Impact of Long-Term Irrigation with Treated Sewage on Soil Magnetic Susceptibility and Organic Matter Content in North China.

This study assessed the effect on magnetic susceptibility and organic matter content of arable soil by irrigation with either treated sewage or groundwater. Results indicated that organic matter and magnetic susceptibility values in the soil irrigated with sewage were increased by 7.1 % and 13.5 %, respectively, compared to agricultural soil that irrigated with groundwater. Both the sewage and groundwater irrigated soils contained a significant fraction of ultrafine superpara magnetic grains, as indicated by high frequency dependent susceptibility (χfd > 6 %). The enhancement of soil magnetic properties was determined to be caused by anthropogenic sewage irrigation and agrochemical use by investigation of vertical soil profiles. Magnetic susceptibility parameters were shown to be significantly correlated with organic matter content (y = 0.0057x + 1.3439, R(2) = 0.09, p < 0.05). This work indicates that measurements of magnetic susceptibility may offer a rapid first step for identifying the potential pollution in arable soils.