A numerical model has been developed to study the temporal and spatial variations of Phosphorus mass and fluxes around the tree islands of Shark River Slough in the Everglades. The developed model is based on a conceptualization of physical, chemical and biological processes that consider advective and diffusive transport of dissolved Phosphorus, adsorption on to soil, input from rainfall and external sources, and Phosphorus cycling in biomass. The biomass related processes are Phosphorus uptake, release as litter, transport as suspended litter and release from the decomposition of the deposited litter. The water flow and transport of dissolved Phosphorus in the numerical model are implemented originally in the simulator MODHMS. However, the transport equations for dissolved Phosphorus were also coded separately, as well as the balance equation for suspended litter particles and deposited litter. The parameterization of the model was conducted by using the data collected by Ross et al. [2004] in three tree islands of Shark River Slough, as well as other parameters reported among the literature. The model was calibrated in three phases. Initially, Manning coefficients were adjusted from surface water velocity data collected by Bazante et al. [2004]. Then the calibration of several groundwater flow parameters was performed from water table data collected at wells by Ross et al. [2004]. In the third phase, the Phosphorus input rate from external sources and the initial concentration of Phosphorus were calibrated by assuming that the average surveyed Phosphorus concentration in soil pore water remains approximately constant over a 10 year period. The quantitative assessment of the spatial distribution and temporal variations of Phosphorus mass and fluxes around tree islands obtained from the developed model corroborate the negative effect of the rainfall events on Phosphorus accumulation in the head of the tree island. However, the possible positive effect of the ET driven water flows on Phosphorous accumulation was found not as relevant as hypothesed by other authors in the literature. According to the model results, most of the Phosphorus transport in the tree islands occurs as suspended particles in surface water, even though the transport of dissolved Phosphorus in pore water cannot be neglected around the head of the island. The model results also suggest that an input of Phosphorus from external sources (e.g., animal activity such as bird guano and other sources) is needed to preserve the average Phosphorus levels in the head and in the whole tree island. Finally, Phosphorus accumulation and losses in certain areas of the tree island suggest changes in vegetation that need to be investigated in future work. The developed model can be used as a predicting tool to gain insight into the potential effects of restoration scenarios in tree islands environments. The model could be run for hypothetical future conditions and contribute to provide quantitative information for conservation and restoration efforts in the Everglades and similar wetlands.

The influence water levels have on CO2 and CH4 efflux were investigated at the Loxahatchee Impoundment Landscape Assessment (LILA) research facility, located in Boynton Beach, FL, USA. Measurements of CO2 efflux were taken for 24 h periods four times for one year from study plots. Laboratory incubations of intact soil cores were sampled for CO2, CH4, and redox potential. Additionally, soil cores from wet and dry condition were incubated for determination of enzyme activity and macronutrient limitation on decomposition of organic matter from study soils. Water levels had a significant negative influence on CO2 efflux and redox, but did not significantly influence CH4 efflux. Study plots were significantly different in CH4 efflux and redox potential. Labile carbon was more limiting to potential CO2 and CH4 production than phosphorus, with the effect significantly greater from dry conditions soils. Enzyme activity results were variable with greater macronutrient responses from dry condition soils.

The West Kendall Tree Island site (8DA1081) is a black dirt midden situated on the northeast end of an everglades tree island. The site has been intensely disturbed by excavation pits, particularly on the highest elevations of the site, and becomes increasingly disturbed by a growing Kendall population. Faunal remains recovered in 2008 are examined to reconstruct past ecological habitats, comparing the faunal composition to tree island sites within the Florida Everglades. Based upon identifications, the composition of the site is similar to those of the region, being comprised primarily of freshwater aquatic species and aquatic reptiles, with minimal selection of terrestrial faunal resources. / Includes bibliography. / Thesis (M.A.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection

Many large terrestrial ecosystems have patterned landscapes as a result of a positive feedback system between vegetation communities and environmental factors. One example is tree island habitats in the Florida Everglades. Although they only occupy a small portion of the Everglades landscape, tree islands are important features as the focus of nutrient accumulation and wildlife biodiversity in the Everglades ecosystem. The hardwood hammock community on the elevated head of tree island habitats can accumulate high phosphorus concentration in the otherwise P-limited Everglades ecosystem. In this dissertation, I examined two hypotheses derived from the chemohydrodynamic nutrient accumulation model, which suggests that high transpiration of tree island hammock plants is the driving force for nutrient accumulation in tree island soil. According to this model, I hypothesized that tree islands with lower dry season transpiration should have less phosphorus accumulated than the tree islands with higher dry season transpiration. By examining the water use and nutrient status from 18 tree islands in both slough (perennially wet) and prairie (seasonally wet) locations, I was able to compare water availability and nutrient accumulation in slough and prairie tree islands with different marsh hydroperiods. Chapter 1 uses elemental and stable isotope analysis to look at water stress and nutrient concentration in tree island plants. I showed that the prairie tree island plants suffer from drought stress during the dry season, when the marshes in the prairies dry out. Prairie tree islands also have lower soil and plant P concentration than the slough tree islands. Moreover, I showed that foliar N isotope ratio serves as a stable proxy for community level P availability for tree island plants, and prairie tree island plants have less P available than slough tree island plants. In Chapter 2, I showed that the satellite imagery derived normalized difference water index (NDWI) provides a robust indicator of community level canopy water content of these tree islands. NDWI, used as a proxy for water status, was positively related to foliar N isotope ratio, which suggests that water availability is linked to nutrient availability in the tree island hardwood hammock plant communities. These findings are consistent to the chemohydrodynamic nutrient accumulation model. In Chapter 3, I used sap flow sensors on individual trees to provide a real-time measurement of plant transpiration. I showed that tree island plant transpiration is affected by multiple factors including weather fluctuations, marsh water depth regulated by local water management, and canopy structure of different tree islands. Overall, my dissertation establishes a link between tree island plant water use and nutrient accumulation. It could be potentially important for future restoration plan of tree islands and Everglades hydrological management.

The Everglades, a wetland ecosystem unique to southern Florida has been degraded by the loss of nearly half of its area to urban and agricultural development as well as by alterations to Florida’s hydrology. Modifications to the flow of water to the Everglades have altered the remaining portion of the Everglades. Most prominent among these changes in the remaining Everglades is the loss of tree islands with a disproportionately greater loss of larger tree islands. Despite their significance as “keystone habitats”, our understanding of how changes to Everglades tree islands will affect fauna is poor. In the work presented, 16 study tree islands of Rock Reef Pass, Everglades National Park, Homestead, FL, were classified into three size classes (large, medium and small) and used animal capture histories collected between February 1994 and December 2005 to investigate the relationship between tree island size classes and indirect indicators of adult female hispid cotton rat (Sigmodon hispidus) and marsh rice rat (Oryzomys palustris) fitness and reproduction. Adult female S. hispidus and O. palustris body weights were used as an indicator of adult female fitness and compared among tree island size classes. The proportions of reproductively active females, the proportions of captures of individuals in the juvenile age class and the number of juveniles per female were used as indirect indicators of female reproduction and compared among island size classes. Animal capture histories were also used to perform multi-state mark-recapture analyses, where sates were defined as three island size classes, to draw inferences about state-specific rates of survival and state transition probabilities for Oryzomys palustris and Sigmodon hispidus as a function of the most salient features of the Everglades ecosystem, namely, its tree islands and its seasonal wet and dry periods. Specifically, Akaike’s, information criterion (AIC) was used to make inferences about factors influencing survival and transition probabilities by comparing the relative fit among models where survival and transition rates are described as functions of tree island size classes and as a function of environmental variables that distinguish seasonal periods (monthly water levels, total monthly rainfall, mean air temperature, days dry, days inundated). The probabilities of individuals remaining within the same island size class were interpreted as an indirect indicator of size-class specific tree island use. Results indicated that greater proportions of S. hispidus adult females were reproductively active and had higher fitness on larger islands than females on smaller islands. The body weights of S. hispidus adult females, the proportions of individuals in the juvenile age class and the number of juveniles per female, were positively correlated with tree island area while the proportions of reproductively active S. hispidus females were not. When compared among tree island size classes, S. hispidus females recaptured on the same large island weighed more than females recaptured on the same and medium or small island suggesting that females with greater fitness are found on larger tree islands. The proportions of reproductively active S. hispidus females and of individuals in the juvenile age class were greater on larger tree islands than on smaller islands, although the number of juveniles per females did not differ among tree islands. The results also indicated that differences in the fitness and reproductive condition of O. palustris females are not as distinct among females on different size tree islands. The body weights O. palustris adult females, the proportions of juveniles and the number of juveniles per female were not correlated with island area, while the proportions of reproductively active females were negatively correlated with tree island area. The body weights of O. palustris adult females recaptured on the same large tree island were higher than those of females on smaller islands while the proportions of females that were reproductively active and the proportions of captures of juveniles were higher on small islands than on large islands. Mark-recapture analysis provided evidence that overall, Sigmodon hispidus survival rates were higher on larger islands than on smaller islands. Evidence was not found that Oryzomys palustris survival rates differed among size classes, perhaps due to the limited spatial scale of this study relative to the spatial sale of O. palustris habitat use. Both species’ survival probabilities differed between seasons with Oryzomys palustris having higher survivorship during wet seasons and Sigmodon hispidus during the dry season. Both Oryzomys palustris and Sigmodon hispidus were more likely to remain on large island than on smaller islands.

Spatial and temporal heterogeneity of water and nutrient pools is closely associated with the existence of different plant communities in hydrologically-controlled ecosystems such as the Everglades. These various communities differ in their flooding and fire tolerances as well as nutrient requirements. Upland plant communities are of particular ecological significance since they have high biodiversity and provide habitat to terrestrial fauna, yet comprise less than 10 % of the total area. Restoration and maintenance of such communities requires an understanding of their water and nutrient requirements. Chapter 2 compares water source utilization in hammocks and pine rocklands on the Miami Rock Ridge using stable isotopes of water. Hammocks do not flood, while adjacent pinelands may flood between 2-3 months. In the wet season, hammocks were found to use phosphorus (P) rich soilwater, a local pool of water and nutrients while pineland plants primarily relied upon groundwater, the regional pool. Access to a rich pool of P in the oligotrophic Everglades was associated with higher community-level foliar P concentration in hammocks. However in the dry season, hammocks utilized groundwater, which suggests sensitivity to extended droughts. Chapter 3 compares the hammock (upland or head) and swamp forests (lowland or tail) on tree islands in the Shark River Slough. Uplands were associated with P-rich soilwater uptake in the wet season, with regional water uptake in the dry season. Accordingly, tree island heads are rich in foliar P and thereby P-hotspots in the Everglades. Foliar nutrient concentrations can thus indicate limiting nutrient availability in the Everglades. Chapter 4 looks at how leaf phenology patterns are tied to water and nutrient pools. Leaf fall in ridge hammocks is associated with high foliar carbon isotope values over the dry season, which is not the case for tree island hammocks. However, in some species, high levels of foliar nitrogen are also associated with high foliar C13 values indicating stomatal limitation of photosynthesis. Growing season for most hammock species is the wet season coinciding with high availability of P, as reflected in high foliar P in this season. Linking water sources to foliar nutrients elucidates roles of water and nutrient pools in leading to different plant communities within an ecosystem.

The decline of tree islands in the freshwater-Everglades wetland because of hydrologic manipulation, has compromised valuable ecosystem services. Although the role of tree islands in maintaining freshwater quality stems largely from evapotranspiration processes, fundamental questions remain about the effects of different geologic materials on their hydrogeochemical functioning. To reduce this uncertainty, the lithological composition of a set of man-made tree islands was investigated coupled with long-term hydrologic and hydrochemical data. Key results indicate that limestone substrates and peat substrates with elevated proportions of sand, facilitated surface water-groundwater interactions and mineral dissolution. However, limestone-based islands were more effective in lowering the water table and concentrating solutes in response to evapotranspiration during low surface water stages. Additionally, the peat substrate of an island with low sand content favored the thermodynamic conditions for calcite accumulation in the phreatic zone, while phosphorus concentrations in the groundwater were associated with the breakdown of organic matter.

The purpose of this study was to determine the general patterns of response by tree species common to Everglades Tree Islands (TI) when conditions limiting optimal growth are improved by fertilization on LILA tree islands. Experiments were conducted on constructed TI in the Loxahatchee Impoundment Landscape Assessment (LILA). Thirty-six trees of two species, Annona glabra and Chrysobalanus icaco, were randomly selected on each of four tree islands. Two tree islands have peat overlying limestone cores and two are composed solely of peat. Each tree was treated with one of three nutrient regimes: +N, +P, or Control (no addition of nutrients). A highly significant P-treatment effect on growth rate, leaf TP and leaf N:P ratio were observed in both species in comparison to Control trees. In contrast, neither of the species responded to N-fertilization. The mass N:P ratios and δ13C in P-treated trees exhibited a positive correlation with Relative Elevation (RE) for both species. These findings suggested that the tree growth at LILA tree islands was P-limited on both substrates (limestone and peat).

Soil building processes were studied in reconstructed tree islands in the Loxahatchee Impoundment Landscape Assessment, Florida. Soil building was evaluated by measuring litter production, litter decomposition, soil accretion, and changes in soil elevation under different hydrologic conditions, and by determining physicochemical characteristics of newly accreted soils. Tree islands showed higher litter production and soil accretion but a larger loss of soil elevation caused by subsidence at higher elevations and shorter inundation periods. Newly accreted soils exhibited higher nutrient concentrations, and organic matter (OM) than older soils. Most of the soil phosphorus was stored in the organic fraction. A positive correlation was found between soil nutrients and OM. Reconstructed tree islands are increasing in soil OM and nutrients, generating a positive feedback that increases tree productivity, and soil building. These findings contribute to the understanding of tree islands’ dynamics and can be used by managers for restoration efforts in the Everglades.