Inferred bioavailability of pyrogenic organic matter compared to natural organic matter from global sediments and surface waters

Wildfires are increasing in severity and extent, creating many negative consequences for aquatic ecosystems. Pyrogenic materials generated by wildfires are transported across terrestrial landscapes into inland waters, where ~10% of organic matter pools may be comprised of black carbon (BC), a major component of pyrogenic organic matter (PyOM). Yet, the heterogeneity of PyOM from various fuels and burn conditions complicates efforts to understand its bioavailability. We used a substrate-explicit model to predict the energy content, metabolic efficiency, and rate of aerobic decomposition of representative PyOM compounds. This enabled us to systematically evaluate a full spectrum of PyOM chemistries that is unfeasible with laboratory experiments. The model relies on the elemental stoichiometry, allowing comparison of known PyOM chemistry to formula assignments of natural organic matter (NOM) from a recent high resolution mass spectrometry assessment of global aquatic NOM. Overall, we found the range of predicted bioavailability of PyOM was similar to NOM. Phenolic and BC molecules had lower metabolic efficiency than other PyOM and NOM compounds, and BC metabolism was less negatively impacted by oxygen limitation. In total, our work supports the recent paradigm shift regarding PyOM bioavailability, highlighting its potential role in global C emissions as the prevalence of wildfires increases.

Etude comparée de la ventilation naturelle et automatique à l’aide de tuyaux perforés et du procédé classique de retournements des andains en compostage

Sur la plateforme de compostage de l’ONG ENPRO, pour chaque tas de compost, cinq retournements sont nécessaires en vue d’apporter de l’air pour une bonne décomposition aérobie. Le retournement d’un seul tas de compost nécessite trois ouvriers pour une durée de trois heures. Donc, pour chaque fréquence de retournement, il faut mobiliser dix-sept ouvriers en une journée. Leur prise en charge pour les cinq retournements s’élève à 595000 FCFA. Face à ce coût élevé, la recherche d’alternatives de réduction du nombre d’ouvriers et du temps s’impose. La ventilation naturelle qui consiste à renouveler de l’air par des forces naturelles à travers des ouvertures, se présente comme la technique la plus optimiste. Ainsi, l’objectif de ce travail est d’optimiser la main d’œuvre et le temps accordé aux retournements. Cinq andains sont élaborés dont un standard et les quatre autres à ventilation naturelle. L’étude comparative des critères de maturité et de stabilité a montré des valeurs similaires pour les deux types de compost. Aussi, la ventilation naturelle a permis de réduire le nombre de retournements à deux et le nombre d’ouvriers à dix contre cinq et dix-sept pour le compostage standard puis le coût de prise en charge des ouvriers d’environ 25%.Mots clés : Compostage, retournement des andains, optimisation du temps, ventilation naturelle. English title: Comparative study of natural and automatic ventilation using perforated pipes and the classic method of turning windrows in compostingOn the composting platform of the NGO ENPRO, for each pile of compost, five turns are necessary in order to provide air for good aerobic decomposition. Turning a single compost heap requires three workers for three hours. So, for each turnaround frequency, seventeen workers must be mobilized in one day. Their cost for the five turnarounds amounts to FCFA 595,000. Faced with this high cost, the search for alternatives to reduce the number of workers and time is essential. Natural ventilation, which consists of renewing air by natural forces through openings, is presented as the most optimistic technique. Thus, the objective of this work is to optimize the manpower and the time allocated to turnarounds. Five windrows are produced, one of which is standard and the other four have natural ventilation. The comparative study of the maturity and stability criteria showed similar values for the two types of compost. Also, natural ventilation has reduced the number of turnovers to two and the number of workers to ten against five and seventeen for standard composting and the cost of supporting workers by around 25%. Keywords: composting, windrow turning, time optimization, natural ventilation

Effect of lead in the aerobic decomposition of Myriophyllum aquaticum (Vellozo) Verdecourt

Lead is a toxic element that has been used since early times and is still employed today in several industrial processes. Events as the collapse of the Fundão dam in Bento Rodrigues, district of Mariana (MG) on November 2015, significantly increase concentrations of metals above-recommended levels, including lead. In this context, this study aims to evaluate the impact of lead in the cycling rate of organic matter in the aquatic environment. Thus, the rates of aerobic decomposition of Myriophyllum aquaticum (Vell.) Verdec at different concentrations of lead (5.0, 10.0, 20.0 and 30.0 mg L-1) were measured, analyzing the dissolved oxygen consumption. Decomposition chambers filled with samples of water and M. aquaticum were incubated at 20° C in the dark for 80 days and periodically had the oxygen concentrations determined by polarography, when the concentrations were less than 2 mg L-1, the incubations were re-aerated. At the lowest concentrations (5.0 and 10.0 mg L-1) of lead the mineralization was lower, however, the reaction coefficients and the amount of oxygen consumed were equivalent to the control. At the highest concentrations (20.0 and 30.0 mg L-1) the mineralization was increased, with the reduction of reaction coefficients and higher oxygen consumption.

THE ELEVATED TEMPERATURE AND GAS COMPONENT WITHIN AN OPERATING SEMI-AEROBIC LANDFILL

The semi-aerobic landfill concept, which is based on passive aeration, is the compulsory standard for planning new landfill projects in Japan. The semi-aerobic landfill concept is also applied in several other countries because of its low construction and operating costs. The landfill gas (LFG) component and the LFG temperature are the main indicators of the aerobization of semi-aerobic landfills. Analysis of LFG, its concentration, and its temperature can be easily carried out on-site to evaluate the passive aeration of an operating semi-aerobic landfill. Therefore, this study observed LFG temperatures and LFG components to assess the partial aerobization within an operating semi-aerobic landfill. The observational data revealed that the methane (CH4) gas concentration of most of the main LFG venting pipes (VPs) was below 15%. The aerobic condition happened effectively surrounding the main LFGVP M2 because over the observation period, the ratio of CH4 to CO2 was less than 1.0. The highest gas temperature was above 60°C within the main LFGVP M2, and there was a trend of high temperatures above 40°C for more than 5 years before the temperature declined to 20°C in the most recent observation. The high LFG temperatures were recorded in the winter months due to the buoyancy effect. High temperature and the CH4/CO2 ratio less than 1.0 potentially representing good indicators showed that aerobic decomposition is becoming dominant. The study showed clearly that the aerobic biodegradation performance in this semi-aerobic landfill is extremely good.

Strong mitigation of net global warming potential (GWP) via short-term aerobic pre-digestion of green manured soil in rice paddy

<p> Cover crop cultivation is strongly recommended during fallow season to increase soil organic carbon (SOC) stock. However, since its biomass recycling as green manure can dramatically increase greenhouse gas (GHG) emission, in particular, methane (CH<sub>4</sub>) during rice cropping season, smart cover crop management strategy should be developed. In our previous research, CH<sub>4</sub> emission during cropping season was dramatically reduced via short-term aerobic decomposition before irrigation (Lee et al.). However, due to a fast response rate of aerobic decomposition, the effect of mitigating CH<sub>4</sub> emission could be offset by SOC depletion which results in accelerating global warming. To evaluate the comprehensive impact of the short-term aerobic decomposition on global warming, net global warming potential (GWP), defined as the difference between GWP and SOC stock change was employed. SOC stock change was estimated using net ecosystem carbon budget (NECB), a balance between soil C input and output. The mixture of barley and hairy vetch cultivated during the dried fallow season, and then its whole biomass was incorporated 0-30 days before irrigation for rice transplanting. The aerobic decomposition of cover crop biomass significantly reduced CH<sub>4</sub> emission by 24-85% over control but negligibly influences N<sub>2</sub>O emission. Total C input and output were unaffected by the aerobic digestion. Although carbon emission before flooding dramatically increased after biomass application in aerobic decomposition treatments, the mineralized C losses exhibited no differences among treatments. Based on these results, NECB values were similar in all treatments. This implies the aerobic decomposition did not stimulate SOC depletion, compared to the control. Finally, the net GWP highly decreased by 30-86% by the aerobic digestion due to the significant reduction of CH<sub>4</sub> emission. In conclusion, earlier application of cover crops before irrigation is a smart strategy to decrease methane emission, maintaining soil carbon sequestration effect of cover crop biomasses application.</p>

A tale of two peats: characterizing ecosystem-driven differences in chemical composition with depth in natural and drained Finnish mires using Py-GC/MS analytical techniques

<p>Intact accumulating peatlands are a globally important terrestrial carbon sink. Climate change and agricultural drainage are degrading these ecosystems, and through increases in aerobic decomposition, shifting their C balance from sink to source. To argue the effectiveness of restoration activities (such as rewetting), techniques are needed that clearly show differences between drained and natural (or drained and rewetted) peatlands. Because these changes are not always macroscopically visible, molecular analysis methods are especially needed to distinguish between ecosystems experiencing net pet growth (sequestering carbon), and those where aerobic decomposition is still a primary driving mechanism. Molecular biomarkers are a useful way to use chemical composition to distinguish these mechanisms.</p><p>This study aimed to compare differences in chemical composition with depth between two peatland sites from a large ombrotrophic mire in Lakkasuo Finland – one natural and one drained. To characterize these chemical shifts, pyrolysis gas chromatography mass spectrometry was used to track changes in relative abundance of various molecular biomarkers and compound classes (ie., aromatics, Sphagnum phenols, lignin, N-containing compounds, n-alkanes, etc.) with depth across both sites. Three replicate cores per site were collected, allowing for statistical evaluation of the relative abundances of these compounds. Using radiocarbon dating at three depths per core, the drained and natural sites were also matched by age for reference purposes. Significant differences were found for the Sphagnum-specific biomarker, p-isopropenylphenol, aromatics, and lignin, to the approximate current depth of the drained peatland water table. Higher phenolic compound class abundance indicated inhibited aerobic decomposition in the natural cores. An increasing trend in lignin biomarker relative abundance with depth was observed in the natural site, despite the identification of comparatively fewer vascular plants during the macroscopic analysis. Rather than a higher abundance of palaeo-ecological vascular plants, this trend is considered to be an indicator of preferential preservation of lignin compounds with anaerobic conditions. Below the depth of the water table, the relative abundances of most biomarkers stabilized, indicating the existance of similar environmental conditions in both sites prior to drainage. These data were compared and are in agreement with findings from elemental analysis (CHNO) and bulk isotopic (<sup>13</sup>C and <sup>15</sup>N) data measured on the same cores. Collectively, these data suggest that observed shifts in chemical composition in the natural and drained cores reflect the effect of different hydrological conditions between the two sites.</p>

How to make intensively used peat meadows sustainable for the future? Four management options to potentially reduce peat oxidation

<p>Almost all peatlands in the Netherlands are drained for agricultural purposes or in the past for peat extraction. What remains is a peatland area of about 300.000 ha of which 85 % is used for agriculture. As a result of peat oxidation, these areas are still subsiding by about 1 cm per year. Another effect is the enormous emission of CO<sub>2</sub>, which contributes to about 4% of total Dutch greenhouse gas emissions. With the awareness of a changing climate and the need for protection against flooding of coastal areas, solutions are being searched to reduce or stop peat oxidation and coinciding land subsidence and CO<sub>2</sub> emission.</p><p>In this presentation we will show four different management options which are currently being tested in the Netherlands. These options all focus on increasing the groundwater table to lower oxygen intrusion and consequently lower aerobic decomposition. Depending on crop choices water levels may need to stay 40 cm below the surface to maximize fodder plant yields. We expect a trade-off between land-use intensity (yields) and CO<sub>2</sub> emission reduction. The management options range from maintaining the current land-use by elevating summer water levels with submerged drainage pipes to the development of peat-forming plant species by complete rewetting. Data of the effects of these management options on CO<sub>2</sub> emission will be shown and with that the effectiveness of reducing peat oxidation.</p>