Ensemble properties of comets in the Sloan Digital Sky Survey

We present the ensemble properties of 31 comets (27 resolved and 4 unresolved) observed by the Sloan Digital Sky Survey (SDSS). This sample of comets represents about 1 comet per 10 million SDSS photometric objects. Five-band (u, g, r, i, z) photometry is used to determine the comets’ colors, sizes, surface brightness profiles, and rates of dust production in terms of the Afρ formalism. We find that the cumulative luminosity function for the Jupiter Family Comets in our sample is well fit by a power law of the form N(<H) ∝ 10^{(0.49±0.05)H} for H < 18, with evidence of a much shallower fit N(<H) ∝ 10^{(0.19±0.03)H} for the faint (14.5 < H < 18) comets. The resolved comets show an extremely narrow distribution of colors (0.57 ± 0.05 in g ? r for example), which are statistically indistinguishable from that of the Jupiter Trojans. Further, there is no evidence of correlation between color and physical, dynamical, or observational parameters for the observed comets.     

The Impact of Hurricane Katrina on Reported Crimes in Louisiana: A Spatial and Temporal Analysis

This research assesses the impact that one natural disaster—Hurricane Katrina—and subsequent population movements have had on crime in the state of Louisiana. Using Index Crimes from the Louisiana Commission on Law Enforcement and population estimates from the U.S. Census Bureau, time series of violent and nonviolent crime rates were first analyzed using autoregressive, integrated, and moving average (ARIMA) models. Cumulative percentile maps were created next to analyze spatial trends of crime hot and cold spots in the study area. Overall, results from this research support theories that suggest that crime rates remain stable or actually decline in regions receiving evacuees from areas hardest hit by the hurricane. In the case of Orleans Parish, results are inconclusive due to unreliable crime rates for the period following Hurricane Katrina until the beginning of 2006. It is suggested that crime rates in Orleans Parish fell drastically after the storm. However, some crime types, including robbery, burglary, and larceny, returned to pre-Katrina levels and murder and aggravated assault even exceeded prestorm averages by the end of December 2007.     

Potential of groundwater contamination by polybrominated diphenyl ethers (PBDEs) in a sensitive bedrock aquifer (Canada)

It is necessary to understand the presence, movement, and persistence of contaminants in aquifers to develop adequate groundwater protection plans. Fractured bedrock aquifers with thin overburden cover are very sensitive to contamination, and little is known about transport processes from the ground surface to depth in this setting. This study was undertaken to investigate the potential of groundwater contamination by polybrominated diphenyl ethers (PBDEs), which are flame retardants, in a natural fractured bedrock aquifer in Canada proven to be sensitive to contamination. PBDEs, which had not been previously measured in groundwater in detail, were detected in the study aquifer at concentrations greater than those observed in surface-water bodies. Potential sources include manure, septic tanks, and the atmosphere. From this scoping study, it is evident that additional surveys of PBDE concentrations in groundwater are warranted, especially in settings with high potential source concentrations coupled with sensitive aquifers.     

Factors Controlling In Situ Biogeochemical Transformation of Trichloroethene: Column Study

In situ biogeochemical transformation involves biological formation of reactive minerals in an aquifer that can destroy chlorinated solvents such as trichloroethene (TCE) without accumulation of intermediates such as vinyl chloride. There is uncertainty regarding the materials and geochemical conditions that are required to promote biogeochemical transformation. The objective of this study was to identify amendments and biogeochemical conditions that promote in situ biogeochemical transformation. Laboratory columns constructed with plant mulch were supplemented with different amendments and were operated under varying conditions of water chemistry and hydraulic residence time. Four patterns of TCE removal were observed: (1) no removal, (2) biotic transformation of TCE to cis‐1,2‐dichloroethene (cis‐1,2‐DCE), (3) biogeochemical transformation of TCE without accumulation of reductive dechlorination products, and (4) mixed behavior where a combination of patterns was observed either simultaneously or over time. Principal coordinates analysis and analysis of variance (ANOVA) identified factors that promoted biogeochemical transformation: (1) high influent sulfate concentration, (2) relatively high hydraulic retention time, (3) supplementation of mulch with vegetable oil, and (4) addition of hematite or magnetite. The combination of the first three factors promoted complete sulfate reduction and a high volumetric sulfate consumption rate. The fourth factor provided a source of ferrous iron and/or a surface to which sulfide could react to form reactive iron sulfides. Many columns demonstrated either no TCE removal or a biotic TCE transformation pattern. Modification of column operation to include all four factors identified above promoted biogeochemical transformation in these columns. These results support the importance of the factors in biogeochemical transformation.     

Isotopic evidence for temporal variation in proportion of seasonal precipitation since the last glacial time in the inland Pacific Northwest of the USA

Large-scale atmospheric circulation patterns determine the quantity and seasonality of precipitation, the major source of water in most terrestrial ecosystems. Oxygen isotope (δ¹⁸O) dynamics of the present-day hydrologic system in the Palouse region of the northwestern U.S.A. indicate a seasonal correlation between the δ¹⁸O values of precipitation and temperature, but no seasonal trends of δ¹⁸O records in soil water and shallow groundwater. Their isotope values are close to those of winter precipitation because the Palouse receives  75% of its precipitation during winter. Palouse Loess deposits contain late Pleistocene pedogenic carbonate having ca. 2 to 3‰ higher δ¹⁸O values and up to 5‰ higher carbon isotope (δ¹³C) values than Holocene and modern carbonates. The late Pleistocene δ¹⁸O values are best explained by a decrease in isotopically light winter precipitation relative to the modern winter-dominated infiltration. The δ¹³C values are attributed to a proportional increase of atmospheric CO₂ in soil CO₂ due to a decrease in soil respiration rate and ¹³C discrimination in plants under much drier paleoclimate conditions than today. The regional climate difference was likely related to anticyclonic circulation over the Pleistocene Laurentide and Ice Sheet.     

Identification of best predictors for forecasting seasonal rainfall and runoff in Australia

The first step towards developing a reliable seasonal runoff forecast is identifying the key predictors that drive rainfall and runoff. This paper investigates the lag relationships between rainfall across Australia and runoff across southeast Australia versus 12 atmospheric‐oceanic predictors, and how the relationships change over time. The analysis of rainfall data indicates that the relationship is greatest in spring and summer in northeast Australia and in spring in southeast Australia. The best predictors for spring rainfall in eastern Australia are NINO4 [sea surface temperature (SST) in western Pacific] and thermocline (20 °C isotherm of the Pacific) and those for summer rainfall in northeast Australia are NINO4 and Southern Oscillation Index (SOI) (pressure difference between Tahiti and Darwin). The relationship in northern Australia is greatest in spring and autumn with NINO4 being the best predictor. In western Australia, the relationship is significant in summer, where SST2 (SST over the Indian Ocean) and II (SST over the Indonesian region) is the best predictor in the southwest and northwest, respectively. The analysis of runoff across southeast Australia indicates that the runoff predictability in the southern parts is greatest in winter and spring, with antecedent runoff being the best predictor. The relationship between spring runoff and NINO4, thermocline and SOI is also relatively high and can be used together with antecedent runoff to forecast spring runoff. In the northern parts of southeast Australia, the atmospheric‐oceanic variables are better predictors of runoff than antecedent runoff, and have significant correlation with winter, spring and summer runoff. For longer lead times, the runoff serial correlation is reduced, especially over the northern parts, and the atmospheric‐oceanic variables are likely to be better predictors for forecasting runoff. The correlations between runoff versus the predictors vary with time, and this has implications for the development of forecast relationship that assumes stationarity in the historical data. Copyright © 2010 John Wiley & Sons, Ltd.     

Using soil and contaminant properties to assess the potential for groundwater contamination to the lower Great Lakes,USA

Contaminant risk factors in surface soil were evaluated within the urbanized Rouge River watershed in southeastern Michigan, USA, which includes metropolitan Detroit. An analytical risk factor model and Geographic Information Systems overlays were used to quantify and characterize the potential impacts of five categories of contaminants including DNAPLs (dense nonaqueous phase liquids), LNAPLs (light nonaqueous phase liquids), PAHs (polynuclear aromatic hydrocarbons), PCBs (polychlorinated biphenyls), and lead. The results indicate that DNAPL compounds released into sand, moraine, and sandy and silty clay soil types have the greatest potential to affect groundwater, and impact the Great Lakes ecosystem and the public health.     

Nutrient availability in support of Karenia brevis blooms on the central West Florida Shelf: What keeps Karenia blooming?

Identifying nutrient sources, primarily nitrogen (N) and phosphorus (P), sufficient to support high biomass blooms of the red tide dinoflagellate, Karenia brevis, has remained problematic. The West Florida Shelf is oligotrophic, yet populations >10⁶ cells L⁻¹ frequently occur and blooms can persist for months. Here we examine the magnitude and variety of sources for N and P that are available to support blooms. Annual average in situ or background concentrations of inorganic N in the region where blooms occur range 0.02–0.2 μM while inorganic P ranges 0.025–0.24 μM. Such concentrations would be sufficient to support the growth of populations up to ∼3×10⁴ cells L⁻¹ with at least a 1 d turnover rate. Organic N concentrations average 1–2 orders of magnitude greater than inorganic N, 8–14 μM while organic P concentrations average 0.2–0.5 μM. Concentrations of organic N are sufficient to support blooms >10⁵ cells L⁻¹ but the extent to which this complex mixture of N species is utilizable is unknown. Other sources of nutrients included in our analysis are aerial deposition, estuarine flux, benthic flux, zooplankton excretion, N₂-fixation, and subsequent release of organic and inorganic N by Trichodesmium spp., and release of N and P from dead and decaying fish killed by the blooms. Inputs based on atmospheric deposition, benthic flux, and N₂-fixation, were minor contributors to the flux required to support growth of populations >2.6×10⁴ cells L⁻¹. N and P from decaying fish could theoretically maintain populations at moderate concentrations but insufficient data on the flux and subsequent mixing rates does not allow us to calculate average values. Zooplankton excretion rates, based on measured zooplankton population estimates and excretion rates could also supply all of the N and P required to support populations of 10⁵ and 10⁶ cells L⁻¹, respectively, but excretion is considered as “regenerated” nutrient input and can only maintain biomass rather than contribute to “new” biomass. The combined estuarine flux from Tampa Bay, Charlotte Harbor, and the Caloosahatchee River can supply a varying, but at times significant level of N and P to meet growth and photosynthesis requirements for populations of approximately 10⁵ cells L⁻¹ or below. Estimates of remineralization of dead fish could supply a significant proportion of bloom maintenance requirements but the rate of supply must still be determined. Overall, a combination of sources is required to maintain populations >10⁶ cells L⁻¹.     

TTGs and adakites: are they both slab melts?

Although both high-Al TTG (tonalite–trondhjemite–granodiorite) and adakite show strongly fractionated REE and incompatible element patterns, TTGs have lower Sr, Mg, Ni, Cr, and Nb/Ta than most adakites. These compositional differences cannot be easily related by shallow fractional crystallization. While adakites are probably slab melts, TTGs may be produced by partial melting of hydrous mafic rocks in the lower crust in arc systems or in the Archean, perhaps in the root zones of oceanic plateaus. It is important to emphasize that geochemical data can be used to help constrain tectonic settings, but it cannot be used alone to reconstruct ancient tectonic settings.

Depletion in heavy REE and low Nb/Ta ratios in high-Al TTGs require both garnet and low-Mg amphibole in the restite, whereas moderate to high Sr values allow little, if any, plagioclase in the restite. To meet these requirements requires melting in the hornblende eclogite stability field between 40- and 80-km deep and between 700 and 800 °C.

Some high-Al TTGs produced at 2.7 Ga and perhaps again at about 1.9 Ga show unusually high La/Yb, Sr, Cr, and Ni. These TTGs may reflect catastrophic mantle overturn events at 2.7 and 1.9 Ga, during which a large number of mantle plumes bombarded the base of the lithosphere, producing thick oceanic plateaus that partially melted at depth.     

Kinetics of sorption and abiotic oxidation of arsenic(III) by aquifer materials

The fate of arsenic in groundwater depends largely on its interaction with mineral surfaces. We investigated the kinetics of As(III) oxidation by aquifer materials collected from the USGS research site at Cape Cod, MA, USA, by conducting laboratory experiments. Five different solid samples with similar specific surface areas (0.6-0.9 m² g⁻¹) and reductively extractable iron contents (18-26 μmol m⁻²), but with varying total manganese contents (0.5-3.5 μmol m⁻²) were used. Both dissolved and adsorbed As(III) and As(V) concentrations were measured with time up to 250 h. The As(III) removal rate from solution increased with increasing solid manganese content, suggesting that manganese oxide is responsible for the oxidation of As(III). Under all conditions, dissolved As(V) concentrations were very low. A quantitative model was developed to simulate the extent and kinetics of arsenic transformation by aquifer materials. The model included: (1) reversible rate-limited adsorption of As(III) onto both oxidative and non-oxidative (adsorptive) sites, (2) irreversible rate-limited oxidation of As(III), and (3) equilibrium adsorption of As(V) onto adsorptive sites. Rate constants for these processes, as well as the total oxidative site densities were used as the fitting parameters. The total adsorptive site densities were estimated based on the measured specific surface area of each material. The best fit was provided by considering one fast and one slow site for each adsorptive and oxidative site. The fitting parameters were obtained using the kinetic data for the most reactive aquifer material at different initial As(III) concentrations. Using the same parameters to simulate As(III) and As(V) surface reactions, the model predictions were compared to observations for aquifer materials with different manganese contents. The model simulated the experimental data very well for all materials at all initial As(III) concentrations. The As(V) production rate was related to the concentrations of the free oxidative surface sites and dissolved As(III), as with apparent second-order rate constants of and for the fast and the slow oxidative sites, respectively. The As(III) removal rate decreased approximately by half for a pH increase from 4 to 7. The pH dependence was explained using the acid-base behavior of the surface oxidative sites by considering a surface pK_a = 6.2 (I = 0). In the presence of excess surface adsorptive and oxidative sites, phosphate diminished the rate of As(III) removal and As(V) production only slightly due to its interaction with the oxidative sites. The observed As(III) oxidation rate here is consistent with previous observations of As(III) oxidation over short transport distances during field-scale transport experiments. The model developed here may be incorporated into groundwater transport models to predict arsenic speciation and transport in chemically heterogeneous systems.