Quantifying Proximity, Confinement, and Interventions in Disease Outbreaks: A Decision Support Framework for Air-Transported Pathogens.

The inability to communicate how infectious diseases are transmitted in human environments has triggered avoidance of interactions during the COVID-19 pandemic. We define a metric, Effective ReBreathed Volume (ERBV), that encapsulates how infectious pathogens, including SARS-CoV-2, transport in air. ERBV separates environmental transport from other factors in the chain of infection, allowing quantitative comparisons among situations. Particle size affects transport, removal onto surfaces, and elimination by mitigation measures, so ERBV is presented for a range of exhaled particle diameters: 1, 10, and 100 µm. Pathogen transport depends on both proximity and confinement. If interpersonal distancing of 2 m is maintained, then confinement, not proximity, dominates rebreathing after 10-15 min in enclosed spaces for all but 100 µm particles. We analyze strategies to reduce this confinement effect. Ventilation and filtration reduce person-to-person transport of 1 µm particles (ERBV1) by 13-85% in residential and office situations. Deposition to surfaces competes with intentional removal for 10 and 100 µm particles, so the same interventions reduce ERBV10 by only 3-50%, and ERBV100 is unaffected. Prior knowledge of size-dependent ERBV would help identify transmission modes and effective interventions. This framework supports mitigation decisions in emerging situations, even before other infectious parameters are known.

Eco-Efficiency Model for Evaluating Feedlot Rations in the Great Plains, United States.

Environmental impacts attributable to beef feedlot production provide an opportunity for economically linked efficiency optimization. Eco-efficiency models are used to optimize production and processes by connecting and quantifying environmental and economic impacts. An adaptable, objective eco-efficiency model was developed to assess the impacts of dietary rations on beef feedlot environmental and fiscal cost. The hybridized model used California Net Energy System modeling, life cycle assessment, principal component analyses (PCA), and economic analyses. The model approach was based on 38 potential feedlot rations and four transportation scenarios for the US Great Plains for each ration to determine the appropriate weight of each impact. All 152 scenarios were then assessed through a nested PCA to determine the relative contributing weight of each impact and environmental category to the overall system. The PCA output was evaluated using an eco-efficiency model. Results suggest that water, ecosystem, and human health emissions were the primary impact category drivers for feedlot eco-efficiency scoring. Enteric CH emissions were the greatest individual contributor to environmental performance (5.7% of the overall assessment), whereas terrestrial ecotoxicity had the lowest overall contribution (0.2% of the overall assessment). A well-balanced ration with mid-range dietary and processing energy requirements yielded the most eco- and environmentally efficient system. Using these results, it is possible to design a beef feed ration that is more economical and environmentally friendly. This methodology can be used to evaluate eco-efficiency and to reduce researcher bias of other complex systems.

Linking plant growth responses across topographic gradients in tallgrass prairie.

Aboveground biomass in grasslands varies according to landscape gradients in resource availability and seasonal patterns of growth. Using a transect spanning a topographic gradient in annually burned ungrazed tallgrass prairie, we measured changes in the height of four abundant C(4) grass species, LAI, biomass, and cumulative carbon flux using two closely located eddy flux towers. We hypothesized that seasonal patterns of plant growth would be similar across the gradient, but the magnitude of growth and biomass accumulation would vary by topographic position, reflecting spatial differences in microclimate, slope, elevation, and soil depth. Thus, identifying and measuring local growth responses according to topographic variability should significantly improve landscape predictions of aboveground biomass. For most of the growth variables measured, classifying topography into four positions best captured the inherent spatial variability. Biomass produced, seasonal LAI and species height increased from the upland and break positions to the slope and lowland. Similarly, cumulative carbon flux in 2008 was greater in lowland versus upland tower locations (difference of 64 g m(-2) by DOY 272). Differences in growth by topographic position reflected increased production of flowering culms by Andropogon gerardii and Sorghastrum nutans in lowland. Varying growth responses by these species may be a significant driver of biomass and carbon flux differences by topographic position, at least for wet years. Using a digital elevation model to classify the watershed into topographic positions, we performed a geographically weighted regression to predict landscape biomass. The minimum and maximum predictions of aboveground biomass for this watershed had a large range (86-393 t per 40.4 ha), illustrating the drastic spatial variability in growth within this annually-burned grassland.

Nutrient accumulation below cattle feedlot pens in Kansas.

Waste excreted on cattle (Bos taurus) feedlot pens is a source of N and other nutrients that could potentially leach into soil and negatively impact local groundwater quality. Analyses of soil chemical and physical properties beneath active open air feedlot pens were conducted at four Kansas locations to determine nutrient accumulation. Results were compared to estimated nutrient deposition, and remediation implications were considered. The surface concentrations of NH(4)-N, organic N, organic C, Cl(-), and extractable P were elevated at the surface and rapidly decreased with depth to 1.0 m. Ammonium N in the top 0.25 m ranged from 8000 to 375 mg kg(-1) but decreased below background (5.6 mg kg(-1)) at 1.0 to 1.3 m. Organic N in the top 0.25 m ranged from 22,000 to 500 mg kg(-1) and was the largest N source. At three of four feedlots, NO(3)-N was below background concentration (4.1 mg kg(-1)) for the entire profile whereas one feedlot had a >75 mg kg(-1) increase from the background concentration in the top 1.0 m. Considering expected nutrient deposition onto the pen surface only a fraction of the nutrients were found beneath feedlot pen surfaces. While in use, these feedlots do not appear to have a high potential for groundwater contamination from NO(3)-N leaching. However, if they were to become inactive NO(3)-N may increase and could leach into groundwater. Upon closing of the feedlots, the land could be largely remediated by removing the top 0.25 m of pen surface, a zone holding 48% of total profile N.

Movement of lagoon-liquor constituents below four animal-waste lagoons.

Movement of liquor constituents from animal-waste lagoons has the potential to degrade ground water quality. The depth of movement and concentrations of lagoon-liquor constituents in the soil underlying three cattle (Bos taurus)-waste retention lagoons and one swine (Sus scrofa)-waste lagoon were determined. Samples were taken by using a direct-push coring machine, dissected by depth, and analyzed for total N, organic C, CaCO3, pH, cation exchange capacity (CEC), texture, and extractable NO3, NH(4), P, Cl, Ca, Mg, K, and Na. Ammonium N concentrations were greatest in the upper 0.5 m of soil under all four lagoons with concentrations ranging from 94 to 1139 mg kg(-1). Organic N was determined to make up between 39 and 74% of the total N beneath all lagoons. The swine lagoon had 2.4 kg N m(-2) in the underlying soil whereas the cattle lagoon with highest quantity of N had 1.2 kg N m(-2) in the underlying soil. Although N concentrations decreased with depth, N was greater than expected background levels at the bottom of some cores, indicating that the sampling efforts did not reach the bottom of the N plume. Nitrate N concentrations were generally less than 5 mg kg(-1) immediately below the lagoon floor. In the uppermost 0.5 m of soil underlying the swine and three cattle lagoons, NH4+ occupied 44% and between 1 and 22% of the soil cation exchange sites, respectively. The depth of movement of N under these lagoons, as much as 4 m, may pose remediation difficulties at lagoon closure.

Lagoon-biogas emissions and carbon balance estimates of a swine production facility.

Gaseous emissions from animal manure storage facilities can contribute to global greenhouse gas inventories. Biogas fluxes were measured for one year from a 2-ha anaerobic lagoon that received waste from a 10500-head swine (Sus scrofa) finishing operation in southwestern Kansas. During 2001, ebullition of biogas was measured continuously by using floating platforms equipped with gas-collection domes. Periodically, the composition of the biogas was determined by using gas chromatography. Detailed records of feed quality and quantity and animal weights and gains also were obtained to determine the carbon budget of the facility (barns and lagoon). Flux of biogas was very seasonal, with peak emission (18.7 mol m(-2) d(-1)) occurring in early June. Nearly 50% of the annual biogas losses occurred during a 30-d period beginning on day of year (DOY) 146. Flux patterns suggest that the start of the high biogas production period was governed by temperature, while the decline in production in mid-June was caused by substrate limitations. Average biogas composition was 0.71 L CH4 L(-1). The quantity of CH4 released from the lagoon was 86.3 Mg yr(-1), which represents about 38 g of CH4 per kg of animal weight gain. The average flux density of biogas from the lagoon was 382 mol m(-2) yr(-1) or 728 mol yr(-1) per resident animal where the resident animal population was 10500. Flux rates of CH4 were 1.7 to 3.4 times less than predictions made with Intergovernmental Panel on Climate Change (IPCC) models. Additional research is needed on the carbon budgets of other animal feeding operations so that better estimates of greenhouse gas emissions can be determined.

Biomass Production in a Tallgrass Prairie Ecosystem Exposed to Ambient and Elevated CO"2.

Responses to elevated CO"2 have not been measured for natural grassland ecosystems. Global carbon budgets will likely be affected by changes in biomass production and allocation in the major terrestrial ecosystems. Whether ecosystems sequester or release excess carbon to the atmosphere will partly determine the extent and rate that atmospheric CO"2 concentration rises. Elevated CO"2 also may change plant community species composition and water status. We determined above- and belowground biomass production, plant community species composition, and measured and modeled water status of a tallgrass prairie ecosystem in Kansas exposed to ambient and twice-ambient CO"2 concentrations in open-top chambers during the entire growing season from 1989 through 1991. Dominant species were Andropogon gerardii, A. scoparius, and Sorghastrum nutans (C"4 metabolism) and Poa pratensis (C"3). Aboveground biomass and leaf area were estimated by periodic sampling throughout the growing season in 1989 and 1990. In 1991, peak biomass and leaf area were estimated by an early August harvest. Relative root production among treatments was estimated using root ingrowth bags which remained in place throughout the growing season. Latent heat flux was simulated with and without water stress. Botanical composition was estimated annually. Compared to ambient CO"2 levels, elevated CO"2 increased production of C"4 grass species, but not of C"3 grass species. composition of C"4 grasses did not change, but Poa pratensis (C"3) declined, and C"3 forbs increased in the stand with elevated CO"2 compared to ambient. Open-top chambers appeared to reduce latent heat flux and increase water-use efficiency similar to the elevated CO"2 treatment when water stress was not severe, but under severe water stress, the chamber effect on water-use efficiency was limited. In natural ecosystems with periodic moisture stress, increased water-use efficiency under elevated CO"2 apparently would have a greater impact on productivity irrespective of photosynthetic pathway.