High Carbon Input Research Articles

Seasonal and diel variation in greenhouse gas emissions from an urban pond and its major drivers

AbstractSmall water systems are important hotspots of greenhouse gas (GHG) emission, but estimates are poorly constrained as data are scarce. Small ponds are often constructed in urban areas, where they receive large amounts of nutrients and therefore tend to be highly productive. Here, we investigated GHG emissions, seasonal and diel variation, and net ecosystem production (NEP) from an urban pond. In monthly 24‐h field campaigns during 11 months, diffusive water–atmosphere methane (CH4) and carbon dioxide (CO2) fluxes and CH4 ebullition and oxidation were quantified. With oxygen (O2) measurements, NEP was assessed. The pond was a net GHG source the entire year, with an emission of 3.4 kg CO2 eq m−2 yr−1. The dominant GHG emission pathway was CH4 ebullition (bubble flux, 50%), followed by diffusive emissions of CO2 (38%) and CH4 (12%). Sediment CH4 release was primarily driven by temperature and especially ebullition increased exponentially above a temperature threshold of 15°C. The pond's atmospheric CO2 exchange was not related to NEP or temperature but likely to a high allochthonous carbon (C) input via runoff and anaerobic mineralization of C. We expect urban ponds to show a large increase in GHG emission with increasing temperature, which should be considered carefully when constructing ponds in urban areas. Emissions may partly be counteracted by pond management focusing on a reduction of nutrient and organic matter input.

Effects of Soil Management on Aggregation and Organic Matter Dynamics in sub-Saharan Africa

Maintenance of soil organic matter (SOM) is important for soil quality and agricultural productivity. However, little is known about the effects of management practices of different intensities on soil aggregation and SOM dynamics in tropical arable cropping systems of sub-Saharan Africa. We investigated the influence of land use practices and management intensity on soil aggregation and SOM dynamics across 12 long-term field experiments in eastern and western Africa. Aggregate size distribution and SOM were measured in arable systems under contrasting management intensities of high carbon, low carbon and a fallow. Aggregate stability indices and SOM were generally higher in the fallow compared to the arable systems. Fallowing and high carbon inputs in arable soils, significantly improved aggregate stability and carbon (C) and nitrogen (N) stabilization in whole soil, and in aggregate fractions. In contrast, no significant improvements in soil aggregation and C and N stabilization were found when organic inputs were either applied in low quantities or not applied at all, thus resulting in low carbon in soils. Our study showed that fallowing and long-term application of organic amendments alone or in combination with mineral fertilizers were the best among the practices tested in this study, for enhanced C and N stabilization in soils with the subsequent benefits of improving soil physical and chemical properties. These results emphasize the importance of management for sustaining soil quality. It is recommended that fallowing be an integral part of sustainable soil management strategies in these regions. Keywords: Soil aggregation, soil organic matter, carbon, nitrogen, management intensity

Simultaneous measurements of dissolved CH4 and H2 in wetland soils.

Biogeochemical processes in wetland soils are complex and are driven by a microbiological community that competes for resources and affects the soil chemistry. Depending on the availability of various electron acceptors, the high carbon input to wetland soils can make them important sources of methane production and emissions. There are two significant pathways for methanogenesis: acetoclastic and hydrogenotrophic methanogenesis. The hydrogenotrophic pathway is dependent on the availability of dissolved hydrogen gas (H2), and there is significant competition for available H2. This study presents simultaneous measurements of dissolved methane and H2 over a 2-year period at three tidal marshes in the New Jersey Meadowlands. Methane reservoirs show a significant correlation with dissolved organic carbon, temperature, and methane emissions, whereas the H2 concentrations measured with dialysis samplers do not show significant relationships with these field variables. Data presented in this study show that increased dissolved H2 reservoirs in wetland soils correlate with decreased methane reservoirs, which is consistent with studies that have shown that elevated levels of H2 inhibit methane production by inhibiting propionate fermentation, resulting in less acetate production and hence decreasing the contribution of acetoclastic methanogenesis to the overall production of methane.

Cropping System Conversion led to Organic Carbon Change in China\u2019s Mollisols Regions

Land use change driven by diet, globalization, and technology advancement have greatly influenced agricultural production and environment in the mollisols region of China, with a marked impact on the depletion of soil organic matter, a signature property of mollisols. Here we report findings on soil organic carbon (SOC) change in three different cropping systems (soybean, soybean/maize, corn) in Northeast China during a 10-year time span. The results indicated that the decline rate of SOC in recent ten years (0.27 g kg−1 yr−1) has slowed down considerably compared to previous decades (1.12 g kg−1 yr−1). Crop system conversion from soybean monocropping to corn monocropping or break system was the critical factor for SOC change, and the background SOC was the second influence factor. When approaching a SOC turning point, conversion from low carbon input crop system (soybeans monocropping) to high carbon input crop system helped slow down the SOC decline (break crop) or even improve SOC (corn monocropping) in mollisols regions. This result implied that imported soybean has brought benefit for Northeast China. But for sustainable goal in China’s mollisols region, straw returning, optimized nitrogen fertilization and no tillage are all necessary whatever in continues maize or rotation system.

Carbon Input and Accumulation in Freshwater to Brackish Marshes on the Barrier Islands of Virginia, USA

Barrier island marshes are exceptionally dynamic systems. The objective of this study was to quantify above and belowground net primary production, above and belowground decay, sedimentation rate, and soil carbon pools within four interdunal fresh to brackish marshes on Hog Island, Virginia, USA and to compare carbon input and soil accumulation among marshes with varied susceptibility to overwash. Major carbon fluxes were assessed by the following methods: aboveground net primary production by harvesting biomass throughout the growing season, belowground net primary production with in-growth cores, sedimentation by deposition on sediment plates, and belowground and aboveground decay with litterbags. We expected sites more susceptible to overwash events to have higher carbon inputs and more accumulation in the soil. Sites in the direct overwash path had slower belowground decay rates, and one of these sites also had the slowest aboveground decay rate. The sites most susceptible to overwash had higher ANPP, but did not have higher soil carbon pools. Sites most susceptible to overwash had a higher salinity and bulk density, but did not store more carbon than other sites. As these sites age and the island accretes vertically, it is expected that soil carbon stocks will increase as well.

Reservoirs as hotspots of fluvial carbon cycling in peatland catchments.

Inland water bodies are recognised as dynamic sites of carbon processing, and lakes and reservoirs draining peatland soils are particularly important, due to the potential for high carbon inputs combined with long water residence times. A carbon budget is presented here for a water supply reservoir (catchment area~9km2) draining an area of heavily eroded upland peat in the South Pennines, UK. It encompasses a two year dataset and quantifies reservoir dissolved organic carbon (DOC), particulate organic carbon (POC) and aqueous carbon dioxide (CO2(aq)) inputs and outputs. The budget shows the reservoir to be a hotspot of fluvial carbon cycling, as with high levels of POC influx it acts as a net sink of fluvial carbon and has the potential for significant gaseous carbon export. The reservoir alternates between acting as a producer and consumer of DOC (a pattern linked to rainfall and temperature) which provides evidence for transformations between different carbon species. In particular, the budget data accompanied by 14C (radiocarbon) analyses provide evidence that POC-DOC transformations are a key process, occurring at rates which could represent at least ~10% of the fluvial carbon sink. To enable informed catchment management further research is needed to produce carbon cycle models more applicable to these environments, and on the implications of high POC levels for DOC composition.

Soil organic carbon simulated with the AMG model in a high-organic-matter Mollisol

Soil organic carbon (SOC) management requires a precise knowledge of how it is affected by soil use. Simulation models could help for this purpose. The AMG model is simple, requires information that is easily available, and uses few parameters. This model has neither been calibrated/adjusted nor validated for loamy soils with high SOC concentrations. We hypothesized that AMG would satisfactorily simulate SOC stock changes in soils with these characteristics. The aims of this work were: 1) to adjust and validate AMG for different tillage systems, nitrogen (N) fertilization levels and crop types for loamy-high-SOC Mollisols, and 2) to simulate future SOC changes under different production scenarios. We used SOC stocks (0-20 cm depth) from three long-term experiments (1976-2012) (tillage systems, crop rotations, and N fertilization) in the Southeastern Buenos Aires Province, Argentina (37º 45' S, 58º 18' W) on a complex of Mollisols. Data from two of those experiments was split into two groups to adjust unknown model parameters and for cross validation. Data from the third experiment was used for independent validation. The model was used to simulate SOC stock variation (30 yr) under different combinations of initial SOC stocks (SOCi, three levels) and crop rotations (six rotations regarding continuous cropping and crop-pasture rotations). Model performance was evaluated through statistical indicators based on observed-simulated value differences, and simple linear regression of observed on simulated values. Cross validation yielded promising indicators with the mean observed-simulated value differences close to 0 (<em>P </em>> 0.05). Root mean square error (RMSE) and RMSE as percentage of the mean of observed values (RMSEp) were 6.0 Mg C ha<sup>-1</sup> and 7.5%, respectively, which are acceptable. Simple linear regression of observed and simulated values was highly significant (<em>P </em>< 0.01) with intercept and slope not different from zero and one (<em>P </em>> 0.05), respectively, although R<sup>2</sup> was low. Indicators of model performance by groups of treatments were, in general, acceptable and did not show clear trends associated with any management type. However, model performance was poorer under no tillage (NT) and N fertilization probably because of little observed data available for that treatment factor combination. Validation with independent data confirmed that AMG simulated SOC change satisfactorily. Future scenario simulations showed that when the SOCi stock was high (close to SOC saturation), even rotations with high intensification and carbon input produced a SOC stock decrease. Conversely, when the SOCi stock was low (35% loss of SOC with respect to saturation) all scenarios led to a SOC stock increase. However, AMG failed to acceptably simulate the expected effect of pastures in the rotation. The AMG model satisfactorily simulated SOC stock changes due to different management techniques of soils with a loamy surface texture and high original SOC stock. Therefore, the model could be used as a tool to help management planning with an admissible simulation error (RMSEp ~6%).

Vegetation-soil system controls soil mechanisms for nitrogen transformations in an oligotrophic Mexican desert

Vegetation communities with high soil carbon (C) inputs, e.g. grassland ecosystems, promote N protection via microbial communities in the soil whereas communities with low soil C inputs, e.g. desert scrub ecosystems, promote nitrification and are therefore susceptible to N loss. This study examines this relationship more closely by assessing the effects of two vegetation-soil systems on soil N transformation, in a grassland-desert scrub in Cuatro Ciénegas Basin, Mexico. Metrics used in our study include: the belowground biomass of C, N and phosphorus (P) in both vegetation types; the availability of C, N and P in the soil; and the potential transformation of these nutrients by the microbial community which was characterized by 16S rRNA clone libraries. We found: (1) a higher NH4+ and microbial N concentration in the grassland soil than in the desert scrub soil, and (2) a different bacterial soil communities between both vegetation-soil systems. These findings suggest an interrelationship between nutrients in the belowground biomass, soil nutrient dynamics, and the soil bacterial community whereby grasslands promote a closed system that conserves N, whereas desert scrub vegetation exhibits an open system that sheds N.

Potential of Bioenergy Production from Microalgae

There is increasing interest for sustainable bioenergy production to mitigate greenhouse gas emissions and reduce reliance on fossil fuels. Biofuel can be generated from a wide variety of feedstock types including algae. Algae are an attractive feedstock for the production of liquid and gaseous biofuels that do not need to directly compete with food production. However, both the sustainability and the economic viability of algal biofuels have been questioned, particularly with regard to high carbon and fertiliser input requirements, and high cultivation and production costs. Improved understanding and modifications at a biological level, of algal genetics, carbon storage metabolism, photosynthesis and algal physiology, have the potential for significant advances in algal biofuel feasibility. This is being driven by advances in genomic technologies to provide the potential for genetic and metabolic engineering, plus the development of high-throughput techniques for the screening of natural strains for suitable biofuel characteristics.

Pacific Walrus (Odobenus rosmarus divergens) Resource Selection in the Northern Bering Sea

The Pacific walrus is a large benthivore with an annual range extending across the continental shelves of the Bering and Chukchi Seas. We used a discrete choice model to estimate site selection by adult radio-tagged walruses relative to the availability of the caloric biomass of benthic infauna and sea ice concentration in a prominent walrus wintering area in the northern Bering Sea (St. Lawrence Island polynya) in 2006, 2008, and 2009. At least 60% of the total caloric biomass of dominant macroinfauna in the study area was composed of members of the bivalve families Nuculidae, Tellinidae, and Nuculanidae. Model estimates indicated walrus site selection was related most strongly to tellinid bivalve caloric biomass distribution and that walruses selected lower ice concentrations from the mostly high ice concentrations that were available to them (quartiles: 76%, 93%, and 99%). Areas with high average predicted walrus site selection generally coincided with areas of high organic carbon input identified in other studies. Projected decreases in sea ice in the St. Lawrence Island polynya and the potential for a concomitant decline of bivalves in the region could result in a northward shift in the wintering grounds of walruses in the northern Bering Sea.

Effects of Reduced Tillage on Crop Yield, Plant Available Nutrients and Soil Organic Matter in a 12-Year Long-Term Trial under Organic Management

A field experiment was performed in Southwest Germany to examine the effects of long-term reduced tillage (2000–2012). Tillage treatments were deep moldboard plow: DP, 25 cm; double-layer plow; DLP, 15 + 10 cm, shallow moldboard plow: SP, 15 cm and chisel plow: CP, 15 cm, each of them with or without preceding stubble tillage. The mean yields of a typical eight-year crop rotation were 22% lower with CP compared to DP, and 3% lower with SP and DLP. Stubble tillage increased yields by 11% across all treatments. Soil nutrients were high with all tillage strategies and amounted for 34–57 mg kg−1 P and 48–113 mg kg−1 K (0–60 cm soil depth). Humus budgets showed a high carbon input via crops but this was not reflected in the actual Corg content of the soil. Corg decreased as soil depth increased from 13.7 g kg−1 (0–20 cm) to 4.3 g kg−1 (40–60 cm) across all treatments. After 12 years of experiment, SP and CP resulted in significantly higher Corg content in 0–20 cm soil depth, compared to DP and DLP. Stubble tillage had no significant effect on Corg. Stubble tillage combined with reduced primary tillage can sustain yield levels without compromising beneficial effects from reduced tillage on Corg and available nutrient content.

Benthic ostracode δ13C as sensor for early Holocene establishment of modern circulation patterns in Central Europe

Shells from adult specimen of the benthic ostracodes Limnocytherina sanctipatricii and Leucocythere mirabilis selected from a 8.7 m long piston core provide continuous stable oxygen and carbon records for the past approximately 16 ka. Oxygen isotopes from both species show identical values and track the general North Atlantic and European temperature history since deglaciation in great detail. Values of ostracode δ18O values suggest that about 16 cal ka the average annual air temperatures were about 11 °C colder than today. Carbon isotopic values from both species of ostracodes are similar during the Lateglacial and early Holocene, and show an overall decrease from −4‰ to −7‰ that is probably related to an increase in photosynthetic productivity in the water column, as suggested by an increase in organic carbon, delivering 13C-depleted organic matter to the bottom waters (carbon pump). About 9 cal ka only L. mirabilis δ13C values decreased about −2.5‰ within 300 years. Higher δ13C variability and ecological evidence suggests that L. mirabilis represents a summer signal, whereas L. sanctipatricii displays a more subdued annual average. After about 7 cal ka another −1.5% decrease for both species, accompanied by an increase in magnetic susceptibility, a decrease in carbonate content, and more positive bulk carbonate isotope values followed, suggesting higher detrital-clastic input into the lake.In order to provide a possible mechanism explaining the negative L. mirabilis δ13C-values, sediment pore water profiles of O2 and CH4 in short cores collected from sites distal to proximal to the Alpine Rhine River delta, were inspected. Sediments in cores from more proximal sites to the Rhine delta become anoxic at shallower sediment depth due to the decay of high allochthonous organic carbon input to the sediment, which greatly increases concentrations of methane in pore waters closer to the Rhine inflow. When methane is oxidized close to the sediment–water-interface, 13C-depleted carbon is added to pore water DIC that is then available for incorporation into ostracode shells. This mechanism suggests that about 9 cal ka the oxygen supply to the bottom waters, especially in summer, decreased. This stimulated methanogenesis close to the sediment–water-interface, and provided δ13C-depleted carbon to benthic dwellers. Independent evidence for methanogenesis is provided by the increase in concentration of tetrahymanol after about 9 cal ka coincident with the decrease in δ13C of L. mirabilis.We suggest that about 9 cal ka the northward retreat of the Northern Hemisphere Ice Sheets, and consequently the polar front, left the alpine region affected by a more oceanic climate, characterized by warmer winters as they occur today especially during the positive North Atlantic Oscillation Index phase. More frequently incomplete mixing of the water column may have shifted the decay of organic matter faster to anaerobic conditions in surficial sediments especially during summer. By about 7 cal ka the North Atlantic region had probably warmed sufficiently to increase precipitation in Central Europe and consequently detrital-clastic runoff to Lake Constance.

Deep-sea scavenging amphipod assemblages from the submarine canyons of the Western Iberian Peninsula

Abstract. Submarine canyons have often been identified as hotspots of secondary production with the potential to house distinct faunal assemblages and idiosyncratic ecosystems. Within these deep-sea habitats, assemblages of scavenging fauna play a vital role in reintroducing organic matter from large food falls into the wider deep-sea food chain. Free-fall baited traps were set at different depths within three submarine canyons on the Iberian Margin. Amphipods from the traps were identified to species level and counted. Scavenging amphipod assemblages were compared at different depths within each canyon and between individual canyon systems. Using data from literature, abyssal plain assemblages were compared to submarine canyon assemblages. Samples from canyons were found to contain common abyssal plain species but in greater than expected abundances. It is proposed that this is a result of the high organic carbon input into canyon systems owing to their interception of sediment from the continental shelf and input from associated estuarine systems. Community composition differed significantly between the submarine canyons and abyssal plains. The cause of this difference cannot be attributed to one environmental variable due to the numerous inherent differences between canyons and abyssal plains.

Soil profile carbon and nutrient stocks under long-term conventional and organic crop and alfalfa-crop rotations and re-established grassland

Soil carbon stocks are useful indicators of both C sequestration capacity and sustainability of agricultural systems. Yet, most investigations have only studied the effects of agricultural management on soil carbon in surface layers (< 0.3m). Current soil organic carbon (SOC), total soil nitrogen (TN) and plant available phosphorus (POlsen) to a depth of 1.2m was measured at two long-term (9 and 18 years) farming systems experiments in southern Manitoba, Canada. Both experiments compared an annual-crop rotation, an alfalfa (Medicago sativa L.)/crop rotation and re-established perennial grassland. At one site the two cropping systems were managed conventionally as well as in adherence to organic farming guidelines, but without manure additions. Due to higher net primary productivity and higher carbon inputs, particularly below ground, SOC stocks (0–120cm) were 21–65tCha−1 higher under the re-established grassland than cropping systems at the clay soil site after 18 years, but not at the site with sandy loam soil after 9 years. On the clay soil, 30–40% of the additional C in the soil profile under the re-established grassland was found below 30cm indicating the capacity of deep plant roots to sequester C in the sub-soil. Using alfalfa cut for hay in crop rotations did not increase SOC or N stocks compared to annual crop rotations, but plant-available P concentrations were depleted, especially under organic management. SOC was 25–30tCha−1 lower under organic than conventionally managed cropping systems, due to lower inputs of plant C (0.8tCha−1yr−1) over the life of the experiment. This highlights that without additional C inputs organic management can reduce SOC compared to conventional cropping systems unless C inputs are maintained which may require manure or compost additions.

Enhanced riverine carbon flux from carbonate catchment to the ocean: A comparative hydrogeochemical study on Ishigaki and Iriomote islands, southwestern Japan

Riverine carbon transportation is an important carbon flux connecting reservoirs of the atmosphere, continents, and oceans. The flux is strongly related to the important roles of rivers such as regulation of climate change and buffering of ocean acidification. Here, to evaluate the linkage of such functions of rivers and geological characteristics of the watersheds, we present the results of a comparative hydrogeochemical study conducted on small subtropical watersheds of aluminosilicate‐dominated Iriomote Island and carbonate‐based Ishigaki Island, southwestern Japan. Rivers on Ishigaki Island exhibited much higher alkalinity than rivers on Iriomote Island, which was even higher than the mean value of major rivers in the world, such as the Saint Lawrence and the Mississippi. This high alkalinity was the result of carbonate dissolution enhanced by soil‐originated CO2. As a result of this high inorganic carbon input, the ratio of inorganic carbon and nutrients of the river water was higher than that of marine organic matter such as the Redfield ratio, making the coastal seas a potential source of CO2 for the atmosphere.

Application of RothC model to predict soil organic carbon stock on agricultural soils of Slovakia

Soil organic matter (SOM) takes part in many environmental functions and, depending on the conditions, it can be a source or a sink of the greenhouse gases. Presently, the changes in soil organic carbon (SOC) stock can arise because of the climatic changes or changes in the land use and land management. A promising method in the estimation of SOC changes is modelling, one of the most used models for the prediction of changes in soil organic carbon stock on agricultural land being the RothC model. Because of its simplicity and availability of the input data, RothC was used for testing the efficiency to predict the development of SOC stock during 35-year period on agricultural land of Slovakia. The received data show an increase of SOC stock during the first (20 years) phase and no significant changes in the course of the second part of modelling. The increase of SOC stock in the first phase can be explained by a high carbon input of plant residues and manure and a lower temperature in comparison with the second modelling part.

Effect of land use history and site factors on spatial variation of soil organic carbon across a physiographic region

Regional scale inventories of soil organic carbon (SOC) stocks often use soil and land use maps as key determinants in the upscaling procedure. Although soil and land use are important determinants for SOC stocks, there are other determinants that could potentially improve regional estimates of SOC stocks. So far, land use history is never used as a determinant for SOC stocks in regional inventories as a result of the limited quantitative knowledge of the effect of land use history on SOC stocks. In this paper we assess how land use, land use history and several site factors are associated with SOC variability in four sites across a physiographic region in the Netherlands. Determinants for SOC variability were identified with empirical analysis. Causality of the identified associations was tested with a process model. Results from both methods were compared and analyzed. Empirical analysis showed that historical land use has a stronger association with SOC variability than present-day land use, mainly because long-term agricultural areas have higher SOC contents than recent reclamations. Process modelling results show that land use systems with high carbon input have a 1.5 times larger SOC stock than low-input land use systems after 200 years. Significant differences between high-input and low-input systems only emerge after several decades and are maintained over 100 years. Due to the long-lasting imprint of historical land use systems combined with the high spatial variability of historical land use, current variability of SOC stocks is related to variation in land use history. The results can be used to calculate region-wide SOC stock estimates in upscaling procedures.

Rotational and Cover Crop Determinants of Soil Structural Stability and Carbon in a Potato System

Understanding processes that ameliorate structural degradation in sandy soils is particularly important in intensively managed potato (Solanum tuberosum L.) systems. Seven 2‐yr potato rotation systems were evaluated over 3 yr in an irrigated field trial comparing winter management systems bare (B) and cover crops: rye (Secale cereale L.; R), rye‐hairy vetch (Vicia villosa Roth; RV) mixture and red clover (Trifolium pratense L.; C). Crops rotated with potatoes (P) were snap bean (Phaseolus vulgaris (L.); SB), wheat (Triticum aestivum L.; W) and sweet corn (Zea mays L.; SC). The systems consisted of: S1 PBSBB; S2 PRSBR; S3 PRSCB; S4 PWWR; S5 PWWCC; S6 PRVSBRV; and S7 PRVSCRV, both entry points evaluated each year. Carbon inputs above‐ and belowground were measured and systems grouped as low (S1 and S4), medium (S2 and S6), and high (S5, S3 and S7): 1.2, 2.0, and 2.8 Mg C ha−1, respectively. Response variables included water stable aggregate (WSA) size fractions, macroaggregates (≥0.25 mm) and microaggregates (&lt;0.25 mm), mean weight diameter (MWD), soil C, nitrogen mineralization potential (NMP), and potato tuber yield. Systems with SC contributed twofold higher biomass than rotations with W or SB, and the presence of RC contributed higher amounts of carbon (1.2 Mg ha−1) compared to R (0.7 Mg ha−1). Only the entry year influenced macroaggregates in 2001; both entry year and cropping system influenced aggregate size classes in 2004. Over 3 yr the macro‐WSAs declined by 13%, except for high carbon input systems. Residue C input was a moderate predictor of total soil C (31% of variability explained), whereas macro‐ and micro‐WSAs were predictors of soil C, accounting for 58 and 72% of observed variability, respectively. Low levels of aggregation were observed in this sandy soil and the modest amounts of C inputs from winter cover crops posed a challenge to detecting treatment effects, which was in part overcome by georeferencing, to improve precision of sampling over time.

O uso da serragem no processo de minicompostagem

Neste trabalho utilizou-se quatro minicomposteiras de PVC cilíndricas e idênticas, com 40 cm de diâmetro, 75 cm de comprimento e com as extremidades abertas. Cada minicomposteira recebeu 35,5 kg de resíduos sólidos orgânicos, previamente triturados e 6 kg de serragem. Foi acompanhado o processo através de análises de C/N, variação da temperatura, grau de umidade e pH. Os resultados mostraram que o uso do resíduo serragem como palhoso, nas minicomposteiras desenvolvidas, utilizando pequena quantidade de resíduos orgânicos, atingiu temperaturas de até 65º C, permanecendo na faixa termofílica por aproximadamente 6 dias. Após 18 dias a massa em degradação atingiu a temperatura ambiente, sendo então, deixada para maturar por 55 dias. A umidade no sistema foi próxima de 60% no início e o pH final ficou na faixa de 8,0 a 8,5. A relação C/N inicial foi 30/1 e chegou a 12/1 após 73 dias.

Climate Policy and the Optimal Extraction of High- and Low-Carbon Fossil Fuels

We study how restricting CO2 emissions affects resource prices and depletion over time. We use a Hotelling-style model with two nonrenewable fossil fuels that differ in their carbon content (e.g., coal and natural gas) and that are imperfect substitutes in final good production. We study both an unexpected constraint and an anticipated constraint. Both shocks induce intertemporal substitution of resource use. When emissions are unexpectedly restricted, it is cost-effective to use high-carbon resources relatively more (less) intensively on impact if this resource is relatively scarce (abundant). If the emission constraint is anticipated, it is cost-effective to use relatively more (less) of the low-carbon input before the constraint becomes binding, in order to conserve relatively more (less) of the high-carbon input for the period when climate policy is active in case the high-carbon resource is relatively scarce (abundant).