Mark Williams, Ph.D.


Documented how agricultural runoff containing nitrogen and phosphorous  used in fertilizers migrate into and pollute waterways, prompting new farming conservation practices to protect the environment.

Mark Williams, Ph.D.

More than 6,000 square miles in the Gulf of Mexico—approximately the size of Hawaii—are now a dead zone, an area of low or no oxygen that is unable to support marine life.  

A major contributing factor to this problem is agricultural runoff containing nitrogen and phosphorous. These nutrients are used in fertilizer to produce food, feed, fuel and fiber, but if transported downstream can cause algae blooms that produce harmful toxins that negatively impact the environment along with commercial and recreational activities. This problem has not only occurred in the Gulf of Mexico, but in over 750 coastal areas globally. 

Mark Williams, 35, a research agricultural engineer with the U.S. Department of Agriculture’s Agricultural Research Service, has become a recognized authority on the movement, distribution and management of water in agricultural settings, and how that water transports pollutants stemming from the use of fertilizers.  

“Mark Williams has made significant contributions and advancements in understanding hydrology and nutrient movement in agricultural tile-drained landscapes,” said Rachel Steele, a USDA science advisor. “He has sought out and developed collaborations and partnerships with federal and state agencies, university partners and industry to accelerate and disseminate his important research findings.” 

Tile drainage is a system of pipes installed below ground to remove excess water from soil, a widely used practice in some agricultural settings. Tile drainage is necessary to prevent the soil from becoming oversaturated with water, which can damage crops and farm machinery as well as increase erosion. However, the drainage system also can end up transporting harmful substances downstream. 

In the past, farmers and researchers did not recognize that these subsurface engineered systems contributed to the movement of phosphorus, nitrogen and other pollutants into waterways.  

”There was a long-held belief that phosphorus would remain in the soil and not move,” said Alberto Pantoja, director of the Agricultural Research Service’s Midwest Area.  

Williams noted that “even a small amount of phosphorus entering a tile drainage system can have devastating effects downstream.”  

Pantoja said Williams is “giving farmers a more accurate picture’’ of how much polluted agricultural runoff is occurring and how to prevent it from happening. 

“Mark has focused on how water moves and where it goes, and therefore where the phosphorus and nitrogen go,” Pantoja said.  

Williams has brought a new understanding to the problem, using dyes and isotopic tracers to track the movement of the agricultural runoff. Steele said Williams’ research has been used by scientists, agronomists, farmers, engineers, federal agencies and academic institutions, and informed conservation policies. 

“Williams’ work has new urgency as the amount of agricultural land using tile drainage in the U.S. is growing, with more than 60 million acres implementing these systems,” Steele said. “Understanding the movement of water through agricultural fields is key to controlling runoff and adapting conservation practices.” 

Kevin King, a USDA agricultural engineer, said Williams has met with large and small groups of farmers to explain his research and propose new practices to curb the harmful effects of the fertilizers. “Some practices are changing because of his work,” King said. 

Williams and his colleagues have been exploring a variety of integrated water, land and crop management systems and conservation practices that can support both profitable agriculture and environmental protection.  

The solutions can be expensive, in some cases requiring assistance to farmers from state and federal governments and nonprofit environmental organizations. Some options include the use of cover crops, reduced tillage, crop rotation and nutrient management. 

A key element of Williams’ work has been providing accurate data on the source and quantity of nutrients from agricultural runoff that is causing harm, understanding different factors such as weather conditions, the amount of rainfall and the direction of the runoff, and outlining the possible remedies. 

Williams said the agricultural community is continually innovating to increase crop yields and minimize environmental impact, motivating him “to push scientific boundaries to provide them with the data and tools they need to succeed.”  

“By quantifying when, where and how much nutrients are lost from fields, my work can serve the agricultural community by providing information that can help it make better informed management and business decisions,” Williams said. “At the same time, my work has helped farmers develop solutions to decrease the impact of agriculture on the environment through the implementation of novel conservation practices.”