| 英文摘要: | Seasonally flooded, freshwater cypress-tupelo wetlands are commonly found in coastal regions of the southeastern United States, from Texas to North Carolina. These wetlands are the main terrestrial source of natural organic matter (NOM) that causes the yellowish tea-colored water in coastal blackwater rivers such as Waccamaw River in South Carolina (SC). Importantly, the concentration of NOM is highly correlated with concentrations of total mercury and methylated mercury, mediating the bioavailability and transport of mercury in coastal ecosystems. On October 1-5, 2015, the interaction between a stalled extratropical cyclone (nor'easter) and hurricane Joaquin caused torrential rain and extensive flooding in a short period of time in the coast of SC, resulting in a large volume of NOM exported from the forested wetlands into the coastal blackwater rivers. Such large quantity of NOM exports on an unprecedented scale could potentially mobilize relatively stable and recalcitrant pools of mercury and carbon from the forested wetlands into the blackwater rivers. This highly interdisciplinary research will dramatically improve understanding of mercury and carbon biogeochemistry under extreme weather conditions and demonstrate the relationships within the context of ecosystems. This study represents a new and unique collaboration between four investigators with different specialties from three universities including two assistant professors respectively in a minority serving institution and an undergraduate institution. This study will also raise the awareness of the impacts of extreme weather events on low-lying coastal areas in the Southeastern United States.
Coastal wetlands are considered as important carbon and mercury sinks. However, extreme weather events under the changing climate could alter the equilibrium status, affecting the stability of carbon and mercury pools in the coastal ecosystems. The goal of this RAPID research is to study the influences of the extreme flooding on carbon and mercury cycles and associated biogeochemical processes in coastal wetlands and blackwater rivers. Specifically, the study will integrate field investigations, controlled field experiments, and hydrological computer modeling to examine carbon and mercury exports, sources, and temporal trends along the hydrograph of the extreme flooding event. The research team has been collecting water samples along the Waccamaw River since Oct 4, 2015, representing the rising limb of the hydrograph. Samples were analyzed for general water quality, dissolved organic carbon, ultraviolet absorbance, nutrients, cations, anions, total mercury, and methylated mercury in the filtered and unfiltered samples. To determine the carbon and mercury budget, a hydrological model will be used to estimate the total water discharge from this flooding event that went into Waccamaw River. The PIs will engage in a transformative research study to assess novel decomposition process routes of terrestrial organic matter in forested wetlands under the influence of extreme flooding event. The PIs contend that the novel method of using stable mercury isotope along the hydrograph of the flooding event, coupled with measurements of dissolved organic matter in water using ultraviolet/visible and fluorescence spectroscopy, will be useful for understanding the relationships between carbon and mercury in coastal blackwater rivers. Determining the temporal variation of carbon and mercury will be useful for developing a mechanistic and landscape-level understanding of how extreme flooding events affect the biogeochemical process of terrestrial organic matter in coastal ecosystems. |