Want to Prevent Algal Blooms? Toilet Train Birds

cormorants resting on a rock in a lake

While they may not be the sole cause, recent research shows that an increase in the population of cormorants on a lake in South Korea may have contributed to algal blooms.(Photo credit: EAGiven/iStock/Getty Images Plus/Getty Images)

Algal blooms are a rapid increase in the population of algae in a body of water. They are characterized by their bright green color. While they can be an entirely natural phenomenon, algal blooms can be very harmful. They can deplete lakes of oxygen, produce toxins, and ultimately kill much of the aquatic life.

Many of the more harmful algal blooms often correspond to human activity. For example, heavy rains can wash excessive amounts of fertilizer into a water body and, therefore promote the growth of algae. If animals and humans depend upon that water source, it may need to be shut down. One such important source is the Maji Agricultural Reservoir in Wonju, Gangwond-do, South Korea, which the farmers in the area rely upon to water their crops in the summer. It happens to lie along a scenic route that Tae Kwon Lee, a professor in the Department of Environmental Engineering at Yonsei University, often follows on his daily runs. One day Lee noticed an excessive amount of cormorants covering the island in the middle of the reservoir, so many that the trees became covered in their feces. Some time later, the reservoir suffered a particularly harmful algal bloom. This got Lee to thinking: could the bird’s feces have influenced the algal bloom? The birds were relatively new to the area but in the past five years had grown to a population of some 500 strong. Lee decided to investigate.

Bird feces is rich in nitrogen and phosphorus and each cormorant can produce enough of the stuff in a day to deposit as much as 4 grams of nitrogen and 2.5 grams of phosphorus into the lake. Lee designed an experiment composed of 14 different “tiny” ecosystems. He collected water, sediment, and, of course, cormorant droppings to construct them. While each mini-ecosystem contained the same amount of lake water and sediment, they differed in the amount of cormorant droppings, from half a gram to 5 grams. Over the next 21 days, he measured the amounts of nitrogen, phosphorus, and other nutrients in each of the samples. He found that even a small amount cormorant droppings had an effect on the values.

Lee also looked at the different rates of growth in microbial communities in both the water itself and the sediment. He found that while the water only experienced marked increases when the feces concentration was relatively large (5 grams or more), the sediment seemed to be affected even at minimal concentration. This might explain why these effects could last for days.

While apparently confirming his suspicions, Lee still can’t blame the algal bloom entirely on the cormorants’ lack of toilet training. Nonetheless, he believes it certainly had an influence.

“Our results confirmed the changes in nutrient condition and microbial community in water caused by a small amount of feces,” Lee concluded. “Fecal input may adversely affect the condition of the reservoir, bringing about undesirable changes such as algae bloom.”

He also recognizes that, however much he tried to replicate actual conditions in the lake, his investigation had some limitations. “Microcosm experiments give researchers more control over variables normally not possible in the real world. But the results don’t fully represent what happens in the real world because the microcosm can’t completely mimic the real environment,” Lee explained.

It also further confirms how the complex interrelations in the natural world need to be fully investigated before proper solutions to disruptive events can be found. For now, the cormorants are there to stay until Lee and his colleagues can determine how large the population can grow before the lake would become seriously polluted.

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