Compost is commonly used as an organic amendment in cropping systems such as vineyards, and has been shown to be beneficial to carbon (C) sequestration and soil health. As perennial crops, grapevines have a larger potential for C sequestration than most crops. Yet, there is a lack of understanding regarding the relationship between compost application rate, the magnitude of C sequestration, and its environmental tradeoff in the form of greenhouse gas (GHG) emissions. In the study, we investigated the effects of compost application rate on soil C sequestration, GHG emissions, crop growth, and overall soil health after two annual compost treatments at J. Lohr Vineyards and Wines, Paso Robles, CA. Compost was broadcasted to the entire plot area between harvest and the first precipitation in fall at the rate of 0 (control), 2, 4, and 6 tons/acre/year. Soil C sequestration, cumulative carbon dioxide (CO2) and nitrous oxide (N2O) emissions and soil physical properties were assessed at two functional locations (tractor row and vine row) and three depth increments (0-15, 15-30, and 30-60 cm). Cover crop biomass was determined in spring before mowing, while clusters per vine, cluster weight and yield were determined each year at harvest. Although compost application did not significantly affect total soil C stocks, significant increases in early indicators of C sequestration such as permanganate oxidizable carbon (POXC), aggregate distribution, and aggregate C content in large macroaggregates without increasing C mineralization suggests that C input from compost increased C stabilization in soil. Cumulative GHG emissions were not significantly affected by compost application. Both CO2 and N2O emissions were higher in the vine row than the tractor row in the dry season, but the trend for CO2 emissions was the opposite in the wet seasons. Seasonal patterns of GHG emissions were likely due to differences in plant activity and irrigation between functional locations. The lower bulk density in topsoil than subsoil, and the higher water holding capacity and aggregate stability in tractor row topsoil than in the vine row demonstrates how high C content improves soil physical properties. Cover crop growth and grape yield components were unaffected by compost application. Based on our results, early signs of C sequestration and improvements on overall soil health can be achieved in a coarse-texture vineyard in the Central Coast region after annually applying compost at a rate between 2 and 6 tons/acre for two years, without increasing GHG emissions or affecting grape yield. Further investigation is recommended to study the potential synergistic effects between compost application and cover cropping in vineyards if both practices are implemented at the same time.

Agricultural production in Sweden account for a large contribution of the territorial GHG emissions. System optimization, fossil fuel removal and increased circularity is therefore of great importance in order to reach the national net zero emission target by 2045. Biochar production from biomass side flows is a cost-efficient method for carbon dioxide removal which could help to reduce the climate impact of agricultural systems. This study aimed to investigate the potential for climate change mitigation by implementing biochar production from wheat straw at farm level in Sweden. A life cycle perspective was used to assess the climate change impact for production of 1 Mg wheat, with three scenarios for straw management 1) biochar production and application on fields 2) straw incorporation into soil and 3) district heat production. A time distributed LCI was used to include the time dynamics of soil processes. Climate impact was assessed using two metrics: Total GWP100 impact(static) and global surface temperature change (time dynamic). Excess thermal energy from the pyrolysis process was assumed to be used for drying of grains and heating buildings at the farm. The results showed a total GWP100 impact of 214 kg CO2-eq/Mg wheat in the scenario with biochar production, which compare to the impact of 425-429 kg CO2-eq/Mg wheat for the scenarios with conventional straw management practices. The temperature response was ca 50 % lower all throughout the analysed time period, compared to the scenarios with straw incorporation or district heat production. The largest contribution to the impact reduction was achieved from carbon sequestration from biochar application to soil amounting to 223 kg CO2-eq/Mg. A sensitivity analysis of the biochar yield (kg biochar produced per kg of dry mass feedstock) for pyrolysis of straw confirmed that biochar production was preferable over other straw management practices for lower biochar yields as well. In conclusion, utilizing straw for biochar production could have a large potential for reducing the climate impact from wheat production in Sweden. However, a combination of measures for climate change mitigation is needed to reach net zero emissions of wheat production. / Jordbruksproduktionen står idag för en betydande del av Sveriges territoriella växthusgasutsläpp. För att minska jordbrukssektorns klimatpåverkan krävs åtgärder såsom material och energiåtervinning, utfasning av fossila bränslen och elektrifiering. För att nå det nationella klimatmålet om nollutsläpp år 2045 krävs även åtgärder för infångning och lagring av koldioxid. Biokolsproduktion av restprodukter och avfall i form av biomassa är en kostnadseffektiv och lättillgänglig metod för kolinlagring. Pyrolys är en termokemisk process som sker när biomassa upphettas till höga temperaturer utan tillgång till syre. Produkterna från processen är syngas, pyrolysolja och biokol. Processen optimeras utifrån vilka produkter som är önskade och syngas förbränns ofta för att tillföra energi och upprätthålla reaktionen. Biokol används därefter främst som jordförbättringsmedel i planteringar men kan även användas för vattenfiltrering, som fyllnadsmaterial i betong, applicering på åkermark och som tillsatts i djurfoder. Efterfrågan och produktionen av biokol är än så länge relativt liten i Sverige. Då det finns en stor tillgång på biomassa från restprodukter inom jordbruket så finns även en stor möjlighet att minska sektorns klimatpåverkan genom pyrolys och biokolsproduktion. Syftet med denna studie är att undersöka hur implementering av biokolsproduktion från vetehalm skulle kunna bidra till minskad klimatpåverkan från veteproduktion. Studien utförs med ett gårdsperspektiv och har målen att: Identifiera och kvantifiera växthusgasutsläpp för relevanta materialflöden och processer inom veteproduktion. Beräkna klimatpåverkan utifrån ett livscykelperspektiv för produktion av 1 Mg vete under tre scenarion för halmhantering 1) biokolsproduktion och applicering på fält 2) halminblanding i jord 3) energiåtervinning genom produktion av fjärrvärme.  Klimatpåverkan, GWP100, beräknades med mätenheten (kg CO2-eq/Mg vete) och beskriver den totala påverkan från de ackumulerade utsläppen över en 100 års tidshorisont som förutsätter att alla utsläpp sker under det första året. För att kunna inkludera ett tidsperspektiv och ta hänsyn till icke-fossila utsläpp av CO2, markprocesser och koncentrationen av växthusgaser i atmosfären över tid, så beräknades även temperaturförändringen av den globala yttemperaturen (K/Mg vete och år), ΔT. Dessa beräkningar utfördes genom att använda tidsdistribuerade utsläpp för en 100 års period och klimatpåverkan, ΔT, beräknades för 150 år. Startåret för beräkningarna och veteproduktionen var satt till år 2019. Gården antogs producera höstvete årligen, utan växelbruk, under en tidsperiod på 20 år. Biokolsproduktion antogs ske på gården och värmeöverskottet antogs användas till torkning av vete och värme till byggnader på gården. En systemexpansion gjordes för att modellera utsläppsminskningen från ett lokalt fjärrvärmeverk där halmen antogs ersätta träpellets producerade av skogsrester.  Resultatet visade en klimatpåverkan av 214 kg CO2-eq/Mg vete. för scenariot med biokolsproduktion, 425 kg CO2-eq/Mg vete för scenariot med fjärrvärmeproduktion och 429 kg CO2-eq/Mg vete för scenariot med hamninblandning i jord. För den tidsdynamiska klimatpåverkan hade scenariot med biokolsproduktion en genomgående ca 50 % lägre temperaturpåverkan under hela tidsperioden. Resultatet visade även att kolinlagringen från biokol var den största bidragande faktorn till den minskade klimatpåverkan. Användning av överskottsvärme från pyrolysprocessen hade även ett betydande påverkan till minskade klimatutsläpp.  Biokolsproduktion av restprodukten vetehalm har därigenom en stor potential till att minska klimatpåverkan från veteproduktion. Effekten av biomassaomvandlingskvoten för pyrolys av halm (mängd producerad biokol per tillförd mängd biomassa) analyserades genom en känslighetsanalys som fann att biokolsproduktion från halm är fördelaktigt även vid lägre omvandlingskvoter, 20 %. En ökning av biomassaomvandlingskvoten med 5 % kan ge ytterligare en minskning på 16-20 % av de totala utsläppen. Även effekten av jordförbättrande egenskaper som skördeökning och minskade markutsläpp av N2O analyserades. Då biokolsmängden per hektar är relativt låg och antas ge effekt endast ett år, så var dessa effekter på den totala klimatpåverkan försumbara. De ackumulerade effekterna av biokol som jordförbättring undersöktes dock inte, men skulle eventuellt kunna ge en mer betydande effekt.  För att bättre kunna analysera klimateffekterna av jordförbättring krävs dock mer forskning om effekter av biokol under svenska odlingsförhållanden över en längre tid. För att dessutom få en mer övergripande bild av potentialen för implementering av biokolsproduktion inom jordbrukssektorn så rekommenderas framtida studier för analys av olika sorters grödor, växtföljder, restprodukter och regioner.  Utifrån resultatet dras slutsatsen att gårdsproduktion av biokol från vetehalm har en möjlighet att minska klimatpåverkan från vete med ca 50 % jämfört med annan halmhantering. Biokolsproduktion är även fördelaktigt när tidsdynamiska effekter av utsläppen inkluderas. För att nå en klimatneutral veteproduktion krävs dock även andra åtgärder.

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Carbon capture and related gas separation processes are critical tools in our efforts to combat climate change. While polymer membranes are seen as a central construct to achieve these goals, their performance needs further improvement to meet current sustainability objectives. It is in this context that membranes composed of polymer-grafted nanoparticles (GNPs) become highly germane. Chemically tethering the available polymer to the nanoparticle (NP) surface in GNP systems helps mitigate difficulties controlling nanoparticle dispersion common when incorporating inorganic filler NPs into polymer (i.e., mixed matrix membranes (MMMs)). Previous work has shown that gas transport in pure GNP membranes can be strongly enhanced relative to that in the corresponding neat polymer. Additionally, we demonstrated that larger gases display greater degrees of permeability enhancement than smaller ones. This work explores the underlying mechanisms governing the unique gas transport behavior observed in GNPs, with the goal of designing materials possessing superior transport properties that can be known and manipulated a priori. We begin with the identification of transport mechanisms for penetrants of different sizes through an exploration of the heterogenous nature of GNPs. In the limit of moderate-to-high grafting density (the number of chains tethered per unit surface area), the chains are overcrowded near the surface and assume extended conformations termed “polymer brushes”. These brushes comprise two regimes: (1) a dry zone of higher polymer stretching closer to the NP surface and (2) the interstitial spaces in the multibody packing of lower polymer density. We find that larger penetrants such as CH₄, with low solubilities, preferentially sorb into the interstitial spaces in the NP packing prior to diffusing through stretched chains in the dry brush region. The nature of small gas permeability enhancement, on the other hand, is due primarily to enhancements in penetrant diffusion through the stretched chain region close to the NP surface – this is because these gases have high enough solubilities to be present everywhere in the polymer layer. Such solubility differences enable the direct control over penetrant transport through the disparate regions of the polymer brush in mixed-gas environments relevant to operation. Elevated CO₂ content, through increasing feed concentrations at higher pressures, yields increased CH₄ permeability and an associated reduction in mixed-gas selectivity relative to ideal gas analogs. Additionally, high-pressure conditioning with CO₂ evidently dilates the material (due to gas adsorption) in a manner that is apparently not recoverable after a pressure decrease. An alternative handle to control penetrant transport is to manipulate the physical brush structure. Such morphological control is accomplished through variations in preparation methodology; in particular, the rate of solvent evaporation in solution-cast samples plays a significant role in dictating the final structure of the jammed colloidal glass. Utilizing high-pressure conditioning in CO₂ as a concentration quench, we combine morphological control over the brush structure with selective penetrant manipulation to dilate the overcrowded brush regime and enhance gas transport performance. Leveraging the colloidal glass nature of GNPs in this way enables the formation of quasi-equilibrium structures with even greater amounts of “free volume”. The remaining chapters focus on employing our knowledge of the gas transport mechanisms in these materials to aid in future experimental design and to form mechanically resilient materials. Implementing a simulated design-of-experiments loop, we find that a surprisingly minimal amount of experimental data is necessary to effectively model the transport properties of new materials to within practical experimental error. Selectively altering the chemistry of specific chain regions achieved slight enhancement in membrane selectivity while significantly improving material toughness and ultimate utility. Our enhanced understanding of gas transport mechanisms in polymer-grafted nanoparticle membranes will aid in the design and implementation of membranes with tunable separation performance through direct control of how penetrants transport and via morphological changes to the brush structure.

Reducing carbon emissions is a looming challenge that will be required to limit global warming. One approach is to replace energy from fossil fuels with renewable electricity that has low carbon footprints. The continuous decrease of renewable electricity prices makes electrochemical processes very promising for environmentally friendly production of fuels and chemicals. One of the mature electrochemical processes is hydrogen (H₂) production from water electrolysis. If only excess solar/wind electricity is used to power water electrolyzers to produce green H₂, the intermittency of the electricity supply will require low-cost electrolyzer technologies. Emerging membraneless water electrolyzers offer an attractive approach to lowering the cost of H₂ production by eliminating membranes or diaphragms that are used in conventional water electrolyzers. One aim of this dissertation is to understand the performance limits of membraneless water electrolyzers compared to the conventional designs. Another key electrochemical process to reduce carbon emissions is the conversion of carbon dioxide (CO₂) to value-added fuels and chemicals. CO₂ captured from air or flue gas needs to be extracted from carbon capture solution and pressurized before feeding to a conventional CO₂ electrolyzer. In order to avoid these energy intensive steps to make pressurized CO₂, there is a growing interest in developing membrane-based electrolyzers that can directly utilize the carbon capture solution to conduct electrochemical CO₂ conversion. This dissertation also explores a scalable membrane-free electrolyzer design that can convert carbon capture solution to syngas. In Chapter 2, a parallel plate membraneless electrolyzer is used as a model system to demonstrate a combined experimental and modeling approach to explore its performance limits. This modeling framework quantitatively describes the trade-offs between efficiency, current density, electrode size, and product purity. Central to this work is the use of in situ high-speed videography (HSV) to monitor the width of H₂ bubble plumes produced downstream of parallel plate electrodes as a function of current density, electrode separation distance, and the Reynolds number (Re) associated with flowing 0.5 M H₂SO₄ electrolyte. These measurements reveal that the HSV-derived dimensionless bubble plume width serves as an excellent descriptor for correlating the aforementioned operating conditions with H₂ crossover rates. These empirical relationships, combined with electrochemical engineering design principles, provide a valuable framework for exploring performance limits and guiding the design of optimized membraneless electrolyzers. This framework shows that the efficiencies and current densities of optimized parallel plate membraneless electrolyzers constrained to H₂ crossover rates of 1% can exceed those of conventional alkaline electrolyzers but are lower than the efficiencies and current densities achieved by zero-gap polymer electrolyte membrane (PEM) electrolyzers. Chapter 3 presents a packed bed membraneless electrolyzer (PBME) design for which liquid bicarbonate electrolyte flows sequentially through alternating porous flow-through anodes and cathodes. Within this design, hydrogen oxidation at porous anodes is used to produce protons that trigger in situ CO₂ release immediately upstream of porous cathodes, where electrochemical CO₂ reduction generates the desired product and returns the solution pH back towards its inlet value. By using the sequential flow-cell arrangement, the PBME offers the ability to mitigate large concentration overpotentials and non-uniform current distributions that naturally arise during scale-up of conventional membrane-based devices that rely on lateral flow of catholyte parallel to the surface of the electrodes. This study uses in situ colorimetric imaging to highlight the ability of PBME to rebalance pH across electrodes. In addition, results obtained with a multi-cell PBME “stack” demonstrate the scalability of this concept and reveal the ability to increase CO₂ utilization from 12.9% for a single-cell PBME up to 20.5% for a four-cell PBME operated under baseline conditions. Modeling results indicate that current utilization values >80% are theoretically possible for optimized multi-cell PBMEs operated at ambient pressure. Chapter 4 demonstrates a stacked PBME design and an elevated pressure system. Hydrogen oxidation at the anode and hydrogen evolution at the cathode are conducted in this device at pressures up to 5 atm. The pressure of the system can be held at a constant value by the use of a back pressure regulator, and product gases can be collected with a gas sampling bag that’s directly connected to the back pressure regulator. The stereolithography 3D printing technology is used to fabricate components of the PBME from clear resin, which is suitable for the elevated pressure operation. Post-processing of the components makes surfaces transparent for imaging bubble dynamics in the device. Within this system, HOR current density of 120 mA cm-2 can be achieved at different pressures. Finally, Chapter 5 provides concluding remarks and discusses future opportunities and challenges for membraneless electrolyzers for water electrolysis and electrochemical CO₂ conversion.

The Mississippi Alluvial Valley (MAV) has undergone losses of bottomland hardwood forests due to agricultural conversion. Hardwood establishment on marginal croplands has been proposed to mitigate effects of deforestation and related loss of carbon-capture potential. However, a possible concern with reforestation is low seedling survival from mammalian herbivory. I surveyed two afforested fields in the MAV of northwest Mississippi to assess damage and mortality from four herbivores on nine species of hardwood seedlings (n = 868). Percentage survival of seedlings was 35%. Mortality of seedlings caused by herbivores was: hispid cotton rat (Sigmodon hispidus; 6.45%), rabbit ((Sylvilagus spp.; 1.95%), pine vole (Microtus pinetorum; 2.99%), and white-tailed deer (Odocoileus virginiana; 0.69%). Of surviving seedlings (n = 316), 10.82% were damaged by cotton rats, pine vole (2.99%), rabbit (8.06%), and deer (7.02%). Green ash (Fraxinus pennsylvanica), water oak (Quercus nigra), and Nuttall oak (Quercus nuttallii) had greatest survival.

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