Impact of long-term wastewater irrigation on the physicochemical properties of humid region soils: “The Living Filter” site case study

Increasing pressure on water resources is a significant challenge for the 21st century. Over the last decade, water reuse has offered a practical approach to wastewater effluent disposal while supporting agricultural production. Irrigation with wastewater can have negative impacts on the soil environment (e.g. increased salinity, reduced hydraulic conductivity) and these are well documented for soils in arid and semi-arid regions; but little research has been conducted for humid regions. Consequently, to understand the impact of wastewater irrigation on humid region soils, a field study was conducted at “The Living Filter” site (central Pennsylvania), where wastewater effluent has been used for irrigation for 50+ years. The study evaluated the differences in physicochemical soil properties throughout the soil profile (to a depth of 120 cm) at wastewater irrigated sites and non-irrigated sites at different landscape positions (summits and depressions). Results showed that both the sodium adsorption ratio (irrigated: 4.93 ± 1.22; non-irrigated: 0.88 ± 1.03) and salinity (irrigated: 0.32 ± 0.12 dS m−1; non-irrigated: 0.07 ± 0.03 dS m−1) of soil extracts were significantly higher in the irrigated soil profiles compared to the non-irrigated soil profiles (but not with regards to landscape position). There was no observable treatment effect on saturated hydraulic conductivity, Ks, (irrigated: 1.96 cm h−1; non-irrigated: 2.39 cm h−1), but Ks had moderately strong inverse relationships with soil pH (R2 = 0.70) and percent organic carbon (R2 = 0.67). Overall, while salts are accumulating in these soils; our data suggest that long-term irrigation with wastewater has not negatively impacted the hydraulic conductivity of this humid region soil. Ongoing monitoring of soil physicochemical properties and wastewater parameters will be needed to maintain the long-term sustainability of the site.