Previously disturbed and regenerating forests make up a significant proportion of the North American land area, and therefore play an important role in the exchanges of heat and trace gases between the terrestrial biosphere and the atmosphere. Assessment of local to global variability in CO2 exchanges by forests requires a combination of CO2 measurements made by eddy covariance (EC), field measurements, remote sensing data, and ecosystem models. The integration of these is problematic because of a mis-match in scale between measurement techniques. Despite the importance of regenerating forests on the global carbon balance, the processes affecting the carbon cycle within these forests is not well understood. Airborne scanning light detection and ranging (lidar) instruments provide new opportunities to examine three-dimensional forest characteristics from the level of individual trees to ecosystems and beyond. Lidar is therefore an effective link between plot measurements, eddy covariance, and low resolution remote sensing pixels. This thesis dissertation presents new science on the use of airborne lidar for evaluating remote sensing products within heterogeneous and previously clearcut ecosystems. The goals of this thesis were to first understand the processes affecting CO2 exchanges within a previously disturbed boreal jack pine chronosequence located in Saskatchewan, Canada and then to apply this understanding to evaluate low resolution remote sensing data products from the Moderate Resolution Imaging Spectroradiometer (MODIS) using airborne lidar. The first objective of this dissertation examined the factors that control light use efficiency (LUE) within the jack pine chronosequence during dry and wet years. The second objective examined the importance of vegetation structure and ground surface elevation on CO2 fluxes within a mature jack pine forest. The third objective developed and tested a simple model of lidar fractional cover and related this to the fraction of photosynthetically active radiation absorbed by the canopy (fPAR). This was then used to evaluate the MODIS fPAR product across the lower part of a watershed. Finally, the fourth objective was to model gross primary production (GPP) from airborne lidar. Lidar estimates of GPP were then compared with those from the EC system at the jack pine chronosequence and with the MODIS GPP (Collection 5) product. / Thesis (Ph.D, Geography) -- Queen's University, 2008-08-22 08:50:51.44

Carbon dioxide (CO2) is the leading contributor to global warming and climate change. The increases in fossil fuel emissions, deforestation, and changes of land use have resulted in increased CO2 levels in the atmosphere from 280 ppm in 1765 to 390 ppm in 2010. Carbon mitigation policies for managing the biosphere to increase net CO2 uptake are dependent upon accurate knowledge of the biosphere fluxes. However, Northern Hemisphere bottom-up and top-down biosphere flux estimates show significant discrepancies, especially in North America. In this study, we design an analysis framework that integrates observations with models with the goal of reducing some of the key uncertainties in estimating CO2 fluxes and concentrations in the Midwest, USA. In this research, the biosphere model, WRF-VPRM model (Ahmadov et al., 2007) is used to simulate CO2 biosphere fluxes and atmospheric CO2 concentrations in the Midwest, USA at high spatial resolution. Reducing uncertainties in the predictions is accomplished by improving the model transport configurations (i.e. the WRF planetary boundary layer (PBL) scheme, the number of vertical layers and the horizontal resolution), utilizing a more detailed land cover map, optimizing VPRM photosynthesis and respiratory parameters for major crops (i.e. corn and soybean) against flux towers, and integrating CO2 tall tower observations and model through a top-down data assimilation method to improve the VPRM model parameters and in turn improving the flux and concentration estimates. The WRF-VPRM model configuration with the YonSei University PBL scheme produced the most accurate CO2 concentration predictions at the WBI tower at all three tower levels with the maximum error reduction of 17.1%. Increasing the number of vertical layers improved the CO2 estimates during nighttime and early morning, especially at 30 m, where the error was reduced by a maximum of ~ 20%. The differences in the monthly average net fluxes over the State of Iowa between the high resolution WRF-VPRM model and coarse resolution Carbon Tracker were significant, 71%, 18%, and 62% in June, July, and August, respectively. The fluxes calculated by the VPRM model are primarily dependent on 4 model parameters, half saturation value of photosynthesis (PAR0), light use efficiency (ë), and respiration parameters (á and â). These parameters are specific to vegetation types, regions, and time period. The default settings do not distinguish between corn and soybean, which are major crops in the Midwest and have significant different photosynthesis rates. When corn and soybean are explicitly included in the model, the flux estimate changed by 31.3% at 12 pm and 24.5% at 12 am. Two different methods were used to optimize for the VPRM model parameters which are optimization against Ameriflux NEE and using a top-down variational method. The simulation using optimized parameters from the variational method reduced the error during the daytime from 11.6 ppm to 7.8 ppm. The average fluxes optimized using the variational method changed by 17% and 38.6% at 12 pm and 12 am, respectively. The more accurate VPRM parameters lead to the more accurate biosphere fluxes, which will ease the evaluation of benefits of different carbon mitigation policies.

Soil CO2 efflux (F-soil) represents a significant source of ecosystem CO2 emissions that is rarely quantified with high-temporal-resolution data in carbon flux studies. F-soil estimates can be obtained by the low-cost gradient method (GM), but the utility of the method is hindered by uncertainties in the application of published models for the diffusion coefficient. Therefore, to address and resolve these uncertainties, we compared F-soil measured by 2 soil CO2 efflux chambers and F-soil estimated by 16 gas transport models using the GM across 1year. We used 14 published empirical gas diffusion models and 2 in situ models: (1) a gas transfer model called Chamber model obtained using a calibration between the chamber and the gradient method and (2) a diffusion model called SF6 model obtained through an interwell conservative tracer experiment. Most of the published models using the GM underestimated cumulative annual F-soil by 55% to 361%, while the Chamber model closely approximated cumulative F-soil (0.6% error). Surprisingly, the SF6 model combined with the GM underestimated F-soil by 32%. Differences between in situ models could stem from the Chamber model implicitly accounting for production of soil CO2, while the conservative tracer model does not. Therefore, we recommend using the GM only after calibration with chamber measurements to generate reliable long-term ecosystem F-soil measurements. Accurate estimates of F-soil will improve our understanding of soil respiration's contribution to ecosystem fluxes.

No description available.

Aquatic plants or macrophytes are known as conduits of Methane (CH4), Carbon dioxide (CO2) and Nitrous oxide (N2O) which contribute to the total fluxes of the Greenhouse gases emissions from lakes. Recent studies emphasized that the knowledge on plant mediated emissions calls for more systematic and comparative data especially in the areas of spatial and temporal variability. In this study I measured diel (24 hour) and diurnal(  daily hours only) plant mediated fluxes during four sampling sessions using chamber method from a  Swedish lake in summer 2012. The measurements were conducted on two macrophyte population patterns of mixed plant communities and Equisetum fluviatile (specie-specific) community. CH4 emissions were higher in darker hours and there were no diel correlation between CH4 fluxes and average diel temperature. CH4 fluxes varied between 0.42 mmol m-2d-1 and 2.3 mmol m-2d-1. The CO2 fluxes had negative fluxes in day and positive during the day which was logical due to macrophyte respiration and photosynthesis mechanisms. Occasional daily positive fluxes were seen (only) during the rainy hours and there were no correlation between temperature and diel CO2 fluxes. The total net CO2 exchange was 2.8mmol m-2d-1 indicating that there was more CO2 release in the littoral zone of that lake. N2O fluxes did not show any clear diel or monthly pattern and the fluxes ranged between positive and negative numbers. The N2O fluxes did not exceed 2µmol m-2 d-1 with the total average flux of 0.8µmol m-2 d-1.

Much research has been devoted to understanding the ocean carbon cycle because of its prominent role in controlling global climate. Coastal oceans remain a source of uncertainty in global ocean carbon budgets due to their individual characteristics and their high spatial and temporal variability. Recent attempts to establish general patterns suggest that temperate and high-latitude coastal oceans act as sinks for atmospheric carbon dioxide (CO2). In this thesis, carbon cycling in two Canadian coastal ocean regions is investigated, and the uptake of atmospheric CO2 is quantified. A combination of ship-board measurements and highly temporally resolved data from an autonomous mooring was used to quantify the seasonal to multi-annual variability in the inorganic carbon system in the Scotian Shelf region of the northwestern Atlantic for the first time. The Scotian Shelf, unlike other shelf seas at similar latitude, acts as a source of CO2 to the atmosphere, with fluxes varying over two orders of magnitude in space and time between 1999 and 2008. The first observations of the inorganic carbon system in the Amundsen Gulf region of the southern Beaufort Sea, covering the full annual cycle, are also presented. Air-sea CO2 fluxes are computed and a carbon budget is balanced. The Amundsen Gulf system acts as a moderate sink for atmospheric CO2; seasonal ice-cover limits winter CO2 uptake despite the continued undersaturation of the surface waters. Biological production precedes the ice break-up, and the growth of under-ice algae constitutes nearly 40% of the annual net community production. The Scotian Shelf may be described as an estuarine system with an outflow of surface water, and intrusion of carbon-rich subsurface water by a combination of wind-driven mixing, upwelling and convection, which fuels the CO2 release to the atmosphere. In contrast, Amundsen Gulf may be described as an anti-estuarine, or downwelling, system, with an inflow of surface waters and an outflow of subsurface waters. Wind-driven and convective mixing are inhibited by ice-cover and restrict the intrusion of carbon- and nutrient-rich waters from below, maintaining the CO2 uptake by the surface waters. / PhD Thesis

Since the industrial evolution, the CO2-levels have been increasing in a way that’s never seen in the history of the earth. To mitigate and adapt to the happening climate change it is really important to understand the global carbon cycle and each component that plays a role in it. Some studies suggest that there has been an underestimation on the influence from inland waters in the total carbon budget.To address this issue, there has been Eddy Covariance measurements going on the boreal Indalsälven river in front of the Kattstrupeforsen water dam. In this study continuous data has been collected which includes air-river CO2-flux, pCO2-values in the air and the water and some more meteorological parameters such as the wind speed, relative humidity and the air and water temperature. The aim of this study is to look into the seasonal variation in pCO2-levels and the CO2-fluxes on the Indalsälven river.The data indicates that the CO2-fluxes are mainly positive from January till July (average flux = 0.2 μmol m-2s-1) and mainly negative from September till November (average flux = -0.59 μmol m-2s-1) with an average flux of 0.212 μmol m-2s-1 during 2019. The main range of CO2-fluxes per month lies between -2 and 2 μmol m-2s-1, with the exception of March and December where there is a bigger range of fluxes. The pCO2-levels in the water mainly range between 400 and 1000 ppm. With the exception of 2 periods, one in the end of May where there is a peak to 4000ppm and more which can be explained by the spring flood and in the end of July and beginning of August where there is a peak to 3000 ppm. / <p>2020-06-17</p>

The role of disturbance is widely recognized as a fundamental driver of ecological organization from individual species to entire landscapes. Anthropogenic disturbances from military training provide a unique opportunity to examine effects of disturbance on vegetation dynamics, physicochemical soil properties, and ecosystem processes. Additionally, plant functional diversity has been suggested as the key to ecosystem processes such as productivity and nutrient dynamics. I investigated how disturbance and functional composition both singly and in combination affect vegetation dynamics, soil physicochemical properties, and ecosystem processes. I conducted my research at Fort Pickett, Virginia, USA to take advantage of the spatially and temporally predictable disturbance regime. In order to investigate the effect of plant functional composition on ecosystem properties, I used functional groups comprised of species with similar physiology and effects on ecosystem processes (C4 grasses, C3 grasses, legumes, forbs, woody plants). My study showed that two distinct disturbances associated with military training, vehicle maneuvers, and fire; affect functional group abundance, within functional group richness, and total species richness. I found strong effects of vehicle maneuvers on soil physical properties including an increase in bulk density and reduction in soil porosity. Fire also influenced soil physical properties but more indirectly through the reduction of above ground litter inputs. Though many of the measured physicochemical soil properties at Fort Pickett exhibited statistically significant effects of disturbance, the strength of these relationships appears to be modulated by influences of previous land use. I found statistically significant (P < 0.05) effects of disturbance on chlorophyll fluorescence, and effect of functional composition on available soil N- NH4+. In addition, I detected a significant interactive effect of disturbance class and functional composition on soil CO2 flux. The interactive effects of disturbance and functional composition on soil CO2 flux demonstrated how the loss of functional diversity could lead to instability in ecosystem processes in disturbed ecosystems.    In a dynamic ecosystem, I demonstrated that the abundance and diversity of plant functional groups was significantly influenced by disturbance. By experimentally altering the abundance and diversity of these functional groups in a disturbance-mediated ecosystem, I showed that functional groups and presumably species influence key ecosystem processes. / Ph. D.

Carbon plays a major role in physical and biogeochemical processes in the atmosphere, the biosphere, and the ocean. CO2 and CH4 are two of the most common carbon-containing compounds in the atmosphere, also recognized as major greenhouse gases. The exchange of CO2 and CH4 between the ocean and the atmosphere is an essential part of the global carbon cycle. The exchange is controlled by the air–sea concentration gradient and by the efficiency of the transfer processes. The lack of knowledge about the forcing mechanisms affecting the exchange of these climate-relevant gases is a major source of uncertainty in the estimation of the global oceanic contributions. Quantifying and understanding the air–sea exchange processes is essential to constrain the estimates and to improve our knowledge about the current and future climate. In this thesis, the mechanisms controlling the air–sea gas exchange in the Baltic Sea are investigated. The viability of micrometeorological techniques for CH4 monitoring in a coastal environment is evaluated. One year of semi-continuous measurements of air–sea CH4 fluxes using eddy covariance measurements suggests that the method is useful for CH4 flux estimations in marine environments. The measurements allow long-term monitoring at high frequency rates, thus, capturing the temporal variability of the flux. The region off Gotland is a net source of CH4, with both the air–sea concentration gradient and the wind as controlling mechanisms. A sensitivity analysis of the gas transfer velocity is performed to evaluate the effect of the forcing mechanisms controlling the air–sea CO2 exchange in the Baltic Sea. This analysis shows that the spatio-temporal variability of CO2 fluxes is strongly modulated by water-side convection, precipitation, and surfactants. The effect of these factors is relevant both at regional and global scales, as they are not included in the current budget estimates.

O sistema climático global e o ciclo do carbono interagem intensamente, e o CO2 constitui um fator dominante na definição do clima, sendo gerado e consumido pelas plantas e pela atividade de microrganismos em ecossistemas aquáticos, terrestres e na atmosfera. Na atmosfera, esse gás contribui para o efeito estufa. Em um ecossistema de floresta tropical, grande parte da produção de CO2 é proveniente da respiração do solo, e os fluxos de CO2 na interface solo-atmosfera dependem de mudanças nas características físicas, químicas e biológicas na superfície do solo. O objetivo desse estudo foi investigar a variabilidade sazonal dos fluxos de CO2, decorrente da respiração do solo de diferentes florestas nativas da Amazônia, localizadas nos municípios de Sinop (MT), Caxiuanã (PA), Manaus (AM) e Santarém (PA), e determinar os principais parâmetros de correlação dos fluxos de CO2 do solo com a temperatura e umidade. As amostragens foram realizadas durante as estações seca e chuvosa em cada local. Os fluxos de CO2 foram medidos por meio de câmaras dinâmicas, que se baseiam na variação da concentração do gás no interior da câmara em função do tempo e foram calculados utilizando-se de equações lineares. Os valores médios encontrados para as regiões estudadas nas estações seca e chuvosa foram respectivamente: Sinop, 3,03 &#956;mol.CO2 m-2s-1 e 5,76 &#956;mol. CO2 m-2s-1; Caxiuanã, 5,07 &#956;mol.CO2 m-2s-1 e 6,09 &#956;mol.CO2 m-2s-1; Manaus, 5,47 &#956;mol.CO2 m-2s-1 e 5,44 &#956;mol.CO2 m-2s-1 e Santarém, 2,90 &#956;mol.CO2 m-2s-1 e 5,64 &#956;mol.CO2 m-2s-1. Estes resultados demonstraram que houve variação regional e influência da sazonalidade na dinâmica do fluxo de CO2 do solo, sendo que, os maiores fluxos foram obtidos durante o período chuvoso, indicando que a disponibilidade de água e a temperatura do solo foram os principais condicionadores da produção do CO2. Foram coletadas amostras de serapilheira e raízes para estimar o estoque e a influencia sobre os fluxos de CO2 do solo, sendo estas, vias de entrada de nutrientes e principalmente de carbono para o solo. Para todas as regiões os maiores estoques foram encontrados na estação seca. / Carbon dioxide is an important contributor to the greenhouse effect, and by extension, the global climate system as a whole; it is generated and consumed through the activities of terrestrial and aquatic microorganisms. Tropical forest CO2 fluxes at the soil-atmosphere interface depend on changes in the physical, chemical and biological characteristics of the soil surface. The objective of the present study is to investigate seasonal variability of CO2 fluxes from soil respiration in Amazonian native forest located in the municipalities of Sinop (MT), Caxiuanã (PA), Manaus (AM) e Santarém (PA) and to determine the effects of determining parameters such as temperature and soil moisture. The CO2 fluxes were measured using dynamic chambers during both dry and wet seasons at each site. As the concentration of the gas inside the chamber varies with time, samples were taken at given time intervals and fluxes then calculated using linear regression equations. The average values found for Sinop in the dry and wet seasons were 3.03 and 5.92 &#956;mol.CO2 m-2s-1 respectively; for Caxiuanã, 5.07 &#956;mol.CO2 m-2s-1 and 6.09 &#956;mol.CO2 m-2s-1; for Manaus, 5.47 and 5.44 &#956;mol.CO2 m-2s-1; and for Santarém, 5.64 &#956;mol.CO2 m-2s-1 in the wet season and during the dry season and 6.09 &#956;mol.CO2 m-2s-1. Our results showed that there was a seasonal variation of the CO2 flux. The results also showed that there was an influence of the seasonality in the dynamics of the soil CO2 flux, where the greater fluxes were obtained during the wet season, indicating that water availability and soil temperature were the main factors determining production. Litter samples had been collected and roots esteem the supply and influence it on the CO2 fluxs of in the soil, being these, ways of entrance of nutrients and mainly of carbon for the ground. For all the regions the biggest supplies had been found in the dry station.