Climate change could unleash nitrogen stored in dry soil, turning northern farmlands into pollution hotspots as rainfall and storms intensify.
For as long as researchers have tracked it, China’s worst cropland nitrogen pollution has occurred in the humid south.
Heavy rain, dense river networks, and fertilizer runoff flowing directly into the water have created a well-known and well-studied problem.
A new modeling study suggests that the pattern is about to change. As the climate shifts, the country’s emerging pollution hotspots could migrate away from the humid south and into the arid and semi-arid regions of the north.
The research comes from a team led by Professor Yongqiu Xia at the Institute of Soil Science, Chinese Academy of Sciences.
Rainfall drove pollution in the south
Nitrogen that crops fail to absorb does not simply vanish. It accumulates in the soil until rain washes it into rivers, lakes, and reservoirs downstream.
Southern China’s heavier rainfall and dense network of waterways have made the region the country’s long-standing hotspot for this type of pollution.
The north, by contrast, has largely escaped the problem. Less rain meant less runoff and, therefore, less nitrogen reaching rivers – or so researchers thought.
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Climate change shifts the balance
That north-south divide was never a law of nature. It reflected a balance, and that balance can shift.
Rising temperatures accelerate the chemical processes that convert nitrogen stored in soil into forms that water can carry away.
Meanwhile, heavier rainfall and more intense storms are becoming increasingly common as the climate warms. These events can mobilize nitrogen that has accumulated in dry soil for years.
Working in the opposite direction, lakes, reservoirs, and rivers naturally remove some of that nitrogen as it travels downstream.
The outcome in any given place therefore comes down to a tug-of-war between how much nitrogen the land releases and how much the water filters out along the way.
Following nitrogen through the water
To capture that balance, the team combined models of cropland nitrogen runoff with simulations that tracked how nitrogen moves through connected river and lake systems. The simulations also accounted for how those systems filter nitrogen.
The researchers built their analysis around the Zhiyuan agricultural nonpoint source pollution model, which draws on 1,485 field observations collected across China.
Older nitrogen pollution models rely on sparse data and tend to overlook important regional differences.
Those differences can determine whether a specific river basin is at risk, so the researchers designed their approach to account for them.
Northern pollution could rise sharply
The results show how uneven the current pattern is.
Southern China exports roughly 0.31 teragrams of cropland nitrogen to the ocean each year, nearly twice the 0.16 teragrams exported by the arid north. By 2050, however, that gap could narrow rapidly.
Northern nitrogen exports could climb by 18.8 percent under a moderate warming scenario and by as much as 53.2 percent under a high-emissions scenario.
Meanwhile, southern nitrogen exports could remain roughly flat or even decline slightly over the same period.
The Hai River Basin appears especially vulnerable. Its nitrogen exports could jump by 88.1 percent under the high-emissions scenario, an increase that stands out among the projections.
Because the region has not historically faced the same level of nitrogen runoff, it may have little institutional experience to guide its response.
Dry soils hide a growing threat
Here is the counterintuitive part: the places carrying the heaviest pollution burden today are not necessarily the ones where pollution will increase fastest.
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In northern drylands, nitrogen has accumulated in the soil for years with nowhere to go.
When rain finally arrives, it can activate runoff pathways that had remained disconnected from the water network. The stored nitrogen can then flush into rivers all at once, releasing years of buildup in a single burst.
Different regions need tailored solutions
The findings do not point toward a single, one-size-fits-all response.
In the north, the researchers recommend weather-responsive fertilization schedules, controlled-release fertilizers, and smaller fertilizer applications spaced out over time.
These measures aim to prevent nitrogen from accumulating in the soil before heavy rain arrives.
In the south, the priority is less about preventing runoff and more about preserving the water network’s ability to remove nitrogen naturally.
The recommended approach begins with reducing fertilizer use at the source. It also includes restoring riparian wetlands, managing aquatic vegetation, and building decentralized systems that capture nitrogen before it travels farther downstream.
The researchers also warn that similar risks could be emerging in other dryland farming regions, from North America’s Great Plains to Australia’s wheat belt.
However, determining the scale of the threat and how to address it will require research tailored to each region. Researchers should not assume that China’s findings apply directly elsewhere.
NOTE – This article was originally published in earth and can be viewed here
Tags: #climate, #climate shifts, #crops, #environment, #getgreengetgrowing, #gngagritech, #greenstories, #nature, #Pollution, #rain, #rainfall, #river, #soil
