David A.N. Ussiri

Carbon Sequestration in Reclaimed Minesoils

Minesoils are drastically influenced by anthropogenic activities. They are characterized by low soil organic matter (SOM) content, low fertility, and poor physicochemical and biological properties, limiting their quality, capability, and functions. Reclamation of these soils has potential for resequestering some of the C lost and mitigating CO2 emissions. Soil organic carbon (SOC) sequestration rates in minesoils are high in the first 20 to 30 years after reclamation in the top 15 cm soil depth. In general, higher rates of SOC sequestration are observed for minesoils under pasture and grassland management than under forest land use. Observed rates of SOC sequestration are 0.3 to 1.85 Mg C ha− 1 yr− 1 for pastures and rangelands, and 0.2 to 1.64 Mg C ha− 1 yr− 1 for forest land use. Proper reclamation and postreclamation management may enhance SOC sequestration and add to the economic value of the mined sites. Management practices that may enhance SOC sequestration include increasing vegetative cover by deep-rooted perennial vegetation and afforestation, improving soil fertility, and alleviation of physical, chemical and biological limitations by fertilizers and soil amendments such as biosolids, manure, coal combustion by-products, and mulches. Soil and water conservation are important to SOC sequestration. The potential of SOC sequestration in minesoils of the US is estimated to be 1.28 Tg C yr−1, compared to the emissions from coal combustion of 506 Tg C yr− 1.

Soil Organic Carbon and Nitrogen Fractions under Different Land Uses and Tillage Practices

ABSTRACT Many questions have surfaced regarding long-term impacts of land-use and cultivation system on soil carbon (C) sequestration. The experiment was conducted at Ohio Agricultural Research and Development Center. Only minor variations of soil organic carbon (SOC) and nitrogen (N) fractions with depth under plow tillage (PT). The SOC, total nitrogen (TN), microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) concentrations were higher under grassland and forestland in the top 0–15 cm depth than arable soils. No-tillage (NT) also increased SOC and N fractions concentrations in the surface soils than PT. Compared to arable, grass and forest could significantly improve proportions of MBC and MBN, and reduce proportions of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON). NT and forest also increased the ratio of SOC/TN, MBC/MBN, and DOC/DON. Overall, grass and forest provided more labile C and improved C sequestration than arable. So did NT under arable land-use.

Miscanthus agronomy and bioenergy feedstock potential on minesoils

The US government has mandated production of 79 million liters of biofuel from lignocellulose biomass and advanced fuels by 2022. To meet this requirement, the Department of Energy is encouraging research to develop herbaceous lignocellulose-based bioethanol for use as transport fuel. Miscanthus × giganteus was introduced in the US during 1930s, and is being widely studied for its potential to produce large biomass yield with minimum input in different soils. Miscanthus × giganteus is highly productive, sterile rhizomatous C4 perennial grass adapted to a wide range of climatic and soil conditions. Since the early 1980s, this crop has been studied under various climate and soil conditions in Europe and used to produce heat and electricity by combustion. This paper summarizes its agronomy and the characteristics which make it a potential dedicated bioenergy crop suitable for the reclaimed minesoils of the Appalachian region: Ohio, West Virginia, Virginia, Pennsylvania, Maryland, Kentucky, and Tennessee. The area which has been mined in the Appalachian region is estimated at 1.1 million hectares and only about 5% has been fully reclaimed. Using minesoils for miscanthus bioenergy feedstock production minimizes competition for arable land and sequesters soil organic carbon in these degraded lands. Reclaimed minesoils in the Appalachian region has potential to produce 9.22 × 106 Mg yr−1 dry biomass of Miscanthus × giganteus feedstock.

Greenhouse Gas Mitigation under Agriculture and Livestock Landuse

Ensuring food security for the growing global population and changing climate are the principal challenges of the modern agriculture. The global population is projected to reach 9.7 billion by 2050. With rising incomes and the increasing proportion of global population living in urban areas, the composition of food demand is changing in fundamental ways. Higher income urban population have more diverse diets that feature a variety of high-value food sources such as livestock that are more resource-intensive to produce and process. This adds to the challenge of preserving the resilience of both natural resources and agricultural ecosystems. Agriculture occupies about 38% of the ice-free Earth’s surface, of which, the cropland is about 12% and grazing land is about 26%. Projections indicate that global food production must increase by 70%, while in many African countries where the challenge is most acute, food production must increase by more than 100% by 2050 to meet the global food demand. The average annual share of agriculture, forest and land use to the total anthropogenic greenhouse gases (GHGs) has been declining over time from 28.7 ± 1.5% in the 1990s and 23.6 ± 2.1% in 2000s, and the annual value of 21.2 ± 1.5% in 2010. In 2010, agriculture contributed 11.2 ± 0.4% of the total anthropogenic GHG emissions compared to 10.0 ± 1.2% of the land use sector. Moreover, agriculture and land use changes associated with it are among the principal contributors of climate change. Agriculture also accounts for 84 and 52% of global nitrous oxide (N2O) and methane (CH4) emissions. Nonetheless, agriculture sector also is the most vulnerable to the adverse effects of global warming, such as more variable rainfall and more extreme weather generated events. Agriculture practices can potentially mitigate GHG emissions through improved cropland, animal husbandry, and grazing land management practices as well as restoration of degraded land and cultivated organic soils. Sustainable land management delivers benefits through C conservation in natural forests, grasslands, and wetlands, C sequestration in both agriculture soils and natural biomass, both of which remove C from the atmosphere and store it in biomass and soils within the terrestrial ecosystems. In addition, best management practices of croplands, grazing lands and also livestock and their byproducts such as manure could reduce the emissions of GHGs from agriculture and contribute to climate change mitigation.

Carbon Capture and Storage in Geologic Formations

Carbon dioxide (CO2) emissions, the most important anthropogenic greenhouse gas (GHG), can be reduced by CO2 capture and storage (CCS). This strategy is applicable to many large stationary sources including power generation plants, oil and gas refinery, cement production and other industrial sectors generating large point source of CO2. While the technology for CCS is currently available, significant improvements are needed to enhance confidence in storage security. In 1996, the first CCS project established for the purpose of mitigation of CO2 emission began injecting CO2 into deep geological formation in offshore aquifer in the North Sea, Norway. Since that time, science has advanced in areas such as geophysics, chemical engineering, monitoring and verification, and other areas, while also governments have funded demonstration projects at various sizes ranging from small-scale proof of concept to industrial-scale demonstration projects. Five industrial-scale CCS projects are currently operational globally with more than 0.035 Pg of CO2 captured and stored since 1996. Observations from these industrial scale projects and commercial CO2 enhanced oil recovery (CO2-EOR), engineered natural analogues as well as theoretical consideration, models and laboratory studies have suggested that appropriately selected and well managed CCS sites are likely to retain almost all of injected CO2 for long time and provide the benefits for the intended purpose of CCS. However, CCS is still struggling to gain foothold as one of the main options for mitigating climate change due to high costs, advances in other options including renewable energy, as well as discovery of shale natural gas and the associated hydrological fracturing extraction techniques, absence of international action by governments and private sectors on climate change, economic crisis-induced low carbon (C) prices, and public skepticism. The estimated costs for CCS varies widely depending on the application—such as gas clean-up versus electricity generation, type of fuel, capture technology , and assumptions about the baseline technology. Generally, for current technology, CCS would increase cost of generating electricity by 50–100%, and parasitic energy requirement of 15–30%. In this case, capital costs and energy requirements are the major cost drivers. In addition, significant scale-up compared to existing CCS activities will be needed to achieve intended large reductions of CO2 emissions. For example, a 5- to 10-fold scale-up in the size of individual projects is needed to capture and store emissions from a typical coal-fired power plant of 500–1000 MW, while a thousand-fold scale-up in size of current CCS enterprise would be needed to reduce emissions by 1 Pg C yr−1. The estimated global oil and gas reservoirs are 1000 Pg CO2, saline aquifers global potential capacity ranges from 4000 to 23,000 Pg CO2. However, there is considerable debate about how much storage capacity actually exists and is available for CCS, particularly in saline aquifers. Research, improved geological assessments and commercial scale demonstration projects will be needed to verify the estimated capacity and improve confidence in storage capacity estimates.

Introduction to Global Carbon Cycling: An Overview of the Global Carbon Cycle

Carbon (C) is the essential attribute of life. Therefore, its cycling gives the overall index of health of the biosphere. Global C cycling involves the exchange of C between its four main reservoirs—the atmosphere, terrestrial biosphere, oceans and sediments. Understanding the biogeochemical processes regulating the movement of C from one reservoir to another is central to control carbon dioxide (CO2) and methane (CH4) emissions and mitigating climate change. This introductory chapter presents an overview of the global C cycle. The atmospheric carbon burden—both CO2 and CH4 concentrations, has increased significantly since the beginning of the Industrial Revolution in response to anthropogenic perturbations of the global C cycle. The major sources of the increase in atmospheric C content are the utilization of fossil fuels for energy, cement production, land use conversion and deforestation. Fossil fuel and cement production released 410 ± 20 Pg C between 1750 and 2015. Similarly, land use change released 190 ± 65 Pg C over the same period. The atmospheric C burden increased by 260 ± 5 Pg between 1750 and 2015. The consequences of changes in global C cycling extend beyond the global warming associated changes in radiation balance caused by increased concentration of trace gases. It causes changes in atmospheric photochemistry, disturbances in terrestrial ecosystems as well as marine chemistry and ecosystems. In the following chapters these effects will be discussed in much more details.

Variability and Change in Climate

Understanding of the current and future climate change requires understanding of mechanisms which controlled climate change both before and after the last glacier ages. Although the Sun played an important role in climate variability and climate change in paleoclimate, it is generally accepted that the Sun has not been a major driver of climate change since the Industrial Era. This chapter describes the observed climate change with particular emphasis on the Industrial Era period. The globally averaged atmospheric mole fraction of carbon dioxide (CO2) reached the abundance of 144% relative to the preindustrial concentrations in 2015, with many other climate variables setting new records in the past few years. For example, atmospheric abundance of methane (CH4) and nitrous oxide (N2O) reached 1845 ± 2 and 328 ± 0.1 ppb in 2015, respectively. Also, 5 major and 15 minor greenhouse gases (GHGs) contributed 2.94 W m−2 of the direct radiative forcing which is 36% greater than their contribution at the onset of Industrial Revolution in 1750. The record high radiative forcing has resulted in the highest annual global surface temperature over ~135 years of modern record keeping. Since oceans absorb about a quarter of anthropogenic CO2 emissions, increase in CO2 concentration during the Industrial Era has resulted in ocean acidification equivalent to approximately 30% increase in H+ concentration in ocean water. Other associated changes include increase in sea surface temperature (SST) and increased thermal energy content of the ocean which absorbs 90% of Earths’ excess heat from GHG forcing. Also ocean warming and increased stratification of the upper ocean caused by global climate change results in deoxygenation of interior oceans with implications for ocean productivity, nutrient cycling, C cycling and marine habitat. Owing to ocean warming and ice melting, the global sea level rise reached 67 mm greater than the 1993 annual mean, when satellite altimetry measurement began, with salty regions of ocean getting saltier while fresh water regions of ocean parts are getting fresher. CO2 therefore, remains the single most important anthropogenic GHG, contributing 65% to long-lived GHGs radiative forcing, and responsible for nearly 83% of the increase in radiative forcing over the decade ending in 2015.

The Global Carbon Inventory

The main reservoirs of global carbon (C) cycle are the atmosphere, the biosphere, the oceans, and the lithosphere. The atmospheric C inventory consists of almost entirely carbon dioxide (CO2) and methane (CH4) with the current (2015) atmospheric concentration of 400 ppm and 1845 ppb for CO2 and CH4, respectively. This is equivalent to atmospheric burden of nearly 849 and 3.7 Pg C for CO2 and CH4, respectively, compared to 589 and 1.49 Pg C in 1750 at the beginning of the Industrial Revolution. Most of the increase since the begining of Industrial Era is associated with the anthropogenic activities of fossil fuel combustion and land use change. The terrestrial biosphere contains C in living biomass of the terrestrial ecosystem and soils. The estimated C in living biomass range from 450 to 700 Pg, while soils contains an estimate of 1500–2400 Pg as soil organic C (SOC) and 720–930 Pg C as soil inorganic C (SIC) in the top 3 m depth. The terrestrial SOC is dominantly preserved in forest biomass and soils. The ocean C inventory amounts to 39,000 Pg, of which, only 700–900 Pg C exist in the surface water layer which is in direct contact with the atmosphere. More than 90% of C is present as bicarbonate (HCO3 −). Additional 2500 Pg C is present in marine carbonate (CO3 2−) sediments which are gradually transformed into sedimentary rock over the geological timescale. Of the dissolved CO2 inventory in the ocean, 170 ± 20 Pg is of anthropogenic, with an estimated uptake of ~3.0 ± 0.5 Pg C yr−1 in 2015. The distribution of C in the ocean is regulated by three processes: biological pump, solubility pump and thermocline circulation. The lithosphere, consisting of Earth crust and mantle is the largest reservoir of C. The C in Earth crust is estimated at 7.8 × 107 Pg, of which, 20% is in organic C (OC)—mostly as fossil fuels—coal, oil and natural gas. An estimated 420 ± 20 Pg C from the fossil C has been released to the atmosphere as CO2 since the Industrial Revolution.

The Modern Carbon Cycle

The contemporary global carbon (C) cycling involves the exchanges of C within and between the atmosphere, the oceans, and biosphere. The C may be transferred from one reservoir to another in seconds (e.g., the fixation of atmospheric carbon dioxide (CO2) by photosynthesis) or over millennia [e.g., the accumulation of fossil carbon (coal, oil, gas) through deposition and diagenesis of organic matter (OM)]. The focus of this chapter is on the exchange of CO2 occurring over the scale of months to a few centuries that are important for the cycling of C over years to decades with the focus on human influence starting from Industrial Era (1750). The cycling of C is important because it approximates the flows of energy around the Earth. The increased use of fossil fuels has led to increase in atmospheric concentration of CO2 and methane (CH4), which are the two most important greenhouse gases (GHGs). Addition of GHGs to the atmosphere enhances the greenhouse effect and is the main cause of the global warming. The rate and extent of the warming depend, in part, on changes in global C cycle. The processes responsible for adding C to, and withdrawing it from, the atmosphere are the part of the global C cycling. Some of the processes that add C to the atmosphere such as the combustion of fossil fuels and changes in land use and land management are under direct human control. Similarly human beings can control removal of CO2 through afforestation and/or reforestation as well as restoration of degraded lands . Others, such as the accumulation of carbon in the oceans or on land as a result of changes in global climate are not under direct human control except through controlling rates of greenhouse gas (GHG) emissions and therefore, climatic change. Because CO2 is more important GHG, and is expected to continue to be in the future, understanding the global C cycle is a vital part of managing the global climate. This chapter will address, first, the natural flows of C on the Earth, then the anthropogenic sources of C to the atmosphere and the sinks of carbon on land and in the oceans that have kept the atmospheric accumulation of CO2 lower than it would otherwise have been. Since 1750, the atmospheric concentration of CO2 has increased by ~44% from 278 ± 5 ppm in 1750 to 400.0 ± 0.1 ppm in 2015, corresponding to atmospheric burden of 260 ± 5 Pg C, largely as a result of fossil fuel combustion, but also from changes in land use and management. At the beginning of Industrial Revolution, the emissions of CO2 were from land use and land use change; now the emissions are largely (~90%) from fossil fuels. The decadal annual rates of fossil fuel CO2 emissions increased from 3.1 ± 0.2 Pg C yr−1 in 1960s to 9.3 ± 0.5 Pg C yr−1 for 2006–2015, while land use CO2 emission decreased from 1.5 ± 0.5 Pg C yr−1 to 1.0 ± 0.5 Pg yr−1 over the same period. The total global anthropogenic CO2 emission from 1750 to 2015 is estimated at 600 ± 70 Pg C, of which, fossil fuels and cement production is estimated at 410 ± 20 Pg C and land use change emission at 190 ± 65 Pg C. About 43% of the total anthropogenic CO2 emission or 260 ± 5 Pg C remained in the atmosphere, while ocean and terrestrial ecosystems sinks were 28 and 27%, respectively. The decadal atmospheric CO2 growth increased from 1.7 ± 0.1 Pg C yr−1 in the 1960s to 4.5 ± 0.1 Pg C yr−1 during 2006–2015, with ocean and terrestrial sinks increasing roughly in line with atmospheric increase over the last 50 years. Although there is no clear signal globally of a saturation of land sink strength, there are some indications suggesting that the ocean total CO2 uptake rate may have declined in recent decades.

The Role of Bioenergy in Mitigating Climate Change

The combustion of fossil fuels drive the steady increase in greenhouse gases (GHG) and global temperatures observed in recent decades. The realization of adverse effects of increase in GHG emissions on the environment, the desire to limit atmospheric CO2 concentration at 450 ppm or lower and limit global temperature increase to ≤2 °C, combined with increasing energy needs have made the quest for sustainable and environmentally benign sources of energy for industrial economies and consumer societies a high priority since 1980s. To limit atmospheric CO2 concentration at 450 ppm, a total CO2 emission reduction of 50–85% is required by 2050. As a result, there are a renewed interests in carbon-neutral or carbon-negative renewable energy sources. Among the renewable energy sources, biofuels are considered as an attractive fuel sources for replacing fossil fuels. Bioenergy is important for many sectors and mitigation perspectives as well as from the perspective of developmental goals such as energy security and rural development. It is argued that increasing the contribution of biofuels will reduce the GHG emission by reducing the carbon intensity of the transport sector and addressing energy security concerns. In addition to global climate change threat, interests in biofuels are enhanced by growing global energy demand and diminishing crude oil supply. However, there is concern about the existing interlink between biomass , bioenergy, land use, food supply, water use, and biodiversity. The first generation biofuels primarily produced from food crops feedstock are unsustainable due to the potential stress their production places on food, feed and fiber production. The second and third generation biofuels produced from abundant biomass and algae respectively are seen as the attractive solution to limitations of the first generation biofuels and also have higher potential for GHG emission mitigation. Yet, the practicalities of deployment of bioenergy at a large scale are mired in controversies over the potential resource conflicts that might occur, particularly over land, water and biodiversity. Additionally, a number of technical huddles must be overcome before their true potential can fully be realized and evaluated. This chapter summarizes the current knowledge of biofuels , the potential role in mitigating GHG emission, societal dilemma in large scale biofuel production, current assumptions on which global bioenergy resource estimates are predicted and future directions of biofuels research with the emphasis on assessments informed by empirical studies.