Effluent irrigation and agricultural soils

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In many arid and semi-arid regions, the demand for drinking water and domestic use is increasing due to population growth and rising living standards, leading to reduced freshwater availability for agriculture. Treated wastewater (TWW) has been a vital water source in Israel for over 40 years, and its use is set to expand. However, TWW's high concentrations of nutrients, salts, and various substances can alter soil properties. This study investigates the impact of organic carbon from TWW irrigation on soil organic carbon (SOC) and microbial activity across different agricultural soils in Israel. It assesses total soil carbon and dissolved organic carbon (DOC) characteristics in TWW-irrigated soils compared to freshwater controls. Findings reveal that subsoils (50-160 cm) from TWW sites show SOC depletion, particularly in areas with extensive TWW use. While DOC levels increased, the aromaticity of organic compounds in soil percolates decreased over time in TWW-irrigated soils. Laboratory experiments indicated that microbial activity in freshwater soils was more responsive to sugars and amino acids than in TWW soils. This effect is pronounced in deeper soil layers, where continuous organic matter input from TWW appears to deplete SOC due to enhanced microbial activity. Consequently, increased mineralization leads to higher CO2 emissions, affecting soil fertility and contributing to climate change.