In the arid landscapes of the world, where water is scarce and climate change is accelerating, a hidden process is altering the way nitrogen moves through ecosystems. This process, involving biogeochemical “hotspots,” could significantly impact water quality and have ripple effects on industries that depend on clean water, including energy production.
Jianning Ren, a researcher at the University of Nevada, Reno, has been delving into this phenomenon. Ren, who leads the study published in the journal Water Resources Research, explains that these hotspots are moist microsites in dryland soils that become disconnected from plant roots as the soil dries out. “These hotspots act like tiny reservoirs,” Ren says. “They accumulate nitrogen over dry periods and then flush it rapidly into streams when the soil wets up again.”
This process is crucial for understanding nitrogen export, a significant concern for water quality. Nitrogen, a key nutrient, can become a pollutant when it accumulates in water bodies, leading to issues like algal blooms and dead zones. For the energy sector, which often relies on large volumes of water for cooling and other processes, understanding and mitigating nitrogen pollution is vital.
Ren and his team developed a framework to represent these hotspots in an ecohydrological model called RHESSys. They conducted virtual experiments to see how uncertainties in model structure and parameters influence nitrogen export to streams. Their findings were striking. Nitrogen export was sensitive to three major factors: the abundance of hotspots, the soil moisture threshold required for subsurface flow from hotspots to reestablish, and the rate at which water diffused out of hotspots as soils dried down.
In a case study, the team found that when hotspots were modeled explicitly, peak streamflow nitrate export increased by 29%. This allowed them to better capture the timing and magnitude of nitrogen losses observed in the field. Moreover, nitrogen export further increased in response to interannual precipitation variability, particularly when multiple dry years were followed by a wet year.
The implications of this research are far-reaching. As climate change continues to alter precipitation patterns, understanding how nitrogen moves through dryland ecosystems will become increasingly important. For the energy sector, this means anticipating and mitigating potential water quality issues. It also means considering the role of hotspots in carbon and nitrogen cycling, which could have implications for carbon sequestration efforts.
Ren’s work, published in the journal Water Resources Research, provides a new tool for projecting future nitrogen export in watersheds where hotspots play an increasingly important role in water quality. As we continue to grapple with the impacts of climate change, this research offers a glimpse into the complex interplay between water, nutrients, and ecosystems in drylands. For industries that depend on clean water, understanding these processes could be the key to sustainable water management in an uncertain future.