Big River Keeps on Rollin’ – Study Finds Little Nitrate Retention in the Upper Mississippi

Luke Loken on the Mississippi River with the FLAMe in action. Photo: John Crawford
Luke Loken on the Mississippi River with the FLAMe in action. Photo: John Crawford

A new study says that, despite dozens of locks and dams and backwater habitats that slow it’s flow, the Upper Mississippi River isn’t good at retaining the nitrates that run into its waters from intensively farmed states like Minnesota, Illinois and Iowa. Published July 12th in Environmental Research Letters, the study finds that only12.5% of the Upper Mississippi’s incoming nitrate load ends up either being taken out of the system by aquatic organisms or settling in sediments at the bottom of the river. The vast majority just flows downstream, ending up in the Gulf of Mexico where it feeds huge blooms of algae and  and creates conditions that fuel the Gulf’s “dead zone.” (Link to the study.)

“In general, dams and reservoirs are nitrate sinks, but the Mississippi dams are too short,” says Luke Loken, the lead author of the report and a recent recipient of a PhD from the University of Wisconsin-Madison’s Center for Limnology. Loken says that the Upper Mississippi’s 29 locks and dams were built to only raise the water level a little bit and allow barges to travel up and down the river. The flooded areas above the dams are relatively shallow, which does not impound that much water. Loken says that the study points to the need for better management of nutrients on the land because, once something’s in the Mississippi, it’s extremely likely that it’s going to end up in the Gulf of Mexico. 
“To get nitrate removal you need the water to stay put for a while which allows physical and biological processes to work. Because the river is big and the dams are small most of the water and the nitrates keep on moving.” There is one exception to this in the form of Lake Pepin, which is a unique feature on the river or, indeed, any river. Lake Pepin is a naturally occurring lake, formed by the sediments that build up where the Chippewa River flows into the Mississippi. Above Lake Pepin, the Mississippi’s waters are full of sediments and nitrates. Below Lake Pepin, the waters are clear and the nitrate loads are greatly reduced – until the next large tributary enters the picture. Loken says that detailing the big role Lake Pepin plays in nitrate removal was “maybe the coolest part [of the study].”
 
However, we’d argue that it’s how Loken and other researchers were able to get their data that is the coolest part of the study. That’s because it involved Fast Limnological Automated Measurements, or “FLAMe,” which is a new tool Loken and other Center for Limnology researchers developed to take real-time measurements of conditions on any water body. A few years back, they strapped the FLAMe on a Boston Whaler and set out on a two-week adventure downriver. That story is below. 
 
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(Originally published Nov. 19, 2015) On the first day of August, at Hidden Falls Regional Park in St. Paul, Minnesota, Center for Limnology (CFL) graduate student, Luke Loken, boarded an 18-foot-long Boston Whaler and headed upstream. At the Washington Avenue Bridge, the starting line of his research adventure, he pointed the boat downriver, where his final destination lay – only two weeks, 26 lock and dams, and 900 river miles away.

One of the many maps produced by the FLAMe's Mississippi River. This one shows nitrate concentrations along the entire 900-mile journey. Image" Luke Loken
One of the many maps produced by the FLAMe’s Mississippi River. This one shows nitrate concentrations along the entire 900-mile journey. Image” Luke Loken

The trip, financed by the United States Geological Survey’s (USGS) “Land Carbon Project,” would be the biggest test yet for a research tool designed by Loken and USGS post doctoral researcher, John Crawford (PhD, 2014). Called the FLAMe, short for “Fast Limnological Automated Measurements,” the contraption consists of a water pump, a series of pipes and tubes and $100,000-worth of sensors. As their boat moved across the surface of the Mississippi, a continuous stream of water would be sucked into the FLAMe and passed over sensors recording everything from turbidity to temperature to nitrate levels, before being discharged back into the river.
“At the heart of the FLAMe are these automated sensors that are commercially available and widely used by limnologists everywhere,” says CFL faculty member, and Loken’s advisor, Emily Stanley. “But what [researchers] usually do is park them on a buoy or put them in a particular place in a stream and they get really good data at that site over time. With the FLAMe, instead of parking these devices in one place, we bring the water to the devices and take the devices everywhere.”
Instead of datasets over long time series, says Stanley, the FLAMe produces maps over large areas. “We don’t have that spatial understanding of our ecosystem in the same way that a terrestrial ecologist does,” she says. “The FLAMe gives us a whole new way of seeing lakes and rivers that we just haven’t had before.”
Part of that new look is now a map of Loken’s journey, showing how the river chemistry and conditions changed as the crew passed through different pools of the river or encountered tributaries flowing into the main channel. Loken was joined for the trek by Crawford, Washington State University postdoc, Steve Powers (Phd, 2012), and a handful of other scientists from the USGS and University of Minnesota.
“We had two main objectives,” says Loken. “One was [to] shoot all the way down the middle of the main navigation channel, lock through the dam and then just keep going. The second was to spend more time in a subset of pools, and head into the backwaters and explore some of the lateral variability of the river.”
The end result of the trip was mountains of data points, one gigantic gas bill and affirmation of the vast possibilities of the FLAMe.
The FLAMe project began early in the summer of 2014 when Loken and Crawford, who was then a graduate student, started thinking about ways to better bring spatial variability into their data collection.
The first version of the FLAMe consisted of about fifty-dollars-worth of PVC pipes and miscellaneous hardware and measured carbon dioxide and methane, the two sensors Crawford already had. But, after a few runs across Lake Mendota, Loken and Crawford put together a map that showed the high variability of gas emissions at any given time. When they showed those maps to CFL faculty, Loken says, “we instantly saw a light bulb going off.” Then, he says, “we started finding the other instruments to go along with it, because if you’re going to measure one thing, you might as well measure all the other things you can.”
That initial success led to requests for FLAMe-collected data on other projects, like CFL director Steve Carpenter’s work on ecosystem regime shifts in northern lakes. And that momentum led to an intense 2015 field season where the FLAMe sampled 84 different lakes and more than a 1,000 miles of rivers.
Looking back at Mississippi River Lock 5. Built to accommodate barge traffic, the locks proved "roomy" for the crew! Photo: Steve Powers
Looking back at Mississippi River Lock 5. Built to accommodate barge traffic, the locks proved “roomy” for the crew! Photo: Steve Powers

That’s a lot of ground covered, but the FLAMe is far from a finished project, says Stanely. “We want to take FLAMe to a new level,” she says, “where we can drive the boat and almost see the map [of conditions] as we drive.” But first, “We need to overcome some of the technical hurdles [Loken and other colleagues] exposed this summer by driving all over northern Wisconsin.”
That’s why Stanley and Loken recently collaborated with the UW-Madison’s Physical Sciences Lab, where some of the same engineers who worked on the UW’s vaunted Ice Cube project in Antarctica, took a look at the FLAMe, upgrading it with stainless steel and anodized aluminum components.
With this new, improved version, Loken hopes to do weekly runs on Lake Mendota next year in the hopes of catching dynamics like changing oxygen levels, water chemistry and algal blooms and, essentially, making a movie of the always shifting surface of the lake from spring to fall.
Even with the all-new FLAMe, though, there’s a catch. “It depends on how much gas they let us burn,” he laughs. “We kind of maxed out [our] gas card last summer.”
Big wheel keeps on turnin'....
Big wheel keeps on turnin’….

To read more coverage about the FLAMe, check out this article from UW-Madison Communications and another entry from the student newspaper, The Daily Cardinal. 

 

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