J.K. Böhlke L.H. Fisher S.R. Hinkle 2008 <div id="abstracts" class="Abstracts"><div id="aep-abstract-id8" class="abstract author"><div id="aep-abstract-sec-id9"><p><span>Septic tank&nbsp;systems are an important source of NO</span>₃⁻<span>&nbsp;to many&nbsp;aquifers, yet characterization of N mass balance and isotope systematics following septic tank&nbsp;effluent&nbsp;discharge into unsaturated sediments has received limited attention. In this study, samples of septic tank effluent before and after transport through single-pass packed-bed filters (sand filters) were evaluated to elucidate mass balance and&nbsp;isotope effects&nbsp;associated with septic tank effluent discharge to unsaturated sediments. Chemical and isotopic data from five newly installed pairs and ten established pairs of septic tanks and packed-bed filters serving single homes in Oregon indicate that aqueous solute concentrations are affected by variations in recharge (precipitation, evapotranspiration), NH</span>₄⁺<span>&nbsp;sorption&nbsp;(primarily in immature systems),&nbsp;nitrification, and gaseous N loss via NH</span>₃<span>&nbsp;volatilization&nbsp;and(or) N</span>₂<span>&nbsp;</span>or N₂O release during nitrification/denitrification. Substantial NH₄⁺<span>&nbsp;</span>sorption capacity was also observed in laboratory columns with synthetic effluent. Septic tank effluent<span>&nbsp;</span><i>δ</i>¹⁵N–NH₄⁺<span>&nbsp;</span>values were almost constant and averaged +&nbsp;4.9‰&nbsp;±&nbsp;0.4‰ (1<span>&nbsp;</span><i>σ</i>). In contrast,<span>&nbsp;</span><i>δ</i>¹⁵N values of NO₃⁻leaving mature packed-bed filters were variable (+&nbsp;0.8 to +&nbsp;14.4‰) and averaged +&nbsp;7.2‰&nbsp;±&nbsp;2.6‰. Net N loss in the two networks of packed-bed filters was indicated by average 10–30% decreases in Cl⁻-normalized N concentrations and 2–3‰ increases in<span>&nbsp;</span><i>δ</i>¹⁵<span>N, consistent with&nbsp;fractionation&nbsp;accompanying gaseous N losses and corroborating established links between septic tank effluent and NO</span>₃⁻<span>&nbsp;</span>in a local, shallow aquifer. Values of<span>&nbsp;</span><i>δ</i>¹⁸O–NO₃⁻<span>&nbsp;</span>leaving mature packed-bed filters ranged from −&nbsp;10.2 to −&nbsp;2.3‰ (mean −&nbsp;6.4‰&nbsp;±&nbsp;1.8‰), and were intermediate between a 2/3 H₂O–O&nbsp;+&nbsp;1/3 O₂–O conceptualization and a 100% H₂O–O conceptualization of<span>&nbsp;</span><i>δ</i>¹⁸O–NO₃⁻<span>&nbsp;</span>generation during nitrification.</p></div></div></div> application/pdf 10.1016/j.scitotenv.2008.08.036 en Elsevier Mass balance and isotope effects during nitrogen transport through septic tank systems with packed-bed (sand) filters article