 I'm starting with Ian Reeves. Ian is a PhD student at the University of North Carolina. He also won this year the Savitsky Student Modeler Award. So a big applause, which is kind of weird in this virtual environment. Ian has a strong numerical background in modeling coastal systems. And today he will present how seagrass dynamics impact a coupled long-term evolution of barrier, marsh, and bay systems. So let's see if we can get Ian's screen up there. Thank you. Go ahead, Ian. There. You seen the slide now? Yes. Yes, cut your slide. And we can hear you. Thank you. So I am excited to share with you this project of mine that investigates the ways in which seagrass impacts the evolution of barrier island coastal systems with a new coupled model of mine. And this new model uses parameterizations developed with data from the Virginia Coast Reserve long-term ecological research site, which is where this picture of a barrier marsh and bay comes from. So barrier marshes, the systems consist of a barrier island separated by an island by salt marsh and a shallow bay. And they're especially valuable both economically and microbiologically, being helped and heavily populated until the most productive and diverse ecosystems known. But the lower leaf of these landforms often results in a very dynamic system that is probable to seal or rise, changes in sense of light and storms. So barrier islands and salt marshes are a naturally sealing environment. So in response to seal or rise, barrier islands seem to migrate upward and landward to maintain the area of exposure. And this is done through the process of overwash, where sediments eroded from the short race and beach is transported landward of the Ducast during storms. And marshes maintain their elevation relative to seal or hold food, both physical and biological feedbacks that couple the rate of seal or rise with the rate of soil accretion. So these feedbacks allow many marshes to survive modern accelerated seal or rise. But a seal or rise is too high or over as flexes too low. Barrier islands respond by disintegrating and drowning plates. Similarly, seal or rise is too fast for some accumulation of marsh platforms to keep pace, marshes will drown. But marshes collapse can also occur from windway origin at the marsh edge. So recent studies have highlighted the importance of the interaction between adjacent subsystems and determining the behavior and evolution of the system of the whole. And have brought the light in important ways in which their islands can impact back their marshes and back their marshes can impact their islands. But now looking at the back their bays, seagrass can also potentially impact the evolution of the coupled system by altering the sediment dynamics and ways which is in this environment. So first, seagrass reduces the wave height in the bay. So therefore, it reduces the wave energy reaching the marsh edge and shorelines. And additionally, seagrass attenuates the wave and continues stresses acting on the sediment bed. So this reduces re-suspension and enhances deposition of fine sediments. This occurs both within the meadow itself but also in the surrounding bear areas of the bay. So these effects along with production of organic matter within the meadow tend to result in seagrass beds having shallower equilibrium depth. But bear portions of the bay also tend to be shallower than they otherwise would in the presence of seagrass. So these dynamics suggest that seagrass can play an important role in the evolution of the entire bear islands marsh and bay system. And those studies previously examined these systems coupled together. So this work aims to investigate the long-term impact of seagrass on bear marsh bay systems by incorporating seagrass dynamics of the back bear bay into the existing bear marsh marmalade G-Best plus plus to create the new model G-Best plus plus seagrass. So G-Best plus plus seagrass is a two-dimensional cross-shore marmalade which will behave well. That simulates the morphologic and also stratigraphic evolution of the bear island transect over decades to millennia in response to seal alliterates in the cinnamon spot. And the model is unique and that allows the user to define the stink striver units with the stink to cinnamon characteristics. Units are labeled here on the left along with the proportion of sand relative to mud for each unit in brackets. So in this new integrated model where seagrass can grow and how dense it can be is determined by the depth of the bay and the distance from the marsh edge. Then in turn the location, size and density of seagrass meadows in the model reduces the depth of the bay and attenuates the wave power reaching the marsh edge which tends to result in less volume of marsh load. And all of these relationships and dynamics were parameterized using empirical data from seagrass experiments as well as morphologic data sets at the Virginia Coast Reserve, L-T-E-R. So here's a short animation of just an example stimulation from the model where you can see the bear islands keeping laneward, the meadow in the bay, the green, the marsh eroding in the bay deepening. You'll notice that eventually the bay becomes too deep for seagrass to persist so the meadow goes away. So in the model, sediment is brought into the back bear basin via the bay sediment flux. This represents the volume of sediments imported into the bay from combination of plurial inputs, temporary storm surge channels and inlet exchange. So this fills the combination space in the bay. Sediment can be lost from the back bear basin via the export flux, which is the fixed percentage of suspended sediment that's eroded from the bottom marsh edge that's lost from the back bear to represent inlet sediment export with the open ocean. So sediment eroded and lost creates a competition space within the bay. And so it's this competition between back bear space being created versus space being filled that determines whether or how much a marsh will propagate or not. And so after developing G-Bus Plus Plus CGS Iran, three sets of experiments to look at the impacts of CGS and both the adjacent marsh and the non-adjacent bearer islands. And so this first set of experiments looks at the effects of CGS on a marsh width. So here I ran simulations with and without CGS at 48 combinations of relative sealer rides increasing on the x-axis and base sediment flux increasing the y-axis. I then calculated the difference in the final width at the end of each simulation between the correspond the CGS and no CGS pairs at each location across the primary space. And this is represented by the coloring where red means the marsh with narrower CGS and blue means the marsh was wider CGS. I then the marsh is pro-grading in the simulations above the diagram line and are eroding the simulations below the diagram line. And then lastly, I ran this exact primary space with three different export flux values. So zero, meaning all sediments was conserved within the back bearer basin which I've shown here as well as 15% and 25%. So for pro-grading marshes, I found that in all cases the marsh is wider with CGS. So therefore CGS enhances marsh propagation. And this is intuitive because as I mentioned for CGS tends to decrease the volume of marsh road by 10 widths. For eroding marshes, where some of the suspended sediments in the back bearers exported to the ocean, marshes also wider with CGS. So therefore CGS reduces erosion in this case. But for eroding marshes, we're also going to consider this thing in the back bearer. I find the CGS tends to do the opposite and it's presently enhances the origin. So the question is why does CGS tend to reduce marsh edge erosion when some sediments is exported from the day but increase marsh edge erosion when export is negligible? Well, CGS reduces the volume of marsh eroded by attenuating race, but there are other less intuitive mechanisms that drive the pattern observed here. So first as the marsh expands further into the bay, the CGS meadow tends to shrink because the encroaching marsh reduces available CGS habitats. And the sediment that's eroded from the edges of the shrinking CGS meadow is then able to be transported to the marsh resulting in further marsh propagation and further CGS loss, so this is a positive feedback. In the reverse case, an expanding CGS meadow, coupled to a receding marsh, can sequester sediment that will be delivered to the marsh and thereby increase marsh erosion risk. So second, the presence of CGS results in a shallower bay invests a shorter marsh skirt. So all other things being equal, a shorter marsh skirt requires more lateral marsh erosion and taller marsh skirt for every unit volume of sediment eroded. So considering this hypothetical case here, where the marsh skirt with CGS is half of the skirt without CGS, in order to erode a volume of V, the marsh has to erode laterally twice as far in the presence of CGS. And so the reverse is also true where a shorter marsh skirt will tend to prograde more under this. So of the three mechanisms that I've discussed, only, so that's less marsh volume eroded and less sequestration of sediments in the shallower equilibrium depth. Only the reduction in the volume of marsh eroded decreases lateral erosion rates whereas the other mechanisms tend to increase lateral erosion rates. So when all sediment is conserved in the back there, the ability of CGS to reduce the volume of marsh sediment eroded becomes basically inconsequential because most of the sediment eroded will just go back to marsh eventually. So under these conditions, the other mechanisms that tend to increase erosion rates control the evolution of marsh. And this particular finding, of course, is only really relevant to natural systems where the back barrier of sediments lost is very small. So we can conclude that CGS increases marsh predation rates and under many circumstances reduces erosion rates, but may enhance marsh erosion when the back barrier of ice sport is negligible. And so the second set of experiments demonstrates the impact of adding or removing CGS to or from the bay. So these are forced simulations during marsh width over time, which you see cases either added or removed after year 100. The input parameters were set to produce either eroding or grading marshes. And the black lines are the control cases for each simulation, which the state changed to not occur. So from this, we can see that the removal of CGS causes a significant marsh predation event. So as the CGS disappears after the first 100 years, they bottom our roads to its new deeper equilibrium depth which stands in this repulse sediment that's eroded from the CGS meadow to the marsh causing the marsh to purgate. When sediment is added, CGS meadow and the surrounding bare portions of the bay sequester all of the sediment delivered to the bay until the bay bottom reaches its new shallower equilibrium depth. So during this time period, the marsh receives less sediment than otherwise would causing it to erode more rapidly. And I think this particular model result may be especially relevant to CGS restoration projects that could perhaps unintentionally impact adjacent marsh in undesirable ways. So these results emphasize the role of sediment as an essential but limited commodity where the growth and preservation of one landform is necessarily at expense of other cover levels. And then this last set of experiments investigates the effects of CGS on bare island migration. So these simulations run for 1,000 more years, both within that CGS using varying base sediment flux to maintain constant marsh widths of 0, 2,000 meters and in the back bay base in completely full marsh. So when no back bay marsh exists, the presence of CGS decreases island migration rates. But when the back bay marsh is greater than zero, CGS has no effect on island migration rates. So in the model, CGS decreases the depth of both the CGS and bare portions of the bay so it reduces back bay accommodation space and reduce accommodations less sediment needs to be eroded from the front of the island and part of it behind the island or for the island to maintain its elevation both to the sea level. So therefore it can migrate landward more slowly. But there's a reduction in accommodation only impacts on immigration if it's within the zone of which overwash reaches the bay and the bare island migrates. So that is only if the marsh is essentially not existent. Otherwise, if the marsh does exist, the island migrates even more slowly and CGS has no impact on greater migration. So in the absence of marsh, these results suggest that CGS can help perhaps stabilize great islands and reduce their vulnerability to sea level. And with that, I will leave you with the key findings of this work as I take in questions.