New study reveals how water pathways control nitrogen pollution from farms to cities

Researchers have uncovered how nitrogen pollution travels through the environment in different ways depending on land use, offering a powerful tool for cleaner water management from rural farmlands to sprawling cities.

A team led by scientists from Hohai University and the Chinese Academy of Sciences developed a new analytical framework that separates how nitrogen moves through three key hydrological pathways—surface flow, subsurface flow, and baseflow. The approach combines flow tracking and chemical fingerprinting to reveal which pathways carry the most nitrogen pollution under different land conditions.

The study, published in Nitrogen Cycling, analyzed data from three watersheds in the Qinhuai River Basin in southeast China that represent a clear rural-to-urban transition. Using high-resolution flow monitoring and water chemistry analysis, the team discovered that the type of water movement strongly controls how and where nitrogen leaves the landscape.

In urban watersheds, underground baseflow was found to carry nearly half of the ammonia nitrogen, mainly due to leaking sewer systems and old drainage infrastructure. In contrast, traditional farming areas exported most of their nitrate through groundwater, while surface runoff during storms mobilized organic forms of nitrogen. Intensive agricultural zones showed the most complex patterns, with fertilizer and animal waste influencing all pathways.

“These findings show that how nitrogen moves is just as important as where it comes from,” said Dr. Yongqiu Xia, senior author of the study. “Managing nitrogen pollution effectively requires recognizing that each flow pathway behaves differently, across both landscapes and seasons.”

Seasonal shifts were also pronounced. During dry seasons, nitrogen mainly traveled through groundwater, while heavy rains in the wet season triggered surface runoff that transported pollutants more rapidly. The results suggest that strategies to reduce nitrogen loss must be adapted to each landscape’s dominant hydrological behavior.

The research offers crucial guidance for policymakers. Improving sewer systems and enhancing green infrastructure such as infiltration basins can reduce nitrogen leakage in cities, while farms can benefit from buffer strips, improved fertilizer timing, and plant cover to reduce runoff and nitrate leaching.

By integrating hydrological and chemical data into one model, the new framework provides a stronger scientific basis for solving one of the most persistent global water quality challenges: how to control nitrogen pollution in a changing, human-dominated world.

=== 

Journal Reference: Huang X, Yang X, Xie Y, Zhang H, Lu N, et al. 2025. Pathway-specific nitrogen export across a rural-urban gradient: integrating hydrograph separation and end-member mixing analysis. Nitrogen Cycling 1: e006  https://www.maxapress.com/article/doi/10.48130/nc-0025-0006  

=== 

About Nitrogen Cycling:
Nitrogen Cycling is a multidisciplinary platform for communicating advances in fundamental and applied research on the nitrogen cycle. It is dedicated to serving as an innovative, efficient, and professional platform for researchers in the field of nitrogen cycling worldwide to deliver findings from this rapidly expanding field of science.

Follow us on Facebook, X, and Bluesky.