It is known that biologically diverse streams are better at cleaning up pollutants than less rich waterways, so Bradley Cardinale of the University of Michigan created 150 miniature model streams to find out why this is.

The model streams use recirculating water in flumes to mimic the variety of flow conditions found in natural streams. Cardinale grew between one and eight species of algae in each of the mini-streams, then measured each algae community’s ability to soak up nitrate, a nitrogen compound that is a nutrient pollutant of global concern. He found that nitrate uptake increased linearly with species richness. On average, the eight-species mix removed nitrate 4.5 times faster than a single species of algae grown alone.

The reason? Niche partitioning, Cardinale said.

In the stream experiments, each algae species was best adapted to a particular habitat in the stream and gravitated to that location—its unique ecological niche. As more algae species were added, more of the available habitats were used, and the stream became a bigger, more absorbent sponge for nitrate uptake and storage.

Sound familiar? Think Charles Darwin. “People as far back as Darwin have argued that species should have unique niches and, as a result, we should see a division of labor in the environment,” Cardinale said.

This is exciting news because nitrate is an ingredient in many fertilizers and is found in surface runoff from agricultural land that makes its way into streams, lakes and coastal zones. It is a leading cause of degraded water quality worldwide.

“The primary implication of this paper is that naturally diverse habitats are pretty good at cleaning up the pollutants we dump into the environment, and loss of biodiversity through species extinctions could be compromising the ability of the planet to clean up after us,” according to Cardinale.

Image credit: Danuta Bennett

Scientists from two southern US universities have recently announced low-tech plant-based solutions to modern problems, hoping they’ll translate to the developing world.

Water Purification by Cactus

According to an abstract published in Environmental Science and Technology earlier this month, “Although nearly all newly derived water purification methods have improved the water quality in developing countries, few have been accepted and maintained for long-term use.” That’s because, according to one of the authors, Norma Alcantar, PhD, the residents don’t know how to actually use or maintain the technology.

She and other scientists from the University of South Florida in Tampa have taken the prickly pear cactus and the thick, gooey mucilage within it and created a type of water purifier.

According to New Scientist, “Alcantar found that the mucilage acted as a flocculant, causing the sediment particles to join together and settle to the bottom of the water samples. The gum also caused the bacteria to combine and settle, allowing 98 per cent of bacteria to be filtered from the water.”

It’s already been helping residents of a rural Mexico town clean their drinking water and Alcantar only sees it going further. “The World Health Organization recognizes a need for developing low-cost ways of cleaning water for household use,” she said, and the cactus, also known as Opuntia ficus-indica, is widely available.

According to the abstract, “This natural material not only displays water purification abilities, but it is also affordable, renewable and readily available.”

Pokeberry Solar Power

Civil War soldiers used the red dye of pokeberries as ink by to write letters home. And now scientists from Wake Forest University are hoping that the dye will help improve the efficiency of solar cells.

Wake Forest’s Center for Nanotechnology and Molecular Materials has already developed a fiber-based solar cell that’s both less expensive and more efficient that standard solar cells. And now the pokeberry dye will make it even more so. The dye acts as an absorber, helping the cell’s tiny fibers trap more sunlight to convert into power.

Pokeberries proliferate even during drought and in rocky, infertile soil. That means residents of rural Africa, for instance, could raise the plants for pennies.

“We could provide the substrate,” David Carroll, Ph.D., the center’s director said. “If Africa grows the pokeberries, they could take it home. It’s a low-cost solar cell that can be made to work with local, low-cost agricultural crops like pokeberries and with a means of production that emerging economies can afford.”

Creative Commons image by Mary Emily Eaton and Daniel Schweich