The impact of resuspension on sediment mercury dynamics, and methylmercury production and fate: A mesocosm study

The objective of this study was to investigate the effects of resuspension on the fate and bioaccumulation of mercury (THg) and methylmercury (MeHg) in shallow estuarine environments, using mesocosms. Two 4-week experiments were conducted in July (Experiment 1) and October (Experiment 2) of 2001 with Baltimore Harbor sediments. Hard clams, Mercenaria mercenaria, were introduced into sediments for Experiment 2. Tidal resuspension (4 h on and 2 h off cycles) was simulated, with 3 replicate tanks for each treatment—resuspension (R) and non-resuspension (NR). Sediment cores were collected during the experiments for THg, MeHg, organic content and AVS analyses, and for the determination of methylation/demethylation using Hg stable isotopes (¹⁹⁹Hg(II) and CH₃¹⁹⁹Hg(II)). Zooplankton samples were collected once a week while clams were taken before and after Experiment 2 for THg and MeHg analyses. Our results suggest that the interplay between Hg methylation and MeHg degradation determines the overall MeHg pool in sediments. Sediment resuspension does not appear to directly impact the Hg transformations but can lead to changes in the association to Hg binding phases, influencing Hg methylation. The bioaccumulation results indicate that sediment resuspension can play an important role in transferring sediment MeHg into organisms.     

Field-based monitoring of sediment runoff from natural gas well sites in Denton County,Texas, USA

This study evaluates sediment runoff from gas well development sites in Denton County, Texas. The magnitude of sediment runoff was investigated by intercepting sediment in traps and weirs at the periphery of each gas well site and by measuring the growth of debris lobes that formed down slope from two sites. Four debris lobes formed at one gas well site and one formed at a second site. Debris lobes ranged in size from 30 to 306 square meters. Sediment from one site entered local creek channels, either as a component of storm water runoff or, in one case, as a debris lobe that flowed into a channel. The study findings suggest that sediment movement is significantly diminished once areas disturbed by gas well construction become naturally re-vegetated. Based on estimates of debris lobe volumes, sediment loading rates of about 54 metric tonnes per hectare per year were calculated for one site. It is concluded that gas well development sites in areas similar to those studied, especially where vegetation has been removed and terrain has relatively steep slopes (greater than 6%), generate sediment runoff comparable to small construction sites and should therefore be considered for regulations requiring erosion and sediment control measures.     

Effects of juniper removal and rainfall variation on tree transpiration in a semi‐arid karst: evidence of complex water storage dynamics

Brush removal is widely practiced as a tool for increasing groundwater recharge, but its efficacy depends greatly on the way in which the removed species interact with the hydrological system relative to the vegetation replacing it. We examined the effects of Ashe juniper removal in the recharge zone of the Edwards Aquifer, Texas, USA, a karst aquifer. The study was conducted in an Ashe juniper (Juniperus ashei)–live oak (Quercus fusiformis) woodland on a hill slope composed of rocky, shallow soils over fractured limestone bedrock. Ashe juniper is a native species that has been encroaching grasslands and savannas over the past century. In September 2008, a plot was cleared of 90% of its juniper trees. Tree transpiration, predawn water potentials and vegetation cover across the cleared plot and an adjacent reference site were measured from May 2009 to December 2011. Stand‐level tree transpiration from May 2009 to March 2010 was diminished by a severe summer drought in 2009, from which trees were slow to recover. Subsequently, tree transpiration was 5–10× higher in the woodland compared to the clearing. For all of 2011, also a drought year, tree transpiration in the woodland exceeded precipitation inputs, indicating a high capacity for water storage at the study site. However, site differences for oak trees were generally larger than for juniper trees. While juniper removal accounted for a 431 mm year^?1 difference in tree transpiration between sites, vegetation cover in the clearing increased from 42% to 90% over two years, suggesting that understory growth was increasingly compensating for the loss of juniper transpiration. We conclude that the removal of a relatively shallow‐rooted tree, when replaced with herbaceous vegetation and low shrubs, has little effect on deep recharge. By contrast, successive years of precipitation extremes may be more effective increasing recharge by lowering the water transport capacity of trees in the aftermath of severe drought. Copyright © 2016 John Wiley & Sons, Ltd.     

Using GIS and streamlined landforms to interpret palaeo‐ice flow in northern Iceland

The properties of streamlined glacial landforms and palaeo‐flow indicators in the valleys of Viðidalur, Vatnsdalur and Svínadalur in northern Iceland were quantified using spatial analyses. Drumlins and mega‐scale glacial lineations (MSGL) were visually identified using satellite imagery from Google Earth, the National Land Survey of Iceland (NLSI) Map Viewer and Landsat satellites, and using aerial photographs from the NLSI. A semi‐automated technique was developed using ENVI to determine regions in northern Iceland likely to contain streamlined landforms. The outlines of the identified landforms were manually delineated in Google Earth, and all analyses were conducted in ArcGIS using a 20 m digital elevation model (DEM) of Iceland from the NLSI. Smaller features such as flutes, grooves and striations were measured in the field. At least 543 drumlins and 90 MSGL were identified in the three valleys. Average elongation ratios for Viðidalur, Vatnsdalur and Svínadalur are 4.3:1, 5.2:1 and 6.7:1, respectively. The average density of streamlined landforms is 2.34 landforms per 1 km². Striations and orientation data of the drumlins and MSGL demonstrate ice flow to the northwest into Húnaflói. Parallel conformity is higher in the valley of Svínadalur (9° standard deviation) than in Viðidalur (12°) and Vatnsdalur (16°). Packing values are generally higher in the centre of each valley. The properties of streamlined landforms in the valleys of Viðidalur, Vatnsdalur and Svínadalur support the presence of palaeo‐ice stream activity on northern Iceland. Palaeo‐ice streams flowed from these regions into Húnaflói, supplying ice to the margin of the Iceland Ice Sheet during the Last Glacial Maximum. These palaeo‐ice streams provide a mechanism for ice centres from the mainland of Iceland to reach the shelf‐slope break.     

High‐frequency precipitation and stream water quality time series from Plynlimon,Wales: an openly accessible data resource spanning the periodic table

This scientific briefing announces the availability of a new multi‐element high‐frequency water quality data set that is openly accessible to the research community. The data set comprises up to 2 years of 7‐hourly water quality data for two streams and one rainfall site in the Upper Severn catchment at Plynlimon in Mid‐Wales. The measurements cover 50 analytes ranging from H⁺ to U and spanning six orders of magnitude in concentration, including major, minor and trace elements as well as nutrients, and they complement decades of weekly measurements of the same analytes at the Upper Severn. Together, the weekly and 7‐hourly time series provide a unique data set for studying both long‐term trends and short‐term dynamics. The data show complex behaviour over a wide range of timescales, challenging our understanding of catchment processes and informing future modelling efforts. Copyright © 2013 John Wiley & Sons, Ltd.     

Forensic geology at the International School Science Fair 2013

In July 2013 the International School Science Fair (ISSF) was hosted by Camborne Science and International Academy, Cornwall, UK. This meeting brings young talented scientists together from around the world to participate in workshops and activities highlighting current scientific developments. As part of ISSF 2013, a workshop on forensic geology was delivered to some of the international participants. This included the preparation of a map to show the mineralogical composition of the soils of the participating schools. The soil mineralogy was determined using automated mineral analysis based on scanning electron microscopy. In addition there were workshops on the recovery of geological trace evidence in a forensic context and the theory and practice of carrying out a geophysical search for hidden items. Data generated as part of this workshop are available to download from the International Union of Geological Sciences, Initiative on Forensic Geology website ( http://www.forensicgeologyinternational.com ).     

Global tsunami deposits database

The National Geophysical Data Center and co-located World Data Center for Geophysics and Marine Geology provide integrated access to historical tsunami event, deposit, and proxy data. Historical events are important for understanding the frequency and intensity of relatively recent tsunamis. Deposit data collected during post-tsunami field surveys provide information on tsunami erosion, sedimentation, flow depths, inundation, and run-up. Deposit data from prehistoric tsunami events extend the record to pre-recorded times, constrain tsunami recurrence intervals, and estimate the minimum magnitude of tsunami inundation. Proxies indicate that an event capable of producing a tsunami occurred, but are not direct evidence of a tsunami. All of these data are used to develop tsunami hazard assessments, provide guidance to warning centers, validate models, inform community preparedness efforts, and educate the public about tsunami risks.     

Decomposition of mineral absorption bands using nonlinear least squares curve fitting: Application to Martian meteorites and CRISM data

This study advances curve-fitting modeling of absorption bands of reflectance spectra and applies this new model to spectra of Martian meteorites ALH 84001 and EETA 79001 and data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). This study also details a recently introduced automated parameter initialization technique. We assess the performance of this automated procedure by comparing it to the currently available initialization method and perform a sensitivity analysis of the fit results to variation in initial guesses. We explore the issues related to the removal of the continuum, offer guidelines for continuum removal when modeling the absorptions and explore different continuum-removal techniques. We further evaluate the suitability of curve fitting techniques using Gaussians/Modified Gaussians to decompose spectra into individual end-member bands. We show that nonlinear least squares techniques such as the Levenberg–Marquardt algorithm achieve comparable results to the MGM model (Sunshine and Pieters, 1993, Sunshine et al., 1990) for meteorite spectra. Finally we use Gaussian modeling to fit CRISM spectra of pyroxene and olivine-rich terrains on Mars. Analysis of CRISM spectra of two regions show that the pyroxene-dominated rock spectra measured at Juventae Chasma were modeled well with low Ca pyroxene, while the pyroxene-rich spectra acquired at Libya Montes required both low-Ca and high-Ca pyroxene for a good fit.     

Consensus among multiple trophic levels during high- and low-water stands over the last two millennia in a northwest Ontario lake

We investigated the modern distribution of fossil midges within a dimictic lake and explored downcore patterns of inferred lake depths over the last 2000 years from previously published proxies. Modern midge distribution within Gall Lake showed a consistent and predictable pattern related to the lake-depth gradient with recognizable assemblages characteristic of shallow-water, mid-depth and profundal environments. Interpretations of downcore changes in midge assemblages, in conjunction with quantitative lake-depth inferences across a priori defined (based on diatom data) ~ 500-yr wet and dry periods, demonstrated that both invertebrate and algal assemblages exhibited similar timing and nature of ecological responses. Midges were quantified by their relative abundance, concentrations and an index of Chaoborus to chironomids, and all showed the greatest differences between the wet and dry periods. During the low lake-level period of the Medieval Climate Anomaly (MCA: AD 900 to 1400), profundal chironomids declined, shallow-water and mid-depth chironomids increased, chironomid-inferred lake level declined and the Chaoborus-to-chironomid index decreased. The coherence between multiple trophic levels provides strong evidence of lower lake levels in Gall Lake during the MCA.