Spatiotemporal Drivers of CO2 Dynamics and Evasion Fluxes from Mountain Streams PDF Download

Author: Asa Lovisa Viktoria Horgby
Publisher:
ISBN:
Category :
Languages : en
Pages : 84

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Mots-clés de l'auteur: Mountain streams ; headwater streams ; CO2 sources ; CO2 drivers ; CO2 evasion fluxes ; spatiotemporal scales.

Author: Nicholas T. Dosch
Publisher:
ISBN:
Category : Carbon cycle (Biogeochemistry)
Languages : en
Pages : 107

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Book Description
We examined the spatial and temporal variability of stream carbon dioxide (CO2) and the drivers of these variations in a headwater catchment. To examine temporal variation and drivers, we measured stream and hyporheic pCO2 at high temporal resolution over 11 months in a 95.9-ha forested headwater catchment in the Western Cascades of Central Oregon, USA. Stream and hyporheic pCO2 showed high seasonal and event-scale variability with distinct stream and hyporheic dynamics during storm discharge events. Hyporheic exchange flow exported 37.5 kg-C yr−1 per watershed hectare (confidence interval 4.0-122.3 kg-C ha−1 yr−1) from the riparian zone to the stream. Summing CO2 evasion and downstream advection suggests that one third of inorganic carbon export originated in the hyporheic zone. Hyporheic exchange flow had greatest influence over stream pCO2 during low and high baseflow, while CO2 evasion had greatest influence during storm discharge events. These findings suggest that the hyporheic zone actively participates in carbon cycling in this headwater stream and continuously replenishes stream CO2. To examine spatial variation and drivers, we measured stream CO2 at monthly intervals from July 2013 through July 2014 at 38 locations across the 6400-ha HJ Andrews Experimental Forest. Stream pCO2 was consistently supersaturated with respect to atmospheric concentrations. Stream pCO2 ranged from atmospheric (~400 [micro]atm) to 20 times atmospheric concentrations (8150 [micro]atm) and exhibited strong spatial and temporal variability. The distribution of pCO2 over the study period was different in small and large streams within the drainage network. At the watershed scale, pCO2 decreased with distance downstream. At the reach scale, we did not detect clear patterns in the downstream direction. However, individual transects displayed persistent profile shape, with consistent high and low pCO2 locations. We found negative relationships between stream pCO2 and stream discharge, mean velocity and the carbon dioxide gas transfer velocity. Stream pCO2 exhibited changes over short distances, with large changes in pCO2 over less than 50 m. Longitudinal variability indicates spatial variability of in-stream controls on pCO2 at this scale. Stream pCO2 shows generally higher concentrations during the summer and lower concentrations in the winter, with considerable intrannual variability.

Author: Sivakiruthika Natchimuthu
Publisher: Linköping University Electronic Press
ISBN: 917685812X
Category :
Languages : en
Pages : 56

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Freshwater bodies such as lakes and streams release the greenhouse gases methane (CH4) and carbon dioxide (CO2) into the atmosphere. Global freshwater CH4 and CO2 emissions have been estimated to be of a similar magnitude to the global land or ocean carbon sink, and are thus significant components of global carbon budgets. However, the data supporting global estimates frequently lacks information regarding spatial and temporal variability and are thus highly inaccurate. In this thesis, detailed studies of the spatio-temporal variability of CH4 and CO2 fluxes were conducted in the open water areas of lakes and streams within a whole catchment in Sweden. One aim was also to evaluate the importance of spatio-temporal variability in lake and stream fluxes when making whole catchment aquatic or large scale assessments. Apart from the expected large spatio-temporal variability in lake fluxes, interactions between spatial and temporal variability in CH4 fluxes were found. Shallow lakes and shallow areas of lakes were observed to emit more CH4 as compared to their deeper counterparts. This spatial variability interacted with the temporal variability driven by an exponential temperature response of the fluxes, which meant that shallow waters were more sensitive to warming than deeper ones. Such interactions may be important for climate feedbacks. Surface water CO2 in lakes showed significant spatio-temporal variability and, when considering variability in both space and time, CO2 fluxes were largely controlled by concentrations, rather than gas transfer velocities. Stream fluxes were also highly variable in space and time and in particular, stream CH4 fluxes were surprisingly large and more variable than CO2 fluxes. Fluxes were large from stream areas with steep slopes and periods of high discharge which occupied a small fraction of the total stream area and the total measurement period, respectively, and a failure to account for these spatially distinct or episodic high fluxes could lead to underestimates. The total aquatic fluxes from the whole catchment were estimated by combining the measurements in open waters of lakes and streams. Using our data, recommendations on improved study designs for representative measurements in lakes and streams were provided for future studies. Thus, this thesis presents findings relating to flux regulation in lakes and streams, and urges forthcoming studies to better consider spatio-temporal variability so as to achieve unbiased large-scale estimates.

Author: Shafi Mohammad Tareq
Publisher: Frontiers Media SA
ISBN: 2832527469
Category : Science
Languages : en
Pages : 144

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Author: Nicole Breanne Hill
Publisher:
ISBN:
Category :
Languages : en
Pages : 334

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Atmospheric carbon dioxide (CO2) contributions from rivers and streams, known as CO2 evasion, are estimated to be an order of magnitude greater than CO2 outgassed from volcanoes. CO2 evasion is a function of the CO2 gas transfer rate coefficient and the CO2 concentration gradient at the surface water - atmosphere interface. Methods to measures surface water - atmosphere gas exchange (i.e. reaeration) rates typically require the use of tracer gases, which are labor intensive, expensive, and are not representative of reaeration rates for all streamflow regimes. This dissertation presents a method to estimate the CO2 reaeration rate coefficient from the diel dissolved oxygen (DO) curve. The partial pressure of free CO2 (pCO2) was monitored in Fall Creek, a stream in New York's Finger Lakes region, from May 2015 - May 2016 to identify hydrological and biophysical controls on CO2 fluxes, evaluate the spatiotemporal variability of CO2 emissions, and estimate the relative proportion of in-stream CO2 derived from internal metabolic processes (autochthonous) compared to CO2 inputs from terrestrial sources (allochthonous). Fall Creek is a net heterotrophic system and requires external organic carbon inputs to sustain this status. The proportion of allochthonous CO2 to autochthonous CO2 in Fall Creek is approximately 1:2.6 in its headwaters and increases to 1:1.7 downstream. CO2 emissions vary on diurnal and seasonal time scales with the highest evasion rates (~6.8 g C m-2 d-1) occurring at nighttime during the summer. These emissions were strongly dependent on the CO2 gas transfer velocity, which was twice as high downstream on the turbulent main channel as it was upstream in the calmer headwaters. Autochthonous CO2 is produced during aquatic respiration, which has a strong Arrhenius temperature dependence. Respiration rates in Fall Creek's headwaters were less sensitive (activation energy, Ea = 0.61 eV) to temperature changes than the downstream location (Ea = 0.67 eV) where CO2 emissions were greater. The highest CO2 emissions were estimated for Fall Creek during low flow conditions due to elevated CO2 reaeration rates (~23 d-1), increased respiration from higher temperatures, and more substantial CO2 contributions (~45% total in-stream CO2) from groundwater. Future climate predictions indicate warmer summers with more erratic storm events for the Northeast, which may lead to prolonged periods of low stream flows during summer droughts and amplified CO2 evasion.

Author: Jaclyn Hatala
Publisher:
ISBN:
Category :
Languages : en
Pages : 272

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The Sacramento-San Joaquin Delta in California was drained for agriculture and human settlement over a century ago, resulting in extreme rates of soil subsidence and release of CO2 to the atmosphere from peat oxidation. Because of this century-long ecosystem carbon imbalance where heterotrophic respiration exceeded net primary productivity, most of the land surface in the Delta is now up to 8 meters below sea level. To potentially reverse this trend of chronic carbon loss from Delta ecosystems, land managers have begun converting drained lands back to flooded ecosystems, but at the cost of increased production of CH4, a much more potent greenhouse gas than CO2. To evaluate the impacts of inundation on the biosphere-atmophere exchange of CO2 and CH4 in the Delta, I first measured and analyzed net fluxes of CO2 and CH4 for two continuous years with the eddy covariance technique in a drained peatland pasture and a recently re-flooded rice paddy. This analysis demonstrated that the drained pasture was a consistent large source of CO2 and small source of CH4, whereas the rice paddy was a mild sink for CO2 and a mild source of CH4. However more importantly, this first analysis revealed nuanced complexities for measuring and interpreting patterns in CO2 and CH4 fluxes through time and space. CO2 and CH4 fluxes are inextricably linked in flooded ecosystems, as plant carbon serves as the primary substrate for the production of CH4 and wetland plants also provide the primary transport pathway of CH4 flux to the atmosphere. At the spatially homogeneous rice paddy during the summer growing season, I investigated rapid temporal coupling between CO2 and CH4 fluxes. Through wavelet Granger-causality analysis, I demonstrated that daily fluctuations in growing season gross ecosystem productivity (photosynthesis) exert a stronger control than temperature on the diurnal pattern in CH4 flux from rice. At a spatially heterogeneous restored wetland site, I analyzed the spatial coupling between net CO2 and CH4 fluxes by characterizing two-dimensional patterns of emergent vegetation within eddy covariance flux footprints. I combined net CO2 and CH4 fluxes from three eddy flux towers with high-resolution remote sensing imagery classified for emergent vegetation and an analytical 2-D flux footprint model to assess the impact of vegetation fractal pattern and abundance on the measured flux. Both emergent vegetation abundance and fractal complexity are important metrics for constraining variability within CO2 and CH4 flux in this complex landscape. Scaling between carbon flux measurements at individual sites and regional scales depends on the connection to remote sensing metrics that can be broadly applied. In the final chapter of this dissertation, I analyzed a long term dataset of hyperspectral ground reflectance measurements collected within the flux tower footprints of three structurally similar yet functionally diverse ecosystems: an annual grassland, a degraded pepperweed pasture, and a rice paddy. The normalized difference vegetation index (NDVI) was highly correlated with landscape-scale photosynthesis across all sites, however this work also revealed new potential spectral indices with high correlation to both net and partitioned CO2 fluxes. This analysis within this dissertation serves as a framework for considering the impacts of temporal and spatial heterogeneity on measured landscape-scale fluxes of CO2 and CH4. Scaling measurements through time and space is especially critical for interpreting fluxes of trace gases with a high degree of temporal heterogeneity, like CH4 and N2O, from landscapes that have a high degree of spatial heterogeneity, like wetlands. This work articulates a strong mechanistic connection between CO2 and CH4 fluxes in wetland ecosystems, and provides important management considerations for implementing and monitoring inundated land-use conversion as an effective carbon management strategy in the California Delta.

Author: Pierre Marrec
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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The raise of atmospheric CO2 due to anthropogenic activities is a major driver of the climate change. The ocean plays a key role in the uptake of this anthropogenic CO2. The constraint of air-sea CO2 fluxes and their variability at various time and spatial levels remain a central task in global carbon cycle and climate studies. The contribution of open ocean to this uptake is presently rather well quantified, whereas the role of the coastal ocean to this process remains ambiguous due to the diversity and the high spatio-temporal variability of the CO2 system and air-sea CO2 fluxes in these ecosystems. This PhD thesis investigated the spatial and temporal variability of the CO2 system and air-sea CO2 fluxes in contrasted ecosystems of the north-west European continental shelf. These highly dynamic biogeochemical ecosystems host numerous key hydrographical structures (permanently well-mixed, seasonally stratified, frontal structures, estuarine) of temperate zones, in which the dynamic of the CO2 system were poorly documented. From tidal to multi-annual variability, from a fixed station off Roscoff to the north-west European continental shelf and from seawater samples to satellite data, this PhD thesis provides an integrative overview of the complexity of the CO2 system dynamics in coastal seas and the ongoing challenges to achieve.

Author: Gene E. Likens
Publisher: Academic Press
ISBN: 0123819970
Category : Science
Languages : en
Pages : 745

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Book Description
A derivative of the Encyclopedia of Inland Waters, Biogeochemistry of Inland Waters examines the transformation, flux and cycling of chemical compounds in aquatic and terrestrial ecosystems, combining aspects of biology, ecology, geology, and chemistry. Because the articles are drawn from an encyclopedia, they are easily accessible to interested members of the public, such as conservationists and environmental decision makers. This derivative text describes biogeochemical cycles of organic and inorganic elements and compounds in freshwater ecosystems

Author: Robert G. Wetzel
Publisher: Academic Press
ISBN: 0080574394
Category : Science
Languages : en
Pages : 1023

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Book Description
Limnology is the study of the structural and functional interrelationships of organisms of inland waters as they are affected by their dynamic physical, chemical, and biotic environments. Limnology: Lake and River Ecosystems, Third Edition, is a new edition of this established classic text. The coverage remains rigorous and uncompromising and has been thoroughly reviewed and updated with evolving recent research results and theoretical understanding. In addition, the author has expanded coverage of lakes to reservoir and river ecosystems in comparative functional analyses.

Author: Jorge L. Sarmiento
Publisher: Princeton University Press
ISBN: 0691017077
Category : Nature
Languages : en
Pages : 526

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Book Description
Ocean Biogeochemical Dynamics provides a broad theoretical framework upon which graduate students and upper-level undergraduates can formulate an understanding of the processes that control the mean concentration and distribution of biologically utilized elements and compounds in the ocean. Though it is written as a textbook, it will also be of interest to more advanced scientists as a wide-ranging synthesis of our present understanding of ocean biogeochemical processes. The first two chapters of the book provide an introductory overview of biogeochemical and physical oceanography. The next four chapters concentrate on processes at the air-sea interface, the production of organic matter in the upper ocean, the remineralization of organic matter in the water column, and the processing of organic matter in the sediments. The focus of these chapters is on analyzing the cycles of organic carbon, oxygen, and nutrients. The next three chapters round out the authors' coverage of ocean biogeochemical cycles with discussions of silica, dissolved inorganic carbon and alkalinity, and CaCO3. The final chapter discusses applications of ocean biogeochemistry to our understanding of the role of the ocean carbon cycle in interannual to decadal variability, paleoclimatology, and the anthropogenic carbon budget. The problem sets included at the end of each chapter encourage students to ask critical questions in this exciting new field. While much of the approach is mathematical, the math is at a level that should be accessible to students with a year or two of college level mathematics and/or physics.