IRIS graduate students do wide-ranging, incredibly important work. In the past month, we had three students with diverse study areas successfully defend. We’d like to extend a huge congratulations to these students, and applaud their hard work during their time at IRIS and the University of Georgia!
Read on to learn more about their research:
–Matheus Fagundes, PhD candidate in Engineering with Emphasis in Environment and Water Engineering in the College of Engineering, University of Georgia, defended his dissertation, “Kelp forest module development for a regional ocean model and its use for ecology and biogeochemistry impacts.”
Abstract: Kelp forests are present across a quarter of all coastlines and are essential vegetated ecosystems. These ecosystems are susceptible to extreme events and climate change, but also modify the physics of in the water column and, consequently, the biogeochemistry and ecology. Although scientists have understood the importance of kelp forests and have studied these domains extensively both in the field and in the laboratory, these studies only provide snapshots or isolated views of kelp forest dynamics. More recently, ocean modeling efforts have been made to address the spatial and temporal variability of the dynamics of these ecosystems, especially for understanding the interaction of nearshore currents and changes in the biogeochemistry in the water column. However, to date kelp forests have not been fully incorporated into coupled hydrodynamic-biogeochemical models. In this dissertation, I develop a 3-D hydrodynamic model for kelp forests in a regional ocean model, add a biogeochemistry model that represents the primary process for kelp forests, and demonstrate the impact of stressors on kelp forests and the effects on local physics and biogeochemistry.
–Daniel X. Buhr, PhD candidate in Engineering with Emphasis in Environment and Water in the College of Engineering, University of Georgia defended his dissertation, “Riparian Nitrogen Cycling and Stream Evolution: Measuring and Modeling the Effects of Channel Incision on Groundwater Dynamics and Denitrification.”
Abstract: Nitrogen pollution in groundwater and surface water can cause eutrophication and harmful algal blooms in receiving waterbodies. Riparian zones can effectively reduce nitrogen loading via denitrification, the conversion of nitrate to nitrogen gas under saturated, anoxic conditions with sufficient carbon. Stream incision can reduce denitrification by lowering groundwater below the carbon-rich root zone. Few studies have characterized the interactions between stream incision and riparian processes, which are also often underrepresented in models. The goal of this research is to further investigate the role of incision on riparian groundwater dynamics and nitrogen cycling by analyzing existing models and collecting field data in watersheds with different soil types and land uses, then coupling denitrification and channel evolution models to estimate long-term changes in nitrogen loading.
I evaluated well-known riparian nitrogen models for their robustness in simulating hydrologic processes, vegetation, soils, nutrients, and channel morphodynamics. I performed global, time-varying sensitivity analyses of the Riparian Ecosystem Management Model (REMM) and the Soil and Water Assessment Tool+ (SWAT+) and found that soil and topographic parameters were most influential for estimating groundwater and nitrogen dynamics. The influence of stream channel depth and incision was underrepresented in all models.
I collected a novel dataset by studying groundwater-surface water interactions and nitrogen dynamics at paired incised and unincised streams at two sites in the southeastern US. Incision lowered the riparian groundwater table and affected the gaining and losing dynamics at each stream. Denitrification was prevalent, removing an average of 40-95% of available nitrogen. I developed statistical models to predict groundwater depth and denitrification for both the overall dataset and two individual sites. I simulated channel evolution over 30 years at each site using the River Erosion Model (REM) and linked the results with the statistical models to estimate the effects of incision on riparian nitrogen loading. The results of this research indicate that incision can substantially increase long-term nitrate loading in small watersheds, underscore the importance of flow management and stream restoration for water quality improvement, and illustrate the need for fully-coupled channel evolution and riparian nitrogen models to improve estimation of nitrogen loading in evolving stream networks.
–Grant S. Bilderback, MS candidate in Civil & Environmental Engineering with Emphasis in Environmental Engineering in the College of Engineering, University of Georgia defended his thesis, “Coastal Inundation Modeling for Coastal Georgia through Automated Finite Unstructured Mesh Generation.”
Storm surge, the coastal inundation that occurs due to tropical cyclones, is the most deadly and costly aspect of tropical storms and hurricanes. To accurately simulate hurricane storm surge, numerical models should include an up-to-date and accurate representation of the coastal landscape. Contemporary storm surge models leverage unstructured, finite element meshes. Unstructured triangular meshes can resolve complex geometries while also balancing computational efficiently through coarse resolution in areas that do not require it. A substantially new development in mesh generation across the coastal floodplain includes the representation of significant vertical features such as dunes, highways, and railways. In addition, newly introduced meshing technology has evolved to allow for automated meshing based on certain user-based domains and geographic inputs. An unstructured, finite-element mesh with integrated geographic features is generated using automatic mesh generation software for coastal flood research and real-time hurricane landfalling prediction purposes. The thesis presents the development of an unstructured storm surge model mesh for coastal Georgia using the latest mesh generation tools and most recently available topographic and bathymetric data.