Carbon Abatement and Emissions Associated with the Gasification of Walnut Shells for Bioenergy and Biochar Production

By converting biomass residue to biochar, we could generate power cleanly and sequester carbon resulting in overall greenhouse gas emissions (GHG) savings when compared to typical fossil fuel usage and waste disposal. We estimated the carbon dioxide (CO2) abatements and emissions associated to the concurrent production of bioenergy and biochar through biomass gasification in an organic walnut farm and processing facility in California, USA. We accounted for (i) avoided-CO2 emissions from displaced grid electricity by bioenergy; (ii) CO2 emissions from farm machinery used for soil amendment of biochar; (iii) CO2 sequestered in the soil through stable biochar-C; and (iv) direct CO2 and nitrous oxide (N2O) emissions from soil. The objective of these assessments was to pinpoint where the largest C offsets can be expected in the bioenergy-biochar chain. We found that energy production from gasification resulted in 91.8% of total C offsets, followed by stable biochar-C (8.2% of total C sinks), offsetting a total of 107.7 kg CO2-C eq Mg-1 feedstock. At the field scale, we monitored gas fluxes from soils for 29 months (180 individual observations) following field management and precipitation events in addition to weekly measurements within three growing seasons and two tree dormancy periods. We compared four treatments: control, biochar, compost, and biochar combined with compost. Biochar alone or in combination with compost did not alter total N2O and CO2 emissions from soils, indicating that under the conditions of this study, biochar-prompted C offsets may not be expected from the mitigation of direct soil GHG emissions. However, this study revealed a case where a large environmental benefit was given by the waste-to-bioenergy treatment, addressing farm level challenges such as waste management, renewable energy generation, and C sequestration

Nitrogen photo-chemistry and the dynamics of CDOM in aquatic environments

Photochemical ammonium production and photo-bleaching of chromophoric dissolved organic matter (CDOM) kinetics were studied in a variety of aquatic environments including freshwater samples of peatland origin, Caithness, a Tyne Estuary (NE, U.K.) estuary and the Iberian Sea. The main aims of the study were to assess seasonal variability within the peatland catchments, in conjunction with a study of regional and geographical variability of dissolved organic matter (DOM) and ammonium photo-production. Samples collected from a variety of aqueous environments covered the CDaM .absofPtion coefficient at 350 nm (a350) range 0.3 to 69.0 m-I. Selected, filtered samples (n=21) were exposed to natural and artificial light, in order to study ~+ photo-production CDaM photo-bleaching. The photo-chemical degradation of CDaM, as indicated by decreases in a350 over time, also led to increases in the spectral slope of sample absorbance over the wavelength range 290-350 nm, and losses of total fluorescence intensity. In addition we observed hypsochromic shifts of long-wave, humic-like fluorescence (fluorophore A). Photo-chemical ammonium release was observed in 19 of the total 21 irradiation experiments. However the kinetics of ammonium production were complex with 4 of the 21 samples showing a near-linear increase in NH/ concentration while other samples showed an initial lag phase, followed by production and then a decline in NH/ concentrations. In order to assess possible impacts of ~+ release on N balance we estimated NH4+ photoproduction potentials from concentration differences between the initial values and maximum ~+ values divided by irradiation time (i1t). Thus obtained ~+ photo-production potentials between sites ranged from 0 to 3.57 JIM r1 h-I (mean ± stdev 0.7) under solar noon irradiance levels. Using calculated daily sky irradiance and seasonal correction factors, annual depth integrated ~+ photo-production rates were estimated, ranging from 0.06 to 8.05 JIMNm-2 yrI( mean ± stdev 2.73). The photo-chemical production ofNH/ indicates that photo-chemically induced nitrogen release could potentially be an important source of biologically labile nitrogen to aquatic ecosystems, with severe impacts upon the biogeochemistry and nutrient limitation of these environments when compared to N-reservoir size and other N fluxes. However, compared to N deposition photo-ammonification is not a major source ofN. Key words: Dissolved organic matter, chromophoric dissolved organic matter, photoammonification, peatlands, estuaries, marine, and fluorescence.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Season and location–specific nitrous oxide emissions in an almond orchard in California

ISSN:1385-1314ISSN:1573-086

Monitoring soil carbon will prepare growers for a carbon trading system

California growers could reap financial benefits from the low-carbon economy and cap-and-trade system envisioned by the state's AB 32 law, which seeks to lower greenhouse gas emissions statewide. Growers could gain carbon credits by reducing greenhouse gas emissions and sequestering carbon through reduced tillage and increased biomass residue incorporation. First, however, baseline stocks of soil carbon need to be assessed for various cropping systems and management practices. We designed and set up a pilot soil carbon and land-use monitoring network at several perennial cropping systems in Northern California. We compared soil carbon content in two vineyards and two orchards (walnut and almond), looking at conventional and conservation management practices, as well as in native grassland and oak woodland. We then calculated baseline estimates of the total carbon in almond, wine grape and walnut acreages statewide. The organic walnut orchard had the highest total soil carbon, and no-till vineyards had 27% more carbon in the surface soil than tilled vineyards. We estimated wine grape vineyards are storing significantly more soil carbon per acre than almond and walnut orchards. The data can be used to provide accurate information about soil carbon stocks in perennial cropping systems for a future carbon trading system

Monitoring soil carbon will prepare growers for a carbon trading system

California growers could reap financial benefits from the low-carbon economy and cap-and-trade system envisioned by the state's AB 32 law, which seeks to lower greenhouse gas emissions statewide. Growers could gain carbon credits by reducing greenhouse gas emissions and sequestering carbon through reduced tillage and increased biomass residue incorporation. First, however, baseline stocks of soil carbon need to be assessed for various cropping systems and management practices. We designed and set up a pilot soil carbon and land-use monitoring network at several perennial cropping systems in Northern California. We compared soil carbon content in two vineyards and two orchards (walnut and almond), looking at conventional and conservation management practices, as well as in native grassland and oak woodland. We then calculated baseline estimates of the total carbon in almond, wine grape and walnut acreages statewide. The organic walnut orchard had the highest total soil carbon, and no-till vineyards had 27% more carbon in the surface soil than tilled vineyards. We estimated wine grape vineyards are storing significantly more soil carbon per acre than almond and walnut orchards. The data can be used to provide accurate information about soil carbon stocks in perennial cropping systems for a future carbon trading system

Cumulative CO₂–C and N₂O-N emissions by sampling year from both tree and tractor rows of a walnut orchard in Winters, CA, USA.

<p>Shown in parentheses is ± one standard error (n = 3). None of the treatments significantly altered the cumulative CO₂–C and N₂O-N emissions at <i>p</i> < 0.05.</p

Walnut shell biochar and soil (Yolo silt loam) physicochemical properties.

<p>Walnut shell biochar and soil (Yolo silt loam) physicochemical properties.</p

Distribution of sampling gas fluxes across the different ranges of water-filled pore space during 29 months of observations (June 2010 to October 2012).

<p>Error bars indicate standard deviation (n = 3).</p

Illustration of the bioenergy-biochar production chain in a walnut farm and processing facility and the CO₂ abatements and emissions associated to these activities.

<p>Illustration of the bioenergy-biochar production chain in a walnut farm and processing facility and the CO₂ abatements and emissions associated to these activities.</p

Biochar alters nitrogen transformations but has minimal effects on nitrous oxide emissions in an organically managed lettuce mesocosm

We investigated the effect of biochar type on plant performance and soil nitrogen (N) transformations in mesocosms representing an organic lettuce (Lactuca sativa) production system. Five biochar materials were added to a silt loam soil: Douglas fir wood pyrolyzed at 410 °C (W410), Douglas fir wood pyrolyzed at 510 °C (W510), pine chip pyrolyzed at 550 °C (PC), hogwaste wood pyrolyzed between 600 and 700 °C (SWC), and walnut shell gasified at 900 °C (WS). Soil pH and cation exchange capacity were significantly increased by WS biochar only. Gross mineralization increased in response to biochar materials with high H/C ratio (i.e., W410, W510, and SWC), which can be favorable for organic farming systems challenged by insufficient N mineralization during plant growth. Net nitrification was increased by W510, PC, and WS without correlating with the abundance of ammonia oxidizing gene (amoA). Increases in N transformation rates did not translate into increases in plant productivity or leaf N content. WS biochar increased the abundance of amoA and nitrite reductase gene (nirK), while SWC biochar decreased the abundance of amoA and nitrous oxide gene (nosZ). Decreases in N2O emissions were only observed in soil amended with W510 for 3 days out of the 42-day growing season without affecting total cumulative N2O fluxes. This suggests that effects of biochar on decreasing N2O emissions may be transient, which compromise biochar’s potential to be used as a N2O mitigation strategy in organic systems. Overall, our results confirm that different biochar materials can distinctively affect soil properties and N turnover.ISSN:0178-2762ISSN:1432-078