Responses of Two New Hampshire (USA) Lakes to Human Impacts in Recent Centuries

This study contrasts the effects of human disturbances on two very different lake/catchment systems: Hatch Pond and Beaver Lake, New Hampshire. Hatch is in a steep mountain catchment remote from urban/industrial centers, and is a small, relatively deep, primarily seepage lake with moderate flushing rate. The catchment has been continuously forested, but disturbed by partial loggings and a forest fire. Beaver’s more extensive and gently sloping catchment is much closer to urban/industrial centers, and has been agricultural and recently suburban. Beaver is a larger but shallower drainage lake with much more rapid flushing than Hatch. We compared the sedimentary records and inferred limnological responses to catchment land uses and air pollution inputs of these mesotrophic lakes, and interpreted differing responses as a function of basic differences between the lakes and their catchments. Some chemical and biological variables in the sediment of both lakes respond sensitively to the first disturbances of the catchments by Euro-American settlers. Diatom-inferred Cl at both lakes indicates a modest increase of salinity at this time. Hatch sediment contains a record of soil erosion starting 1810 with first logging and fire. For ~125 years, erosion was largely of upper eluviated soil, but by 1935 it reached deeper into the illuviated (enriched) horizon. Maximal lake trophic state based on diatom-inferred limnological variables occurred in the mid-1900’s period of maximum sedimentation of illuviated soil. The sediment record since 1964 reflects forest maturation, and soil stabilization and acidification, but not lake acidification. At Beaver, the limnological effects of forest clearance and agriculture starting ~1700 were relatively mild due to gentleness of slopes and soil characteristics favoring stability. A near doubling of earth elements, and major increases in trace metal pollutants and coal combustion particles (CCP) occurred in sediment dating around 1900. Landscape analysis as well as historical and sedimentary records preclude the catchment as the major source of these increases. The most likely source is atmospheric fallout of CCP with its metal load. Despite controls on CCP and other emissions starting 1960, concentrations of earth elements and trace metals in Beaver sediment remain high due to soil mobilization by residential development of the catchment. The trophic state of Beaver Lake has increased, but the relative increase has been smaller than at Hatch, despite more intensive land uses and greater aerial inputs at Beaver. We propose that this lesser eutrophication is due to rapid flushing of Beaver Lake with stream water from relatively undeveloped parts of the extensive catchment, and lower sensitivity to nutrient inputs of this naturally more eutrophic lake. A major shift from unicellular to colonial chrysophytes at Hatch starts in the late-1800’s, and at Beaver in the early 1900’s. Colonial taxa in lesser quantities appear at the time of first settlement of the Beaver catchment. At both lakes the shifts are correlated with increasing metal fluxes from the opening of catchment biogeochemical cycles, as with the aforementioned erosional sequence at Hatch. But at Hatch aerial inputs of trace metals, and at Beaver aerial inputs major and trace metals associated with CCP are also correlated with the major chrysophyte shift. It appears that the chrysophytes have responded to stressors associated with both catchment disturbance and regional atmospheric inputs.     

Geochemical,mineralogical and microbiological characteristics of sediment from a naturally reduced zone in a uranium-contaminated aquifer

Localized zones or lenses of naturally reduced sediments have the potential to play a significant role in the fate and transport of redox-sensitive metals and metalloids in aquifers. To assess the mineralogy, microbiology and redox processes that occur in these zones, several cores from a region of naturally occurring reducing conditions in a U-contaminated aquifer (Rifle, CO) were examined. Sediment samples from a transect of cores ranging from oxic/suboxic Rifle aquifer sediment to naturally reduced sediment were analyzed for U and Fe content, oxidation state, and mineralogy; reduced S phases; and solid-phase organic C content using a suite of analytical and spectroscopic techniques on bulk sediment and size fractions. Solid-phase U concentrations were higher in the naturally reduced zone, with a high proportion of the U present as U(IV). The sediments were also elevated in reduced S phases and Fe(II), indicating it is very likely that U(VI), Fe(III), and SO₄ reduction has occurred or is occurring in the sediment. The microbial community was assessed using lipid- and DNA-based techniques, and statistical redundancy analysis was performed to determine correlations between the microbial community and the geochemistry. Increased concentrations of solid-phase organic C and biomass in the naturally reduced sediment suggests that natural bioreduction is stimulated by a zone of increased organic C concentration associated with fine-grained material and lower permeability to groundwater flow. Characterization of the naturally bioreduced sediment provides an understanding of the natural processes that occur in the sediment under reducing conditions and how they may impact natural attenuation of radionuclides and other redox sensitive materials. Results also suggest the importance of recalcitrant organic C for maintaining reducing conditions and U immobilization.     

Further seasonal changes in Uranus’ cloud structure observed by Gemini-North and UKIRT

Near-infrared observations of Uranus were made in October/November 2010 with the Gemini-North telescope in Hawaii, using NIFS, an integral field spectrograph, and the NIRI instrument in imaging mode. Observations were acquired using adaptive optics and have a spatial resolution of approximately 0.1–0.2″.The observed spectra along Uranus’ central meridian were analysed using a multiple-scattering retrieval algorithm to infer the vertical/latitudinal variation in cloud optical depth, which we compare with previous observations made by Gemini-North/NIFS in 2009 and UKIRT/UIST observations made between 2006 and 2008. Assuming a continuous distribution of small particles (r ～ 1 μm, and refractive index of 1.4 + 0i) with the single scattering albedo set to 0.75 and using a Henyey–Greenstein phase function with asymmetry parameter set to 0.7 at all wavelengths and latitudes, the retrieved cloud density profiles show that the north polar zone at 45°N has continued to steadily brighten while the south polar zone at 45°S has continued to fade. As with our previous analyses we find that, assuming that the methane vertical profile is the same at all latitudes, the clouds forming these polar zones at 45°N and 45°S lie at slightly lower pressures than the clouds at more equatorial latitudes. However, we also find that the Gemini data can be reproduced by assuming that the main cloud remains fixed at ～2 bar at all latitudes and adjusting the relative humidity of methane instead. In this case we find that the deep cloud is still more opaque at the equator and at the zones at 45°N and 45°S and shows the same seasonal trends as when the methane humidity remain fixed. However, with this approach the relative humidity of methane is seen to rise sharply from approximately 20% at polar latitudes to values closer to 80% for latitudes equatorward of 45°S and 45°N, consistent with the analysis of 2002 HST observations by Karkoschka and Tomasko (Karkoschka, E., Tomasko, M. [2009]. Icarus 202, 287–302), with a possible indication of seasonal variability. Overall, Uranus appeared to be less convectively active in 2010 than in the previous 4 years, supporting the conclusion that now the northern spring equinox (which occurred in 2007) has passed, the atmosphere is settling back into the more quiescent state seen by Voyager 2 in 1986.     

辽南变质核杂岩饮马湾山和赵房岩体锆石SHRIMP U-Pb年龄及其地质意义

辽南变质核杂岩形成于晚中生代华北岩石圈伸展和减薄背景下,其演化过程分为三个阶段：第一阶段（约130Ma）,在伸展作用下辽南地区发育拆离断层及其下伏韧性剪切带;第二阶段（130~120Ma）,同构造花岗质岩体的主动侵位影响了拆离断层的演化;同时在124Ma变质核杂岩的构造-岩浆活动达到峰值;第三阶段（113Ma之后）花岗质岩体在较浅层次侵位于停止活动的拆离断层带。辽南变质核杂岩发育与演化过程在年代学意义上揭示了华北板块晚中生代时期的区域性岩石圈伸展与减薄过程。本文认为由伸展后期侵位的赵房岩体所记录的拆离断层停止的时限（113Ma）可以作为华北岩石圈强烈构造岩浆活动的转捩点,113Ma之前华北板块广泛发育变质核杂岩、拉分盆地等一系列伸展构造,之后则以平稳的隆升和冷却过程为主。     

HARP/ACSIS: a submillimetre spectral imaging system on the James Clerk Maxwell Telescope

This paper describes a new Heterodyne Array Receiver Program (HARP) and Auto-Correlation Spectral Imaging System (ACSIS) that have recently been installed and commissioned on the James Clerk Maxwell Telescope. The 16-element focal-plane array receiver, operating in the submillimetre from 325 to 375 GHz, offers high (three-dimensional) mapping speeds, along with significant improvements over single-detector counterparts in calibration and image quality. Receiver temperatures are ∼120 K across the whole band, and system temperatures of ∼300 K are reached routinely under good weather conditions. The system includes a single-sideband (SSB) filter so these are SSB values. Used in conjunction with ACSIS, the system can produce large-scale maps rapidly, in one or more frequency settings, at high spatial and spectral resolution. Fully sampled maps of     size can be observed in under 1 h.
The scientific need for array receivers arises from the requirement for programmes to study samples of objects of statistically significant size, in large-scale unbiased surveys of galactic and extra-galactic regions. Along with morphological information, the new spectral imaging system can be used to study the physical and chemical properties of regions of interest. Its three-dimensional imaging capabilities are critical for research into turbulence and dynamics. In addition, HARP/ACSIS will provide highly complementary science programmes to wide-field continuum studies and produce the essential preparatory work for submillimetre interferometers such as the Submillimeter Array (SMA) and Atacama Large Millimeter/Submillimeter Array (ALMA).     

Evidence for a lost population of close-in exoplanets

We investigate the evaporation history of known transiting exoplanets in order to consider the origin of observed correlations between mass, surface gravity and orbital period. We show that the survival of the known planets at their current separations is consistent with a simple model of evaporation, but that many of the same planets would not have survived closer to their host stars. These putative closer-in systems represent a lost population that could account for the observed correlations. We conclude that the relation underlying the correlations noted by Mazeh et al. and Southworth et al. is most likely a linear cut-off in the   M ²/ R ³  versus   a ⁻²  plane, and we show that the distribution of exoplanets in this plane is in close agreement with the evaporation model.     

On the asteroid belt's orbital and size distribution

For absolute magnitudes greater than the current completeness limit of H-magnitude ∼15 the main asteroid belt's size distribution is imperfectly known. We have acquired good-quality orbital and absolute H-magnitude determinations for a sample of small main-belt asteroids in order to study the orbital and size distribution beyond H=15, down to sub-kilometer sizes (H>18). Based on six observing nights over a 11-night baseline we have detected, measured photometry for, and linked observations of 1087 asteroids which have one-week time baselines or more. The linkages allow the computation of full heliocentric orbits (as opposed to statistical distances determined by some past surveys). Judged by known asteroids in the field the typical uncertainty in the (a/e/i) orbital elements is less than 0.03 AU/0.03/0.5°. The distances to the objects are sufficiently well known that photometric uncertainties (of 0.3 magnitudes or better) dominate the error budget of their derived H-magnitudes. The detected asteroids range from HR=12-22 and provide a set of objects down to sizes below 1 km in diameter. We find an on-sky surface density of 210 asteroids per square degree in the ecliptic with opposition magnitudes brighter than mR=23, with the cumulative number of asteroids increasing by a factor of 10^0.27/mag from mR=18 down to the mR?23.5 limit of our survey. In terms of absolute H magnitudes, we find that beyond H=15 the belt exhibits a constant power-law slope with the number increasing proportional to ¹⁰0.30H from H?15 to 18, after which incompleteness begins in the survey. Examining only the subset of detections inside 2.5 AU, we find weak evidence for a mildly shallower slope for H=15-19.5. We provide the information necessary such that anyone wishing to model the main asteroid belt can compare a detailed model to our detected sample.     

Radio source calibration for the Very Small Array and other cosmic microwave background instruments at around 30 GHz

Accurate calibration of data is essential for the current generation of cosmic microwave background (CMB) experiments. Using data from the Very Small Array (VSA), we describe procedures which will lead to an accuracy of 1 per cent or better for experiments such as the VSA and CBI. Particular attention is paid to the stability of the receiver systems, the quality of the site and frequent observations of reference sources. At 30 GHz the careful correction for atmospheric emission and absorption is shown to be essential for achieving 1 per cent precision.
The sources for which a 1 per cent relative flux density calibration was achieved included Cas A, Cyg A, Tau A and NGC 7027 and the planets Venus, Jupiter and Saturn. A flux density, or brightness temperature in the case of the planets, was derived at 33 GHz relative to Jupiter which was adopted as the fundamental calibrator. A spectral index at ∼30 GHz is given for each.
Cas A, Tau A, NGC 7027 and Venus were examined for variability. Cas A was found to be decreasing at 0.394 ± 0.019 per cent yr⁻¹ over the period 2001 March to 2004 August. In the same period Tau A was decreasing at 0.22 ± 0.07 per cent yr⁻¹. A survey of the published data showed that the planetary nebula NGC 7027 decreased at 0.16 ± 0.04 per cent yr⁻¹ over the period 1967–2003. Venus showed an insignificant (1.5 ± 1.3 per cent) variation with Venusian illumination. The integrated polarization of Tau A at 33 GHz was found to be 7.8 ± 0.6 per cent at position angle =148°± 3°.