HABs produce potent toxins, including microcystins, which can be harmful or even fatal to humans and animals that ingest or come into contact with them.

Additionally, as algal blooms on the water’s surface, it can create a ceiling too dense for sunlight to penetrate deeper layers. Aquatic plants require sunlight for photosynthesis and will struggle to grow or fight off diseases. As plants die, so do the fish that eat or use them for shelter.

Finally, it’s important to note how blooms, including those that don’t produce algal toxins, impact equipment. Algae blooms are known to clog filters and lead to an increased risk of damaged pumps and reduced efficiency.

Algal Bloom Causes in Dams

Algal blooms often look like slimy clumps or mats of green muck. Fortunately, they are hard to miss if you regularly monitor your dam’s water condition.

Regardless of the cause, algal blooms can form in just a few days, so it’s heavily recommended that treatment be proactive instead of reactive.

Excess Nutrients

Nutrients enter water bodies through agricultural runoff and untreated wastewater. Other contributors include animal waste, fertilisers, and household products from nearby urban environments.

This nutrient pollution encourages blooms, with phosphorus being a catalyst for larger blooms to form. Another common nutrient, nitrogen, can increase bloom toxicity, especially in cyanobacteria, which produce harmful toxins like microcystins.

Warm Water Temperatures

Warmer temperatures foster algae growth, particularly for cyanobacteria, which thrive above 15°C. Seasonal changes and climate change influence these temperatures and are unavoidable, but the stagnant nature of dam water exacerbates the impact of even a slight temperature increase.

Stagnant Water

Stagnant or slow-moving water is characteristic of dam reservoirs, where flow is often restricted. This lack of circulation allows nutrients to settle, creating an environment where algae can grow without dispersing. In naturally flowing rivers, nutrients tend to move downstream, but in dam reservoirs, stagnant conditions hold them, contributing to bloom formation.

Sunlight Exposure

Algae rely on sunlight for photosynthesis, making sunlight exposure another critical factor in bloom formation. Dams, especially those with shallow areas, allow sunlight to penetrate easily, boosting photosynthetic activity.

When blooms form a dense layer on the water’s surface, they block sunlight from reaching deeper water, impacting submerged plant life that depend on light, leading to further oxygen depletion as these plants die.

How to Mitigate HABs in Dams?

We know the causes, but what can be done to prevent them? Fortunately, you can try various mitigation methods depending on your situation, budget, and algae level.

Among the most effective solutions are nanobubbles, an advanced aeration technique that uses nanoscopic bubbles to put dissolved oxygen in the water.

Nanobubbles can penetrate deep into the water column, oxygenating dead zones and breathing life back into the water body. If you have a large dam, nanobubbles are especially useful as they offer comprehensive cover for months. You don’t need expensive, invasive equipment or chemicals.

The stagnant water of dams provides algae with a suitable environment in which to grow. A great solution is to use specialised equipment like fountains to mix up the water gently. This integrates oxygen into the water and breaks up the blooms.

Mixing water also helps combine thermally stratified water layers, another cause of blue-green algae and other harmful algal species. Some dam operators also periodically release water to increase flow and reduce stagnation.

Finally, if agricultural runoff or erosion is the main source of algal blooms in your dam water, you can opt for vegetative buffers. This approach involves planting trees and shrubs around the dam’s circumference, catching debris before it rolls into the dam, forming nutrient pollution.