Nitrate accumulation and transformation processes within a karst conduit system: Insights from hydrochemistry, stable isotopes, metagenomics, and tracer tests.

Nitrate levels increase from 1.56 to 14.23 mg L-1 along karst conduit flow, driven mainly by nitrification within the subsurface system.

• Why it matters: Understanding nitrate transformation in karst aquifers is crucial for protecting drinking water, yet subsurface complexity hampers tracing its sources and processes.
• What they did: The study used hydrochemistry, isotopic analysis, metagenomics, and tracer tests to investigate nitrate sources and transformations in the Lanfeng karst watershed, focusing on functional gene abundance and concentration changes.
• The result: Findings reveal that karst conduits act as active reactors producing nitrate endogenously, emphasizing the importance of considering internal nitrification in nitrate risk assessments and pollution mitigation strategies.