Modeling processes in coastal sediments: Applications in chronology and denitrification

Numerical modeling is a powerful tool for simulating sedimentary and diagenetic processes that are difficult to monitor in the field or reproduce in the lab. In this study, I apply numerical models to two processes that are important but difficult to quantify in estuarine and coastal sedimentary environments: sediment accumulation and denitrification.; Accurate sediment chronology is essential for retrospective analysis based on sediment stratigraphy and some other sediment studies. Interpretation of chronological tracer distributions from estuarine and coastal sediments may be complicated by the occurrence of episodic events such as hurricanes and major storms. In this study, I have developed non-steady-state sedimentation models to simulate episodic events. The models have been applied to sediment cores collected in the Neuse River Estuary and the Chesapeake Bay. Episodic deposition during Tropical Storm Agnes (1972) and episodic erosion during the hurricane season in 1999 have been recognized and quantified in the upper Chesapeake Bay and in some Neuse River Estuary stations. I further develop a non-steady-state 7Be model to simulate monthly variations of sediment accumulation in Cape Lookout Bight during a two-year period.; Many rivers and estuaries around the world are facing increased nutrient loading, especially nitrogen, and experiencing serious eutrophication and resulting water quality problems. Denitrification is the primary process to remove nitrogen by converting nitrate into dinitrogen gas that is unavailable to most algae. Denitrification rates measured by different techniques often disagree. Insight into the denitrification process and the controlling factors is needed to resolve these methodological differences. I have developed a numerical model to simulate processes that influence the denitrification rate. The model has been used to test the effect of environmental controls and the basic assumptions in isotope pairing technique.; This study shows that numerical models are capable of simulating very complicated sedimentary processes. These models provide detailed information regarding relationships that are not amenable to direct measurements.