A study completed and authored by former UCSB biologist Bradley J. Cardinale confirms biodiversity as the driver of nutrient uptake in streams — a process which acts as the ecosystem’s natural cleaning system.

Performed at UCSB’s stream flume facility, the study shows that streams with more biodiversity have a positive linear correlation with increased uptake of nitrate — a common pollutant.

The study’s importance stems from current issues regarding watershed pollution, largely caused by habitat loss or conversion as a result of urbanization.

According to the study, the control of nutrient levels in watersheds, which are areas where drainage from bodies of water occur, is a primary concern of environmental policymakers, since excessive nutrient load is a leading cause of water pollution globally.

When extrapolated to conditions outside the laboratory setting, the study’s results suggest that biodiversity increases efficiency in removing pollutants from watersheds.

According to Cardinale, Santa Barbara’s own network of streams is a prime example of urbanization’s role in polluting watersheds.

Streams higher up in the Santa Ynez Mountains in Santa Barbara are clean and biologically diverse. However, the streams become ridden with pollution by the time they have trickled through the more polluted hillside neighborhoods and eventually into the city.

The study is still juvenile; biologists are striving to transpose results found in the lab to similar results in the actual field. According to Cardinale, however, concrete and field-applicable data may surface in the next three to five years.

Cardinale said increasing species diversity does not improve nitrogen uptake forever, and a certain limit should exist for how efficient adding more species to the system may be.

“Once you get into the fields and you are dealing with many species, there is a point where we don’t need every single species to maximize nitrogen uptake, you should hit diminishing returns at some point,” Cardinale said. “Intuitively and mathematically, we know that not every species is making an impact on what we are interested in.”

At Michigan, Cardinale is currently in search of a concrete numerical range which will signify how much biodiversity is necessary to maximize nitrate uptake.

“How many species do you need? It is more than eight and less than 200 [species],” Cardinale said. “We are trying to narrow that down quantitatively and mathematically.”

It took Cardinale two years of research at UCSB to complete this preliminary study, which provides evidence for causation between niche partitioning due to biodiversity and cleaner water.

According to Cardinale, the study took longer than he had hoped, largely due to technical difficulties within the flume stream facility at UCSB. Unforeseen issues, such as nitrate measurements being thrown off by stray ash in the building, caused delays in the experiment.

“It was quite a difficult facility because it was not environmentally controlled,” Cardinale said, “It took eight tries over two years to get three of them to work.”

Cardinale is now researching at the University of Michigan which, according to him, offers a more supportive environment for his research endeavors.

Once this information is found, the hope is that it can be successfully applied to polluted watersheds and may help manage damage caused by excessive levels of nutrient pollutants such as nitrate.

While the study has set the ball rolling toward a rather useful discovery and positive changes for threatened aquatic habitats, it is not a complete solution to the problem.

According to Cardinale, employing nature’s natural cleaning system through encouraging optimum levels of biodiversity patches the problem of polluted ecosystems but does not eliminate it.

“Working on the solution without going directly to the source is pretty much a Band-Aid. It is not going to work in the long run,” Cardinale said. “You are not addressing the bigger, serious threats to species. We can try to maintain diverse habitats and species, but it doesn’t do anything meaningful in the long run.”

A long-term approach would entail setting aside habitats away from areas of urbanization and human-induced pollution so that they could clean themselves naturally and prevent pollution in the first place.