Science Inventory

Modeling Nitrogen and Carbon Dynamics in Wetland Soils and Water Using Mechanistic Wetland Model

Citation:

Sharifi, A., M. Hantush, AND L. Kalin. Modeling Nitrogen and Carbon Dynamics in Wetland Soils and Water Using Mechanistic Wetland Model. Rao S. Govindaraju (ed.), Journal of Hydrologic Engineering . American Society of Civil Engineers (ASCE), Reston, VA, 22(1):1-18, (2017). https://doi.org/10.1061/(ASCE)HE.1943-5584.0001441

Impact/Purpose:

In this article, the authors extend WetQual to unsaturated sections of wetland and demonstrate its application. The model described in this article is a modification of an earlier wetland model (Hantush et al. 2013; Sharifi 2013), which was only capable of capturing nutrient dynamics in continuously ponded wetlands. The goal of this paper is, therefore, to present the development and evaluation of the wetland model to variably saturated wetland conditions. To this end, it is necessary to implement a new modeling approach for tracking moisture in wetland soil. Once the daily soil moisture profile of a wetland soil is attained, model relationships are updated to simulate geochemical reactions and track concentrations of nitrogen (N) and carbon (C) related constituents in unsaturated wetland soil.

Description:

In this article, extension and application to variably saturated wetland conditions of a process-based wetland model is demonstrated. The new model described in this article is an improved version of an earlier model, which was only capable of capturing nutrient dynamics in continuously ponded wetlands. The upgraded model is capable of simulating nutrient cycling and biogeochemical reactions in both ponded and unsaturated wetland zones. To accomplish this goal, a comprehensive module for tracking water content in wetland soil was implemented in the model, and biogeochemical relationships were added to explain cycling of nitrogen (N) and carbon (C) in variably saturated zones of wetlands. The developed model was applied to a small, restored wetland receiving agricultural runoff, located on Kent Island, Maryland. On average, during the two-year study period, the ponded compartment of the study wetland covered 65% of the total 1.2 ha area. Through mass balance analysis, it was revealed that the mass of nitrogen lost to denitrification at the variably saturated compartment of the study wetland was about three times higher than that of the ponded compartment (32.7 ± 29.3 kg versus 9.5 ± 5.5 kg), whereas ammonia volatilization at the variably saturated compartment was a fraction of that of ponded compartment (1.2 ± 1.9 kg versus 11.3 ± 11.8 kg). Sensitivity analysis showed that cycling of carbon-related constituents in variably saturated compartment had high sensitivity to temperature and available soil moisture.