Studying Nitrate in the Mississippi and Algae in Mendota

Luke Loken, a graduate student at the University of Wisconsin-Madison Center for Limnology (CFL), and John Crawford, a CFL graduate, are Mississippi River explorers of a more modern sort. They have embarked on a journey to learn more about the chemistry of its waters, using technology they invented

The Mississippi River has long had its explorers. From de Soto to Marquette, Lewis and Clark to Clemens, the fourth largest river in the world has for centuries inspired enchantment.

Luke Loken, a graduate student at the University of Wisconsin-Madison Center for Limnology (CFL), and John Crawford, a CFL graduate, are Mississippi River explorers of a more modern sort. They have embarked on a journey to learn more about the chemistry of its waters, using technology they invented.

They call their technology FLAMe, for Fast Limnology Automated Measurements platform, a mobile sensor system they attach to a boat and use to gather data from the water while on the move. They began in the Mississippi in July 2014, conducting six seasonal surveys of a 20-mile stretch of river near La Crosse. This August, Loken and Crawford charted a continuous course from Minneapolis to Kentucky, taking measurements along the way.

"We want to understand how the chemistry of the river changes as we move along its length," Loken says, "and we want to know how large rivers process carbon and nitrogen."

He and Crawford, who is now a postdoctoral researcher at the U.S. Geological Survey National Research Program, want to study how the river contributes to the storage of carbon and its release back into the atmosphere. They want to know where algae bloom-promoting nitrate — from a pollutant found in manure and chemical fertilizers — is running into the river, and where it's being soaked back up. And they want to show what their new technology can do.

By "flaming" bodies of water, Loken and his colleagues are hoping to answer questions about river and lake behavior, water quality, the variability of freshwater systems and more, lending a hand to land managers and policymakers tasked with making informed decisions. And they want to help inform the public.

Over the course of two weeks on the Mississippi this summer, Loken and Crawford gathered a quarter of a million data points using FLAMe. The system pulls in surface water while the boat moves and circulates it through a collection of sensors, allowing the researchers to measure everything from nitrate to carbon dioxide and temperature, every second of the way. That data feeds into a computer and within 20 minutes of returning to shore, can be used to tell a story about the chemistry of a waterway. On this trip, part of that story was nitrate.

Nitrate accumulates in freshwater when nitrogen-rich agricultural runoff makes its way into lakes, rivers and streams. It can cause algal blooms that block light to deeper water and scum up the surface, kill fish and beneficial plants, and present a hazard to swimmers. It can also contaminate drinking water and impact human health.

"We measured the Mississippi River and its major tributaries in order to identify the sources of nitrogen to the river and areas that may serve as nitrogen sinks," says Loken, a member of limnology and zoology Professor Emily Stanley's lab.

With the data they collected cruising the Upper Mississippi, Loken and Crawford generated "heat maps" of the stretch they traveled, where it's easy to see nitrate levels rise in agricultural regions and fall back as contaminated waters sieve through adjacent backwater lakes, wetlands and large impoundments, like Lake Pepin, a "giant natural lake in the middle of the river," Loken says. Lake Pepin is about 60 miles downriver from St. Paul.

"You see water clarity improve and nitrate decline. They're cleaning the water, acting like giant kidneys," Loken says. "Maps like this are the first step. After seeing the data, we can start to unravel the ecology of the river."

FLAMe offers researchers the ability to study freshwater in ways they never have before — to study the breathing and turnover and changes of this natural resource as they occur, over space and over time, all while traveling quickly over a body of water.

"Lakes and rivers are active places for carbon cycling and greenhouse gas emissions," says Loken. "With climate change, we want to know where the carbon is and where it's entering the atmosphere. We hope to better understand the role of freshwaters in the global carbon cycle and with FLAMe, we can identify 'hotspots' in the system and follow up with more extensive studies in these particular areas."

At Trout Lake Station in Boulder Junction, Loken, another CFL graduate student in Stanley's lab, Vince Butitta, and a team of undergraduates have also spent time flaming area lakes to learn how variable they are and to better understand differences and similarities between small lakes (with lots of shoreline) and larger ones.

At the University of Notre Dame Environmental Research Center, which borders Wisconsin and Upper Michigan (not far from Trout Lake), CFL Director Steve Carpenter and collaborators from the University of Virginia are studying early warning signs of algae blooms in experimental lakes. Can they see, before it happens, a lake on the brink of an algae bloom? To find out, Butitta flamed the study lakes this summer, capturing changes over time and space.

"He will hopefully pick up the signal of lakes changing states," Loken says. "We are testing whether we can detect the lakes' impending doom, whether it will or will not shift based on the spatial pattern of a set of variables."

Back in Madison, Loken untied a small boat from the dock in the boathouse beneath the Arthur D. Hasler Laboratory of Limnology. He turned on the engine and backed the boat, named The Procaryote, onto Lake Mendota.

It was cool on the water, and windy, and the sun was taking a break behind gray skies. Loken steered toward the lake's center before killing the engine. He turned to the large, rugged black box in the back of the boat and unlatched its lid, revealing the inner workings of FLAMe.

Lake Mendota is perhaps one of the best-studied lakes in the world — the place where the study of freshwater began. It was on its shores that the idea for FLAMe was born and here that the graduate students tested the new technology.

Source: University of Wisconsin-Medison

Read More Related Content On This Topic - Click Here

Media

Taxonomy

• River Studies
• Algae
• Lake Management