Hydrological connectivity affects nitrogen migration and retention in the land‒river continuum

Area of Science:

• Environmental Science
• Water Quality Research
• Biogeochemistry

Background:

• Land use change and nitrogen loading degrade water bodies globally.
• The influence of hydrological connectivity on nitrogen cycling and river water quality is not well understood.

Purpose of the Study:

• To investigate river nitrogen dynamics and controlling factors at watershed, hydrologically sensitive areas (HSAs), and riparian zone scales.
• To explore the role of hydrological connectivity in linking watershed land use to river N biogeochemistry and water quality.

Main Methods:

• Studied 15 subwatersheds in the Jiulong River watershed during a dry baseflow period (2018).
• Analyzed 3-year (2017-2019) nutrient monitoring data from 5 subwatersheds.
• Examined river nitrogen (dissolved nutrients, dissolved gases, functional genes) at three hydrological connectivity scales.

Main Results:

• Land use in HSAs and at the watershed scale similarly affected river nitrogen variation.
• HSAs act as critical hotspots for transporting terrestrial nitrogen into river systems.
• Agricultural land influenced river nitrate and nitrous oxide (N₂O), while built-up land affected ammonium and nitrite.
• Riparian zone soils and sediments played a key role in nitrogen retention processes like nitrification and denitrification.

Conclusions:

• Hydrologically sensitive areas and riparian zones are crucial for managing river nitrogen loading.
• Targeted management strategies for HSAs and riparian zones can effectively improve river water quality.