The results made audiences gasp.
"Five percent of all the nitrogen in the Gulf of Mexico comes from Minnesota and 11 percent comes from Iowa," said John A. Downing, director of the University of Minnesota Sea Grant College Program. "Few people thought it was possible for such small patches of land to have major effects on enormous bodies of water."
These and other eye-popping findings were possible only after the publication of the scientific paper "Regional nitrogen budgets and riverine N [nitrogen] & P [phosphorus] fluxes for the drainages to the North Atlantic Ocean: Natural and human influences," by Robert Howarth of Cornell University, Downing and co-authors in the journal Biogeochemistry. The paper was the first to quantify the relationship between human activities and the amount of nitrogen entering coastal oceans.
This week the authors were honored with the John H. Martin Award by the Association for the Sciences of Limnology and Oceanography as having led to fundamental shifts in research focus and interpretation of a large body of previous observations. The award is for high-impact papers at least 10 years old.
"The seas were once viewed as too enormous for people to have an impact," said Downing. "When we published this paper in 1996 people knew nutrients, including fertilizers, applied to agricultural lands ran off, but not to the extent that we calculated."
The objective of the paper was to estimate the total amount of nitrogen exported from all the major rivers draining into the North Atlantic Ocean, to assess how much nitrogen export has changed since preindustrial times and to identify the sources of the nitrogen.
"We have local water-quality problems everywhere," Downing said. "But when nutrient-rich water runs downhill and eventually into the sea we create global problems and we can't fix global water issues until we understand what happens locally."
Nitrogen and phosphorus are essential nutrients for plant and animal growth, but nitrogen in excess of plant demand can leach from soils into waterways and contribute to excessive algae growth. Excess soil nitrogen can also be released into the atmosphere as nitrogen gas, where it can travel long distances and precipitate back to Earth as acid rain.
"We are delighted to present the John H. Martin Award to such a landmark study that has clearly had long-lasting relevance," said ASLO President Linda Duguay. "The identification of fertilizer and atmospheric deposition as two of the largest components of anthropogenic nitrogen in rivers were key findings that drove future research directions in nitrogen biogeochemical cycling."
The paper also accelerated a fundamental shift in Downing's research career.
"I concentrated my work in Iowa on where those nutrients came from and began educating people on how they can better manage landscapes," said Downing. "I also started doing large-scale research on marine and freshwater ecosystems to understand where in the world nitrogen and phosphorus are a problem."
Downing continues to use the data from the paper today and it still generates gasps from audiences. "Minnesota is this little tiny patch of land, but the intensity of its runoff is driving nutrient input in the second largest body of water in the world," Downing said. "Because of the global importance of this paper, I continue to use it in presentations because it helps people understand the enormity of agricultural fertilizer inputs to marine systems."
Helping people understand and use the best water science to ensure healthy people and healthy water is the focus of Downing's current work with Minnesota Sea Grant.
"Minnesota Sea Grant helps Minnesotans understand and manage water," Downing said. "We teach the Watershed Game to community members who want to understand the connection between land use and water quality, and we offer the Nonpoint Education for Municipal Officials, called NEMO, for elected and appointed decision-makers. If the science people need doesn't exist, we try to find the funding and the scientists to make it happen."
Downing and co-authors will be officially presented with the award at the ASLO summer meeting in Victoria, British Columbia, Canada, in June 2018.
"This paper was the first that enabled scientists and the public to understand the global importance of water choices we make locally and I'm honored to be among the scientists recognized by ASLO for this paper," Downing said. "Bringing understanding to those who need water science is a big part of what I enjoy about my work for Minnesota Sea Grant."
CONTACTS: John A. Downing, Director, Minnesota Sea Grant; Professor of Biology, Department of Biology and Scientist, Large Lakes Observatory, University of Minnesota Duluth; firstname.lastname@example.org, 218-726-8715.