Large tank experiment on nitrate fate and transport: the role of permeability distribution |
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Authors: | M Mastrocicco N Colombani S Palpacelli G Castaldelli |
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Institution: | 1.Dipartimento di Scienze della Terra,Università di Ferrara,Ferrara,Italy;2.Dipartimento di Scienze della Terra,Università “Sapienza” di Roma,Rome,Italy;3.Dipartimento di Scienze dei Materiali,Università Politecnica delle Marche,Ancona,Italy;4.Dipartmento di Biologia ed Evoluzione,Università di Ferrara,Ferrara,Italy |
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Abstract: | A long-term elution experiment to study the saturated transport of pre-accumulated fertilizers by-products, was conducted
within a large tank (4 × 8 × 1.4 m) equipped with 26 standard piezometers. Sandy sediments (35 m3), used to fill the tank, were excavated from an unconfined alluvial aquifer near Ferrara (Northern Italy); the field site
was connected to a pit lake located in a former agricultural field. To evaluate spatial heterogeneity, the tank’s filling
material was characterized via slug tests and grain-size distribution analysis. The investigated sediments were characterized
by a large spectrum of textures and a heterogeneous hydraulic conductivity (k) field. Initial tank pore water composition exhibited high concentration of nitrate (NO3
−) sulfate (SO4
2−) calcium (Ca2+), and magnesium (Mg2+), due to fertilizer leaching from the top soil in the field site. The initial spatial distribution of NO3
− and SO4
2− was heterogeneous and not related to the finer grain-size content (<63 μm). The tank’s material was flushed with purified
tap water for 800 days in steady-state conditions; out flowing water was regularly sampled to monitor the migration rate of
fertilizer by-products. Complete removal of NO3
− and SO4
2− took 500 and 600 days, respectively. Results emphasized organic substrate availability and spatial heterogeneities as the
most important constraints to denitrification and nitrogen removal, which increase the time required to achieve remediation
targets. Finally, the obtained clean-up time was compared with a previous column experiment filled with the same sediments. |
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