Scientists Use Plants To Determine "Tipping Point" in Ecosystems

No longer just interesting for their dietary habits, carnivorous plants have recently attracted the attention of Harvard Forest researchers by offering insight into the early detection of irreversible water pollution.

By using small carnivorous plants to analyze oxygen depletion in aquatic ecosystems, a recent study by Harvard Forest researchers aims to foretell the amount of time before an ecosystem reaches its “tipping point” and is unable to restore its proper chemical balance.

Fertilizer, for instance, can overload a water environment with an abundance of nutrients, inducing large bursts in algae populations. This, in turn, causes an influx of predator-bacteria populations to bloom, depleting the once oxygen-rich water.

According to Aaron M. Ellison, a senior ecologist at Harvard Forest and co-author of the study, bringing bodies of water back from this state can be extremely intricate and difficult, prompting him and his research team to look for early warning signs.

“How much lead time do you need to prevent reaching that point? To turn pollution off and save the body of water?” Ellison said.

The researchers studied this process in carnivorous pitcher plants, which contain a water-filled pocket that allowed the researchers to compare pitcher plants to a body of water where larger organisms exist.

“Pitcher plants are ideal models of larger aquatic ecosystems because they contain a well-characterized food web,” Ellison said.

The other reason Ellison found pitcher plants ideal was because of their easy availability.

“If you go into a bog, there will be thousands of pitcher plants. You can have many individual replicates that make it easier to do experiments in controlled environments,” Ellison said.

To recreate organic pollution in their experiment, researchers added increments of ground-up wasp. The procedure continued until plants were no longer able to digest the material and their water system became overloaded.

The use of pitcher plants allowed Ellison and his team to study what would take generations to study in a full-size lake.

“In a pitcher plant, generations of bacteria go by in minutes. It’s like watching a lake for centuries,” Ellison said.

The study showed consistent results for all plants, providing further supporting evidence that a certain “tipping point” does exist—at the 45-hour mark, according to data in the study.

Ellison said he hopes that the results inspire others to become aware of the sensitive “tipping points” exhibited by ponds, lakes, and other bodies of water, and to act now to prevent such irreversible pollution.