Denitrification during infiltration for managed aquifer recharge: Infiltration rate controls and microbial response
Galen Gorski1, Hannah Dailey1, Andrew T Fisher1
1Department of Earth and Planetary Sciences, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, United States.
The Science of the Total Environment
|April 26, 2020
Summary
Managed aquifer recharge (MAR) systems enhance water quality by removing nitrate. Carbon-rich barriers and optimal infiltration rates significantly boost microbial denitrification, improving nitrogen removal.
Area of Science:
- Environmental Science
- Geochemistry
- Microbiology
Background:
- Managed aquifer recharge (MAR) systems offer a dual benefit of increasing water supply and improving water quality.
- Nitrate removal during infiltration is crucial for MAR effectiveness, primarily achieved through microbial denitrification.
- Understanding the interplay between infiltration rates, carbon availability, and microbial communities is key to optimizing MAR performance.
Purpose of the Study:
- To investigate the impact of infiltration rate and carbon-rich permeable reactive barriers (PRBs) on nitrate removal during MAR.
- To quantify the relationship between infiltration parameters, PRB composition, and microbial ecology shifts.
- To identify optimal conditions for enhancing nitrate removal via denitrification in MAR systems.
Main Methods:
- Laboratory flow-through column experiments using intact soil cores from MAR sites.
- Testing various infiltration rates (0.3-1.4 m/day) with different PRB materials: native soil (NS), woodchips (WC), and a WC/native soil mixture (MIX).
- Analysis of nitrate removal efficiency, denitrification rates, and shifts in soil microbial community structure.
Main Results:
- Carbon-rich PRBs (WC and MIX) significantly increased nitrate removal amounts and rates compared to NS.
- Highest nitrate removal fractions occurred at the lowest infiltration rates across all treatments.
- Optimal nitrogen mass removal (∆NL) was observed at 0.4-0.7 m/day for WC and MIX, and ~0.3 m/day for NS.
- Carbon-rich PRBs altered microbial ecology, reducing diversity and increasing abundance of carbon-degrading and nitrogen-metabolizing bacteria.
Conclusions:
- Infiltration rates and carbon availability are critical factors for successful denitrification in MAR systems.
- Optimized PRB design and controlled infiltration can significantly enhance nitrate removal efficiency.
- MAR system performance is closely linked to the structure and function of the associated soil microbial communities.
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