In many arid and semi-arid regions of the world the demand for drinking water and other domestic uses is constantly growing due to demographic growth and increasing standard of living. Therefore, less freshwater is available for agricultural irrigation and new water sources are needed. Treated wastewater (TWW) already serves as an important water source in Israel since more than 40 years and its usage will further be extended. Due to the high concentration of nutrients, salts, organic and inorganic substances the water can cause a change in physical, chemical and biological soil properties. In this study the impact of organic carbon derived from TWW irrigation on the soil organic carbon (SOC) and the soil microbial activity was investigated on different agricultural soils in Israel. Total soil carbon contents and the characteristics of dissolved organic carbon (DOC) in soils irrigated with TWW and freshwater as a control were determined. Subsoils (50-160 cm) from TWW irrigated sites were depleted in SOC with the largest differences occurring on sites with the longest TWW irrigation history. The amount of DOC increased and the aromaticity of the organic compounds in the soil percolates decreased over the irrigation period in the TWW irrigated soil compared to the freshwater irrigated one. These can cause a change of soil properties. Laboratory incubation experiments with additions of labelled organic compounds to the soils showed that microbial activity in freshwater irrigated soils was much more stimulated by sugars or amino acids than in TWW irrigated soils. The pronounced effect seems to be relevant in deeper soil horizons with continuously input of organic matter which percolates in the soil. According to our hypothesis, the SOC in deeper soil horizons of TWW irrigated sites is depleted because of stimulated microbial activity due to substrate inputs from the effluents. The effect has influence on the fertility of the soils. Due to enhanced mineralization of organic material a greater amount of CO2 is released from the soil which changes the C-balance and may therefore contribute to climate change.
Aktualisiert: 2019-12-20
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