Humid Region Salt Accumulation in Soils Under Wastewater Irrigation.

Irrigation reuse of municipal wastewater effluent conserves freshwater resources and avoids direct nutrient discharge to surface waters. Since the early 1960’s, Penn State University has used effluent from its wastewater treatment plant to irrigate agricultural and forested land at its Living Filter site.

                Salt affected soils are generally not an issue for humid regions. However, at the Living Filter site, effluent concentrations of sodium (Na⁺), magnesium (Mg²⁺), and calcium (Ca²⁺) have all increased over the years.  It is also significant that monovalent concentrations have increased disproportionally due to the installation of water softeners on Penn State’s campus. Sodium has increased to 446% its initial concentration, while Ca²⁺ and Mg²⁺have increased only 28% and 53% of their initial concentrations respectively. This asymmetric increase of cations has led to a much higher Sodium Adsorption Ratio (SAR) than was initially present. This raises concerns for long-term sustainability and management as the application of high SAR water can reduce the hydraulic conductivity of the soil.

This project provides data describing the present condition of soils at the Living Filter with regards to hydraulic conductivities, specific salt concentrations and electrical conductivities of the soil solution. This data is compared to data collected in 2009 and both sets of data are compared with model outputs from HYDRUS 2-D. Data will also be presented that highlights how solutions with varying SAR and electrical conductivities impact the physical properties of the iron oxide soils of Central Pennsylvania.  This research provides insight with regards to the anthropogenic impacts of wastewater irrigation on the long-term sustainability of soil structure at effluent-irrigated sites in humid regions.