Quantifying the effect of humic matter on the emission of mercury from artificial soil surfaces

A set of surface samples was created using purified laboratory grade sand treated with 0.05 μg/g Hg as the HgCl₂ salt and various concentrations of purified humic and fulvic acids. Emissions of elemental Hg from these substrates to the atmosphere were inversely correlated with the organic content of the samples (99% confidence level). The greatest differences in Hg emissions were found between samples containing the lowest concentrations of humic matter (0% versus 0.01% humic, and 0.01% versus 0.1% humic), only small differences in Hg flux were found to exist for samples with higher concentrations of humic acid (1%, 5%, and 100%). This effect was independent of the type of humic substance used, with both humic and fulvic acids showing an inhibitory effect on surface Hg emissions.     

Diurnal Variations in the Characteristics of Cloud-to-Ground Lightning Activity in the Great Lakes Region of the United States

Cloud-to-ground (CG) lightning observations for the warm seasons (May-September) of 1989 and 1990 were analyzed for the Great Lakes region in order to assess the diurnal variations in the lightning characteristics. Several parameters, including flash rate, the spatial extent of lightning activity, first stroke peak current, and the percentage of positive flashes, varied markedly over the course of the day. In contrast, other parameters, such as the frequency of lightning periods and the multiplicity of both negative and positive CG flashes, displayed little diurnal variation. A large degree of intraseasonal (i.e., month-to-month) variation was observed in the diurnal patterns for several of the lightning parameters.     

Lawn People: How Grasses,Weeds, and Chemicals Make Us Who We Are

Forty percent of all firms in the United States are owned and operated by women. At current growth rates, women could own 50% of the nation's businesses by the turn of the century. Women have been prompted to start their businesses for many reasons, including the desire to avoid gender-based discrimination in the workplace. But female entrepreneurs who venture out on their own must still contend with gender discrimination. This study examines female entrepreneurship in Illinois through rural versus urban comparisons of male and female business owners. We surveyed 4,200 business owners to test the hypothesis that gender and geographic location combined to hinder the entrepreneurial success of women. Business owners were asked about personal attributes including gender, work experience, education, training, and prior career status. Entrepreneurs were also asked about firm characteristics such as financing sources, number of employees, revenues, problems encountered during startup, sector of new firm, geographic location, and the importance of selected community characteristics. Our results show that rural female entrepreneurs face more obstacles to business success than their male or urban female counterparts.     

Investigation of the mud crab (Scylla serrata) as a potential bio-monitoring species for tropical coastal marine environments of Australia

Mud crabs, Scylla serrata, were sampled from four estuaries (the Normanby, Herbert, Burdekin and Fitzroy Rivers) along the coast of northern Queensland, Australia, representing a pollution gradient from low to high contamination based upon previous chemical monitoring. Four biomarkers; glutathione-S-transferase (GST) activity, cholinesterase (ChE) inhibition and the urinary metabolite concentrations of naphthalene (NPH) and benzo-a-pyrene (BaP) were evaluated in S. serrata hepatopancreas, haemolymph and urine. Site-specific evidence of elevated GST activity and BaP metabolite concentrations and significant ChE inhibition was detected. Biomarker responses from this field study provide evidence of contaminant exposure of S. serrata from river estuaries along the coast of northern Queensland and indicate that further investigation is warranted. Based on the current results, and with further work on characterising the dose-response and seasonal variation in this species, mud crabs have great potential as indicator species for water quality and ecosystem monitoring programs across tropical coastal regions of Australia.     

Observed and simulated water and energy budget components at SCAN sites in the lower Mississippi Basin

Land surface models are typically constrained by one or a few observed variables, while assuming that the internal water and energy partitioning is sensitive to those observed variables and realistic enough to simulate unobserved variables. To verify these assumptions, in situ soil climate analysis network (SCAN) observations in the Lower Mississippi Basin (2002–2008) are analysed to quantify water and energy budget components and they are compared to Community Land Model (CLM3·5) simulations. The local soil texture is identified as a major indicator for water storage characteristics and the Normalized Difference Vegetation Index shows potential as a drought indicator in summer months. Both observations and simulations indicate a regime where, except in some summer months, evapotranspiration controls soil moisture. CLM simulations with different soil texture assignments show discharge sensitivity to soil moisture, but almost no impact on evapotranspiration and other energy balance components. The observed and simulated water budgets show a similar partitioning. However, the SCAN observed water balance does not close because of precipitation measurement errors, unobserved irrigation, lack of specific storage change measurements and errors in the computed actual evapotranspiration. The simulated heat flux partitioning differs from that ‘observed’, with a larger (resp. smaller) fraction of net radiation being used by latent (resp. sensible) heat flux, and unobserved freeze and thaw events. The comparison between observations and model simulations suggests that a consistent observation collection for multiple variables would be needed to constrain and improve the full set of land surface variable estimates. Copyright © 2010 John Wiley & Sons, Ltd.     

Causes of systematic over‐ or underestimation of low streamflows by use of index‐streamgage approaches in the United States

Low‐flow characteristics can be estimated by multiple linear regressions or the index‐streamgage approach. The latter transfers streamflow information from a hydrologically similar, continuously gaged basin (‘index streamgage’) to one with a very limited streamflow record, but often results in biased estimates. The application of the index‐streamgage approach can be generalized into three steps: (1) selection of streamflow information of interest, (2) definition of hydrologic similarity and selection of index streamgage, and (3) application of an information‐transfer approach. Here, we explore the effects of (1) the range of streamflow values, (2) the areal density of streamgages, and (3) index‐streamgage selection criteria on the bias of three information‐transfer approaches on estimates of the 7‐day, 10‐year minimum streamflow (Q_{7, 10}). The three information‐transfer approaches considered are maintenance of variance extension, base‐flow correlation, and ratio of measured to concurrent gaged streamflow (Q‐ratio invariance). Our results for 1120 streamgages throughout the United States suggest that only a small portion of the total bias in estimated streamflow values is explained by the areal density of the streamgages and the hydrologic similarity between the two basins. However, restricting the range of streamflow values used in the index‐streamgage approach reduces the bias of estimated Q_{7, 10} values substantially. Importantly, estimated Q_{7, 10} values are heavily biased when the observed Q_{7, 10} values are near zero. Results of the analysis also showed that Q_{7, 10} estimates from two of the three index‐streamgage approaches have lower root‐mean‐square error values than estimates derived from multiple regressions for the large regions considered in this study. Published in 2011 by John Wiley & Sons, Ltd.     

Intraspecific Interactions and Risk of Predation for Dyspanopeus sayi (Decapoda: Xanthidae) Living on Polychaete (Filograna implexa,Serpulidae) Colonies*

Abstract. Along the Atlantic coast of the United States, the mud crab Dyspanopeus sayi frequently occurs in crevices and depressions within aggregated calcareous tubes (termed “heads”) of the serpulid polychaete Filograna implexa. In New Jersey, U.S.A., waters, crab number was significantly correlated with the logarithm of worm tube colony volume. Laboratory experiments suggested that crabs compete for shelter within worm colonies. Additional laboratory experiments indicated that colony occupancy greatly decreased the risk of predation by blue crabs (Callinectes sapidus), and field tethering experiments also demonstrated that colony occupancy significantly decreased predation risk. Thus, the consequence of holding space on worm tube heads is a greatly increased probability of survival.     

Nature and origin of the J‐magnetic anomaly offshore Iberia–Newfoundland: implications for plate reconstructions

The nature and origin of the J‐magnetic anomaly along the Iberia–Newfoundland margins are controversial and its validity for plate kinematic reconstructions questioned. At present, it is interpreted as either an oceanic isochron or an edge effect of oceanic crust corresponding to lithosphere breakup. Both interpretations result in restorations that are in conflict with the current knowledge from Pyrenean and North Atlantic geology. We combine seismic interpretations and dating of magmatic additions with magnetic data to examine the nature and formation process of this anomaly and discuss its value for plate restorations. We show that the J‐anomaly is the result of polygenic and multiple magmatic events occurring during and after the formation of the first oceanic crust. Therefore, we conclude that the J‐anomaly cannot be used for plate kinematic studies and, more generally, we question the validity of using ill‐defined magnetic anomalies outside unequivocal oceanic domains for plate reconstructions.     

Plant migration and plant communities at the time of the “green Sahara”

Around 8500 cal years BP, at the time of the maximum of the African Humid Period, lakes and wetlands expanded in the present-day Sahara while large paleodrainages were formed or re-actived, in response to an orbitally-induced increase in monsoon rainfall. It has been suggested that the direct consequence of this increase in rainfall was the northward displacement of the Sahara/Sahel boundary, thought to have reached 23°N in central and eastern Africa. Here, we show a more complex situation characterized by an increase in biodiversity as the desert accommodated more humid-adapted species from tropical forests and wooded grasslands: tropical plant species now found some 400 to 500 km to the south probably entered the desert as gallery-forest formations along rivers and lakes where they benefited from permanent fresh water. At the same time, Saharan trees and shrubs persisted, giving rise to a vegetation that has no analogue today. In this article, we present distribution maps of selected plant species to show both the amplitude of the vegetation change compared to the present and the composition of the past plant communities. We also estimate the migration rate of tropical plant taxa to their northernmost position in the Sahara. This study is based on the use of several data sets: a data set of the modern plant distribution in northern Africa and a data set of modern and fossil pollen sites (from the African Pollen Database, http://fpd.mediasfrance.org/ and http://medias.obs-mip.fr/apd/).     

The fluvial and geomorphic context of Indian Knoll,an Archaic shell midden in West‐Central Kentucky

Indian Knoll is the largest Archaic shell midden excavated by WPA archaeologists in Kentucky. Situated in a large alluvial valley, the site is not associated with a known river shoal as might be expected, making its fluvial and geomorphic setting of interest. Based on sediment cores and auger samples, undisturbed portions of the site remain despite extensive excavations. In undisturbed portions, a shell‐bearing layer is overlain by a shell‐free midden layer. Profiles of organic matter and calcium carbonate content for both layers are similar to those of other Green River shell middens. New radiocarbon determinations date the shell deposit at 5590–4530 cal yr B.P. Analysis of mussel species collected from the Indian Knoll indicates that shell fishing took place in a swiftly flowing, shallow to moderately deep setting of the main river channel. Overall, the prehistoric river setting adjacent to Indian Knoll was characterized by deeper water on average with variable but finer‐grained substrate compared to other Green River shell midden sites. © 2002 Wiley Periodicals, Inc.