Nitrogen Fate and Transport in a Conventional Onsite Wastewater Treatment System Installed in a Clay Soil: Experimental Results. Issue 3 (15th August 2013)

• Record Type: Journal Article
• Authors: Bradshaw, James K.; Radcliffe, David E.
• Is Part Of: Vadose zone journal. Volume 12:Issue 3(2013)
• Page Start: 1
• Page End: 20
• Publication Date: 2013-08-15
• Subjects: Soil science -- Periodicals; Zone of aeration -- Periodicals; Groundwater flow -- Periodicals; Groundwater flow; Zone of aeration; Periodicals; Electronic journals; 631.4
• DOI: 10.2136/vzj2012.0149
• Languages: English
• ISSNs: 1539-1663

Abstract

Abstract : Relationships between N transport and hydraulic function of onsite wastewater treatment systems (OWTSs) in clay‐textured soils are largely unknown. The objectives of this study were to quantify N concentrations in a clay soil and estimate denitrification in the vadose zone beneath a conventional OWTS. An OWTS installed in the Piedmont region of Georgia was dosed with residential strength wastewater three times per day for 2 yr. Soil near trench bottoms cycled between saturated and unsaturated conditions under the dosing schedule we used. Mean NH4 –N concentrations decreased to <1 mg L −1 within 90 cm of trench bottoms due to adsorption, immobilization, and nitrification. Mean NO3 –N concentrations increased as the drainfield matured and ranged from 10 to 25 mg L −1 near the end of the two year study period. Mean pressure heads and Cl − concentrations measured at 3.3 m and 6.6 m from trench inlets indicated that significantly more water infiltrated the drainfield at the 3.3 m position. Wet conditions at the 3.3 m position may have restricted nitrification, while dry conditions at the 6.6 m caused rapid nitrification. Nitrogen:chloride ratios suggested that 61% of N entering the drainfield was lost, potentially as volatile N‐species. The 30‐cm zone directly beneath the trenches had high biomass N and C contents (15 mg kg −1 N and 60 mg kg −1 C) and was presumably the most biologically active zone. The fate and transport of N was dynamic in this system due to variable moisture conditions near the trench‐soil interface which may have intermittently stimulated denitrification.