Graduation Year
2024
Document Type
Dissertation
Degree
Ph.D.
Degree Name
Doctor of Philosophy (Ph.D.)
Degree Granting Department
Marine Science
Major Professor
Frank Muller-Karger, Ph.D.
Committee Member
Susan Bell, Ph.D.
Committee Member
Pamela Muller, Ph.D.
Committee Member
Enrique Montes, Ph.D.
Committee Member
Brigitta van Tussenbroek, Ph.D.
Keywords
blue carbon ecosystems, coastal wetland vulnerability, satellite remote sensing, sea level, seagrass extent, time series
Abstract
Coastal wetlands and seagrass meadows provide multiple services to nature and human society, but their spatial and temporal changes are often not well characterized. They are habitats that are threatened by natural and human causes such as changes in water quality, urban development, pollution, and climate change, among others. Coastal ecosystems rely on water quality and sea level variability for survival, and changes in those variables and their potential effects are of concern to many coastal communities. Satellite remote sensing is a powerful tool that has been used for mapping ecosystem distribution on land and in the ocean. Satellite sensors can provide data at diverse temporal and spatial resolutions that enable the capacity to map ecosystems and assess temporal changes. For this dissertation I used multiple time series of satellite remote sensing observations to map seagrasses and coastal wetlands of the US Gulf of Mexico and the east coast of Florida. The research evaluated historical, current, and projected coastal habitat changes and vulnerability to sea level rise.
This dissertation includes five chapters. Chapter 1 is an overview of the dissertation, and Chapter 2 through Chapter 5 address science results. Chapter 2 outlines a mapping workflow to identify seagrass beds in optically-complex water quality conditions. The objective was to detect temporal changes in seagrass extent and water quality in Tampa Bay and surrounding areas, including St. Joseph Sound, Clearwater Harbor, and Sarasota Bay in west Florida. Satellite imagery from Landsat-5, Landsat-7, Landsat-8, and Sentinel-2 sensors hosted in Google Earth Engine (GEE) was used for mapping seagrass beds. Imagery that met specific quality criteria over 16 years between 1990–2021 were used. The long-term trends in seagrass extent estimated for west Florida were on average positive. Changes matched those found in previous seagrass extent assessments from aerial mapping techniques (r > 0.61). Overall, seagrass extent for the region increased by ~50 km2 (40.6%), or ~1.4% yr1, from 1990 through 2021. Increases in seagrass extent coincided with improvements in water quality throughout the region (i.e., a general decrease in chlorophyll-a concentration, phosphorus, nitrogen concentration, and turbidity). The positive trends are in part due to the efforts to restore water quality by estuary research programs in the region including the Tampa Bay Estuary Program, other similar Estuary Programs and National Estuarine Research Reserves, and their partners.
In Chapter 3, I investigated the feasibility of monitoring seasonal to interannual changes in seagrass extent in Tampa Bay, Florida, from 1987 to 2023 using remote sensing. This included data from the Landsat-5, Landsat-7, Landsat-8, and Sentinel-2 satellite sensor series. Seagrasses in Tampa Bay showed long-term increases in extent. The highest increasing rates over 1987–2023 were observed in Hillsborough Bay (+5.7% yr-1) and Old Tampa Bay (+3.5% yr-1). Intra-annual changes in seagrass extent were observed during 2021–2023. Intra-annual coefficient of variation was estimated to be as low as 3% in Boca Ciega Bay and as high as 60% in Hillsborough Bay. Seagrass extent estimated by remote sensing was highly correlated with the airborne reference data (r > 0.71). The results showed that seagrass extent assessments using public satellite imagery are feasible.
Chapter 4 describes an effort to detect seagrass changes at other sites of the Gulf of Mexico and Florida. I used similar methods and satellite sensors as described in Chapters 2 and 3. Satellite remote sensing detected 7,687 km2 of seagrasses in 40 different locations in the U.S. Gulf of Mexico and Florida. To evaluate temporal variability, 15 sites were mapped repeatedly during the period 1987–2021. This effort required 1,415 satellite images to run 1,764 classifications. Seagrass extent trends between 1987 and 2021 in the region were positive, with an increase of 11.9% or 279.44 km2. Seagrass conservation efforts can further help conserve this habitat by continuing to focus on improvements in local water quality.
In Chapter 5, I outline a team effort to develop a land cover map at high spatial resolution (2 m pixels) of low-lying coastal areas of the US Gulf of Mexico and Florida. This was then used to estimate the surface-area losses in wetlands due to projected sea-level rise. Coastal wetlands and other land cover classes were mapped with the WorldView-2 and WorldView-3 commercial satellite sensors (MaxarTM) at 2 m per pixel. A digital elevation model (DEM) with a 2 m horizontal resolution and 0.1 m vertical resolution was derived for the entire region using airborne-lidar observations archived by the NOAA Coastal Services Center. Florida and Louisiana had 72% of the total vegetated area within an elevation range of 0–10 m in the region spanning the east coast of Florida to Texas. Of these, 61% of the coastal wetlands were observed in Florida. Projected sea level rise by 2100 indicated potential losses relative to 2012–2015 vegetation area by 12,587 km2, of which 3,224 km2 would correspond to coastal wetlands. The coast of Louisiana would suffer the largest losses in vegetation (80%) and coastal wetlands (75%) by 2100. Such high-resolution maps will help to improve adaptation plans in the region, including planning for wetland conservation and coastal development.
In summary, this work provides historical, current, and projected estimates of coastal ecosystem changes for a large area. Massive satellite data volumes are now easily accessible through cloud technologies for archival and data processing.
Scholar Commons Citation
Lizcano-Sandoval, Luis, "Satellite-based mapping of seagrass habitats and coastal wetlands in the US Gulf of Mexico and Florida: A remote sensing approach for environmental conservation and management" (2024). USF Tampa Graduate Theses and Dissertations.
https://digitalcommons.usf.edu/etd/10644
