Water quality and hydrogeochemistry of a basin and range watershed in a semi-arid region of northern New Mexico     

Benjamin Linhoff  Patrick Longmire  Michael Rearick  Denis McQuillan  George Perkins 《Environmental Earth Sciences》2016,75(8):640

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Fine‐scale patterns in the day,night and crepuscular composition of a temperate reef fish assemblage          下载免费PDF全文

Elisabeth M. V. Myers  Euan S. Harvey  Benjamin J. Saunders  Michael J. Travers 《Marine Ecology》2016,37(3):668-678

The distribution, abundance and composition of marine fish assemblages are influenced by changes in behaviour and movement associated with the diel cycle. The majority of studies exploring day–night differences have demonstrated that there is a greater abundance and diversity of fishes during diurnal compared with nocturnal hours, and that fish assemblage composition varies with time of day or night. We investigated fine‐scale (hourly) diel cycles in the composition and relative abundance of temperate reef fishes using unbaited remote underwater video systems. We observed short crepuscular changeover periods with the hours around dawn and dusk sharing many species, some of which are nocturnal and others diurnal. Diurnal surveys recorded a greater number of individuals (16,990) and species (70) than nocturnal surveys (1053 individuals and 19 species). There was a clear difference between the diurnal assemblage, which was characterized by benthic invertivores, and the nocturnal assemblage composition, which contained zooplanktivores and generalist feeders. Within the diurnal period the hourly temporal variation was relatively homogenous, indicating that standardization of diurnal sampling to a particular time of day may not be necessary.  相似文献   

A modeling study of coastal inundation induced by storm surge,sea-level rise,and subsidence in the Gulf of Mexico   总被引：2，自引：2，他引：0  

Zhaoqing Yang  Taiping Wang  Ruby Leung  Kathy Hibbard  Tony Janetos  Ian Kraucunas  Jennie Rice  Benjamin Preston  Tom Wilbanks 《Natural Hazards》2014,71(3):1771-1794

The northern coasts of the Gulf of Mexico (GoM) are highly vulnerable to the direct threats of climate change, such as hurricane-induced storm surge, and such risks are exacerbated by land subsidence and global sea-level rise. This paper presents an application of a coastal storm surge model to study the coastal inundation process induced by tide and storm surge, and its response to the effects of land subsidence and sea-level rise in the northern Gulf coast. The unstructured-grid finite-volume coastal ocean model was used to simulate tides and hurricane-induced storm surges in the GoM. Simulated distributions of co-amplitude and co-phase lines for semi-diurnal and diurnal tides are in good agreement with previous modeling studies. The storm surges induced by four historical hurricanes (Rita, Katrina, Ivan, and Dolly) were simulated and compared to observed water levels at National Oceanic and Atmospheric Administration tide stations. Effects of coastal subsidence and future global sea-level rise on coastal inundation in the Louisiana coast were evaluated using a “change of inundation depth” parameter through sensitivity simulations that were based on a projected future subsidence scenario and 1-m global sea-level rise by the end of the century. Model results suggested that hurricane-induced storm surge height and coastal inundation could be exacerbated by future global sea-level rise and subsidence, and that responses of storm surge and coastal inundation to the effects of sea-level rise and subsidence are highly nonlinear and vary on temporal and spatial scales.  相似文献   

The Chemical Nature of Phosphorus in Subtropical Lake Sediments   总被引：1，自引：0，他引：1  

Isabela C. Torres  Benjamin L. Turner  K. Ramesh Reddy 《Aquatic Geochemistry》2014,20(4):437-457

The phosphorus (P) composition of sediment profiles in three subtropical lakes of contrasting trophic state in Florida, USA, was determined by sequential fractionation and solution ³¹P NMR spectroscopy. Sediment from Lake Annie, an oligo-mesotrophic sinkhole with moderately acidic sediment (pH 5.4; loss on ignition 58 %), contained higher total P concentrations than sediment from eutrophic Lake Okeechobee (pH 7.7, loss on ignition 36 %) and hyper-eutrophic Lake Apopka (pH 7.5, loss on ignition 69 %). The chemical nature of sediment P varied markedly among the three lakes, suggesting the predominance of different diagenetic processes. Lake Okeechobee sediment was dominated by inorganic P, indicating the dominance of abiotic reactions; Lake Annie sediment contained abundant organic P throughout the sediment profile, indicating the importance of organic P stabilization at acidic pH; Lake Apopka contained almost half of its sediment P in microbial biomass, indicating the importance of biotic processes in regulating P dynamics. Solution ³¹P NMR spectroscopy of NaOH–EDTA extracts revealed that organic P occurred mainly as phosphomonoesters in all lakes. However, sediment from Lake Apopka also contained abundant phosphodiesters and was the only lake to contain detectable concentrations of polyphosphate, perhaps due to a combination of alternating redox conditions and high concentrations of inorganic phosphate and organic carbon. Organic P concentrations determined by sequential fractionation and solution ³¹P NMR spectroscopy were similar for all lakes when microbial P was included in values for sequential fractionation. We conclude that the chemical nature of sediment P varies markedly depending on trophic state and can provide important information on the dominant processes controlling P cycling in subtropical lakes.  相似文献   

Modeling fluid injection in fractures with a reservoir simulator coupled to a boundary element method     

Benjamin Ganis  Mark E. Mear  A. Sakhaee-Pour  Mary F. Wheeler  Thomas Wick 《Computational Geosciences》2014,18(5):613-624

We describe an algorithm for modeling saturated fractures in a poroelastic domain in which the reservoir simulator is coupled with a boundary element method. A fixed stress splitting is used on the underlying fractured Biot system to iteratively couple fluid and solid mechanics systems. The fluid system consists of Darcy’s law in the reservoir and is computed with a multipoint flux mixed finite element method, and a Reynolds’ lubrication equation in the fracture solved with a mimetic finite difference method. The mechanics system consists of linear elasticity in the reservoir and is computed with a continuous Galerkin method, and linear elasticity in the fracture is solved with a weakly singular symmetric Galerkin boundary element method. This algorithm is able to compute both unknown fracture width and unknown fluid leakage rate. An interesting numerical example is presented with an injection well inside of a circular fracture.  相似文献   

Electrical-hydraulic conductivity model for a weathered-fractured aquifer system of Olbanita,Lower Baringo Basin,Kenya Rift     

SOSI Benjamin  BARONGO Justus  GETABU Albert  MAOBE Samson 《地下水科学与工程》2014,7(4):360-372

Groundwater yield in the Kenya Rift is highly unsustainable owing to geological variability. In this study, field hydraulic characterization was performed by using geo-electric approaches. The relations between electrical-hydraulic (eh) conductivities were modeled hypothetically and calibrated empirically. Correlations were based on the stoch-astic models and field-scale hydraulic parameters were contingent on pore-level parameters. By considering variation in pore-size distributions over eh conduction interval, the relations were scaled-up for use at aquifer-level. Material-level electrical conductivities were determined by using Vertical Electrical Survey and hydraulic conductivities by analyzing aquifer tests of eight boreholes in the Olbanita aquifer located in Kenya rift. VES datasets were inverted by using the computer code IP2Win. The main result is that ln T=0.537 (ln Fa)+3.695; the positive gradient indicating eh conduction through poresurface networks and a proxy of weathered and clayey materials. An inverse (1/F-K) correlation is observed. Hydraulic parameters determined using such approaches may possibly contri-bute significantly towards sustainable yield management and planning of groundwater resources.  相似文献   

Arsenic repartitioning during biogenic sulfidization and transformation of ferrihydrite   总被引：4，自引：0，他引：4  

Benjamin D. Kocar  Scott Fendorf 《Geochimica et cosmochimica acta》2010,74(3):980-6788

Iron (hydr)oxides are strong sorbents of arsenic (As) that undergo reductive dissolution and transformation upon reaction with dissolved sulfide. Here we examine the transformation and dissolution of As-bearing ferrihydrite and subsequent As repartitioning amongst secondary phases during biotic sulfate reduction. Columns initially containing As(V)-ferrihydrite coated sand, inoculated with the sulfate reducing bacteria Desulfovibrio vulgaris (Hildenborough), were eluted with artificial groundwater containing sulfate and lactate. Rapid and consistent sulfate reduction coupled with lactate oxidation is observed at low As(V) loading (10% of the adsorption maximum). The dominant Fe solid phase transformation products at low As loading include amorphous FeS within the zone of sulfate reduction (near the inlet of the column) and magnetite downstream where Fe(II)_(aq) concentrations increase; As is displaced from the zone of sulfidogenesis and Fe(III)_(s) depletion. At high As(V) loading (50% of the adsorption maximum), sulfate reduction and lactate oxidation are initially slow but gradually increase over time, and all As(V) is reduced to As(III) by the end of experimentation. With the higher As loading, green rust(s), as opposed to magnetite, is a dominant Fe solid phase product. Independent of loading, As is strongly associated with magnetite and residual ferrihydrite, while being excluded from green rust and iron sulfide. Our observations illustrate that sulfidogenesis occurring in proximity with Fe (hydr)oxides induce Fe solid phase transformation and changes in As partitioning; formation of As sulfide minerals, in particular, is inhibited by reactive Fe(III) or Fe(II) either through sulfide oxidation or complexation.  相似文献   

Phytoplankton Community Indicators of Short- and Long-term Ecological Change in the Anthropogenically and Climatically Impacted Neuse River Estuary, North Carolina, USA     

Hans W. Paerl  Karen L. Rossignol  S. Nathan Hall  Benjamin L. Peierls  Michael S. Wetz 《Estuaries and Coasts》2010,33(2):485-497

Estuarine and coastal systems represent a challenge when it comes to determining the causes of ecological change because human and natural perturbations often interact. Phytoplankton biomass (chlorophyll a) and group-specific photopigment indicators were examined from 1994 to 2007 to assess community responses to nutrient and climatic perturbations in the Neuse River Estuary, NC. This system experienced nutrient enrichment and hydrologic variability, including droughts, and an increase in hurricanes. Freshwater input strongly interacted with supplies of the limiting nutrient nitrogen (N) and temperature to determine the location, magnitude, and composition of phytoplankton biomass. Multi-annual, seasonal, and episodic hydrologic perturbations, including changes in the frequency and intensity of tropical storms, hurricanes and droughts, caused significant shifts in phytoplankton community structure. Climatic oscillations can at times overwhelm anthropogenic nutrient inputs in terms of controlling algal bloom thresholds, duration, and spatial extent. Eutrophication models should incorporate climatically driven changes to better predict phytoplankton community responses to nutrient inputs and other anthropogenic perturbations.  相似文献   

Earthquakes in Switzerland and surrounding regions during 2009     

Nicholas Deichmann  John Clinton  Stephan Husen  Benjamin Edwards  Florian Haslinger  Donat Fäh  Domenico Giardini  Philipp Kästli  Urs Kradolfer  Iris Marschall  Stefan Wiemer 《Swiss Journal of Geoscience》2010,103(3):535-549

This report of the Swiss Seismological Service summarizes the seismic activity in Switzerland and surrounding regions during 2009. During this period, 450 earthquakes and 68 quarry blasts were detected and located in the region under consideration. The three strongest events occurred about 15 km NW of Basel in southern Germany (M_L 4.2), near Wildhaus in the Toggenburg (M_L 4.0) and near Bivio in Graubünden (M_L 3.5). Although felt by the population, they were not reported to have caused any damage. With a total of 24 events with M_L ≥ 2.5, the seismic activity in the year 2009 was close to the average over the previous 34 years.  相似文献   

The CO₂ system in rivers of the Australian Victorian Alps: CO₂ evasion in relation to system metabolism and rock weathering on multi-annual time scales     

Benjamin Hagedorn  Ian Cartwright 《Applied Geochemistry》2010

The patterns of dissolved inorganic C (DIC) and aqueous CO₂ in rivers and estuaries sampled during summer and winter in the Australian Victorian Alps were examined. Together with historical (1978–1990) geochemical data, this study provides, for the first time, a multi-annual coverage of the linkage between CO₂ release via wetland evasion and CO₂ consumption via combined carbonate and aluminosilicate weathering. δ¹³C values imply that carbonate weathering contributes ∼36% of the DIC in the rivers although carbonates comprise less than 5% of the study area. Baseflow/interflow flushing of respired C3 plant detritus accounts for ∼50% and atmospheric precipitation accounts for ∼14% of the DIC. The influence of in river respiration and photosynthesis on the DIC concentrations is negligible. River waters are supersaturated with CO₂ and evade ∼27.7 × 10⁶ mol/km²/a to ∼70.9 × 10⁶ mol/km²/a CO₂ to the atmosphere with the highest values in the low runoff rivers. This is slightly higher than the global average reflecting higher gas transfer velocities due to high wind speeds. Evaded CO₂ is not balanced by CO₂ consumption via combined carbonate and aluminosilicate weathering which implies that chemical weathering does not significantly neutralize respiration derived H₂CO₃. The results of this study have implications for global assessments of chemical weathering yields in river systems draining passive margin terrains as high respiration derived DIC concentrations are not directly connected to high carbonate and aluminosilicate weathering rates.  相似文献