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Author: Jeff Cornell
Publisher:
ISBN:
Category :
Languages : en
Pages : 78
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Author: Jeff Cornell
Publisher:
ISBN:
Category :
Languages : en
Pages : 78
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Author: Alma Vázquez-Lule
Publisher:
ISBN:
Category :
Languages : en
Pages : 205
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Salt marshes are one of the most productive ecosystems in the world with the capacity to store large amounts of carbon per unit area, referred as Blue Carbon. This carbon can remain in the ecosystem, be emitted to the atmosphere as carbon dioxide (CO2) or methane (CH4), or laterally exported by the tidal exchange of water. The influence of vegetation on the CO2 and CH4 exchange between salt marsh ecosystems and the atmosphere is uncertain, as a response to the high temporal and spatial variability in these ecosystems. This information is needed for a better understanding of the role of salt marsh ecosystems into the global carbon cycle. In this PhD study, I aim to understand the influence of the salt marsh vegetation on the exchange of carbon between a temperate salt marsh and the atmosphere. I describe and quantify the influence of different plant phenological phases on the CO2 and CH4 exchange, as well as their influence on the Gross Primary Productivity (GPP) at the ecosystem and canopy scale (i.e., canopy photosynthesis by each dominant salt marsh species; FA). For that, I use proximal canopy sensing (PCS; PhenoCam, hyperspectral reflectance data and spectral vegetation indices) to measure and monitor the temporal and spatial variability of the exchange of carbon. This study was performed on the East Coast of the United States, within the Mid-Atlantic in the State of Delaware. The study site is a temperate tidal salt marsh dominated by grasses (i.e., Spartina alterniflora and S. cynosuroides). My main results show that contrasting biophysical factors influence Net Ecosystem Exchange (NEE) of CO2 and CH4 exchange across the diel cycle and plant phenological phases (i.e., Greenup, Maturity, Senescence, Dormancy). I find that plant phenological phases have a substantial influence on the exchange of carbon, being Senescence and Dormancy the phases where this salt marsh ecosystem is emitting more CO2 and CH4 to the atmosphere. (Chapter 2). My results show that plant phenological phases also have an influence on the daily GPP variability, and that PCS is also able to model and predict this variability across the annual cycle and during the beginning of the growing season, but challenges remain for the rest of the plant phenological phases, as a response to changes in the salt marsh vegetation and exposition of soils. I find that vegetation indices used to explain changes in the chlorophyll/carotenoid ratio were more useful to model GPP variability, in contrast to some indices used to explain changes on the greenness condition of the vegetation. My results also show that the use of hyperspectral data from the visible and infrared sregion (VIS-IR) coupled with the partial least square regression (PLSR) approach, is more useful to model and predict daily GPP than specific areas of the electromagnetic region such as the Sun Induced Fluorescence (SIF), red edge (RedEdge) and infrared (IR) (Chapter 3). I find that the spatial heterogeneity in salt marshes influences the relationship between canopy photosynthesis (FA) and leaf nutrients for the most dominant species of vegetation. Nitrogen leaf nutrient (N) has an influence on the FA of S. cynosuroides but not on the FA of S. alterniflora, as a response of the availability of vegetation to uptake this nutrient from soils under lower redox conditions. Leaf nutrients such as phosphorus (P), potassium (K) and sodium (Na) are related with FA for the most dominant salt marsh species in this ecosystem. My results show the promising application of hyperspectral PCS and PLSR approach for linking information of leaf nutrients with FA in canopy salt marshes (Chapter 4). My PhD results are useful to better understand and monitor the carbon cycle in temperate salt marshes, to reduce the uncertainty on the carbon exchanged within the atmosphere and to improve estimations and models of blue carbon in coastal wetlands.
Author: Society of Wetland Scientists (U.S.). Meeting
Publisher:
ISBN:
Category : Wetlands
Languages : en
Pages : 262
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Author: Sommer Faith Starr
Publisher:
ISBN:
Category :
Languages : en
Pages : 152
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Coastal wetlands mitigate excess nutrient inputs by acting as important sites of denitrification. Despite their role in removing excess nitrogen, coastal wetland area has declined by more than 50% in the 20th century, representing a potential loss of ecosystem service. To restore lost function, managers have devoted much effort to salt marsh restoration and construction. However, constructed marshes have lower function than natural marshes even with similar plant biomass. I conducted two experimental studies to 1) compare nitrogen (N) cycling rates between constructed and natural marshes, and 2) to assess microbial biomass/activity and carbon (C) quality differences as potential factors influencing the return of N cycling in constructed Gulf of Mexico salt marshes. In the first experiment, sediment was collected from a constructed and natural marsh and treated with inhibitors to isolate bacterial and fungal contributions to total denitrification. The constructed marsh had 3x lower total denitrification, 4x lower sediment fungal biomass and lower fungal denitrification than the natural marsh. Increased process rates following microbial inhibition in the natural marsh indicate the occurrence of microbial competition for nitrate. These results suggest that fungi and bacteria contribute differently to rates of incomplete denitrification between natural and constructed marshes and that constructed marshes have lower fungal biomass than natural marshes. In the second experiment, sediment was incubated for 19 days in ~149L aquaria and treated with labile or recalcitrant C under ambient or high nitrate conditions. Denitrification and dissimilatory nitrate reduction to ammonium (DNRA) rates and microbial biomass were measured at three points during the incubation, and overlying water was sampled every two days for nutrient concentrations. Both denitrification and DNRA rates were similar between marshes, and labile C additions increased DNRA by more than 12x and reduced the ratio of denitrification to DNRA by as much as 22x. Nutrient concentrations were similar between marshes. Both fungal and bacterial biomass were lower in the constructed marsh. Collectively, the results of these experiments highlight that constructed marshes can reach functional recovery after 30 years and remove N as effectively as reference marshes, despite differences in microbial biomass and starting C and N stocks.
Author: Carlos E. Quintana Alcántara
Publisher: LAP Lambert Academic Publishing
ISBN: 9783659610073
Category :
Languages : en
Pages : 52
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Wetlands take part on the global carbon cycle holding organic carbon in biomass, soils and sediments. In recent year, researches worldwide have been investigated the wetland carbon sequestration capacity due to the increase of the concentrations of greenhouse gasses implicated in global warming and climate change such as carbon dioxide, methane and nitrous oxide in the atmosphere. This paper investigated the carbon sequestration capacity on coastal wetland ecosystems. Based on published studies conducted worldwide, this study also summarizes the environmental conditions and factors associated with carbon fixation, production and storage in tidal salt marshes and mangrove ecosystems. The results showed that coastal wetland ecosystems are significant carbon pool. Global estimations indicated that carbon storage in coastal wetland range from 0.4 to 8.9 Pg C (1 Pg = 1015g carbon). Environmental and hydrologic conditions including salinity gradients and tidal regimes play a crucial role in the biogeochemistry of carbon, methane and nitrous oxide on coastal wetlands. The overview about methane and nitrous oxide production and emission indicated that tidal salt marshes and mangrove
Author: M.P. Weinstein
Publisher: Springer Science & Business Media
ISBN: 0306475340
Category : Science
Languages : en
Pages : 862
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In 1968 when I forsook horticulture and plant physiology to try, with the help of Sea Grant funds, wetland ecology, it didn’t take long to discover a slim volume published in 1959 by the University of Georgia and edited by R. A. Ragotzkie, L. R. Pomeroy, J. M. Teal, and D. C. Scott, entitled “Proceedings of the Salt Marsh Conference” held in 1958 at the Marine Institute, Sapelo Island, Ga. Now forty years later, the Sapelo Island conference has been the major intellectual impetus, and another Sea Grant Program the major backer, of another symposium, the “International Symposium: Concepts and Controversies in Tidal Marsh Ecology”. This one re-examines the ideas of that first conference, ideas that stimulated four decades of research and led to major legislation in the United States to conserve coastal wetlands. It is dedicated, appropriately, to two then young scientists – Eugene P. Odum and John M. Teal – whose inspiration has been the starting place for a generation of coastal wetland and estuarine research. I do not mean to suggest that wetland research started at Sapelo Island. In 1899 H. C. Cowles described successional processes in Lake Michigan freshwater marsh ponds. There is a large and valuable early literature about northern bogs, most of it from Europe and the former USSR, although Eville Gorham and R. L. Lindeman made significant contributions to the American literature before 1960. V. J.
Author: Theodore Paul Winfield
Publisher:
ISBN:
Category : Halophytes
Languages : en
Pages : 102
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Author: L. R. Pomeroy
Publisher: Springer Science & Business Media
ISBN: 1461258936
Category : Science
Languages : en
Pages : 277
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Ecologists have two long-standing ways to study large ecosystems such as lakes, forests, and salt-marsh estuaries. In the first, which G. E. Hutchinson has called the holological approach, the whole ecosystem is first studied as a "black box," and its components are investigated as needed. In the second, which Hutchinson has called the merological approach, the parts of the system are studied first, and an attempt is then made to build up the whole from them. For long-term studies, the holological approach has special advantages, since the general patterns and tentative hypotheses that are first worked out help direct attention to the components of the system which need to be studied in greater detail. In this approach, teams of investigators focus on major func tions and hypotheses and thereby coordinate their independent study efforts. Thus, although there have been waves, as it were, of investigators and graduate students working on different aspects of the Georgia salt-marsh estuaries (personnel at the Marine Institute on Sapelo Island changes every few years), the emphasis on the holo logical approach has resulted in a highly differentiated and well-coordinated long-term study. Very briefly, the history of the salt-marsh studies can be outlined as follows. First, the general patterns of food chains and other energy flows in the marshes and creeks were worked out, and the nature of imports and exports to and from the system and its subsystems were delimited.
Author: Christina Codden
Publisher:
ISBN:
Category : Carbon cycle (Biogeochemistry)
Languages : en
Pages : 174
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"Salt marshes are blue carbon systems that sequester carbon at higher rates than many terrestrial ecosystems due to a coupled relationship between high primary production and slow decomposition in anaerobic sediments. Annually, this coupled relationship allows for over 10 Tg of organic carbon to be sequestered in global salt marsh sediments alone, or a storage equivalent of over 55,000 Blue Whales per year. In turn, this storage ability enables salt marshes to help mitigate increasing atmospheric CO2. Despite high primary production in salt marshes and their ability to help mitigate increasing atmospheric CO2, a long-standing question remains in coastal carbon cycling and ecology which asks: Is a fraction of salt marsh produced carbon, prior to sequestration or mineralization, exported (i.e., outwelled) as dissolved organic carbon (DOC) to the coastal ocean? Answering this question of salt marsh DOC outwelling is critical for quantifying the significance of salt marsh carbon outwelling in comparison to total salt marsh carbon storage, total salt marsh primary production, and broader coastal carbon cycling. Because the question of DOC outwelling first arose on the Georgia coast and because the Georgia coast houses some of the most productive salt marshes in the world, this dissertation focuses on analyzing DOC outwelling in Groves Creek, a tidally-driven salt marsh creek on the Georgia coast. Groves Creek was additionally chosen as it lacks a freshwater head and has limited freshwater input, making the analysis of marsh-only DOC fluxes through the estuarine water possible without confounding results from terrestrial DOC input. In Groves Creek and other Georgia salt marsh creeks, DOC is a master variable that controls the light field, initiates photochemical reactions, and provides sustenance to microbes. The dynamics of DOC in these systems are complex as multiple DOC sources, sinks, and patterns of mixing occur. The complexity in salt marsh DOC dynamics plus the failure of past studies to capture export trends in marsh-derived DOC at both high-temporal resolution and across seasons may explain why it remains unclear whether salt marshes generally export DOC (i.e., outwell). Thus, at a Groves Creek study station, this dissertation sought to answer the question of salt marsh DOC outwelling over three research captures. At Groves Creek study station, Chapter 1 captured hydrology (water level, velocity, flow) at 10-minute resolution over 16-months using an in situ Acoustic Doppler Profiler (ADP) deployed in the creek bed over 7 deployments. After data collection, the hydrology record indicated that the ADP instrument was not deployed in precisely the same location of the creek bed for all deployments. Thus, to make hydrology comparable over the entire study, hydrology records required alignment using a novel alignment approach in which non-tidal signals from individual ADP deployments were added to an extrapolated tidal signal based upon three already aligned deployments. Chapter 2 went on to assess DOC concentration at Groves Creek study station at the same temporal resolution and study length as Chapter 1. As no in situ instrument exists that could directly measure DOC concentration, DOC was estimated in Chapter 2 through the use of site-specific machine learning and linear algorithms coupled with optical and other low-to-zero cost predictors (e.g., water level, salinity, local rainfall) collected at high-temporal resolution. Models were trained using 306 discrete lab-based DOC measurements collected as water samples from the study station. These discrete samples served as ground truth. Work from Chapter 2 included the first-ever incorporation of non-linear machine learning to estimate DOC concentration. By combining DOC concentration (Chapter 2) with water flux (Chapter 1), plus measured salinity (Chapter 3), Chapter 3 was able to calculate DOC fluxes at Groves Creek and ultimately assess the long-standing and inconclusive topic of DOC outwelling. Chapter 3 provided the first-ever estimation of both high-temporal (10-minute) and cross-seasonally (16-month) resolved DOC fluxes. Results show Groves Creek is hydrologically complex with ebb-dominated tidal asymmetry and often more water flowing into the main channel than out (Chapter 1). Since the marsh is hydrologically balanced overall, net imported water likely drained the marsh via unsampled flow paths (e.g., smaller channels, overmarsh flow at marsh edge). Concerning DOC estimation (Chapter 2), at seasonal timescales, machine learning (mean absolute error (MAE) 3.7%) modestly improved upon the accuracy of linear methods (MAE 6.5%) but offered substantial instrumentation cost reductions (~90%) by requiring only cost-free predictors (online data) or cost-free predictors in combination with low-cost in situ predictors (temperature, salinity, depth). At intratidal timescales, linear methods proved ill-equipped (median Pearson's correlation coefficient (R) 0.55) to predict DOC concentration compared to machine learning (median R 0.87-0.94), and again machine learning offered a substantial instrumentation cost reduction (~90%). Thus, one of the main advances set forth in this dissertation is a novel, improved accuracy, and lower-cost method to estimate DOC concentrations in complex aquatic ecosystems. The results of this portion of the dissertation, as presented in Chapter 2, are under a second round of review at Limnology and Oceanography: Methods. Chapter 3 marks the culmination of my PhD research by combining hydrologic fluxes (Chapter 1) and DOC estimates from the two top-performing machine learning algorithms (Chapter 2) to estimate net DOC fluxes through Groves Creek and test the hypothesis that salt marshes outwell DOC (Chapter 3). DOC flux results show that cumulative net DOC-flow and DOC-salt relationships were largely conservative, indicating DOC outwelling was not supported over most of the study period at the Groves Creek study station. However, during summer 2014, the conserved DOC-flow and DOC-salt relationships were disturbed with a loss of DOC from the marsh relative to salt and water fluxes. This discursion from conservative behavior marked a short-lived period of DOC outwelling from the marsh creek to the estuary in summer 2014 during which an estimated 5.7 to 42.1 tons of DOC were exported. Although this is a modest carbon flux, the outwelled DOC remains a significant net term in the marsh carbon budget (e.g., up to 12% of the annual organic carbon sequestration in Groves Creek salt marsh) and an important process to capture in mechanistic models of long-term carbon production, export, and storage for marshes and other blue carbon ecosystems. Results also indicate DOC outwelling from salt marshes may occur as a pulse during highly productive summer months. Resolving these hot moments of DOC export at high-temporal resolution across larger salt marsh ecosystems is required to assess the true extent and quantitative significance of DOC outwelling to coastal carbon cycles, coastal ecology, and the carbon budgets of salt marshes"--Author's abstract.
Author: Mary E. Kentula
Publisher:
ISBN:
Category : Restoration ecology
Languages : en
Pages : 496
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