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Integrated Climate Change Super Model

Christina Tague: Pursuing the Elusive Nitrogen-Tracking Super Model
Collaboration aims to create an integrated model for the Pacific Northwest

No element is an island. Take nitrogen, for example.


Christina Tague

Inert nitrogen, the kind that makes up most of the air we breathe (and about 3 percent of our body) and does not react chemically with anything else, is essential to life on Earth. But human activities – primarily burning fossil fuels and synthesizing fertilizers for agriculture – have produced vast quantities of reactive nitrogen, which interacts with other elements to cause a wide range of environmental problems.

Nitrogen released when fossil fuels are burned becomes smog in the atmosphere before being sent back to earth as acid rain, where it continues to filter through various terrestrial systems. It also interferes with the ability of trees to take up – i.e. sequester – carbon.

As for fertilizers, only about half of the nitrogen they contain gets absorbed by plants. The rest is released in runoff water, which seeps into the land and drains into streams and rivers that lead to the ocean, where excessive amounts of nitrogen cause acidification, algal blooms, red tides, and oxygen-deprived “dead zones.” Reactive nitrogen can also evaporate back into the atmosphere as ozone-depleting nitrous oxide.

It’s the interactive gift that keeps on giving us environmental problems.

Bren assistant professor Christina Tague is part of a team of researchers who are embarking on a new five-year, $3 million NSF-funded collaboration with the goal of better understanding carbon-nitrogen-water interactions at the regional scale and in the context of climate change.

To do that they must first create BioEarth, a sort of “super model,” by integrating several individual state-of-the-art modeling protocols into one. BioEarth is intended to support decision makers as they seek the best strategies for managing natural and agricultural resources in changing climatic conditions.

Tague is one of seven co-principal investigators from six institutions working on the project, each of whom is the lead developer or user of one of the modeling frameworks. For the past several years, Tague has been shepherding the evolution of RHESSys, a GIS-based hydrology and biogeochemical modeling program that simulates the cycling of, and interactions among, carbon, water, and nutrients in watersheds.

Each of the models contributes a distinct focus in a relevant area of carbon-nitrogen cycling: natural ecosystem dynamics (RHESSys), meteorology, atmospheric chemistry and transport, hydrology, agricultural dynamics, aquatic nutrient transport, and economic interactions.

The collaborators seek to synchronize the models to create an integrated regional model for the Pacific Northwest. The region is considered an ideal setting in which to test such an integrated approach because it is has an array of local climates and is home to landscapes ranging from agricultural lands and forested coastal and inland mountains to grasslands, high desert, and densely populated urban areas.

“As the climate changes, so, too, do interactions among nitrogen, carbon, and water in forests, grasslands, crops and their soils. Changes in hydrology occur, too, as snow melts earlier and precipitation patterns shift,” says Tague. “Since water is the main transport mechanism for nitrogen in landscapes, a change in hydrology can affect how much of it is retained by or lost from landscapes. For instance, when there is excess nitrate in the soil (after a fire or when fertilizer is applied) and warming is resulting in more rain and less snow, you might flush out more nitrogen or change the timing of when nitrate losses occur.”

Having the ability to predict those interactions and movements for a broader range of climate scenarios will be important for land-use managers, foresters, farmers, and urban planners seeking to make strategic decisions. The researchers will be interacting extensively with such stakeholders as they proceed on the complex task of enabling the diverse models to interact with each other, just as the systems the models represent interact in the real world.

“If all the models are running together in a system, we will be able to look at the many land-use planning scenarios and determine say, which forest management practices worsen the situation and which practices improve it,” Tague says.

If reactive nitrogen is the island poisoning the archipelago, BioEarth is conceived as a kind of super sleuth — with connections.