Impact of Long-Term Application of Patranala Sewage on Carbon Sequestration and Heavy Metal Accumulation in Soils

There is a gradual decline in good quality irrigation water for crop production. Farmers are forced to use poor quality water for crop production in peri-urban areas. Among the wastewater, sewage water generally contains higher amount of plant nutrients and dissolved organic matter. A case study was conducted to investigate the impact of untreated sewage water application on physicochemical properties and carbon sequestration in soil. For this purpose, peri-urban agricultural lands irrigated with sewage water from Patranala, Bhopal were selected. Such lands around both sides of the Patranala were being irrigated with sewage water for more than last 50 years. The soil samples were collected at various soil depths i.e., 0-15, 15-30, 30-45 and 45-60 cm from these fields; and sampling points were at about 2 km intervals along the channel direction and also at the distance interval of about 0.5, 1.0, 1.5 and 2.0 km away from the sewage carrying channel. The soil microbial population and enzymatic activities were considerably higher in the sewage irrigated fields as compared to those in tubewell irrigated area. Concentrations of heavy metals in surface soils were also higher in sewage irrigated fields. Maximum soil organic carbon (SOC) contents were found in surface layer (0-15 cm), which decreased with depth at all the locations. Net stock of carbon in upper 60 cm of the soil depth was higher in sewage irrigated lands as compared to those irrigated with tubewell water. Thus, long-term application of sewage water for crop production enhanced sequestration of sewage borne carbon in soil profile, which otherwise could pollute the surface water bodies and emit in the atmosphere as greenhouse gases. However, heavy metals build-up in the sewage irrigated area is a major concern.