Two-stage ditches reduce nitrogen pollution while draining farmfields

January 28th, 2019 by

Waterways along Midwestern farmlands are typically managed to move stormwater away from crop fields quickly, but this efficient process can wash nutrients and sediment into lakes and rivers, nearby and downstream. Illinois-Indiana Sea Grant researchers have found that a change in waterway management practices can lead to a win-win—water is still quickly drained from crops with two-stage ditches, but because they have more floodplain area, stormwater slows down so more nitrogen is retained along the way.

Sara McMillan at Purdue University and Jennifer Tank at University of Notre Dame are monitoring nitrogen and phosphorus loads coming from two-stage ditches in farmland waterways to document how effective restored floodplains are at holding nutrients in place. “By restoring mini-floodplains on each side of these formerly channelized ditches, you add the potential for enhanced biology and hydrology to cleanse the water through nutrient and sediment removal,” said Tank, whose primary work is in ecology and environmental biology.

“Floodplains provide a way for water to spread out and slow down—allowing sediment to accumulate and plants and soil microbes to thrive. When plants thrive, this allows organic matter in the soil to increase,” said McMillan. In this environment, microbes use nitrogen for energy, removing it from the water as they transform it into a gas—a process called denitrification.

BGC Graphic

(Graphic courtesy of Brittany Hanrahan)

Brittany Hanrahan, whose doctoral research at Notre Dame was a part of this study, compared the effectiveness of reducing nitrogen in two-stage ditches with waterways in which traditional channelization management has stopped for at least a decade. Over time, these channels in northern Indiana developed mini-floodplains and began to look like more natural streams. The two-stage ditches in the study were about 10 years old.

Hanrahan, who now has a postdoctoral position with the USDA Agricultural Research Service, found that denitrification was 30 percent higher along two-stage floodplains compared to the naturalized ones. The two-stage ditches have more floodplain area than the naturalized channels and are designed to flood more often, which allows denitrification to happen more frequently.

“We calculated that it would take nearly 30 years for the floodplain in the naturalized ditch to accumulate the surface area of floodplain that is constructed in just one day in the two-stage ditch,” said Hanrahan. “Jump-starting the biology with two-stage construction really helps to remove more nitrogen even immediately after construction.”

While slowing down floodwater is conducive to denitrification, phosphorus goes through a different biological process. In fact, if floodwater stands long enough, phosphorus may be released from particles in the soil and water. On the other hand, creating space for water to spread out and slow down can enhance the settling of sediment particles with phosphorus attached.

The design of the two-stage ditch, including the height and width of the floodplain, can make a difference in terms of flooding frequency and duration. One general practice, according to McMillan, is to triple the width of the channel—if it is a 10-foot wide channel, 10 feet are added on either side so it is 30 feet wide.

“We’re pretty confident from previous research that it takes a long time for phosphorus to be released, so it’s not likely that we’re causing a net release of phosphorus that is stored in soils,” said McMillan, who is in Purdue’s Department of Agricultural and Biological Engineering. “While we think that these ditches pose a net benefit for both phosphorus and nitrogen, phosphorus is indeed more complicated.”

Most two-stage ditches can be found in Indiana, which may be because the USDA Environmental Quality Incentives Program covers the majority of the cost of installing them in the state. It’s a one-time construction cost, whereas dredging to maintain trapezoidal channels needs to happen every few years, depending on the system. “With a two-stage ditch, the velocities in the main channel, which is the original channel, are fast enough during high flows that it is always self-cleaning,” said Tank. “You never have to dredge again.”

Scientists, communities get help from NASA soil moisture mapper

February 17th, 2015 by
The mission of NASA’s newest Earth satellite may sound simple, but its findings could have huge impacts across the world and right here in the Midwest. When it launched last month, the Soil Moisture Active Passive, or SMAP, began a three-year project to collect data on a key player in the water and carbon cycles that determine plant growth and drive weather patterns: soil moisture. IISG’s Michael Brennan has the details. 

As the name suggests, soil moisture data tells us how much water the soil can absorb and store. These measurements play a crucial role in everything from knowing when to plant crops to community flood planning. If there isn’t enough moisture in the soil, plants can’t take root and grow. And if the soil’s storage capacity has been maxed out, any additional rain or snowfall will runoff into nearby rivers and lakes—carrying nutrients and contaminants with it. 

Due to the earth’s vast landscape, tracking and assessing soil moisture is extremely challenging, especially in remote locations. In fact, a lack of detailed soil moisture data has historically been a significant hurdle for community planners, farmers, and climate and weather forecasters. SMAP has the potential to change all of that. Its microwave radiometer and radar instruments will give us the most accurate, high-resolution moisture data ever collected from space. And its orbital path will ensure we have measurements from pole to pole. 

NASA has said that it expects to release the first set of measurements within nine months, with fully-validated data expected in 15 months. With these numbers in hand, farmers will be able to hone in on the ideal time for planing and harvesting and community decision makers will be able to pinpoint their flood risk—and plan accordingly. The data will also tell scientists how much carbon is being stored in or released by plants, allowing them to refine the climate models that we rely on to predict and prepare for the impacts of climate change.  

The NASA space program is responsible for a lot of technological and scientific advancements, but SMAP may be its greatest contribution yet. 

For more information on SNAP for video showing its launch and orbit, visit


In the news: Cause of Lake Erie’s algae becoming clearer

April 16th, 2014 by
Lake Erie is one of the Great Lakes that is most affected by toxic algal blooms, and finding the cause for them is the first step in reducing or preventing them. Scientists may be closer to understanding just what causes these harmful blooms. 
“Algal blooms and dead zones in Lake Erie were severe during the 1960s, caused primarily by large releases of phosphorus from sewage and industrial plants. The 1972 federal Clean Water Act and the 1978 bi-national Great Lakes Water Quality Agreement led to dramatic reductions in phosphorus from these sources and a rapid improvement in water quality.
Lake Erie, however, saw a reemergence of the algal blooms and the growth of the dead zone in the mid-1990s, and the problems are worsening. In 2011, for example, Lake Erie experienced its most severe bloom of toxic algae on record. Last fall a toxic algal bloom in the lake forced officials to shut off a public water supply system in Ohio.
The new studies, part of the Ecological Forecasting (EcoFore) Lake Erie project led by researchers at the University of Michigan, found that the current targets to reduce phosphorus to alleviate algal blooms in Lake Erie may not be low enough to revive the dead zone. That conclusion informed the International Joint Commission’s recommendations in February for improving Lake Erie’s water quality.
The findings, and those of other studies from across the Great Lakes region, are delivering an ever clearer picture of the specific causes of nonpoint phosphorus runoff, algal blooms, and dead zones. The basic drivers of these problems are no longer unknown. The new research fills a critical void in information that has been often cited as a reason that strict regulations on nonpoint pollution sources, including agriculture, were not regulated under the 1972 federal Clean Water Act.”
Read the complete article and findings at the link above.

In the news: Aquaculture a growing food field in Indiana

August 19th, 2013 by

Aquaculture, the business of raising fish for commercial sale, is a growing part of Indiana’s agriculture practice, and Illinois-Indiana Sea Grant’s Kwamena Quagrainie is just one of the people helping to make that possible. 

From Purdue University

“Estimated sales from Indiana fish farms amounted to more than $15 million in 2012, an increase from $3.5 million in 2006, according to the publication Economic Importance of the Aquaculture Industry in Indiana. There are about 50 fish producers in Indiana, compared with 18 just seven years ago.

‘While aquaculture is not the most well-known industry in Indiana’s agriculture sector, it is definitely present and very important to the state’s economy,’ Kwamena K. Quagrainie, aquaculture marketing specialist in Purdue University’s Department of Agricultural Economics, said in the report. He conducted the study with graduate student Megan C. Broughton.

‘The industry has seen steady growth over the past few years, and it is important to know exactly how much economic activity is associated with aquaculture in Indiana,’ Quagrainie said.
Indiana’s aquaculture industry ranges from small-scale producers raising fish in their backyards to large-scale producers growing fish to sell in national and international markets, the report says. The industry includes production of fish for human food, ornamental fish for aquariums and recreational fish that are stocked in private and public ponds and lakes.”
Follow the link above to read the complete article, and learn more at our aquaculture page.
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