Browsing by Subject "Sea level rise"

According to IPCC estimates, sea levels will rise between .18 and .6 meters by 2100. More recent estimates indicate that actual amounts of sea level rise may be much more, and that 1 meter of sea level rise by 2100 is likely a conservative estimate. These rising sea levels will result not only in more flooding during storm events, but also increased erosion and gradual inundation of coastal property. At the same time, coastal populations in the United States continue to increase rapidly: over half of all Americans live in coastal counties, and at least 25 million more people are expected to move to the coast by 2015. The end result is that human populations, coastal infrastructure, and coastal ecosystems will become increasingly vulnerable to the impacts of climate change. This study examines the political and legal constraints to and opportunities for adaptation to rising sea levels. Using legal and policy analysis and case studies from California, North Carolina and Texas, this study explores the ability of governments to use market tools, land use regulations, and property acquisition to promote adaptation to rising sea levels. Because of market dynamics and political factors including flaws in public risk perception, I conclude that governments who wish to avoid extensive coastal engineering, , can address coastal community vulnerability through a combination of regulations and incentives that spur state and local governments to engage in forward land use planning and other measures to reduce their exposure to sea level rise impacts.

Climate change is driving vegetation community shifts in coastal regions of the world, where low topographic relief makes ecosystems particularly vulnerable to sea level rise, salinization, storm surge, and other effects of global climate change. Salinization has clear effects on vegetation, as few plant species can survive in brackish water, and these shifts in vegetation lead to declines in biomass carbon stocks, as well as significant changes in habitat structure and biodiversity. The rate and extent of these impacts on other wetland ecosystem properties and function is far less certain. This dissertation investigates the ecosystem consequences of saltwater intrusion in coastal wetlands, from shifting vegetation at the landscape scale, to soil biogeochemistry and wetland carbon cycling.Coastal plant communities globally are highly vulnerable to future sea-level rise and storm damage, but the extent to which these habitats are affected by the various environmental perturbations associated with chronic salinization remains unclear. In 2016, a series of vegetation plots across the Albemarle-Pamlico Peninsula that had been surveyed 7-13 years earlier were revisited in order to measure changes in tree basal area and community composition over time. I found reduced tree basal area in plots at lower elevations and with higher current soil salt content, while these factors explained only a small fraction of the measured changes in tree community composition. While tree basal area increased in the majority of plots, I measured declines in basal area in multiple sites with high soil salt content or low elevation. This decadal comparison provides convincing evidence that increases in soil salinity and saturation can explain recent changes in tree biomass, and potential shifts in community composition in low-elevation sites along the North Carolina coast. In Chapter 3, I quantified land and land cover change in the Alligator River National Wildlife Refuge (ARNWR), North Carolina’s largest coastal wildlife preserve, from 1985 to 2019 using classification algorithms applied to a long-term record of satellite imagery. Despite ARNWR’s protected status, and in the absence of any active forest management, 32 % (31,600 hectares) of the refuge area has changed land cover classification during the study period. A total of 1151 hectares of land was lost to the sea and ~19,300 hectares of coastal forest habitat were converted to shrubland or marsh habitat. As much as 11 % of all forested cover in the refuge transitioned to ghost forest, a unique land cover class that is characterized by standing dead trees and fallen tree trunks. This is the first attempt to map and quantity coastal ghost forests using remote sensing. These unprecedented rates of deforestation and land cover change due to climate change may become the status quo for coastal regions worldwide, with implications for wetland function, wildlife habitat and global carbon cycling. Salinization of freshwater wetlands is a symptom of climate change induced sea level rise. The ecosystem consequences of increasing salinity are poorly constrained and highly variable within prior observational and experimental studies. Chapter 4 presents the results of the first attempt to conduct a salinization experiment in a coastal forested wetland. Over four years, marine salts were applied to experimental plots several times annually with the goal of raising soil salinity to brackish levels while soil porewater in control plots remained fresh. Each year I measured aboveground and belowground vegetation biomass along with soil carbon stocks and fluxes. Despite adding more than 1.5 kg of salt per m2 to our experimental plots over four years, the ecosystem responses to salt treatments were subtle and varied over the multi-year experiment. In the final year of the experiment, soil respiration was suppressed, and bulk and aromatic soil carbon became less soluble as a result of salt treatments. The more stable carbon pools—soil organic carbon and vegetation associated carbon—remained unaffected by the salt treatment. This experiment demonstrates substantial ecosystem resistance to low dose salinity manipulations. The inconsistent soil carbon responses to experimental salinization I observed in the field led me to question how differences in soil pH and base saturation might alter the impacts of salinity of soil microbial activity. To test this, I performed a salt addition experiment on two series of wetland soils with independently manipulated salt concentrations and solution pH to tease apart the effect of these seawater components on soil carbon cycling (Chapter 5). Microbial respiration and dissolved organic carbon solubility were depressed by marine salts in both soils, while pH manipulation alone had no effect. Salinity treatments had a far greater effect on soil pH than did our intentional pH manipulation and there was a strong interaction between salt treatments and soil type that affected the magnitude of soil carbon responses. Site soils varied significantly in pH and base saturation, suggesting that the interaction between salinity and edaphic factors is mediating soil carbon processes. The degree of salinization and the effective pH shift following seawater exposure may vary widely based on initial soil conditions and may explain much of the variation in reports of salt effects on soil carbon dynamics. I suggest that these edaphic factors may help explain the heretofore inconsistent reports of carbon cycle responses to experimental salinization reported in the literature to date.

Coastal ecosystems provide a wide range of services including protecting the mainland from the destructive effects of storms, nutrient cycling, water filtration, nurseries for fish and crustaceans, and carbon sequestration. These zones are threatened by human impacts and climate change through more frequent intense storms and sea level rise with a projected increase of up to 16 mm/yr for the last two decades of the 21st century. However, it is not fully understood what mechanisms control the formation and degradation of these landforms, and determine their resilience to environmental change. In this work, I highlight the role of various physical characteristics and environmental parameters that contribute to the formation and stability of coastal environments.

First, I develop and use remote sensing analyses to quantitatively characterize coastal dune eco-topographic patterns by simultaneously identifying the spatial distribution of topographic elevation and vegetation biomass in order to understand the coupled dynamics of vegetation and coastal dunes. LiDAR-derived leaf area index and hyperspectral-derived normalized difference vegetation index patterns yield vegetation distributions at the whole-system scale which are in agreement with each other and with field observations. LiDAR-derived concurrent quantifications of biomass and topography show that plants more favorably develop on the landward side of the foredune crest and that the foredune crestline marks the position of an ecotone, which is interpreted as the result of a sheltering effect sharply changing local environmental conditions. The findings reveal that the position of the foredune crestline is a chief ecomorphodynamic feature resulting from the two-way interaction between vegetation and topography.

Next, to shed light on the vertical depositional dynamics of salt marshes in response to sea level rise, I investigate the hypothesis that competing effects between biomass production and aeration/decomposition determine an approximately spatially constant contribution of soil organic matter (SOM) to total accretion. I use concurrent observations of SOM and decomposition rates from marshes in North Carolina. The results are coherent with the notion that SOM does not significantly vary in space and suggest that this may be the result of an at least partial compensation of opposing trends in biomass productivity and decomposed organic matter. The analyses show that deeper soil layers are characterized by lower decomposition rates and higher stabilization factors than shallower layers, likely because of differences in inundation duration. However, overall, decomposition processes are sufficiently rapid that the labile material in the fresh biomass is completely decomposed before it can be buried and stabilized. The findings point to the importance of the fraction of initially refractory material and of the stabilization processes in determining the final distribution of SOM within the soil column.

Finally, I develop a process-based model to evaluate the relative role of watershed, estuarine, and oceanic controls on salt marsh depositional/erosional dynamics and define how these factors interact to determine salt marsh resilience to environmental change at the estuary scale. The results show that under some circumstances, vertical depositional dynamics can lead to transitions between salt marsh and tidal flat equilibrium states that occur much more rapidly than marsh/tidal flat boundary erosion or accretion could. Additionally, the analyses reveal that river inputs affect the existence and extent of marsh/tidal flat equilibria by both modulating exchanges with the ocean (by partially “filling” the basin) and by providing suspended sediment.