While nutrient export models are abundant, a knowledge gap remains regarding how climate and land-use changes specifically affect dissolved inorganic nitrogen (DIN) export in subtropical catchments. This understanding is essential for developing effective watershed management strategies.

A new study led by Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, examines DIN export from a typical subtropical catchment in southeastern China. The study evaluates the primary causes of variations in DIN export and the impacts of expected future changes in climate and land use by the Hydrological Predictions for the Environment (HYPE).

The HYPE model simulated streamflow dynamics from 2000 to 2019 and captured inter-annual variations in DIN export. Elevated DIN loads during spring and summer were primarily driven by agricultural fertilizer use, along with denitrification processes occurring in both soils and river systems.

Model projections indicate that land-use change alone—specifically a 7.0% expansion of arable land and a 7.5% reduction in forest cover between 2015 and 2050—would raise riverine DIN concentration by 12.8% and DIN load by 19.1%, due to increased nitrogen inputs. In contrast, annual evapotranspiration and runoff remained relatively stable, showing only a minor change of about 0.5%.

Climate change projections for 2031–2050 indicate divergent trends in runoff across different climate models and emission scenarios, with estimates ranging from a decline of 24.0% to an increase of 24.8%. Under the same period, the average DIN concentration will increase by up to 36.0% compared to the baseline conditions of 2000–2019, depending on specific hydroclimatic variability.

The integrated impacts of future land-use and climate change are expected to increase the riverine DIN loads by up to 32.6%. The study further reveals that climate-driven effects dominate runoff variations and may amplify the influence of land-use changes on nitrogen pollution in subtropical catchments like the Yifeng River basin. This amplification is attributed to reduced precipitation and river discharge, which diminish the water body’s capacity to dilute nitrogen inputs.

These findings were published in Journal of Hydrology on December 29, 2025.