Iceland stream warming study gives preview of climate change

Xylem’s technology was recently used to study how global climate change could affect rivers and streams. In Hengill, Iceland, researchers warmed streams and enriched them with nutrients over several years. The results were measured by Xylem’s YSI ProODO handheld optical dissolved oxygen meters.

The Hengill region of Iceland is a landscape coursing with crystalline streams that flow at dramatically different temperatures. Just a few steps from each other, one brook may babble at 7°C (44.6°F) while another, warmed by a small patch of geothermally heated earth, can run as high as 30°C (86°F).

“Within that landscape, it’s just so easy to do ecology. It’s a really fun ecosystem to work in,” says Jim Hood, an assistant professor of aquatic ecology at Ohio State University.

Studying how temperature and nutrients affects algae growth

“It’s the interaction between temperature and nutrients that really drives the research,” says Jon Benstead of the University of Alabama. He helped lead the design of an ingenious set of studies for Hengill, funded largely by the National Science Foundation.

The studies examine the impact of temperature increases and different nutrient levels on ecosystem metabolism and invertebrate communities in streams. This includes studying the growth of algae and its respiration, as well as the decomposition of organic matter.

Collecting data using Xylem’s versatile YSI ProODO meters

In 2010, researchers started collecting monthly data on two streams in Hengill, setting the baseline for respiration and life in each. Then they raised the temperature of the cooler stream by about 4°C using a three-stage, gravity-fed heat exchanger system submerged in geothermally warmed water. This allowed them to study the effects on stream metabolism, nutrient cycling, flora and fauna.

YSI ProODO handheld dissolved oxygen meters provide extreme durability for measuring dissolved oxygen with optical, luminescent-based technology. Benstead says that he chose YSI ProODO meters because of their versatility and plug-and-play interface.

“We were looking for something we could use in the field at very low temperatures,” Benstead explains. Just a fraction of the price of more sophisticated sondes – a huge consideration when stocking up on 20 instruments – the ProODO meters combined handheld versatility with onboard datalogging and a large memory.

“They’re very rugged, simple to use,” Benstead says. “It doesn’t take long for students to learn how to set them up – setting up the logger is pretty intuitive. It’s pretty simple to synchronize them all, the clocks are good in them, and there’s plenty of memory.”

Results: algae growing after warming needed less nitrogen

Results from the Hengill study, now being published in a series of papers and journals, including Global Change Biology and Ecology, yielded some surprises. In the stream warming experiment, warming led to flushes of Ulva, a filamentous alga that dramatically shifted nutrient cycling and nitrogen efficiency patterns.

“Algae growing after warming tended to need less nitrogen,” explains Hood. “They were more efficiently using it. We also think there was more efficient cycling in algal mats – little bugs eat and release nitrogen more quickly at warmer temperatures.”

Implications for water carrying nitrogen runoff

The Hengill experiments demonstrated that the theories derived from single-species lab studies may be challenged in real-world conditions.

“It’s allowed us to tackle some of these theoretical ideas in the real world,” says Hood. “It’s allowed us to see where the theory works and where it doesn’t.”

The studies can have big implications for scientists trying to predict the impact of nitrogen runoff when temperatures rise. The studies can also help policymakers trying to decide whether wastewater treatment plants should continue focusing only on phosphorus reduction, or if nitrogen should be controlled, too.

Read the full story in Mission: Water magazine:
www.ysi.com/mission-water

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