Legacy-buffered groundwater nitrate limits predictability from short-term hydroclimatic windows across intensive...

Area of Science:

• Environmental Science
• Soil Science
• Hydrogeology

Background:

• Intensive agriculture leads to groundwater nitrate contamination.
• Short-term weather variability often fails to predict long-term aquifer contamination.
• Understanding the disconnect between surface and subsurface nitrate dynamics is crucial for effective management.

Purpose of the Study:

• To investigate the relationship between hydroclimatic variability, soil nitrogen dynamics, and groundwater nitrate contamination.
• To determine if short-term surface signals can predict groundwater nitrate levels in intensive croplands.
• To elucidate the factors controlling nitrate persistence in aquifers under agricultural land use.

Main Methods:

• Field study across a south-to-north transect in Henan Province, China, with wheat-maize rotation.
• Quantification of antecedent hydroclimatic windows and soil inorganic nitrogen stocks (0-50 cm).
• Measurement of soil N-cycling enzyme activities, groundwater nitrate-N, and nitrate isotopes (δ15N-NO3- and δ18O-NO3-).
• Principal component analysis to summarize hydroclimatic variability.

Main Results:

• Drier antecedent conditions correlated with higher soil nitrate storage (41% of variance).
• Groundwater nitrate showed weak short-term coupling with surface conditions (only 19% of variability explained).
• Nitrate isotope data indicated multiple sources and transport lags influencing groundwater nitrate.

Conclusions:

• Groundwater nitrate contamination is poorly predictable from short-term surface indicators due to subsurface storage and time lags.
• Management strategies should focus on sustained reduction of nitrogen surplus.
• Monitoring designs must account for subsurface dynamics and delayed aquifer responses.