David S. Shafer

Wildfire responses to abrupt climate change in North America

It is widely accepted, based on data from the last few decades and on model simulations, that anthropogenic climate change will cause increased fire activity. However, less attention has been paid to the relationship between abrupt climate changes and heightened fire activity in the paleorecord. We use 35 charcoal and pollen records to assess how fire regimes in North America changed during the last glacial–interglacial transition (15 to 10 ka), a time of large and rapid climate changes. We also test the hypothesis that a comet impact initiated continental-scale wildfires at 12.9 ka; the data do not support this idea, nor are continent-wide fires indicated at any time during deglaciation. There are, however, clear links between large climate changes and fire activity. Biomass burning gradually increased from the glacial period to the beginning of the Younger Dryas. Although there are changes in biomass burning during the Younger Dryas, there is no systematic trend. There is a further increase in biomass burning after the Younger Dryas. Intervals of rapid climate change at 13.9, 13.2, and 11.7 ka are marked by large increases in fire activity. The timing of changes in fire is not coincident with changes in human population density or the timing of the extinction of the megafauna. Although these factors could have contributed to fire-regime changes at individual sites or at specific times, the charcoal data indicate an important role for climate, and particularly rapid climate change, in determining broad-scale levels of fire activity.

A Holocene climatic record for the Sonoran Desert from pollen analysis of Montezuma Well, Arizona, USA

Abstract Pollen and macrofossil analyses of a radiocarbon-dated core, 1125 cm long, from Montezuma Well, elev. 1125 m, Yavapai County, Arizona, provide a record of summer precipitation similar to that of other monsoonal regions of the world. Precipitation was least from 4000 to 5000 yr B.P., and generally was greater than today before 8400 yr B.P. During the early-Holocene moist period, oak and grass pollen are abundant, and the best modern analogs are within the Arizona Monsoon boundary, so increased summer precipitation is indicated. Climatic parameters are estimated with the technique of best modern analogs for fossil samples. Temperature was highest ca. 3400 and 5700 yr B.P., and generally was cooler than today before 6800 yr B.P. Brief cold intervals in the Holocene match periods of global cooling and of positive 14 C and 10 Be anomalies.

A New Technique for Characterizing the Efficacy of Fugitive Dust Suppressants

Abstract The Portable In-Situ Wind Erosion Laboratory (PI-SWERL) instrument was evaluated for testing the effectiveness of dust suppressants for a range of native and constructed soils. The PM10 (particles with diameter ≤10 µm) emissions from dust suppressant-treated and untreated soil surfaces were measured periodically over 14 months. No statistically significant differences were found among soil surfaces treated with three dilution mixtures of the dust suppressant. The temporal variation of PM10 emissions from treated and untreated plots for native and constructed soil textures indicated that: (1) reductions of PM10 emissions by the dust suppressant were significant within 2–3 months after the application and diminished substantially thereafter, (2) decomposition of the protective treated layer resulted in high PM10 emissions for longer environmental exposure times, and (3) emissions from untreated soil surfaces declined over time because of the formation of a natural crust. These results demonstrated that the PI-SWERL can provide qualitative and quantitative information on PM10 emissions for a range of soil textures and can be used to estimate the effectiveness of dust suppressants exposed to actual environmental (i.e., weather and solar radiation) conditions over long periods of time.

In situ observations of soil minerals and organic matter in the early phases of prescribed fires

[1] We examined the chemical composition of aerosol samples collected during a prescribed fire at a Great Basin Desert site in the context of samples collected from controlled combustion of vegetation clippings from the same site and resuspension of soil samples obtained prior to and after the burn event. We observed a distinct difference in the composition of organic carbon resuspended soil dust after the burn, reflecting changes caused by the heating of the soil. The relative abundances of minerals and organic carbon fractions in aerosols collected during the first period of the burn were identical to those measured in soil dust. For aerosol samples collected for the remaining two periods of the burn event, the profiles of both minerals and organic carbon matched quite well those observed for vegetation combustion. Reconstruction of aerosol samples collected during the burn event showed that vegetation combustion dominated emissions but mineral soil dust may account for about 10% of PM10 emissions (reconstructed) during the early stages of the fire. A large fraction of emissions during the first two hours was also unaccounted mainly because of the insufficient conversion of organic carbon to organic mass. The abundance of heavier non-volatile organics in soil dust suggested the presence of humic/fulvic acids that exhibit higher OM-to-OC ratios and thus, account for a proportion of the unaccounted emissions. These findings indicated that soil dust may be released into the air during a fire event, probably due to the enhanced turbulent mixing near the burn front.

Late Quaternary landscape evolution at Flat Laurel Gap, Blue Ridge Mountains, North Carolina

Abstract Analysis of colluvial, fluvial, and bog sediments at Flat Laurel Gap (1500 m) in the Blue Ridge Mountains of North Carolina provides a record of late Quaternary landscape evolution. Thermoluminescence (TL) analysis provides the first absolute-age determinations available for presumed periglacial deposits in the southern Appalachian Mountains. The Pleistocene/Holocene transition, dated between 11,900 and 10,100 yr B.P., represents a period of climatic amelioration and a change from colluvial to alluvial processes. A TL date of 7400 ± 1000 yr B.P. for matrix within a block-stream indicates possible early Holocene reworking of Pleistocene periglacial colluvium. Organic sediment deposition in a bog that began about 3400 yr B.P. increased in rate from 0.02 to 0.09 cm/yr with the onset of logging and land clearance about 1880 A.D.

Soil humic-like organic compounds in prescribed fire emissions using nuclear magnetic resonance spectroscopy.

Here we present the chemical characterization of the water-soluble organic carbon fraction of atmospheric aerosol collected during a prescribed fire burn in relation to soil organic matter and biomass combustion. Using nuclear magnetic resonance spectroscopy, we observed that humic-like substances in fire emissions have been associated with soil organic matter rather than biomass. Using a chemical mass balance model, we estimated that soil organic matter may contribute up to 41% of organic hydrogen and up to 27% of water-soluble organic carbon in fire emissions. Dust particles, when mixed with fresh combustion emissions, substantially enhances the atmospheric oxidative capacity, particle formation and microphysical properties of clouds influencing the climatic responses of atmospheric aeroso. Owing to the large emissions of combustion aerosol during fires, the release of dust particles from soil surfaces that are subjected to intense heating and shear stress has, so far, been lacking.

Spatiotemporal patterns in nutrient loads, nutrient concentrations, and algal biomass in Lake Taihu, China

Abstract Lake Taihu, Chinas third largest freshwater lake, exemplifies the severity of eutrophication problems in rapidly developing regions. We used long term land use, water quality, and hydrologic data from 26 in-lake and 32 tributary locations to describe the spatiotemporal patterns in nutrient loads, nutrient concentration, algal biomass, measured as chlorophyll a (Chl-a), in Lake Taihu. Point and nonpoint sources, as determined by chemical oxygen demand, contributed approximately 75 and 25% of the total nutrient loads to the lake, respectively. Spatial patterns in total phosphorus (TP) and total nitrogen (TN) concentrations in Lake Taihu strongly corresponded with observed loads from adjoining rivers with high concentrations proximate to densely populated areas. Chl-a concentrations exhibited spatial patterns similar to TP and TN concentrations. Generally, nutrient and Chl-a concentrations were highest in the northwestern region of the lake and lowest in the southeastern region of the lake. Seasonally, the largest nutrient loads occurred during summer. The annual net retention rate of TP and TN in Lake Taihu was approximately 30% of the total load. This study identifies regions of the lake and the watershed that are producing more nutrients to develop targeted management strategies. Reducing external P and N input from both point and nonpoint sources is obviously critical to address water quality issues in the lake. In addition, atmospheric deposition and resuspension of existing lake sediments also likely play a role in eutrophication processes and harmful algal blooms occurrence.

Sensitivity of Solute Advective Travel Time to Porosities of Hydrogeologic Units

An integral approach is proposed to quantify uncertainty and sensitivity of advective travel time to the effective porosities of hydrogeologic units (HGUs) along groundwater flow paths. The approach is applicable in situations where a groundwater flow model exists, but a full solute transport model is not available. The approach can be used to: (1) determine HGUs whose porosities are influential to the solute advective travel time; and (2) apportion uncertainties of solute advective travel times to the uncertainty contributions from individual HGU porosities. A simple one-dimensional steady-state flow example is used to illustrate the approach. Advective travel times of solutes are obtained based on the one-dimensional steady-state flow results in conjunction with the HGU porosities. The approach can be easily applicable to more complex multi-dimensional cases where advective solute travel time can be calculated based on simulated flow results from groundwater flow models. This approach is particularly valuable for optimizing limited resources when designing field characterization programs for uncertainty reduction by identifying HGUs that contribute most to the estimation uncertainty of advective travel times of solutes.

Coupled Environmental Processes and Long-term Performance of Landfill Covers in the northern Mojave Desert

Evapotransiration (ET) covers have gained widespread acceptance as a closure feature for waste disposal sites, particularly in the arid and semi-arid regions of the southwestern U.S. But as landforms, ET covers are subject to change over time because of processes such as pedogenesis, hydrologic processes, vegetation establishment and change, and biological processes. To better understand the effects of coupled process changes to ET covers, a series of four primary analog sites in Yucca Flat on the Nevada Test Site, along with measurements and observations from other locations in the Mojave Desert, were selected to evaluate changes in ET covers over time. The analog sites, of varying ages, were selected to address changes in the early post-institutional control period, the 1,000-year compliance period for disposal of low-level and mixed low-level waste, and the 10,000-year compliance period for transuranic waste sites.

Community Environmental Monitoring Program: a case study of public education and involvement in radiological monitoring.

The publics trust in the source of information about radiation is a key element of its acceptance. The public tends to trust two groups where risk communication is concerned: (1) scientists with expertise who are viewed as acting independently; and (2) friends, family, and other close associates who are viewed as sharing the same interests and concern, even if they have less knowledge of the subject. The Community Environmental Monitoring Program (CEMP) bridges both of these groups by having members of the public help operate and communicate results of a network of 29 radiation monitoring stations around the Nevada National Security Site (NNSS), formerly known as the Nevada Test Site (NTS), the principal continental location where the United States conducted nuclear tests. The CEMP stations, spread across a 160,000 km2 area, help provide evidence to the public that no releases of radiation of health concern are occurring from the NNSS to public receptors. The stations provide continuous measurements of gamma radiation and collect air particulate samples that are analyzed for radioactivity and meteorological measurements that aid in interpreting variations in background radiation. A public website (http://cemp.dri.edu) provides data for most instruments. Twenty-three of the 29 stations upload their data in near-real time to a public website as well as to digital readout displays at the stations, both of which are key elements in the CEMPs transparency. The remaining six stations upload their data hourly. Public stakeholders who are direct participants provide the most significant element of the CEMP. The “Community Environmental Monitors,” who are residents of towns where the stations are located, are part of the chain-of-custody for the air samples, perform minor station maintenance, and most significantly in terms of trust, serve as lay experts on issues concerning the NNSS and on ionizing radiation and nuclear technologies in general. The CEMP meets nearly all of the principles for stakeholder engagement identified by the International Radiation Protection Association.