Large tank experiment on nitrate fate and transport: the role of permeability distribution

Abstract

A long-term elution experiment to study the saturated transport of pre-accumulated fertilizers by-products, was conducted within a large tank (4 x 8 x 1.4 m) equipped with 26 standard piezometers. Sandy sediments (35 m(3)), 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 (NO(3) (-)) sulfate (SO(4) (2-)) calcium (Ca(2+)), and magnesium (Mg(2+)), due to fertilizer leaching from the top soil in the field site. The initial spatial distribution of NO(3) (-) and SO(4) (2-) was heterogeneous and not related to the finer grain-size content (< 63 mu m). 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 NO(3) (-) and SO(4) (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

Assessment of the intrinsic vulnerability of agricultural land to water and nitrogen losses: case studies in Italy and Greece

“…In the FP, the unconfined aquifer texture is sand and silty-sand, with higher spatial heterogeneity due to the presence of palaeochannels and alluvial fans interconnected with alluvial fan and marsh lagoon environments (Amorosi et al 2003). The unconfined aquifer thickness usually ranges between 2 and 7 m, but in some cases may exceed 45 m (Mastrocicco et al 2011b). The water table depth ranges between 0.5 and 5.5 m below ground level (b.g.l.).…”

Delineation of Suitable Zones for the Application of Managed Aquifer Recharge (MAR) in Coastal Aquifers Using Quantitative Parameters and the Analytical Hierarchy Process

“…In coastal zones, multilayer sampling is critically important to define the vertical distribution of salinity [51], while the determination of groundwater residence time [52] could further increase the effectiveness of MAR application. Although the SuSAM index was developed to be compatible with a coastal hydrogeological environment, parameters of agricultural activities and nitrate pollution could be included in the method with the aim of reducing nitrate pollution [53]. An expanded DSS-MAR system could include agricultural planning [54] and groundwater vulnerability maps, which are useful tools for groundwater management [55].…”

Preventing Groundwater Pollution Using Vulnerability and Risk Mapping: The Case of the Florina Basin, NW Greece

“…It is worth mentioning that the permeability of the vadose zone has been obtained by lithological profiles in this study. In the literature, it is clear that the permeability influences the nitrate and ammonium transport [31][32][33] as well as the organic matter [34], which is not considered in DRASTIC method. Nevertheless, the pollution risk map overcomes this drawback, increasing the correlation with nitrate concentrations and hence the reliability of the map.…”