NASA images show extent of algal blooms at Hartbeespoort Dam [pics]

NASA satellite imagery reveals recurring and extensive algal blooms at Hartbeespoort Dam in South Africa, with bright green swirls visible across the reservoir’s waters.

Harmful Algal Blooms at Hartbeespoort Dam

The images, compiled from data collected between June 2022 and July 2023 by multiple Earth-observing satellites operated by NASA and the European Space Agency, show the growth, movement, and eventual fading of these blooms – which then return.

Algae are natural organisms essential to healthy ecosystems, but rapid multiplication can cause problems. These outbreaks, known as harmful algal blooms (HABs), are often triggered by excess nutrients, such as phosphorus from agricultural runoff and wastewater.

NASA scientist Bridget Seegers likened the process to over-fertilizing a garden, stating, “If you add a lot of nutrients, you’re going to have a lot of growth.”

As algal blooms die, bacteria break them down, consuming oxygen in the water. This can lead to hypoxia – dangerously low oxygen levels – which can kill fish and other aquatic life. A major fish kill at Hartbeespoort Dam in April 2023 was linked to these conditions.

Invasive Aquatic Plants

Located approximately 25 kilometers west of Pretoria, Hartbeespoort Dam is primarily used for irrigation and recreation and has long faced water quality challenges. The reservoir regularly experiences blooms of toxin-producing cyanobacteria and is also affected by invasive water hyacinth, which exacerbates the problem as it decomposes.

A 2022 study analyzing algae levels at the dam over 40 years found that warm temperatures and high phosphorus levels were the primary drivers of bloom growth. Algae also tend to be more concentrated near river inflows and areas with limited water circulation.

While water samples are needed to confirm toxicity, satellite images provide a broad overview. NASA states that upcoming missions will enhance the ability to detect and monitor HABs.