Greenhouse Gas Emission Inventories Research Articles

Greenhouse gases emission from soils under major crops in Northwest India

Quantification of greenhouse gases (GHGs) emissions from agriculture is necessary to prepare the national inventories and to develop the mitigation strategies. Field experiments were conducted during 2008–2010 at the experimental farm of the Indian Agricultural Research Institute, New Delhi, India to quantify nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2) emissions from soils under cereals, pulses, millets, and oilseed crops. Total cumulative N2O emissions were significantly different (P>0.05) among the crop types. Emission of N2O as percentage of applied N was the highest in pulses (0.67%) followed by oilseeds (0.55%), millets (0.43%) and cereals (0.40%). The emission increased with increasing rate of N application (r2=0.74, P<0.05). The cumulative flux of CH4 from the rice crop was 28.64±4.40kgha−1, while the mean seasonal integrated flux of CO2 from soils ranged from 3058±236 to 3616±157kgCO2ha−1 under different crops. The global warming potential (GWP) of crops varied between 3053kgCO2eq.ha−1 (pigeon pea) and 3968kgCO2eq.ha−1 (wheat). The carbon equivalent emission (CEE) was least in pigeon pea (833kgCha−1) and largest in wheat (1042kgCha−1). The GWP per unit of economic yield was the highest in pulses and the lowest in cereal crops. The uncertainties in emission values varied from 4.6 to 22.0%. These emission values will be useful in updating the GHGs emission inventory of Indian agriculture.

Uncertainties in City Greenhouse Gas Inventories

Cities worldwide are on the route to implement the Global Protocol for Community-Scale Greenhouse Gas Emission Inventories (GPC). However, many of these cities are already reporting or have reported their GHG emission in non GPC conform tools. We use a city heat cadaster integrated into an OGC CityGML 3D model to compare mapping schemes from the cCR by ICLEI, ECOSPEED Region and GPC. We demonstrate potential information losses and inconsistencies leading to potential uncertainties. In conclusion consistent data structures like CityGML are essential in order to use city GHG data for Monitoring, Reporting and Verification (MRV).

Mexico's contribution to global radiative forcing by major anthropogenic greenhouse gases: CO2, CH4 and N2O

The IPCC (2013) gives simplified formulas to compute the radiative forcing (RF) resulting from the increase in anthropogenic greenhouse gases (AGG): carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and halocarbons. These formulas allow to compute the global RF of these gases relative to their pre-industrial (1750 A.D.) concentrations, and are used in this work to estimate the contribution of Mexico to the global RF by its emissions of CO2 (the most significant of the AGG), CH4 and N2O during the period 1990-2011, which are reported in the Inventario Nacional de Emisiones de Gases de Efecto Invernadero (National Inventory of Greenhouse Gases Emissions, INEGEI) (INECC, 2013). In comparison, by 2010 the national emissions per capita of Argentina, Spain and the United States were 108.8, 110.8 and 327.0% of the Mexican emissions, respectively, in units of equivalent CO2. Mexico's CO2 emissions retained in the atmosphere during 1990-2011 amount to 4 624 457 Gg; they are higher than those of Spain and Argentina together, and represent 1/12 of the USA contribution. Mexico's contribution is 1.47% of the global RF due to CO2, with a similar proportion than Spain and Argentina, but a smaller fraction compared to that of the USA (1/15). The main uncertainties of our computations for Mexico's contribution to the global RF come from national emissions; the INEGEI indicates that the emissions considered for the calculation of uncertainties represent 89% of the total emissions of the inventory, resulting in a total uncertainty of ±5.6%. We are aware that, as a consequence, the concentration increase of CH4 and N2O due to Mexico's emissions retained in the atmosphere during 1990-2011 is lower than their respective uncertainties for global concentrations: 1.72 vs. 2 ppbv and 0.13 vs. 1 ppbv.

Modelling GHG emissions in the mineral products industry in Poland: An uncertainty analysis

An improvement of methods for the inventory of greenhouse gas (GHG) emissions is necessary to ensure effective control of commitments to emission reduction. In this article the mathematical models of greenhouse gas emission processes from cement, lime, and glass production at the level of individual plants in Poland have been analysed. Results of the spatial analysis are presented in the form of a geo-spatial database of emissions, and visualised as layers on digital maps. Uncertainty of the inventory results is calculated using the Monte Carlo approach.

Implication of Land-Use and Land-Cover Change into Carbon Dioxide Emissions in Karang Gading and Langkat Timur Wildlife Reserve, North Sumatra, Indonesia

Mangrove forest in the context of climate change is important sector to be included in the inventory of greenhouse gas (GHG) emissions. The present study describes land-use and land-cover change during 2006–2012 of a mangrove forest conservation area, Karang Gading and Langkat Timur Laut Wildlife Reserve (KGLTLWR) in North Sumatra, Indonesia and their implications to carbon dioxide emissions. A land-use change matrix showed that the decrease of mangrove forest due to increases of other land-use such as aquaculture (50.00%) and oil palm plantation (28.83%). Furthermore, the net cumulative of carbon emissions in KGLTLWR for 2006 was 3804.70 t CO2-eq year-1, whereas predicting future emissions in 2030 was 11,318.74 t CO2-eq year-1 or an increase of 33.61% for 12 years. Source of historical emissions mainly from changes of secondary mangrove forests into aquaculture and oil palm plantation were 3223.9 t CO2-eq year-1 (84.73%) and 959.00 t CO2-eq year-1 (25.21%), respectively, indicating that the KGLTLWR is still a GHG emitter. Mitigation scenario with no conversion in secondary mangrove forest reduced 16.21% and 25.8% carbon emissions in 2024 and 2030, respectively. This study suggested that aquaculture and oil palm plantation are drivers of deforestation as well as the largest of GHG emission source in this area.

Produto Sustentável: Equipamento de Proteção Individual Fabricado com Plástico Verde

This study analyzed the case of manufacturing of Personal Protective Equipment (PPE) using as raw material biopolymers produced from ethanol from sugar cane, known as green polypropylene, produced since 2008 by BRASKEM. This article studied the PPE for the employee’s head protection, named helmet by NR 6, which is used in situations of exposure to weather and work scenarios in places where there is risk of impact from falling or projecting objects, burns, electric shock, and solar radiation. The MSA, green helmet manufacturer, made an inventory of greenhouse gas emissions into the atmosphere by comparing the two manufacturing processes of the helmet shell, covering the January 1 to December 31, 2011 period. It concluded that the sustainable helmet (green polyethylene and pigments) robs 231g of CO 2 from the atmosphere per produced unit, while the helmet’s production with traditional raw materials (polyethylene and petrochemical pigments) found that, for each unit produced, 1029g of CO 2 are emitted into the atmosphere. The study showed that substitution of raw materials has led to reduction in the impact generated in the helmets’ production.

상향식 공정분석을 통한 국내 유리산업의 온실가스 인벤토리 산정

The glass production is classified into an energy intensive industry. This study develops a systematic procedure to derive Greenhouse Gas (GHG) emission inventory for the Korean glass industry. Based on the bottom-up approach in which the energy intensity in each production process is characterized, the EBs (energy balances) of glass production processes are derived. And the GHG emission is calculated for each of four types of glasses-flat glass, container glass, fiber glass, and LCD glass.

An approach for verifying biogenic greenhouse gas emissions inventories with atmospheric CO2 concentration data

Verifying national greenhouse gas (GHG) emissions inventories is a critical step to ensure that reported emissions data to the United Nations Framework Convention on Climate Change (UNFCCC) are accurate and representative of a country’s contribution to GHG concentrations in the atmosphere. Furthermore, verifying biogenic fluxes provides a check on estimated emissions associated with managing lands for carbon sequestration and other activities, which often have large uncertainties. We report here on the challenges and results associated with a case study using atmospheric measurements of CO2 concentrations and inverse modeling to verify nationally-reported biogenic CO2 emissions. The biogenic CO2 emissions inventory was compiled for the Mid-Continent region of United States based on methods and data used by the US government for reporting to the UNFCCC, along with additional sources and sinks to produce a full carbon balance. The biogenic emissions inventory produced an estimated flux of −408 ± 136 Tg CO2 for the entire study region, which was not statistically different from the biogenic flux of −478 ± 146 Tg CO2 that was estimated using the atmospheric CO2 concentration data. At sub-regional scales, the spatial density of atmospheric observations did not appear sufficient to verify emissions in general. However, a difference between the inventory and inversion results was found in one isolated area of West-central Wisconsin. This part of the region is dominated by forestlands, suggesting that further investigation may be warranted into the forest C stock or harvested wood product data from this portion of the study area. The results suggest that observations of atmospheric CO2 concentration data and inverse modeling could be used to verify biogenic emissions, and provide more confidence in biogenic GHG emissions reporting to the UNFCCC.

Estimating nitrous oxide emission flux from arable lands in China using improved background emission and fertilizer-induced emission factors

A nitrous oxide (N2O) emission database was compiled for arable land (284 measurements from 62 studies) to establish predictive models for building a greenhouse gas emission inventory in China. Arable lands were grouped into dry land and rice paddy based on the IPCC 2006 guidelines. The results of the meta analysis show that the annual mean N2O fluxes from dry land and rice paddy were 4.69±4.62 (SD) and 5.89±3.23kg N2O–N ha–1 yr–1. Fertilizer–induced N2O emission factors were 0.68±0.41% for dry land, and 0.49±0.43% for rice paddy. The relationship between N2O flux from arable lands and various environmental variables were analyzed, and the magnitude of N2O emissions from zero mineral N addition control plots (background emission) was determined based on precipitation. Based on the above background emissions and correlation coefficients, two new predictive models were established to estimate N2O emissions from arable lands in China. Comparison showed that the precipitation–rectified background emissions could largely improve the model predictions, and the two new models had better performance than the 1996 IPCC guideline method. Therefore, it is strongly recommended that the important local environmental variables be included in the estimates when compiling a national N2O emission inventory.

Mobile measurements of climate forcing agents: Application to methane emissions from landfill and natural gas compression

Measuring greenhouse gas (GHG) source emissions provides data for validation of GHG inventories, which provide the foundation for climate change mitigation. Two Toyota RAV4 electric vehicles were outfitted with high-precision instrumentation to determine spatial and temporal resolution of GHGs (e.g., nitrous oxide, methane [CH4], and carbon dioxide [CO2]), and other gaseous species and particulate metrics found near emission sources. Mobile measurement platform (MMP) analytical performance was determined over relevant measurement time scales. Pollutant residence times through the sampling configuration were measured, ranging from 3 to 11 sec, enabling proper time alignment for spatial measurement of each respective analyte. Linear response range for GHG analytes was assessed across expected mixing ratio ranges, showing minimal regression and standard error differences between 5, 10, 30, and 60 sec sampling intervals and negligible differences between the two MMPs. GHG instrument drift shows deviation of less than 0.8% over a 24-hr measurement period. These MMPs were utilized in tracer-dilution experiments at a California landfill and natural gas compressor station (NGCS) to quantify CH4 emissions. Replicate landfill measurements during October 2009 yielded annual CH4 emissions estimates of 0.10 ± 0.01, 0.11 ± 0.01, and 0.12 ± 0.02 million tonnes of CO2 equivalent (MTCO2E). These values compare favorably to California GHG Emissions Inventory figures for 2007, 2008, and 2009 of 0.123, 0.125, and 0.126 MTCO2E/yr, respectively, for this facility. Measurements to quantify NGCS boosting facility-wide emissions, during June 2010 yielded an equivalent of 5400 ± 100 TCO2E/yr under steady-state operation. However, measurements during condensate transfer without operational vapor recovery yield an instantaneous emission rate of 2–4 times greater, but was estimated to only add 12 TCO2E/yr overall. This work displays the utility for mobile GHG measurements to validate existing measurement and modeling approaches, so emission inventory values can be confirmed and associated uncertainties reduced.Implications: Measuring greenhouse gas (GHG) source emissions provides data and validation for GHG inventories, the foundation for climate change mitigation. Mobile measurement platforms with robust analytical instrumentation completed tracer-dilution experiments in California at a landfill and natural gas compressor station (NGCS) to quantify CH4 emissions. Data collected for landfill CH4 agree with the current California emissions inventory, while NGCS data show the possible variability from this type of facility. This work displays the utility of mobile GHG measurements to validate existing measurement and modeling approaches, such that emission inventory values can be confirmed, associated uncertainties reduced, and mitigation efforts quantified.

Improving the accuracy of vehicle emissions profiles for urban transportation greenhouse gas and air pollution inventories.

Metropolitan greenhouse gas and air emissions inventories can better account for the variability in vehicle movement, fleet composition, and infrastructure that exists within and between regions, to develop more accurate information for environmental goals. With emerging access to high quality data, new methods are needed for informing transportation emissions assessment practitioners of the relevant vehicle and infrastructure characteristics that should be prioritized in modeling to improve the accuracy of inventories. The sensitivity of light and heavy-duty vehicle greenhouse gas (GHG) and conventional air pollutant (CAP) emissions to speed, weight, age, and roadway gradient are examined with second-by-second velocity profiles on freeway and arterial roads under free-flow and congestion scenarios. By creating upper and lower bounds for each factor, the potential variability which could exist in transportation emissions assessments is estimated. When comparing the effects of changes in these characteristics across U.S. cities against average characteristics of the U.S. fleet and infrastructure, significant variability in emissions is found to exist. GHGs from light-duty vehicles could vary by -2%-11% and CAP by -47%-228% when compared to the baseline. For heavy-duty vehicles, the variability is -21%-55% and -32%-174%, respectively. The results show that cities should more aggressively pursue the integration of emerging big data into regional transportation emissions modeling, and the integration of these data is likely to impact GHG and CAP inventories and how aggressively policies should be implemented to meet reductions. A web-tool is developed to aide cities in improving emissions uncertainty.

Direct measurements of methane emissions from abandoned oil and gas wells in Pennsylvania.

Abandoned oil and gas wells provide a potential pathway for subsurface migration and emissions of methane and other fluids to the atmosphere. Little is known about methane fluxes from the millions of abandoned wells that exist in the United States. Here, we report direct measurements of methane fluxes from abandoned oil and gas wells in Pennsylvania, using static flux chambers. A total of 42 and 52 direct measurements were made at wells and at locations near the wells ("controls") in forested, wetland, grassland, and river areas in July, August, October 2013 and January 2014, respectively. The mean methane flow rates at these well locations were 0.27 kg/d/well, and the mean methane flow rate at the control locations was 4.5 × 10(-6) kg/d/location. Three out of the 19 measured wells were high emitters that had methane flow rates that were three orders of magnitude larger than the median flow rate of 1.3 × 10(-3) kg/d/well. Assuming the mean flow rate found here is representative of all abandoned wells in Pennsylvania, we scaled the methane emissions to be 4-7% of estimated total anthropogenic methane emissions in Pennsylvania. The presence of ethane, propane, and n-butane, along with the methane isotopic composition, indicate that the emitted methane is predominantly of thermogenic origin. These measurements show that methane emissions from abandoned oil and gas wells can be significant. The research required to quantify these emissions nationally should be undertaken so they can be accurately described and included in greenhouse gas emissions inventories.

High resolution inventory of GHG emissions of the road transport sector in Argentina

Air quality models require the use of extensive background information, such as land use and topography maps, meteorological data and emission inventories of pollutant sources. This challenge increases when considering the vehicular sources. The available international databases have uneven resolution for all countries including some areas with low spatial resolution associated with large districts (several hundred km). A simple procedure is proposed in order to develop an inventory of emissions with high resolution (9 km) for the transport sector based on a geographic information system using readily available information applied to Argentina. The basic variable used is the vehicle activity (vehicle – km transported) estimated from fuel consumption and fuel efficiency. This information is distributed to a spatial grid according to a road hierarchy and segment length assigned to each street within the cell. Information on fuel is obtained from district consumption, but weighted using the DMSP-OLS satellite “Earth at night” image. The uncertainty of vehicle estimation and emission calculations was tested using sensitivity Montecarlo analysis. The resulting inventory is calibrated using annual average daily traffic counts in around 850 measuring points all over the country leading to an uncertainty of 20%. Uncertainties in the emissions calculation at pixel level can be estimated to be less than 12%. Comparison with international databases showed a better spatial distribution of greenhouse gases (GHG) emissions in the transport sector, but similar total national values.

Nitrous oxide and methane emissions and nitrous oxide isotopic composition from waste incineration in Switzerland

Solid waste incineration accounts for a growing proportion of waste disposal in both developed and developing countries, therefore it is important to constrain emissions of greenhouse gases from these facilities. At five Swiss waste incineration facilities with grate firing, emission factors for N2O and CH4 were determined based on measurements of representative flue gas samples, which were collected in Tedlar bags over a one year period (September 2010–August 2011) and analysed with FTIR spectroscopy. All five plants burn a mixture of household and industrial waste, and two of the plants employ NOx removal through selective non-catalytic reduction (SNCR) while three plants use selective catalytic reduction (SCR) for NOx removal.N2O emissions from incineration plants with NOx removal through selective catalytic reduction were 4.3±4.0g N2O tonne−1 waste (wet) (hereafter abbreviated as t−1) (0.4±0.4g N2O GJ−1), ten times lower than from plants with selective non-catalytic reduction (51.5±10.6g N2O t−1; 4.5±0.9g N2O GJ−1). These emission factors, which are much lower than the value of 120g N2O t−1 (10.4g N2O GJ−1) used in the 2013 Swiss national greenhouse gas emission inventory, have been implemented in the most recent Swiss emission inventory. In addition, the isotopic composition of N2O emitted from the two plants with SNCR, which had considerable N2O emissions, was measured using quantum cascade laser spectroscopy. The isotopic site preference of N2O – the enrichment of 14N15NO relative to 15N14NO – was found to be 17.6±0.8‰, with no significant difference between the two plants. Comparison to previous studies suggests SP of 17–19‰ may be characteristic for N2O produced from SNCR. Methane emissions were found to be insignificant, with a maximum emission factor of 2.5±5.6g CH4 t−1 (0.2±0.5g CH4 GJ−1), which is expected due to high incinerator temperatures and efficient combustion.

Methane Emissions From Natural-Gas Systems: A Comparative Assessment for Select Industry Segments

Summary The recent rapid expansion of natural-gas developments and usage worldwide are bringing into focus the need to improve understanding and characterization of greenhouse-gas (GHG) emission sources, including methane (CH4), associated with petroleum and natural-gas systems. New production technologies and practices, including those involving hydraulic fracturing, necessitate a thorough review of existing quantification methods for fugitive CH4 emissions from venting, flaring, and equipment leaks associated with petroleum and natural-gas systems and operations. In the past few years, widely divergent estimates have emerged regarding CH4 emissions from the US natural-gas-industry sector. Some discrepancies noted by industry surveys have led to a thorough review of newly available information and are leading to the improvement of estimation methods and emission factors associated with activities that comprise natural-gas systems. This has manifested itself in the engineering estimations that are used for compiling the national GHG Emissions Inventory and in the methods used by companies for reporting under the mandatory national GHG Reporting Program. Both the inventory and the reporting program are programs of the US Environmental Protection Agency (EPA). This paper presents results of a comparative analysis of GHG-emissions data, including CH4, for key industry segments such as on-shore natural-gas production and natural-gas processing and their contribution to the Petroleum and Natural Gas Systems sector. The data analyzed will contrast the “top-down” assessments used in developing the GHG Emissions Inventory with the “bottom-up” estimation of actual emissions as reported under Subpart W of the GHG Reporting Program. The analysis will provide a comparison of the estimation methods and evaluation of the contribution of key sources with overall CH4 emissions. The ultimate goal of this effort is to incorporate the new information that is becoming available into consistent methods that can be used both for national GHG inventory development and for corporate reporting. Harmonization of these methods is expected to contribute to informing the public debate on natural-gas use and its role in mitigating overall GHG emissions.

Forest carbon accounting methods and the consequences of forest bioenergy for national greenhouse gas emissions inventories

While bioenergy plays a key role in strategies for increasing renewable energy deployment, studies assessing greenhouse gas (GHG) emissions from forest bioenergy systems have identified a potential trade-off of the system with forest carbon stocks. Of particular importance to national GHG inventories is how trade-offs between forest carbon stocks and bioenergy production are accounted for within the Agriculture, Forestry and Other Land Use (AFOLU) sector under current and future international climate change mitigation agreements. Through a case study of electricity produced using wood pellets from harvested forest stands in Ontario, Canada, this study assesses the implications of forest carbon accounting approaches on net emissions attributable to pellets produced for domestic use or export. Particular emphasis is placed on the Forest Management Reference Level (FMRL) method, as it will be employed by most Annex I nations in the next Kyoto Protocol Commitment Period. While bioenergy production is found to reduce forest carbon sequestration, under the FMRL approach this trade-off may not be accounted for and thus not incur an accountable AFOLU-related emission, provided that total forest harvest remains at or below that defined under the FMRL baseline. In contrast, accounting for forest carbon trade-offs associated with harvest for bioenergy results in an increase in net GHG emissions (AFOLU and life cycle emissions) lasting 37 or 90 years (if displacing coal or natural gas combined cycle generation, respectively). AFOLU emissions calculated using the Gross-Net approach are dominated by legacy effects of past management and natural disturbance, indicating near-term net forest carbon increase but longer-term reduction in forest carbon stocks. Export of wood pellets to EU markets does not greatly affect the total life cycle GHG emissions of wood pellets. However, pellet exporting countries risk creating a considerable GHG emissions burden, as they are responsible for AFOLU and bioenergy production emissions but do not receive credit for pellets displacing fossil fuel-related GHG emissions. Countries producing bioenergy from forest biomass, whether for domestic use or for export, should carefully consider potential implications of alternate forest carbon accounting methods to ensure that potential bioenergy pathways can contribute to GHG emissions reduction targets.

Estimation of CO2 emissions in the life cycle of roads through the disruption and restoration of environmental systems

Effects of disruption and restoration of terrestrial ecosystems have been largely overlooked when conducting assessments of greenhouse gas (GHG) emissions in road construction projects. This is an important oversight given the intensive land-conversion generated by linear infrastructure development, as well as the relevance given to carbon pool variations associated with land use and land-use changes by national inventories of GHG emissions and global reports. This paper describes the implementation of a methodology to classify those environmental systems in land-uses categories, to determine their carbon stocks (vegetation and soil), and to quantify CO2 emissions and removal related to their management at the different stages of road construction projects. The procedure is illustrated through its application in the impact assessment of road projects in the territory of Spain. This methodology integrates currently available information on carbon stocks and considers the accounting criteria adopted in national GHG emissions inventories. It is intended to constitute part of an integral assessment tool for GHG emissions in linear infrastructure projects. Four case studies are presented in which emissions from the disruption of environmental systems range from 0.55 to 3.66kTCO2km−1. This represents 5 to 13% of the total emissions in the construction stage, and 3.5 to 7% of the net CO2 balance, i.e., once the initial carbon sequestration by restoration planting has been discounted. Results also indicate that under ideal conditions the long-term effect of restoration may even fully offset this impact, though really such conditions are far from being the case in the usual development of plantations. This study confirms the advisability of systematically incorporating the analysis of land use and land-use changes into the assessment of GHG emissions of road projects for consideration in decision-making from the design stage to the maintenance stage in such projects.

저탄소 그린캠퍼스 조성을 위한 온실가스 인벤토리 구축 및 감축잠재량 분석 - 대구대학교를 중심으로

저탄소 그린캠퍼스 조성을 위한 온실가스 인벤토리 구축 및 감축잠재량 분석 - 대구대학교를 중심으로

Characteristics of direct CO2 emissions in four full-scale wastewater treatment plants

Direct CO2 emissions from wastewater treatment plants (WWTPs), which are commonly excluded from the greenhouse gas emission inventory as proposed by the International Panel on Climate Change, should be partly taken into consideration, because some of the fossil organic carbons (i.e. detergents, cosmetics, and pharmaceuticals) are also biodegradable, leading to the emission of CO2 during wastewater treatment. For the purpose of understanding the characteristics of direct CO2 emissions during biological nutrient removal from urban WWTPs, we investigated four different processes. Full-scale tests were carried out continuously during a two-year period, consisting of the anoxic/anaerobic/oxic (A2O) process, the anoxic/oxic (AO) process, the oxidation ditch, and the sequencing batch reactor (SBR) processes. Our experimental results show large differences in CO2 fluxes in the various treatment tanks (or periods), e.g. the aerated units/periods in four different WWTPs all contributed more than 96.0% of the entire direct CO2 emission caused by aerobic respiration and aeration stripping. On the other hand, CO2 emissions from non-aerated areas were quite low giving rise to small amounts of CO2 emissions during anaerobic metabolism. The direct emission of CO2 when treating per m3 wastewater (g CO2/m3 wastewater) corresponded with the following descending order among the four processes: SBR (347.34) > oxidation ditch (343.78) > A2O (175.68) > AO (173.37). However, this order changed into SBR (0.97) > oxidation ditch (0.76) > AO (0.68) > A2O (0.58) when treating per kilogram COD (kg CO2/kg COD).

Carbon stocks and changes in tropical secondary forests of southern Mexico

The role of tropical secondary forests in carbon accumulation has been widely acknowledged, but the rates of changes in carbon stocks still remain uncertain. The aim of this study was to analyze the changes in carbon pool sizes and accumulation rates associated with growth, recruitment and mortality of trees at different ages of forest succession in semi-evergreen tropical forests and relate these to the age of the secondary vegetation and prior land use intensity. The study was carried out in a chronosequence of secondary and mature forests around Calakmul Biosphere Reserve in southern Yucatan Peninsula, Mexico. Permanent monitoring plots were established and measured in 2011 and 2012 to account all carbon stocks and changes due to tree increments, establishment of new trees and tree mortality in different age classes of secondary forests.We found that carbon stocks in living tree biomass increased rapidly in the early stages and decreased in the older secondary forests. The annual carbon dynamics of trees were higher in younger secondary forest compared to older forests due to higher tree growth and recruitment. Growth functions predict that the secondary forests recover live aboveground biomass carbon stocks to pre-disturbance levels (99.56MgCha−1) at the age of about 125 years or more, while the basal area (33.2m2ha−1) regains this level at the age of about 85 years. The longer carbon recovery time can be explained by the fact that mature forests are dominated by hardwood species whereas secondary forests are composed of softwood species and that species composition turnover during succession is relatively slow. Secondary forests of 35 years look similar to mature forests in terms of basal area, but this is located in large number of small and medium sized trees, whereas in mature forests, most of the basal area is in trees of >20cm diameter. In addition, the intensity of slash and burn agriculture can negatively alter the velocity of carbon accumulation. These findings have important implications for national forest carbon monitoring systems, greenhouse gas emission inventories and regional level REDD+ strategies.