Wastewater Irrigation Drives Depth‐dependent Microbial Functions and Soil Organic Carbon Dynamics in Peri‐urban Agricultural Soils

Abstract

Soil organic carbon (SOC) is the foundation of soil fertility and ecosystem stability, which is a major regulator of nutrient cycles and water retention in agricultural lands. The enzymatic activities of microbial players cause the breakdown and stabilization of organic materials, which has a major impact on the health of soil and its long-term sustainability. The current study was undertaken to investigate the long-term effects of contrasting irrigation water sources (domestic DWW, municipal MWW, and mixed wastewater MixWW and canal water CW as control) on soil organic carbon dynamics and microbial activity across two soil depths (0–15 and 15–30 cm) in peri-urban agricultural soils of Faisalabad, Pakistan. Results revealed clear differences among irrigation regime. At 15–30 cm depth, DWW maintained relatively high mineral associated organic carbon (MAOC) and was 44.3% higher than that of MWW. Mix WW reduced microbial biomass carbon by 61.8% and FDA activity by 87.2% relative to CW at the same depth. Surface soil organic carbon (SOC) was 38.4–49.8% lower under wastewater irrigations compared to that of CW. In contrast, DWW increased subsurface SOC (1.6% higher than CW) and MAOC (44% higher than MWW), suggesting enhanced carbon stabilization and long-term sequestration potential in wastewater irrigation regime. Principal component analysis highlighted strong positive correlations between SOC, MAOC, and enzyme activities, while negative correlations were observed among soil pH, cation exchange capacity, and organic carbon pools. These findings highlight contrasting patterns in soil organic carbon fractions, microbial biomass and enzyme activities among the four long-term agricultural fields under different irrigation regime, emphasizing the need for replicated multi-site studies before generalizing the observed associations to irrigation-water quality effects. Microbial functioning and carbon stabilization, emphasizing the need for targeted wastewater management practices to mitigate adverse effects of wastewater irrigation on soil health and optimize long term organic matter retention in soil.

Graphical Abstract