Reducing nitrogen runoff from farmland

Project Overview

Engineering Denitrification Hotspots in Agricultural Landscapes

Nitrogen is a crucial nutrient in agricultural production, but excess nitrogen runoff creates chronic pollution in coastal ecosystems. This project aims to reduce nitrogen pollution by engineering field-based bioreactors, and identifying the conditions under which they work best.

Nitrogen is a crucial nutrient in agricultural production, but excess nitrogen runoff creates chronic pollution in coastal ecosystems by feeding the excessive growth of algae, which chokes out other life. Extreme examples of this problem include the recurring “dead zones” in the Gulf of Mexico and the Chesapeake Bay. Although many human activities contribute excess nitrogen to waterways, runoff from nitrogen fertilizer used in agriculture is a primary source. This project sought to reduce nitrogen pollution by engineering field-based bioreactors that can convert dissolved nitrogen into nitrogen gasses, a process referred to as denitrification.

Some parts of landscapes are naturally well-suited to high denitrification rates. The overarching purpose of this project was to reveal the underpinning environmental and microbial genetic conditions that promote full denitrification, i.e., conversion of nitrate to inert di-nitrogen gas. One step in the sequence of nitrogen transformations produces nitrous oxide, which is an aggressive greenhouse gas; therefore, we sought to create a process that minimizes nitrous oxide and maximizes di-nitrogen. We used state-of-the-art microbial DNA analyses to understand how microbial functions necessary for denitrification are distributed over landscapes, and how these patterns change over time.

The Impacts

Our initial efforts to engineer artificial denitrification hotspots have been inconsistent in their nitrogen removal, and nitrous oxide emissions. However, we have answered several fundamental questions about how denitrification, and the genes necessary to produce it, varies over landscapes and among bioreactors. For example, denitrification genes are strongly correlated to patterns of average soil moisture across a landscape; however, other factors like nitrate supply and pH can also play important roles in determining which genes are present at any particular point in the landscape. We also learned that patterns of gene distributions across a watershed remain very stable over time, even with environmental changes, such as drought. Denitrification genes are good indicators of long-term denitrification process; however, disruptions to the soil environment appear to take years to make a difference. Findings from this project have been disseminated through peer-reviewed journals, conference presentations, and invited seminars.

Principal Investigator

Michael Walter

Project Details

  • Funding Source: Hatch
  • Statment Date: 2019
  • Status: Completed project
  • Topics: Water, nitrogen, sustainability