Nitrate Migration and Transformation in Low Permeability Sediments: Laboratory Experiments and Modeling

Abstract

The excessive application of fertilizers and the uncontrolled discharge of untreated wastewater on land contribute to the nitrogen pollution of groundwater. Low permeability sediment plays an important role in slowing down the migration of nitrate in groundwater systems. This study focuses on the mechanisms that affect nitrate transport in the low permeability layer. A soil column experiment was conducted and an MT3D transport model (a modular three-dimensional multispecies transport model) of nitrate was proposed. The results show that a low permeation layer could act as a strong barrier to nitrate migration and transportation, as demonstrated by the column soil experiment. The denitrification rates were controlled by many other factors, including nitrate concentration, flow rate, pH values and sediment particle characteristics. This indicated that denitrification is the most important factor in the attenuation of nitrate in low permeability sediments. This study clarified the law of migration and transformation of nitrate in low permeability soils and the factors that influence these processes. The results not only provide a basis for large-scale nitrate simulations, but also provide a reference for nitrate treatment in low permeability layers.

Using MODFLOW to Model Riparian Wetland Shallow Groundwater and Nutrient Dynamics in an Appalachian Watershed

“…Considering chemical reactions (Scenario 2), a total of 639 g of nitrate was lost from the SGW to the stream from 2020 to 2021; however, 1406 g of nitrate was lost due to denitrification (Figure 9b). These findings align with previous research [52][53][54], where denitrification was identified as the primary nitrogen sink. In January and February 2020, NO 3 -N loss from SGW to the stream initially exceeded denitrification (Figure 9b).…”

“…The reaction rate constant was specified as 0.07 day −1 . This value is approximately the average rate of denitrification found in soils and aquifers worldwide and represents a half-life of 10 days [12,[54][55][56]. Generally, water flow from the aquifer to the stream (gaining stream) was observed in the study area, specifically for the piezometers close to the stream [31].…”

“…NO 3 -N has a low sorption capacity. Therefore, the delay factor is set to 1.0 to indicate no sorption following previous studies [52][53][54][55]. The denitrification rate law was specified using first-order kinetic expression [54].…”

“…Therefore, the delay factor is set to 1.0 to indicate no sorption following previous studies [52][53][54][55]. The denitrification rate law was specified using first-order kinetic expression [54]. The reaction rate constant was specified as 0.07 day −1 .…”

In-Situ Improvement of the Sediment Microenvironment by Nitrate in Tailwater of Wastewater Treatment Plants Combined with Aerobic Denitrifying Bacteria under Low-DO Regulation

“…The key genes present in nitrogen cycling included denitrification genes (such as narH, napA, nirK, nosZ, and norB), nitrogen fixation genes (such as nifD and nifH), ammonia oxidation genes (such as amoA and amoB), and DNRA genes (such as nirB and nirD) [32,33]. Nitrogen fixation and DNRA genes facilitate the formation of NH 3 -N, whereas denitrification and ammonia oxidation genes promote nitrogen removal [34,35]. The relative abundance of nitrogen fixation genes and DNRA genes in the deep sediment layer (−20~−12 cm) was significantly higher than that in the shallow sediment layer (−12~0 cm).…”