Numerical Modeling of Nitrate Removal in Anoxic Groundwater during River Flooding of Riparian Zones

Abstract

A numerical study demonstrates the effects of flooding on subsurface hydrological flowpaths and nitrate removal in anoxic groundwater in riparian zones with a top peat layer. A series of two-dimensional numerical simulations with changing conditions for flow (steady state or transient with flooding), hydrogeology, denitrification, and duration of flooding demonstrate how flowpaths, residence times, and nitrate removal are affected. In periods with no flooding groundwater flows horizontally and discharges to the river through the riverbed. During periods with flooding, shallow groundwater is forced upwards as discharge through peat layers that often have more optimal conditions for denitrification caused by the presence of highly reactive organic matter. The contrast in hydraulic conductivity between the sand aquifer and the overlying peat layer, as well as the flooding duration, have a significant role in determining the degree of nitrate removal.

Development of a Distributed Mathematical Model and Control System for Reducing Pollution Risk in Mineral Water Aquifer Systems

“…The interaction and change of the temperature field must be considered in the development of the control system [32,33]. Only with a detailed calculation of the intensity of mutual influence and considering the results obtained when determining the permissible production volumes, the stability of the operation process and the structural integrity of the fields can be guaranteed [34,35].…”

Groundwater–surface water interaction in Denmark

“…The study of nutrient transport continues to be one of the major reasons for investigating groundwater–surface water interactions, not just to assess the contaminant load to a surface water body, that is, a lake, by combining conservative and nonconservative tracers (Kristensen et al, 2018), but also to quantify the effects of redox conditions in groundwater on the fate of nitrate before discharging to streams (Jensen et al, 2021; Nilsson et al, 2017; Ribas et al, 2017). In the field of wetland restoration, problems due to the release of phosphate are a new concern (Audet et al, 2020).…”

“…This will affect the riparian flow path type. For example, Jensen et al (2017Jensen et al ( , 2021 have shown that flooding leads to groundwater upwelling near the flood limit and groundwater-fed surface flow to the stream. This can have positive and negative effects on nitrate removal, depending on whether there is a top organic peat layer.…”

“…Geology can also have effects on a local scale. Peat layers can have a significant impact both on groundwater discharge (Duque et al, 2018) and nitrate attenuation (Jensen et al, 2017(Jensen et al, , 2021. These layers are frequently not identified on geological maps as they have small dimensions and when looking at the bigger picture can be viewed as irrelevant or only of local interest, despite their frequent identification.…”