Nitrite formation and nitrous oxide emissions as affected by reclaimed effluent application

Area of Science:

• Environmental Science
• Soil Science
• Microbiology

Background:

• Irrigation with reclaimed effluent (RE) is a growing practice, but its impact on soil nitrogen (N) transformations, particularly nitrite formation and nitrous oxide (N2O) emissions, remains poorly understood.
• Secondary-treated RE may alter soil microbial processes, potentially affecting nutrient cycling and greenhouse gas emissions.

Purpose of the Study:

• To investigate the effects of secondary-treated RE irrigation on nitrite formation, N2O emissions, and N mineralization in Grumosol soil.
• To elucidate the mechanisms and rates of N transformations under RE irrigation using isotopic labeling.

Main Methods:

• Incubation of Grumosol soil with fresh water (FW) and RE, labeled with 15NO3- and 15NH4+.
• Measurement of nitrite levels, N2O emissions, and N mineralization rates under varying moisture and soil aggregate conditions.
• Isotopic analysis to determine the primary pathways of nitrite formation.

Main Results:

• RE irrigation led to a tenfold increase in soil nitrite levels compared to FW irrigation, with peak concentrations at 60% moisture content.
• N2O emissions from RE-treated soil were double those from FW-treated soil, with nitrification accounting for approximately 42% of these emissions.
• Nitrification rates were higher in RE-irrigated bulk soil (15.8 mg N kg(-1) soil d(-1)) compared to FW-irrigated soil (11.3 mg N kg(-1) soil d(-1)).

Conclusions:

• Secondary-treated RE irrigation stimulates soil nitrification and increases N2O emissions.
• Elevated nitrification may result from long-term adaptation of the nitrifier population to RE, potentially increasing nitrate leaching risks.
• Understanding these N transformations is crucial for sustainable water management and mitigating environmental impacts.