A Mechanistic Analysis of Wetland Biogeochemistry in Response to Temperature, Vegetation, and Nutrient Input Changes

Abstract

<p>Wetlands represent the most significant natural greenhouse gas (GHG) source and their annual emissions tightly depend on climatic and anthropogenic factors. Biogeochemical processes occurring in wetlands are still poorly described by mechanistic models and hence their dynamic response to environmental changes are weakly predicted. We investigated wetland GHG emissions, relevant electron acceptors and donors concentrations, and microbial composition resulting from changes in temperature, CH₄ plant uptake efficiency, and SO²⁻₄ deposition using a mechanistic biogeochemical model (here called BAMS3) that integrates the carbon (C), nitrogen (N), and sulfur (S) cycles. Parameters constraining the coupled C-N-S cycles were retrieved from controlled experiments and were validated against independent field data of CH₄ emissions, and CH₄(aq) and SO²⁻₄ concentration profiles in a wetland in southern Michigan, USA (Shannon & White, 1994, <a href="http://hdl.handle.net/102.100.100/236252? index=1">http://hdl.handle.net/102.100.100/236252? index=1</a>). We found that +1.75 ^◦C increase in temperature leads to 22% and 30% increment in CH₄ and N₂O emissions, respectively. A decrease in the CH₄ plant uptake efficiency causes the prevalent CH₄ emission pathway to become diffusion mediated and resulted in 50% increase in the daily average CH₄ emissions. Finally, a decreasing SO²⁻₄ deposition rate can increase CH₄ emissions up to 5%. We conclude that the increasing GHG emissions from wetlands is a result of both environmental and anthropogenic causes rather than global warming alone. An increase in model complexity does not necessary improve the estimation of GHG emissions but it aids interpretation of intermediate processes to a greater detail.</p> <p>Plain Language Summary</p> <p>Wetlands are the largest natural source of greenhouse gasses; hence, climate change and human development have become a major concern for the conservation of these ecosystems. In this study, we explore the effect of rising temperature, plants community, and changes in nutrient input rate on the emission rate and quality in a wetland. The assessment was conducted using a mechanistic model that accounts for carbon, nitrogen, and sulfur cycles on test scenarios. The model was initially tested on field data of a wetland in southern Michigan, and then used for scenarios predictions. Results suggest that increasing the average soil temperature leads to a substantial increase in greenhouse gas emissions; in particular, methane emissions increase by 22%. Methane emissions are also affected by the plant composition, which controls the main emission pathway; small composition changes can induce high emissions variations. Finally, we showed how a change in atmospheric sulfate deposition to wetlands can control the methane emissions. We conclude that modeling coupled chemical, biological, and physical processes helped to describe wetland nutrients dynamics under both climate change and anthropogenic factors.</p>