Swamp ecology in a dynamic coastal landscape: an investigation through field study and simulation modeling

Increased flooding, nutrient and sediment deprivation, and saltwater intrusion have been implicated as probable causes of coastal swamp deterioration in the Mississippi Delta. An understanding of the interactive effects of these factors is required to enable successful planning of wetland restoration activities. I used field data collected from 2000 till 2005 at forty study sites to characterize the baseline conditions of the Maurepas swamp. I used a cluster analysis to identify four swamp habitat clusters, and characterized the clusters on the basis of soil properties, salinity, basal area, stem density, and other tree-related variables. ANOVA and related statistical techniques showed that three of the four habitat clusters exhibited tree biomass and densities indicative of flooding stress, and one cluster showed high tree mortality in response to salt-water intrusion. I then developed a two-species individual-based forest succession model (IBM) of a coastal swamp. The IBM followed the weekly growth, mortality, and reproduction of individuals of Taxodium distichum and Nyssa aquatica trees in a 1-km2 spatial grid, using historical time-series of stage and salinity data as inputs. IBM simulations predicted that increased flooding leads to swamps with reduced basal areas and stem densities, while increased salinity (~1-3 psu) resulted in lower basal areas. The IBM showed a tendency to overestimate wood production and the dominance of T. distichum in comparison to field data. Lastly, I compared the predictions of the IBM and a widely-used landscape model. I used salinity and flooding conditions simulated by the landscape model in eight of its 1-km2 cells as input to the IBM, and compared both models’ predictions of habitat change over 100 years. The models showed good agreement in their predictions of marsh persistence and swamp to marsh conversion. The IBM, however, showed higher sensitivity to changes in both salinity and flooding than the landscape model, and never predicted swamp persistence. The next generation of models for forecasting coastal habitat change in the Mississippi Delta will likely be a combination of the individual-based and landscape models used in this dissertation

Evaluation of Tidal Fresh Forest Distributions and Tropical Storm Impacts Using Sentinel-2 MSI Imagery

Situated in the transitional zone between non-tidal forests upstream and tidal fresh marshes downstream, tidal fresh forests occupy a unique and increasingly precarious habitat. The threat of intensifying anthropogenic climate change, compounded by the effects of historical logging and drainage alterations, could reduce the extent of this valuable ecosystem. The overall goals of this project were to identify forest communities present in the Altamaha tidal fresh forest; develop satellite imagery-based classifications of tidal fresh forest and tidal marsh vegetation along the Altamaha River, Georgia; and to quantify changes in vegetation distribution in the aftermath of hurricanes Matthew and Irma. Based on vegetation data gathered during our field survey, we identified at least eight distinct forest communities with hierarchical clustering methods. Using Sentinel-2 Multispectral Imager (MSI) satellite imagery and a balanced random forest classifier, we mapped land cover for six anniversary images from 2016 to 2021 to examine changes in vegetation distributions. Overall classification accuracies ranged from 80 to 86%, and we were able to accurately discriminate between several classes at the species level. Over our six year study period we did not observe any substantial changes in land cover, including the forest-marsh transition, suggesting resilience to tropical weather impacts. We postulate that this stasis may be due to the large volume of freshwater delivered by the Altamaha River and the extensive tidal marshes of the Altamaha estuary, which protect freshwater wetlands from the short-term effects of saltwater intrusion by reducing salinity and buffering them from acute pulse events such as hurricane storm surges

Science-based restoration monitoring of coastal habitats, Volume Two: Tools for monitoring coastal habitats

Healthy coastal habitats are not only important ecologically; they also support healthy coastal communities and improve the quality of people’s lives. Despite their many benefits and values, coastal habitats have been systematically modified, degraded, and destroyed throughout the United States and its protectorates beginning with European colonization in the 1600’s (Dahl 1990). As a result, many coastal habitats around the United States are in desperate need of restoration. The monitoring of restoration projects, the focus of this document, is necessary to ensure that restoration efforts are successful, to further the science, and to increase the efficiency of future restoration efforts

Rapidly Changing Range Limits in a Warming World: Critical Data Limitations and Knowledge Gaps for Advancing Understanding of Mangrove Range Dynamics in the Southeastern USA

Climate change is altering species’ range limits and transforming ecosystems. For example, warming temperatures are leading to the range expansion of tropical, cold-sensitive species at the expense of their cold-tolerant counterparts. In some temperate and subtropical coastal wetlands, warming winters are enabling mangrove forest encroachment into salt marsh, which is a major regime shift that has significant ecological and societal ramifications. Here, we synthesized existing data and expert knowledge to assess the distribution of mangroves near rapidly changing range limits in the southeastern USA. We used expert elicitation to identify data limitations and highlight knowledge gaps for advancing understanding of past, current, and future range dynamics. Mangroves near poleward range limits are often shorter, wider, and more shrublike compared to their tropical counterparts that grow as tall forests in freeze-free, resource-rich environments. The northern range limits of mangroves in the southeastern USA are particularly dynamic and climate sensitive due to abundance of suitable coastal wetland habitat and the exposure of mangroves to winter temperature extremes that are much colder than comparable range limits on other continents. Thus, there is need for methodological refinements and improved spatiotemporal data regarding changes in mangrove structure and abundance near northern range limits in the southeastern USA. Advancing understanding of rapidly changing range limits is critical for foundation plant species such as mangroves, as it provides a basis for anticipating and preparing for the cascading effects of climate-induced species redistribution on ecosystems and the human communities that depend on their ecosystem services

Rapidly Changing Range Limits in a Warming World: Critical Data Limitations and Knowledge Gaps for Advancing Understanding of Mangrove Range Dynamics in the Southeastern USA

Climate change is altering species’ range limits and transforming ecosystems. For example, warming temperatures are leading to the range expansion of tropical, cold-sensitive species at the expense of their cold-tolerant counterparts. In some temperate and subtropical coastal wetlands, warming winters are enabling mangrove forest encroachment into salt marsh, which is a major regime shift that has significant ecological and societal ramifications. Here, we synthesized existing data and expert knowledge to assess the distribution of mangroves near rapidly changing range limits in the southeastern USA. We used expert elicitation to identify data limitations and highlight knowledge gaps for advancing understanding of past, current, and future range dynamics. Mangroves near poleward range limits are often shorter, wider, and more shrublike compared to their tropical counterparts that grow as tall forests in freeze-free, resource-rich environments. The northern range limits of mangroves in the southeastern USA are particularly dynamic and climate sensitive due to abundance of suitable coastal wetland habitat and the exposure of mangroves to winter temperature extremes that are much colder than comparable range limits on other continents. Thus, there is need for methodological refinements and improved spatiotemporal data regarding changes in mangrove structure and abundance near northern range limits in the southeastern USA. Advancing understanding of rapidly changing range limits is critical for foundation plant species such as mangroves, as it provides a basis for anticipating and preparing for the cascading effects of climate-induced species redistribution on ecosystems and the human communities that depend on their ecosystem services

Site-specific Habitat and Landscape Associations of Rusty Blackbirds Wintering in Louisiana

The Rusty Blackbird (Euphagus carolinus) has gained notoriety in recent years as one of the fastest declining North American bird species, with a global population loss of as much as 95%. Causes of the decline are not completely understood, but the high rate of forested wetland change in the southeastern United States suggests that wintering habitat degradation may be a primary driver. To better inform management on critical wintering grounds, I surveyed 68 sites in Louisiana where Rusty Blackbirds had been known to occur to address how occupancy changes with habitat type and colonization and extinction rates vary with ground cover, rainfall, and invertebrate biomass. Rusty Blackbirds use a large area while foraging on the wintering ground, therefore management may need to be targeted to even larger spatial scales. I assessed the relationship between statewide Rusty Blackbird abundance data from the Louisiana Winter Bird Atlas and landscape scale habitat within 512 unique USGS 7.5-minute quadrangles using datasets on land cover, cropland cover, and soil type. Results indicate that forested wetlands are important habitats associated with Rusty Blackbird presence, but only under certain conditions. Rusty Blackbirds prefer shallow water for foraging. At my sites, deep water cover increased with the cover of forested wetlands and may have deterred Rusty Blackbirds from using primarily forested wetland sites. The most important variables associated with transience were wet leaf litter and invertebrate biomass, which were both positively associated with colonization and negatively associated with extinction probability. For the Louisiana Winter Bird Atlas data, the top model included all explanatory variables for Rusty Blackbird abundance. Abundance increased with cover of soil hydrologic groups C, C/D, and D, which are capable of retaining surface water, suggesting that at larger scales water cover is more important than any particular habitat type. Pecans are an important food source for wintering Rusty Blackbirds and pecan orchards had the strongest positive relationship with abundance. In addition to maintaining pecan groves on the landscape, Rusty Blackbirds may benefit from management for shallowly flooded forested wetlands that can support high amounts of wet leaf litter on the ground’s surface and abundant invertebrates

Landscape analysis of vegetation change in coastal Louisiana following hurricanes Katrina and Rita

Investigations of hurricane disturbances on coastal vegetated communities are common, but relatively few are comprehensive across broad geographic regions. The 2005 hurricanes, Katrina and Rita, exposed Louisiana coastal landscapes to physical modifications and extensive and prolonged flooding, resulting in measurable physicochemical changes. This research used remote sensing and field investigations to regionally assess (1) porewater salinity and sulfide impacts to and recovery of coastal Louisiana vegetation communities, and (2) the importance of mineral sediment deposition on accretionary processes. Hurricane effects were most direct and prominent in eastern Louisiana from Katrina and western Louisiana from Rita, compared to central Louisiana exposed to indirect affects from Rita. A coastwide analysis of moderate resolution imagery found over 4,714 km2 of the prestorm coastal wetland area experienced a substantial decline in vegetation density and vigor in October 2005, with the majority of persistent damage through November 2006 in the west (1,046 km2). In the east region, 91.8% of persistent damage was accounted for by conversion of marsh to new open water; whereas in the west region, 71% was associated with other vegetation stressors. The physical landscape disruption in the east contributed to a high abundance of disturbance species in fresh and intermediate marsh from fall 2006 to fall 2007. Salinity and sulfide stress persisted throughout the west region, contributing to low vegetative cover, slow recovery of Spartina patens, and shifts towards more saline marsh classifications by fall 2007. Hydrologic barriers, including impoundments in the west, contributed to salinity and sulfide stress; however, these same structures facilitated trapping of mineral sediments delivered by Hurricane Rita, providing critical supplies of bulk sediment and nutrients. Large periodic sediment inputs partially compensate for reduced vertical accretion found in impounded marshes. However, management actions should endeavor to optimize organic matter production to support vertical accretion. Two full growing seasons after the 2005 hurricanes, marshes directly impacted in the east and west regions were still recovering. Although vegetation cover values were approaching pre-hurricane levels, species composition is still indicative of a disturbance environment

Decadal Changes of Soil Physiochemical Properties in A Freshwater Wetland After Hydrologic Reconnection

Sediment, nutrient deprivation and salt water intrusion, among other factors, are driving widespread organic soil collapse and marsh loss in the Mississippi River Delta. Freshwater diversions were designed to reintroduce Mississippi River water and dissolved nutrients into the adjacent basins to manage salinity and slow land loss by maintaining marsh vegetation and nutrient cycling functions. These diversions are controversial by a few, suggesting that nutrient enrichment without a sediment subsidy can lead to further wetland loss in the receiving basins. In this study, a soil characterization is presented for the receiving marsh of the Davis Pond diversion in 2007, just as full-scale operation began, and again in 2018 after 11 years of diversion influence. Data for the top 10 cm of soil from 140 stations in both years were used in spatial analysis to create maps of soil properties. As a result of sedimentation from the diversion, there has been a significant increase of soil mineral content, and consequently soil bulk density. Elevated soil δ15N isotope values and increased inorganic phosphorus stocks suggest elevated rates of nutrient enrichment in the wetland, leading to increased mean organic matter and carbon content, especially in those immediate areas of diversion influence. Changes to biogeochemical cycling is apparent in altered soil nutrient ratios. Multivariate methods demonstrate the effectiveness of certain soil parameters for monitoring impacts of river diversions in wetlands. The δ15N isotope is an important indicator of river water-influenced soils, whereas mineral content and inorganic phosphorus can identify in which areas a river sediment subsidy was provided. Previous to this study, the long-term impacts of lower Mississippi River hydrologic restoration projects had yet to be statistically quantified due to little or no pre-sampling. The results of this study have implications for monitoring diversion impacts, providing guidance for continued use of freshwater diversions in Louisiana, and informing future management strategies in coastal areas around the world

Investigation of Coastal Vegetation Dynamics and Persistence in Response to Hydrologic and Climatic Events Using Remote Sensing

Coastal Wetlands (CW) provide numerous imperative functions and provide an economic base for human societies. Therefore, it is imperative to track and quantify both short and long-term changes in these systems. In this dissertation, CW dynamics related to hydro-meteorological signals were investigated using a series of LANDSAT-derived normalized difference vegetation index (NDVI) data and hydro-meteorological time-series data in Apalachicola Bay, Florida, from 1984 to 2015. NDVI in forested wetlands exhibited more persistence compared to that for scrub and emergent wetlands. NDVI fluctuations generally lagged temperature by approximately three months, and water level by approximately two months. This analysis provided insight into long-term CW dynamics in the Northern Gulf of Mexico. Long-term studies like this are dependent on optical remote sensing data such as Landsat which is frequently partially obscured due to clouds and this can that makes the time-series sparse and unusable during meteorologically active seasons. Therefore, a multi-sensor, virtual constellation method is proposed and demonstrated to recover the information lost due to cloud cover. This method, named Tri-Sensor Fusion (TSF), produces a simulated constellation for NDVI by integrating data from three compatible satellite sensors. The visible and near-infrared (VNIR) bands of Landsat-8 (L8), Sentinel-2, and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) were utilized to map NDVI and to compensate each satellite sensor\u27s shortcomings in visible coverage area. The quantitative comparison results showed a Root Mean Squared Error (RMSE) and Coefficient of Determination (R2) of 0.0020 sr-1 and 0.88, respectively between true observed and fused L8 NDVI. Statistical test results and qualitative performance evaluation suggest that TSF was able to synthesize the missing pixels accurately in terms of the absolute magnitude of NDVI. The fusion improved the spatial coverage of CWs reasonably well and ultimately increases the continuity of NDVI data for long term studies

Spatial analyses of pedosphere carbon stock and sequestration potential in Louisiana\u27s watersheds

This dissertation research aimed to quantify current soil organic carbon (SOC) stocks across Louisiana’s landscape, examine the spatial relationships between SOC and terrain factors at the watershed and river basin scales, and predict SOC changes in surface soils during future climate change. Using Louisiana as an example, a spatially-explicit modeling framework was developed that is conducive to watershed-scale prediction of soil carbon stock and change. SOC densities at the watershed scale were estimated using the USDA NRCS Soil Geographic Database (STATSGO). Louisiana watersheds and National Land Cover Database (NLCD) were used to aggregate total soil carbon and estimate average soil carbon density. Watershed drainage densities and slopes were quantified with 1:24 K Digital Elevation Models (DEM) data and the Louisiana hydrographic water features. Potential changes in SOC under 0.5° x 0.5° high-resolution climate change projections in Louisiana were simulated using a RothC model at a watershed scale under three greenhouse gas emissions scenarios (A1FI, A2, B2) based on the HadCM3 climate model. LIDAR and DEM datasets were used to assess the spatial distribution of potential inundated coastal areas; estimate the current wetland areas, SOC storage, and nitrogen contents at risk in Louisiana, classified by the National Wetlands Inventory (NWI) and DEM datasets. The research found that SOC density ranged from 22 to 108 tons/ha in the upper 30-cm soil at the watershed scale, with the highest density in emergent herbaceous wetlands. Among Louisiana’s 12 river basins, the Barataria, Terrebonne, and Lake Pontchartrain Basins in southeast Louisiana showed the highest SOC density. SOC density was positively correlated with watershed drainage density (r2=0.43), but negatively correlated with watershed slope gradient (r2=0.52) and elevation (r2=0.50). The modeling study on climate change effects showed that SOC storage in the top 30-cm soil layer of Louisiana forests, croplands, and grasslands would significantly decrease under all climate change scenarios. Coastal areas in southeastern Louisiana have some freshwater and estuarine wetland ecosystems that store a large quantity of organic carbon. Much of these areas have elevations less than 100 centimeters and are, therefore, prone to inundation of sea level rises during future climate change