Regional Analysis of Nitrogen Flow within the Chesapeake Bay Watershed Food Production Chain Inclusive of Trade

In the Chesapeake Bay Watershed, excess nitrogen has
contributed
to poor water quality, leading to nitrogen mitigation efforts to restore
and protect the watershed. The food production system is a top contributor
to this nitrogen pollution. While the food trade plays a vital role
in distancing the environmental impacts of nitrogen use from the consumer,
previous work on nitrogen pollution and management in the Bay is yet
to carefully consider the effect of embedded nitrogen found in products
(nitrogen mass within the product) imported and exported throughout
the Bay. Our work advances understanding across this area by creating
a mass flow model of nitrogen embedded in the food production chain
throughout the Chesapeake Bay Watershed that separates phases of the
production and consumption processes for crops, live animals, and
animal products and considers commodity trade at each phase by combining
aspects of both nitrogen footprint and nitrogen budget models. Also,
by tracking nitrogen embedded in products imported and exported in
these processes, we distinguished between direct nitrogen pollution
and nitrogen pollution externalities (displaced N pollution from other
regions) from outside of the Bay. We developed the model for the watershed
and all its counties for major agricultural commodities and food products
for 4 years 2002, 2007, 2012, and 2017 with a specific focus on 2012.
Using the developed model, we determined the spatiotemporal drivers
of nitrogen loss to the environment from the food chain within the
watershed. Recent literature leveraging mass balance approaches has
suggested that previous long-term declines in nitrogen surplus and
improvements in nutrient use efficiency have stagnated or begun to
reverse. Our results suggest that within the Chesapeake Bay, increased
corn and wheat acreage and steadily increasing livestock/poultry production
may have led to the stagnation in decreasing N loss trends from agricultural
production observed over the past two decades. We also show that at
the watershed scale, trade has reduced the food chain nitrogen loss
by about 40 million metric tons. This model has the potential to quantify
the effect of various decision scenarios, including trade, dietary
choices, production patterns, and agricultural practices, on the food
production chain nitrogen loss at multiple scales. In addition, the
model’s ability to distinguish between nitrogen loss from local
and nonlocal (due to trade) sources makes it a potential tool to optimize
regional domestic production and trade to meet local watershed’s
needs while minimizing the resulting nitrogen loss.