Adapting Agriculture to Climate Variability: Executive Summary

These paired conferences were an outgrowth of a joint meeting of Canadian and American agricultural leaders at Fargo, N.D., on Sept. 30, 2009, to explore the potential impacts of increased climatic variability on agriculture. A committee was formed to bring together agricultural leaders from the prairie provinces of Canada and the Northern Central Region of the United States of America to increase awareness of the importance of a proactive approach by the agricultural sectors in addressing the research, education, public policy, and technology transfer challenges associated with climate variability on the long-term sustainability of agriculture. Paired conferences were conducted in Winnipeg and Kansas City in March 2010. A key outcome of these meetings was the recognition that a collaborative effort is required for agriculture to respond to weather variability. The implications to regional economic sustainability, national food security, and the viability of the bio-fuel industry motivated participants to support immediate action

Particle Deposition of Silica and Polystyrene during Drop Evaporation

In various industries, such as creating pigments, ceramics, emulsifiers, and catalysis, having silica particles that have a small size distribution, or are monodisperse, are important. In these products, particles with higher mono-dispersity lead to higher quality products. The problem with forming silica particles of a certain size is determining how the reagents and the alcohol solvent affect the particle size and size distribution. Concentrations of ammonia and water were varied, as well as the type of alcohol solvent. Analysis on the particle size and distribution was conducted through dynamic light scattering. After analysis, silica particles were centrifuged and then suspended in de-ionized water. As the concentration of ammonia increased, and as the alcohol solvent had a larger ethanol to methanol ratio, the particles’ size increased. The effect of the water concentration on the silica particles showed varied results. The silica particles synthesized were then used for drop-drying experiments. In the pharmaceutical industry, an efficient method for creating oral dosage strips and tablets is through drop-printing of drug suspensions. Drop-on-demand printing allows for controllable deposition of active pharmaceutical ingredients. For drop-printing, the problem is to find how to print the active ingredient evenly distributed on the substrate. Polystyrene particles were added to a suspension of the silica nanoparticles and drop-drying experiments were conducted. For the drop-drying experiments, the smaller silica particles deposited closer to the contact line than the larger polystyrene particles

Seasonal patterns and controls on net ecosystem CO2 exchange in a boreal peatland complex

We measured seasonal patterns of net ecosystem exchange (NEE) of CO2 in a diverse peatland complex underlain by discontinuous permafrost in northern Manitoba, Canada, as part of the Boreal Ecosystems Atmosphere Study (BOREAS). Study sites spanned the full range of peatland trophic and moisture gradients found in boreal environments from bog (pH 3.9) to rich fen (pH 7.2). During midseason (July‐August, 1996), highest rates of NEE and respiration followed the trophic sequence of bog (5.4 to −3.9 μmol CO2 m−2 s−1) \u3c poor fen (6.3 to −6.5 μmol CO2 m−2 s−1) \u3c intermediate fen (10.5 to −7.8 μmol CO2 m−2 s−1) \u3c rich fen (14.9 to −8.7 μmol CO2m−2 s−1). The sequence changed during spring (May‐June) and fall (September‐October) when ericaceous shrub (e.g., Chamaedaphne calyculata) bogs and sedge (Carex spp.) communities in poor to intermediate fens had higher maximum CO2 fixation rates than deciduous shrub‐dominated (Salix spp. and Betula spp.) rich fens. Timing of snowmelt and differential rates of peat surface thaw in microtopographic hummocks and hollows controlled the onset of carbon uptake in spring. Maximum photosynthesis and respiration were closely correlated throughout the growing season with a ratio of approximately 1/3 ecosystem respiration to maximum carbon uptake at all sites across the trophic gradient. Soil temperatures above the water table and timing of surface thaw and freeze‐up in the spring and fall were more important to net CO2 exchange than deep soil warming. This close coupling of maximum CO2 uptake and respiration to easily measurable variables, such as trophic status, peat temperature, and water table, will improve models of wetland carbon exchange. Although trophic status, aboveground net primary productivity, and surface temperatures were more important than water level in predicting respiration on a daily basis, the mean position of the water table was a good predictor (r2 = 0.63) of mean respiration rates across the range of plant community and moisture gradients. Q10 values ranged from 3.0 to 4.1 from bog to rich fen, but when normalized by above ground vascular plant biomass, the Q10 for all sites was 3.3

Relationship between ecosystem productivity and photosynthetically-active radiation for northern peatlands

We analyzed the relationship between net ecosystem exchange of carbon dioxide (NEE) and irradiance (as photosynthetic photon flux density or PPFD), using published and unpublished data that have been collected during midgrowing season for carbon balance studies at seven peatlands in North America and Europe. NEE measurements included both eddy-correlation tower and clear, static chamber methods, which gave very similar results. Data were analyzed by site, as aggregated data sets by peatland type (bog, poor fen, rich fen, and all fens) and as a single aggregated data set for all peatlands. In all cases, a fit with a rectangular hyperbola (NEE = α PPFD Pmax/(α PPFD + Pmax) + R) better described the NEE-PPFD relationship than did a linear fit (NEE = β PPFD + R). Poor and rich fens generally had similar NEE-PPFD relationships, while bogs had lower respiration rates (R = −2.0μmol m−2s−1 for bogs and −2.7 μmol m−2s−1 for fens) and lower NEE at moderate and high light levels (Pmax = 5.2 μmol m−2s−1 for bogs and 10.8 μmol m−2s−1 for fens). As a single class, northern peatlands had much smaller ecosystem respiration (R = −2.4 μmol m−2s−1) and NEE rates (α = 0.020 and Pmax = 9.2μmol m−2s−1) than the upland ecosystems (closed canopy forest, grassland, and cropland) summarized by Ruimy et al. [1995]. Despite this low productivity, northern peatland soil carbon pools are generally 5–50 times larger than upland ecosystems because of slow rates of decomposition caused by litter quality and anaerobic, cold soils

Carbon isotope discrimination of arctic and boreal biomes inferred from remote atmospheric measurements and a biosphere-atmosphere model

Estimating discrimination against ^(13)C during photosynthesis at landscape, regional, and biome scales is difficult because of large-scale variability in plant stress, vegetation composition, and photosynthetic pathway. Here we present estimates of ^(13)C discrimination for northern biomes based on a biosphere-atmosphere model and on National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory and Institute of Arctic and Alpine Research remote flask measurements. With our inversion approach, we solved for three ecophysiological parameters of the northern biosphere (^(13)C discrimination, a net primary production light use efficiency, and a temperature sensitivity of heterotrophic respiration (a Q10 factor)) that provided a best fit between modeled and observed δ^(13)C and CO_2. In our analysis we attempted to explicitly correct for fossil fuel emissions, remote C4 ecosystem fluxes, ocean exchange, and isotopic disequilibria of terrestrial heterotrophic respiration caused by the Suess effect. We obtained a photosynthetic discrimination for arctic and boreal biomes between 19.0 and 19.6‰. Our inversion analysis suggests that Q10 and light use efficiency values that minimize the cost function covary. The optimal light use efficiency was 0.47 gC MJ^(−1) photosynthetically active radiation, and the optimal Q10 value was 1.52. Fossil fuel and ocean exchange contributed proportionally more to month-to-month changes in the atmospheric growth rate of δ^(13)C and CO_2 during winter months, suggesting that remote atmospheric observations during the summer may yield more precise estimates of the isotopic composition of the biosphere

Modeling methane fluxes in wetlands with gas-transporting plants. 3. Plot scale.

A process model based on kinetic principles was developed for methane fluxes from wetlands with gas-transporting plants and a fluctuating water table. Water dynamics are modeled with the 1-D Richards equation. For temperature a standard diffusion equation is used. The depth-dependent dynamics of methane, oxygen, molecular nitrogen, carbon dioxide, soil carbon, electron acceptors in oxidized and in reduced form are affected by transport processes and kinetic processes. Modeled transport processes are convection and diffusion in the soil matrix, ebullition, and plant-mediated gas transport. Modeled kinetic processes are carbon mineralization, aerobic respiration, methane production, methane oxidation, electron acceptor reduction, and electron acceptor reoxidation. Concentration gradients around gas-transporting roots in water-saturated soil are accounted for by the models from the two previous papers, ensuring an explicit connection between process knowledge at the kinetic level (millimeter scale) and methane fluxes at the plot scale. We applied the model to a fen, and without any fitting, simulated methane fluxes are within 1 order of magnitude of measured methane fluxes. The seasonal variations however, are much weaker in the simulations compared to the measurements. Simulated methane fluxes are sensitive to several uncertain parameters such as the distribution over depth of carbon mineralization, the total pool size of reduced and oxidized electron acceptors, and the root-shoot ratio. Because of the process-based character of the model it is probable that these sensitivities are present in reality as well, which explains why the measured variability is usually very high. Interestingly, heterogeneities within a rooted soil layer seem to be less important than heterogeneities between different soil layers. This is due to the strong influence of the interaction between water table and profile scale processes on the oxygen input to the system and hence on net methane production. Other existing process models are discussed and compared with the presented model