Search

Agricultural development may produce highly fragmented landscapes, which can influence population genetic structure for organisms restricted to insularized breeding habitats. Common Nighthawks (Chordeiles minor) in agriculturally dominated landscapes nest on urban gravel rooftop and might be subject to reduced gene flow among isolated urban sites. We conducted an analysis of the genetic variability and population genetic structure of Common Nighthawks nesting on rooftops in four towns in southeastern South Dakota, an area that has experienced extreme conversion of native prairie to agriculture. Using sequence data from a 725 bp region of the cytochrome b (cytb) mitochondrial gene sampled from 37 individuals representing a total of 30 different nests collected in summers 2014-2016, we found evidence of a recent population bottleneck and reduced mtDNA variability. The spatial dispersion of the 14 detected haplotypes and the presence of nine haplotypes unique to one of the four sampled towns further suggested a lack of panmixia among these nighthawks. These data are consistent with a hypothesis of habitat fragmentation due to agricultural expansion resulting in population isolation within this species of conservation concern., INTRODUCTIONSince the 1980s aerial insectivorous birds have experienced one of the most prominent population declines of any bird guild (Sauer et al., 2007; Nebel et al., 2010). This decline may [...]

Whole air drawn from four heights within the high elevation (3,340 m asl), deep, winter snowpack at Niwot Ridge, Colorado, were sampled into stainless steel canisters, and subsequently analyzed by gas chromatography for 51 volatile inorganic and organic gases. Two adjacent plots with similar snow cover were sampled, one over bare soil and a second one from within a snow-filled chamber where Tedlar/Teflon-film covered the ground and isolated it from the soil. This comparison allowed for studying effects from processes in the snowpack itself versus soil influences on the gas concentrations and fluxes within and through the snowpack. Samples were also collected from ambient air above the snow surface for comparison with the snowpack air. Analyzed gas species were found to exhibit three different kinds of behavior: (1) One group of gases, i.e., carbon dioxide (CO₂), chloroform (CHCl₃), dimethylsulfide (CH₃)₂S, carbondisulfide (CS₂), and dichlorobromomethane (CHBrCl₂), displayed higher concentrations inside the snow, indicating a formation of these species and release into the atmosphere. (2) A second group of compounds, including carbon monoxide (CO), carbonyl sulfide (COS), the hydrocarbons methane, ethane, ethyne, benzene, and the halogenated compounds methylchloride (CH₃Cl), methylbromide (CH₃Br), dibromomethane (CH₂Br₂), bromoform (CHBr₃), tetrachloromethane (CCl₄), CFC-11, CFC-12, HCFC-22, CFC-113, 1,2-dichloroethane, methylchloroform, HCFC-141b, and HCFC-142b, were found at lower concentrations in the snow, indicating that the snow and/or soil constitute a sink for these gases. (3) For 21 other gases absolute concentrations, respectively concentration gradients, were too low to unequivocally identify their uptake or release behavior. For gases listed in the first two groups, concentration gradients were incorporated into a snowpack gas diffusion model to derive preliminary estimates of fluxes at the snow-atmosphere interface. The snowpack gradient flux technique was found to offer a highly sensitive method for the study of these surface gas exchanges. Microbial activities below this deep, winter snowpack appear to be the driving mechanism behind these gas sources and sinks. Flux results were applied to a simple box model to assess the potential contribution of the snowpack uptake rates to atmospheric lifetimes of these species.

Measurements of organic carbon compounds in both the gas and particle phases made upwind, over and downwind of North America are synthesized to examine the total observed organic carbon (TOOC) in the atmosphere over this region. These include measurements made aboard the NOAA WP-3 and BAe-146 aircraft, the NOAA research vessel Ronald H. Brown, and at the Thompson Farm and Chebogue Point surface sites during the summer 2004 ICARTT campaign. Both winter and summer 2002 measurements during the Pittsburgh Air Quality Study are also included. Lastly, the spring 2002 observations at Trinidad Head, CA, surface measurements made in March 2006 in Mexico City and coincidentally aboard the C-130 aircraft during the MILAGRO campaign and later during the IMPEX campaign off the northwestern United States are incorporated. Concentrations of TOOC in these datasets span more than two orders of magnitude. The daytime mean TOOC ranges from 4.0 to 456 mu gCm(-3) from the cleanest site (Trinidad Head) to the most polluted (Mexico City). Organic aerosol makes up 3-17% of this mean TOOC, with highest fractions reported over the northeastern United States, where organic aerosol can comprise up to 50% of TOOC. Carbon monoxide concentrations explain 46 to 86% of the variability in TOOC, with highest TOOC/CO slopes in regions with fresh anthropogenic influence, where we also expect the highest degree of mass closure for TOOC. Correlation with isoprene, formaldehyde, methyl vinyl ketone and methacrolein also indicates that biogenic activity contributes substantially to the variability of TOOC, yet these tracers of biogenic oxidation sources do not explain the variability in organic aerosol observed over North America. We highlight the critical need to develop measurement techniques to routinely detect total gas phase VOCs, and to deploy comprehensive suites of TOOC instruments in diverse environments to quantify the ambient evolution of organic carbon from source to sink.

We present data collected from a number of snow-covered environments including two polar locations (Summit, Greenland and the South Pole) and two mid-latitude regions (a remote site in northern Michigan, and Niwot Ridge, Colorado). At each site, concentrations of CH3 I and C2 H5 I were enhanced within the interstitial air near the snow surface, compared to levels in boundary layer air. Fluxes of CH3 Br from surface snow to the atmosphere were observed at each site except Niwot Ridge, where CH3 Br appeared to have a sink. The mid-latitude sites showed significant emissions of CH3 Cl, mostly originating at the ground surface and traveling up through the snow, while at the polar locations CH3 Cl emissions from firn air were relatively small. In general, methyl halide mixing ratios in firn air were significantly greater at Summit than at the South Pole, with Summit showing a strong diurnal cycle in the production of alkyl halides that was well correlated with actinic radiation and firn temperature. We suggest that the most likely route to alkyl halide formation is through an acid catalyzed nucleophilic substitution of an alcohol type function by a halide, both of which should be preferentially segregated to the quasi-liquid layer at the surface of the snow grains. A series of experiments using a snow-filled quartz chamber irradiated by natural sunlight allowed estimation of emission trends that were hard to measure in the natural snowpack. These static chamber experiments confirmed significant production of the primary alkyl halides, following the order CH3 Cl > CH3 Br > C2 H5 Cl > CH3 I > C2 H5 Br > C2 H5 I > 1 - C3 H7 Br > 1 - C3 H7 I. Our observations at all four locations, including polar and mid-latitude sites, imply that alkyl halide production may be associated with all surface snows. © 2007 Elsevier Ltd. All rights reserved.

Experiments were performed at Summit, Greenland (72°34′ N, 38°29′ W) to investigate hydroxyl mixing ratios in the sunlit surface snowpack (or firn). We added a carefully selected mixture of hydrocarbon gases (with a wide range of hydroxyl reactivities) to a UV and visible light transparent flow chamber containing undisturbed natural firn. The relative decrease in mixing ratios of these gases allowed estimation of the lower limit mixing ratio of hydroxyl radicals in the near-surface firn pore spaces. Hydroxyl mixing ratios in the firn air followed a diurnal cycle in summer 2003 (10-12 July), with peak values of more than 3.2×106 molecules cm-3 between 13:00 and 16:00 local time. The minimum value estimated was 1.1×106 molecules cm-3 at 20:00 local time. Results during spring of 2004 showed lower, but rapidly increasing, peak hydroxyl mixing ratios of 1.1×106 molecules cm-3 in the early afternoon on 15 April and 1.5×106 molecules cm-3 on 1 May. Our firn hydroxyl estimates were similar to directly measured above-snow ambient levels during the spring field season, but were only about 30% of ambient levels during summer. © 2007 Elsevier Ltd. All rights reserved.