Long-term Treated Wastewater Irrigation Effects on Hydraulic Conductivity and Soil Quality at Penn State's Living Filter
Open Access
- Author:
- Larson, Zachary Marcus
- Graduate Program:
- Soil Science
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- None
- Committee Members:
- John Earl Watson, Thesis Advisor/Co-Advisor
John Earl Watson, Thesis Advisor/Co-Advisor - Keywords:
- Living Filter
Treated wastewater irrigation
Effluent irrigation - Abstract:
- Increased awareness of the impacts of eutrophication on streams and estuaries from the disposal of treated waste water (TWW) has resulted in finding alternate means for effluent disposal that will improve water quality. Concerns about water quality have become particularly important within the Chesapeake Bay Watershed, with states committing to reduce the discharge of nitrogen and phosphorus from point and non-point sources within the bay. As a means of renovation TWW irrigation has been utilized worldwide to address those concerns with the added benefit of meeting crop water demands and acting as a source of groundwater recharge. Penn State’s Office of Physical Plant has been using The Living Filter to irrigate crop and forest land with TWW for over 40 years and it has served as a research site for the soil’s ability to remove nutrients. However, physical changes that occur due to the irrigation of over 250 cm of TWW per year in addition to 100 cm of rainfall has not been as well researched. Most research concerning soil physical properties under TWW irrigation has been performed on soils of arid lands, with a focus on issues resulting from high sodium concentrations in TWW or naturally occurring in the soil. Far less research has been performed in temperate regions and under their vastly different soils. Land use managers at The Living Filter reported that there appeared to be an increase in runoff of irrigation from the site than when it was first developed. It was hypothesized that soil water infiltration rates declined due to the long term application of TWW. Therefore, in 2008 8 sampling blocks were laid out radiating from sprinklers, encompassing irrigated and non-irrigated areas of the Living Filter. Infiltration rates of both areas were compared using a tension infiltrometer at the soil surface and the top of the Bt1 horizon. In addition, surface soil bulk density and surface horizon clay and organic matter contents were evaluated with respect to distance from the sprinklers. Finally, soil cores were taken in 2009 and comparison of irrigated and non-irrigated areas were made between soil pH, electrical conductivity (EC), sodium adsorption ratio (SAR), total organic carbon (TOC) and clay content for each identified soil horizon. All experiments were arranged in a complete block or split-plot design. Results suggest that irrigated areas have greater surface horizon hydraulic conductivities than comparable non-irrigated areas. Analysis of Bt horizon hydraulic conductivity rates revealed that there was no difference between irrigated and non-irrigated areas. Analysis of bulk density suggests that distance from the sprinkler head has an effect on 0-10 cm bulk density, with areas within the sprinkler irrigated radius having lower bulk densities. Increases in soil structure resulting form increased soil microbial production, increased plant rooting and a greater number of freezing-thawing cycles many be causes for the differences between treatments for Ap horizon hydraulic conductivity and bulk density. Additionally, distance from the sprinkler head had an effect on clay content, with reduced clay contents within the irrigated area. Although this suggests that irrigation is translocating clay to lower horizons, further analysis needs to be performed before any conclusion can be made. Analysis of soil cores revealed that soil pH was approximately 1.0 unit greater in the irrigated area than the non-irrigated area for all identified horizons, with irrigated-area pH values reflecting that of the irrigation water. Soil EC was also greater in the irrigated area, with the greatest differences between areas occurring in the Bt2 through Bt4 horizons. Soil SAR was greater in the irrigated area when compared to the non-irrigated area, with SAR increasing with depth throughout the profile. This suggests a removal of sodium from the Ap horizon and the consequent movement and deposition of sodium deeper in the soil profile. The increased SAR values combined with relatively low EC values may result in reductions in hydraulic conductivity in the Bt2 through Bt4 horizons and monitoring should be performed to determine if the higher sodium concentrations are negatively impacting the soil. Initial findings suggest that TWW irrigation does not have a negative effect on soil hydraulic conductivity. Also, soil quality appears to have improved with TWW irrigation, resulting in a greater potential for increased water renovation and crop yields. When considering the lack of negative effects of TWW irrigation, one can see that the Living Filter should continue to serve as a viable way of eliminating nutrient discharge into local waterways and demonstrates that TWW irrigation can be an effective alternative for the tertiary treatment of wastewater.