Spatially distributed lateral nitrate transport at the catchment scale.

Area of Science:

• Environmental Science
• Hydrology
• Biogeochemistry

Background:

• Nitrogen (N) transformation and storage during lateral transport are critical for controlling N loads in surface waters.
• Current approaches lack the ability to spatially represent lateral flows and associated N transformations.
• Understanding these processes is vital for managing water quality in river catchments.

Purpose of the Study:

• To develop a novel conceptual model for simulating lateral nitrate transport and transformation in subsurface flow.
• The model aims to link N source areas to receiving water bodies in a spatially distributed manner.
• To provide a tool for targeting N sources and assessing their impact on surface water N loads.

Main Methods:

• Development of a new conceptual N transport and transformation model within the Object Modeling System (OMS) framework.
• Integration of the J2000 hydrological model, MetaCandy nitrate recharge model, and a novel groundwater N routing component.
• Stoichiometric calculation of nitrate degradation based on oxidizable substrate in groundwater.

Main Results:

• The model was tested in a German agricultural catchment, showing good performance during calibration (Nash and Sutcliff coefficient = 0.78) and validation (NS = 0.75).
• A strong correlation was found between hydrological simulation accuracy and nitrate concentration prediction.
• Nitrate degradation was primarily observed in slow base flow components due to short interflow residence times.

Conclusions:

• The developed model effectively simulates lateral nitrate transport and transformation in river catchments.
• It provides a valuable tool for identifying critical N source areas and quantifying their contribution to surface water N loads.
• The approach enhances spatially distributed assessments of nitrogen dynamics in aquatic ecosystems.