Special Issue on Advances in Wetland Hydrology and Water Quality Processes Modeling

Wetlands are low-lying, regularly inundated ecosystems that emerge at the fringe of aquatic and upland terrestrial systems. They exist near and along streams or isolated within depressions in upper lands. These ecosystems are recognized for their significant ecologic and economic values owing to the wide variety of services they offer at ecosystem and watershed level. The importance of wetlands to water quality purification, flood control, wildlife habitats, and biodiversity is well recognized. Such clear benefits were the reasons behind the creation of artificial wetlands (constructed wetlands), which are widely used for water quality treatment, shallow aquifer recharge, and others.

Wetland hydrology and biogeochemistry is still a relative new and emerging field. Scientists are still trying to understand the physical, biological, and chemical processes and their interactions to better benefit from these complex ecosystems. Whereas some use field- and laboratory-scale experiments and observations for this purpose, others develop and apply mathematical models to simulate hydrology, water quality, and biomass growth in wetlands. Wetland models not only can provide new insights on wetland functions and ecosystem services but are also useful for the design of constructed wetlands and predicting the treatment effectiveness of a wetland. When built within a watershed model framework, they can help predict at larger than field scale the effectiveness of wetlands on water quality improvement relative to traditional abatement strategies (BMPs).

The level of rigor of currently available wetland models in describing the transformation of pollutants, such as nutrients, pesticides, and metals, as they interact with the biogeochemistry of the wetland environment merits more research and further model improvements. More research is needed in the areas of experimentation and modeling to improve extant wetland nutrients models. Laboratory experiments, mesocosm, and field studies, which generate data under controlled, semicontrolled, and natural conditions, not only lead to better understanding of salient features of wetland processes and provide new insights on complex interactions but also produce observational data that could be used to validate wetland models and improve their predictive capability. Adequacy of current design models for constructed wetlands is a deserving research area, as many of these models rely on the assumptions of steady-state water flow conditions and first-order decay of pollutants. Do current models account for all import and export and loss pathways (e.g., inflow, burial, plant harvesting, gaseous losses, outflow, groundwater discharge or recharge, atmospheric deposition, and floating biomass export)? Are existing models suitable only for simulating wetlands as single retention and treatment systems, or could they be scaled up to simulate patches of wetlands (e.g., riparian wetlands) as buffers between upland diffuse source areas and the receiving stream segments and water bodies? Plant uptake of nutrients, and pollutants in general, furnishes a temporary storage and retention of these constituents, but with annual harvesting, it is a permanent nutrient loss pathway (i.e., sink). Plant uptake modules vary in complexity and scale of application, and more room for model improvement obviously is available for better management of wetland plants. Ability of models to account for channelization and variability of flow velocity should be examined because flow variations impact retention capacities of nutrients in wetlands.

The scope of the special issue “Advances in wetland hydrology and water quality processes modeling” in Journal of Hydrologic Engineering is on recent advances leading to improved description of hydrologic and water quality processes in natural and constructed/treatment wetlands. There are 11 papers in the special issue, including research papers on new wetland model development (Michot et al. 2015; Rezaeianzadeh et al. 2015; Sharifi et al. 2015), improvement of existing models (Chu 2015; Paudel and Jawitz 2016; Sharifi et al. 2016), novel case-study model applications (Ahmed 2016; Mahmoudi et al. 2015), and laboratory- and field-scale studies aiming at furthering the understanding of physical and biogeochemical wetland processes (Bernal et al. 2016; Gülbaz and Kazezyılmaz-Alhan 2016; Pierfelice et al. 2015).

We, the guest editors, recognize that the selected papers represent a small subset of the topics from the field wetland hydrology and biogeochemistry. Nevertheless, we hope that the selected high-quality technical articles generate more interest in this emerging field and help improvement in new or better wetland models.