The marked decline in tree island cover across the Everglades over the last century, has been attributed to landscape-scale hydrologic degradation. To preserve and restore Everglades tree islands, a clear understanding of tree island groundwater-surface water interactions is needed, as these interactions strongly influence the chemistry of shallow groundwater and the location and patterns of vegetation in many wetlands. The goal of this work was to define the relationship between groundwater-surface water interactions, plant-water uptake, and the groundwater geochemical condition of tree islands. Groundwater and surface water levels, temperature, and chemistry were monitored on eight constructed and one natural tree island in the Everglades from 2007-2010. Sap flow, diurnal water table fluctuations and stable oxygen isotopes of stem, ground and soil water were used to determine the effect of plant-water uptake on groundwater-surface water interactions. Hydrologic and geochemical modeling was used to further explore the effect of plant-groundwater-surface water interactions on ion concentrations and potential mineral formation. A comparison of groundwater and surface water levels, along with calculated groundwater evapotranspiration rates, revealed that the presence of a water table depression under the islands was concurrent with elevated groundwater uptake by the overlying trees. Groundwater chemistry indicated that the water table depression resulted in the advective movement of regional groundwater into the islands. A chloride budget and oxygen isotopes indicated that the elevated ionic strength of tree island groundwater was a result of transpiration. Geochemical modeling indicated that the elevated ionic strength of the groundwater created conditions conducive to the precipitation of aragonite and calcite, and suggests that trees may alter underlying geologic and hydrologic properties. The interaction of tree island and regional groundwater was mediated by the underlying soil type and aboveground biomass, with greater inputs of regional groundwater found on islands underlain by limestone with high amounts of aboveground biomass. Variations in climate, geologic material and aboveground biomass created complex groundwater-surface water interactions that affected the hydrogeochemical condition of tree islands.

A general multimedia mass balance model was developed for Big Dam West, Kejimkujik Park, Nova Scotia to predict mercury (Hg) flux and fate in lakes. This model can be used as a screening-level tool by researchers with little to no modeling experience. The model requires no recalibration when applied to other lakes and few input variables (i.e., concentration of Hg in air and inflow water, lake and inflow water suspended particulate matter (SPM), lake temperature, mean depth, surface area, volume, precipitation rate, sedimentation and resuspension rate) need to be changed for any given location. Limits of this model termed "Hg Environmental Ratios Multimedia Ecosystem Sources" (HERMES) model were tested through reapplication and verification on Harp and Dickie Lake, along with Lake Ontario. The HERMES model predicts that small lakes with short water residence times and larger lakes with longer residence times are dominated by water inflow Hg concentration and atmospheric Hg concentration, respectively. For Lake Ontario, air concentrations of mercury appear to be most important. These results contrast with the currently held belief that the Niagara River is the main source of Hg to the lake. To improve model applicability to lakes with limited datasets, as was the case for many of the lakes used in this thesis, estimation methods were developed or adapted from the literature to estimate the most sensitive model input variables (i.e., water inflow Hg concentration, SPM, sediment resuspension rate, water inflow rate) when measured values are missing. Methyl mercury (MeHg) is the bioavailable form that accumulates through food webs, so estimation methods were developed or found to estimate the relative amount of methylated Hg in water inflow, water, and sediment as well. Error contributions to the model from estimation methods were tested through model application to thirty-five lakes in Ontario using three estimation methods (i.e., SPM, resuspension rate, water inflow Hg). The added value of SPM and resuspension rate estimates were assessed through comparisons with fixed values. A comparison between measured and predicted values for these lakes using these estimation methods revealed no significant difference for sediments. The HERMES model was used to derive water inflow Hg concentration values from measured sediment Hg. Regression of the derived water inflow Hg values against watershed and lake variables resulted in the following equation: log water inflow Hg concentration = (0.165 x log watershed area (km2)) + (0.102 x dissolved organic carbon (mg L-1)) -- (0.342 x log water inflow rate (m3 h-1)) + 0.000778 x direct runoff (mm yr-1)) + (0.0154 x mean lake depth (m)) + 0.492 (r2 = 0.68, p < 0.0001). A comparison between the water inflow Hg concentration estimation method (i.e., equation) derived in this study and average measured values for sixteen lakes located in different parts of the world (e.g., Antarctica, Russia, Canada) showed a deviation of only 15.7+/-18.0%, and was within reported ranges (n = 6). This was found to be a significant (p < 0.05) improvement over the previous estimation method for water inflow Hg concentration.

Despite the importance of tropical rivers to the global carbon cycle, the nature of carbon cycling within these watersheds has been dealt with by only a handful of studies. The current work attempts to address this lack of information, using stable isotope and concentration measurements to constrain sources and sinks of carbon in two Peninsular Malaysian watersheds. The basins are located on the central-western and northeastern coasts of the Malaysian Peninsula, and are drained by the Langat and Kelantan Rivers, respectively. Water samples were collected from three points along the two rivers twice a month, in addition to the sampling of groundwater in adjacent aquifers. Principal component analyses (PCA) on water chemistry parameters in the Langat and Kelantan Rivers show the dominance of geogenic and anthropogenic influences, grouped in 4 to 6 components that comprise over 50 % of the total dataset variances. The geogenic input is reflected by components showing strong loadings by Ca, Mg, Mn, Si, and Sr, while anthropogenic influences via pollution are indicated via strong loadings by NO3, SO4, K, Zn and Cl. The carbon isotope and concentration data appear unrelated to these groups, suggesting that the riverine carbon cycle in both locations is dominated by other factors. These may include alternative sources of organic pollution, or inputs from the local vegetation and soils. The mean riverine 13CDOC of -27.8 ± 2.9 ‰ and -26.6 ± 2.2 ‰ in the Langat and Kelantan Basins, respectively, are consistent with the dominance of C3-type vegetation in both watersheds. Riverine 13CDIC signatures approach C3-like values at high DIC concentrations, with measurements as low as -19 ‰ in the Kelantan Basin and -20 ‰ observed in the Langat Basin, consistent with a biological origin for riverine DIC. However, the average 13CDIC in river water is 13C-enriched by about 10 ‰ relative to the expected C3 source in both rivers, and this 13C- enrichment appears to be largest with smaller DIC concentrations. Because of the overpressures of CO2 in the rivers, entrainment of isotopically-heavy atmospheric CO2 is not a likely explanation for the observed 13C-enrichment. Theoretically, dissolution of carbonates could be an alternative source of 13C-enriched carbon, but this lithology is scarce, particularly in the Langat watershed. The increase in DIC downstream and generally high pCO2 values in most river sections argues against aquatic photosynthesis as a primary causative factor for the observed isotopic enrichment. This elimination process leaves the speciation of riverine DIC and the evasion of CO2 as the most likely mechanisms for 13C-enrichment in DIC, via isotope fractionation during HCO3- hydration and CO2 diffusion. Potentially, methanogenic activity could also be, at least partially, responsible for the 13C-enrichment in DIC, particularly immediately downstream of the Langat Reservoir, but due to the absence of empirical data, this must remain only a theoretical proposition. The aquatic chemistry and dissolved carbon data suggests that pollution discharge into the Langat and Kelantan Rivers is the major factor that is responsible for the considerable CO2 overpressures and high DIC and DOC concentrations in the river waters, particularly in the downstream sections. This pollution is likely of biological origin, via sewage and palm oil mill effluent (POME) discharge, and therefore isotopically indistinguishable from natural C3 plant sources. Carbon budgets of the Langat and Kelantan River show CO2 degassing to be a significant mechanism of fluvial carbon loss, comprising roughly 50 %, or more, of the total riverine carbon export in both watersheds. The remainder of the river carbon is transported to the ocean in the form of DIC, DOC and POC in broadly comparable proportions. However, the combined riverine carbon export from the Kelantan and Langat Basins amount to 2 % or less of the total carbon sequestration of the watersheds. Thus, most of the sequestered carbon is returned to the atmosphere via respiration, with smaller amounts incorporated into ecosystem biomass . These results highlight the complexity of carbon cycling in tropical rivers, and agree with previous studies in showing riverine systems to be more than simple conduits of carbon from the land to the ocean.

Coastal nutrient loading is a growing concern in urbanized communities and has led to alterations in above- and belowground processes throughout estuarine systems. Mangrove forests are highly productive coastal habitats that exhibit large carbon stocks contained mostly to the deep soils. Since nutrient enrichment has been found to increase mangrove aboveground growth, it’s presumed that nutrient enrichment will also increase belowground respiration rates. Disturbances in soil nutrient content may alter the mangrove carbon cycle by increasing the amount of CO2 lost to the atmosphere from enhanced microbial and root respiration. In this study, soil respiration responded greatest to nitrogen enrichment, but pneumatophore root respiration responded greatest to phosphorus enrichment. Nutrient limitation can shift between different ecological processes and responses to nutrient enrichment tend to be system specific in tidally influenced ecosystems. Understanding the implications of coastal nutrient loading will improve ecosystem models of carbon exchange and belowground processes. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2021. / FAU Electronic Theses and Dissertations Collection

Since the industrial revolution human activities have more than doubled the amount of bioavailable nitrogen (N) on earth leading to far-reaching ecological consequences for coastal marine ecosystems. Salt marsh systems, including their intertidal creek and mudflat sediments, serve as nutrient filters transforming nitrogen and removing it through denitrification. However, as hotspots of nitrogen transformation, these ecosystems are also thought to be sources of nitrous oxide, a powerful greenhouse gas, to the atmosphere. We investigated the influence of various scales of anthropogenic fertilization on the nitrogen cycling in intertidal creek and mudflat sediments in the salt marsh ecosystem of Plum Island Ecosystem Long Term Ecological Research site in northern Massachusetts, USA. Benthic fluxes from whole core incubations showed that long-term fertilization of tidal creek sediment stimulated net denitrification with significantly higher rates in the fertilized creek compared to the reference (162.7 ± 32 and 0.74 ± 39 μmol N m^-2 hr^-1, respectively). However, fertilization also appeared to stimulate dissimilatory nitrate reduction to ammonium (DNRA) with calculated rates also significantly higher in the fertilized compared to reference creek and representing 45 and 11% of total nitrate uptake, respectively. These results indicate that DNRA may outcompete denitrification at higher nitrate concentrations, thus anthropogenic fertilization may be driving tidal creek sediments toward this N regeneration process and thus inhibiting the overall nitrogen removal capacity of the ecosystem. Conversely, a smaller scale, short-term nitrogen addition experiment had no significant impact on nearby tidal flat sediments likely because the fertilization exposure time on the tidal sediments was too short. Overall benthic flux rates were lower in the tidal flat compared to the tidal creeks. However, the tidal flat was also a net N filter with an average net N2 flux of 5.7 ± 2.6 μmol N N m^-2 hr^-1. Rates of nitrification and therefore coupled nitrification-denitrification appeared to be affected by the active microphytobenthos (MPB) community within the tidal flat sediments with oxygen production from photosynthesis fueling coupled denitrification in the light while N fixation dominated under dark conditions. As in the tidal creeks, we found evidence that DNRA is also an important N transformation process within tidal flat sediments. Finally, sediment microprofiling measurements showed these tidal mudflat sediments to be a net sink of N2O (average -6.9 ± 1.7 μmol N2O N m^-2 hr^-1) with significantly higher rates of uptake the longer sediments were exposed to the atmosphere at low tide. Fluxes were shown to be driven by nutrient supply and nitrate limitation of denitrifiers with tidal pulsing. Additionally, smaller, core scale nutrient additions revealed an increase in N2O flux with dissolved inorganic nitrogen (DIN) addition. Importantly, N2O uptake was found to be phosphorus limited. Again, nutrient enrichment appeared to stimulate DNRA over denitrification indicating that fertilization may not only hamper nitrogen removal capacity, but also increase N2O flux to the atmosphere.

The logistical difficulties of research in extremely low temperatures and lack of access to the Arctic have meant that there is a historic dearth of knowledge of coastal Arctic biogeochemistry, especially during winter when sea ice is present. Recent observations, however, indicate that the Arctic is changing rapidly. Changes include increased temperatures, decreased extent and volume of sea ice, and increased freshwater inputs. How these changes influence biogeochemical cycles is an open question, especially in the highly productive coastal regions of the Chukchi Sea. Here I present nitrogen (N) uptake and regeneration rates for phytoplankton and bacteria measured in the shallow waters and landfast sea ice near Barrow, Alaska. Experiments were performed using tracer-level incubations of stable isotope (15N) ammonium, nitrate, urea, and amino acids during January, April, and August over two successive years (2010 --- 2012). Autotrophic versus heterotrophic N uptake was measured with traditional size fractionation. In brief, I found that outside of the spring phytoplankton bloom period, ammonium and amino acids were the preferred N substrates assimilated. Regeneration of N and nitrification were especially high during winter. A high-speed cell sorting flow cytometer was used to distinguish bacterial sub-populations and their uptake rates. Low nucleic acid populations were active in taking up N compounds, although not at quite the same rate as high nucleic acid cells. The difference was less pronounced during winter compared to summer. Additional experiments were designed to artificially warm the samples to demonstrate that ammonium uptake rates increased with temperature and substrate availability, whereas nitrification rates did not. Uptake and regeneration of ammonium and nitrate along with nitrification was also measured in landfast sea ice. This is the first report of N uptake from within the sea ice matrix in the Chukchi Sea. Given the paucity of information on N cycling in the Arctic Ocean, these data can inform modeling efforts to predict future changes in the system and also provide a baseline by which to compare future observations.

Approximately 40% of the bottom of Chesapeake Bay is less than 2.0 m in depth and many of these broad shoal environments are bordered by wetlands. The vegetated and nonvegetated subtidal and intertidal environment is a dynamic mosaic of highly productive estuarine habitats linked by the exchange of waterborne materials. This study developed simulation models of primary production and material exchange for four littoral zone habitats of the Goodwin Islands National Estuarine Research Reserve (NERR) in lower Chesapeake Bay. Field studies were conducted to determine the sediment biogeochemical and biomass characteristics of sandy shoal, seagrass, silt-mud, and marsh habitats. Ecological models were developed for each habitat based upon their position and ecological characteristics. The models simulate the dynamics of phytoplankton, particulate and dissolved organic carbon, dissolved inorganic nitrogen, sediment microalgae, Zostera marina, and Spartina alterniflora. Following sensitivity analysis and validation the models were used to estimate annual primary production, nitrogen processes, and material exchange. The net annual rate of phytoplankton production was 66.0, sediment microalgae ranged 101-169, Zostera marina community production was approximately 350 gC m&\sp{lcub}-2{rcub}& yr&\sp{lcub}-1{rcub}&, and Spartina alterniflora shoots and root-rhizomes produced 1150 gC m&\sp{lcub}-2{rcub}& yr&\sp{lcub}-1{rcub}& (gC m&\sp{lcub}-2{rcub}& yr&\sp{lcub}-1{rcub}&). Nitrogen uptake was in excess of demand in phytoplankton while the reverse was true for the macrophytes. The marsh habitat accounted for 43% of the total annual primary production for the ecosystem despite being the smallest habitat while the largest habitat (nonvegetated subtidal) required 52% of the total ecosystem nitrogen demand. All four habitats imported phytoplankton, particulate organic carbon, and dissolved inorganic nitrogen annually. While the intertidal habitats imported dissolved organic carbon the subtidal habitats showed net annual export. These models were developed to assess ecosystem structure, function, and change in the littoral zone of Chesapeake Bay. Ecosystem structure was assessed through field research and model development. Ecosystem function was assessed by using the model to generate annual producer, habitat, and ecosystem carbon and nitrogen budgets. The model is currently being used to investigate the interactive effects of water quality, primary production, and habitat composition in order to assess potential change in the estuary.

Soil bacteria and fungi play a central role in the biogeochemical cycling of both carbon (C) and nitrogen (N) through terrestrial ecosystems. In the C cycle, soil microbial groups regulate the depolymerization of large stocks of soil organic matter and contribute 35-69 Pg C to the atmosphere annually through heterotrophic respiration. Soil microbial groups also mediate several important transformations of N, including making limiting nutrients available for uptake by plants through N-fixation, converting N between inorganic forms through nitrification, and returning N to the atmosphere through denitrification. While each of these functions is performed by soil microbes, scaling microbial physiology and community structure to biogeochemical cycling remains a significant research challenge. This dissertation integrates three distinct approaches to characterizing relationships between microbial physiology, microbial community structure and biogeochemical cycling. First, I explore the role of microbial physiology in C cycling by developing a novel method to predict bacterial carbon use efficiency (CUE) from genomes using metabolic modeling. I find that bacterial CUE is phylogenetically structured, with the class and order levels explaining the greatest proportion of variance in CUE, and I identify particular bacterial traits that most strongly predict CUE. These findings highlight the importance of accounting for microbial physiology when modeling soil C cycling. Second, I explore how differences in the abundance and activity of microbial functional groups and their interactions with mycorrhizal fungi impact temperate forest N cycling. I find that N availability and rates of N-fixation, nitrification and denitrification are structured in relation to mycorrhizal fungal types, but that the abundances of bacterial functional groups are not correlated with biogeochemical fluxes. Finally, I use a soil biogeochemical model to identify sources of uncertainty and data needs in advancing our understanding of microbially-mediated soil biogeochemical cycling. I isolate specific microbial physiological and enzyme kinetic parameters that have disproportionately large impacts on projections of coupled C and N cycling, and I quantify the potential for particular types of data to help reduce uncertainties. Overall, this dissertation advances our understanding of how microbial processes impact the biogeochemical cycling of C and N in terrestrial ecosystems.

Agricultural bioenergy crops (“bioenergy”) are a promising renewable fuel source if carbon (C) emitted during the production and combustion of bioenergy is less than emissions associated with fossil fuel analogs. Despite the importance of belowground C sequestration in determining the net C sink potential of bioenergy, belowground C cycling processes in bioenergy crops remains largely uncharacterized. This study seeks to quantify and characterize the response of belowground C pools and fluxes to farm management scenarios (nitrogen (N) fertilization, stand age, and genotype) in two crops proposed as potential sources of bioenergy, Miscanthus x giganteus (Miscanthus) and Sorghum bicolor (Sorghum). This study additionally seeks to compare the belowground C fluxes in two crop species and draw conclusions about the potential for belowground C storage to mitigate carbon dioxide (CO2) emissions associated with the production and combustion of bioenergy derived from these two crop species. We quantified fine root biomass, soil organic carbon (SOC) content, and CO2 emissions associated with root respiration under five nitrogen (N) fertilization levels in Miscanthus and Sorghum. For perennial Miscanthus, we also quantified fine root biomass and root respiration among stands established over three different years to observe how the net belowground C flux changed over time and as a function of establishment year. Both fine root biomass and root respiration rates did not change as a function of fertilization in Sorghum stands, but SOC content in Sorghum was significantly greater in the <0.053 and 2-0.25mm size fractions in unfertilized stands compared to fertilized. In Miscanthus stands, N fertilization did not affect SOC content. Nitrogen fertilization decreased the belowground C storage capacity of Miscanthus by depressing fine root biomass. Simultaneously, N fertilization increased mass-specific rates of root respiration rates in Miscanthus. Despite increased mass-specific root respiration with N fertilizer addition, Miscanthus plot-scale root respiration did not change with increasing N application due to decreased fine root biomass observed with increasing amounts of N fertilization. Fine root biomass was six-fold greater in Miscanthus stands than Sorghum, while mass-specific root respiration rates were lower in Miscanthus stands than Sorghum. When scaled up, plot-scale root respiration emissions were lower in Miscanthus compared to Sorghum stands, while SOC content was greater in Miscanthus stands than Sorghum stands. Our results indicate Miscanthus has greater C sink potential than Sorghum via C allocated belowground to fine root biomass production and lower rates of root respiration.

No description available.