Impacts of a Habitat-Forming Exotic Species on Estuarine Structure and Function: An Experimental Assessment of Eurasian Milfoil     

Charles W. Martin  John F. Valentine 《Estuaries and Coasts》2011,34(2):364-372

It is widely believed that successful colonization of ecosystems by non-native species will have catastrophic consequences for the recipient system. Within the Mobile–Tensaw Delta, AL, exotic Eurasian milfoil (Myriophyllum spicatum) has been reported to trigger degradation of ecosystem structure and function. We evaluated the impacts of structurally complex milfoil on food web structure and predator-prey interactions via comparisons with two native grasses, structurally simple wild celery (Vallisneria americana) and the more complex water stargrass (Heteranthera dubia). While significant differences were not detected in the faunal compositions of milfoil and stargrass habitats, significant differences between milfoil and wild celery were found. Laboratory experiments showed that rainwater killifish, a key contributor to these differences, preferred milfoil over wild celery, but did not occupy milfoil more than stargrass. Subsequent experiments indicated that survivorship was drastically lower in wild celery. Though many of the documented impacts of Eurasian milfoil have been cast as detrimental, shelter-seeking organisms may perceive milfoil in the same way as other complex native species.  相似文献   

Diel Aquatic CO<Subscript>2</Subscript> System Dynamics of a Bermudian Mangrove Environment     

John A. Zablocki  Andreas J. Andersson  Nicholas R. Bates 《Aquatic Geochemistry》2011,17(6):841-859

Mangrove ecosystems play an important, but understudied, role in the cycling of carbon in tropical and subtropical coastal ocean environments. In the present study, we examined the diel dynamics of seawater carbon dioxide (CO₂) and dissolved oxygen (DO) for a mangrove-dominated marine ecosystem (Mangrove Bay) and an adjacent intracoastal waterway (Ferry Reach) on the island of Bermuda. Spatial and temporal trends in seawater carbonate chemistry and associated variables were assessed from direct measurements of dissolved inorganic carbon, total alkalinity, dissolved oxygen (DO), temperature, and salinity. Diel pCO₂ variability was interpolated across hourly wind speed measurements to determine variability in daily CO₂ fluxes for the month of October 2007 in Bermuda. From these observations, we estimated rates of net sea to air CO₂ exchange for these two coastal ecosystems at 59.8 ± 17.3 in Mangrove Bay and 5.5 ± 1.3 mmol m⁻² d⁻¹ in Ferry Reach. These results highlight the potential for large differences in carbonate system functioning and sea-air CO₂ flux in adjacent coastal environments. In addition, observation of large diel variability in CO₂ system parameters (e.g., mean pCO₂: 390–2,841 μatm; mean pH_T: 8.05–7.34) underscores the need for careful consideration of diel cycles in long-term sampling regimes and flux estimates.  相似文献   

Hydrostratigraphic analysis of the Darling River valley (Australia) using electromagnetic induction data and a spatially constrained algorithm for quasi-three-dimensional electrical conductivity imaging   总被引：1，自引：0，他引：1  

John Triantafilis  Fernando Ac��cio Monteiro Santos 《Hydrogeology Journal》2011,19(5):1053-1063

Efforts are being made to improve the irrigation efficiency in the Murray-Darling River Basin, Australia, to deal with predicted rainfall decline and to reduce the incidence of secondary soil and water salinization. The latter commonly occurs as a result of locating water reservoirs upon relic drainage channels. To better manage irrigation, information is required about the spatial distribution of soil type and the stratigraphic features capable of redistributing deep-draining water. In previous research, electromagnetic (EM) induction instruments (e.g. EM38 and EM34) have been used to map the distribution of soil type, hydrological processes (e.g. deep drainage) and vadose-zone features. The aim of this research is to demonstrate how a joint inversion of EM38 and EM34 data, using a one-dimensional spatially constrained algorithm for quasi three-dimensional (quasi-3D) electrical conductivity imaging, can be used to infer the areal distribution of soil types and physiographic and hydrogeological units. The quasi-3D modeling of true electrical conductivity provides a framework for future environmental monitoring and management to mitigate the hydrological processes that drive localized secondary salinization in the study area.  相似文献   

Petrography and geochemistry of clastic sedimentary rocks as evidences for provenance of the Lower Cambrian Lalun Formation, Posht-e-badam block, Central Iran     

N. Etemad-Saeed  M. Hosseini-Barzi  John S. Armstrong-Altrin 《Journal of African Earth Sciences》2011,61(2):142-159

Petrography and geochemistry (major, trace and rare earth elements) of clastic rocks from the Lower Cambrian Lalun Formation, in the Posht-e-badam block, Central Iran, have been investigated to understand their provenance. Petrographical analysis suggests that the Lalun conglomerates are dominantly with chert clasts derived from a proximal source, probably chert bearing Precambrian Formations. Similarly, purple sandstones are classified as litharenite (chertarenite) and white sandstones as quartzarenite types. The detrital modes of purple and white sandstones indicate that they were derived from recycled orogen (uplifted shoulders of rift) and stable cratonic source. Most major and trace element contents of purple sandstones are generally similar to upper continental crust (UCC) values. However, white sandstones are depleted in major and trace elements (except SiO₂, Zr and Co) relative to UCC, which is mainly due to the presence of quartz and absence of other Al-bearing minerals. Shale samples have considerably lower content in most of the major and trace elements concentration than purple sandstones, which is possibly due to intense weathering and recycling. Modal composition (e.g., quartz, feldspar, lithic fragments) and geochemical indices (Th/Sc, La/Sc, Co/Th, Cr/Th, Cr/V and V/Ni ratios) of sandstones, and shales (La/Sc and La/Cr ratios) indicate that they were derived from felsic source rocks and deposited in a passive continental margin. The chondrite-normalized rare earth element (REE) patterns of the studied samples are characterized by LREE enrichment, negative Eu anomaly and flat HREE similar to an old upper continental crust composed chiefly of felsic components in the source area. The study of paleoweathering conditions based on modal composition, chemical index of alteration (CIA), plagioclase index of alteration (PIA) and A–CN–K (Al₂O₃ − CaO + Na₂O − K₂O) relationships indicate that probably chemical weathering in the source area and recycling processes have been more important in shale and white sandstones relative to purple sandstones. The results of this study suggest that the main source for the Lalun Formation was likely located in uplifted shoulders of a rifted basin (probably a pull-apart basin) in its post-rift stage (Pan-African basement of the Posht-e-badam block).  相似文献   

A demonstration of an affinity between pyrite and organic matter in a hydrothermal setting     

Paula Lindgren  John Parnell  Nils G Holm  Curt Broman 《Geochemical transactions》2011,12(1):3

One of the key-principles of the iron-sulphur world theory is to bring organic molecules close enough to interact with each other, using the surface of pyrite as a substrate in a hydrothermal setting. The present paper explores the relationship of pyrite and organic matter in a hydrothermal setting from the geological record; in hydrothermal calcite veins from Carboniferous limestones in central Ireland. Here, the organic matter is accumulated as coatings around, and through, pyrite grains. Most of the pyrite grains are euhedral-subhedral crystals, ranging in size from ca 0.1-0.5 mm in diameter, and they are scattered throughout the matrix of the vein calcite. The organic matter was deposited from a hydrothermal fluid at a temperature of at least 200°C, and gives a Raman signature of disordered carbon. This study points to an example from a hydrothermal setting in the geological record, demonstrating that pyrite can have a high potential for the concentration and accumulation of organic materials.  相似文献   

Mass fluxes of xenobiotics below cities: challenges in urban hydrogeology     

Mario Schirmer  Frido Reinstorf  Sebastian Leschik  Andreas Musolff  Ronald Krieg  Gerhard Strauch  John W. Molson  Marion Martienssen  Kristin Schirmer 《Environmental Earth Sciences》2011,64(3):607-617

Urban areas are the focus of major ecological, social and economical activity. They are thus also prime locations of increasing conflict with regard to water use and water protection. As a direct and/or indirect consequence of urban land use and human activity, urban water systems are frequently polluted with organic contaminants including waste water-born xenobiotics such as pharmaceuticals, personal care products (collectively known as PPCPs) and endocrine-active substances. This study reviews new integrated methodologies including flux calculations as well as chemical investigations for determining the impact of human activities on urban water systems and on processes within the urban watershed. The use of indicator substances, representing different contaminant sources and pathways, integral pumping tests and mass balance approaches are suitable alternatives within these environments. The issues are explored using contaminant mass balance examples from Halle/Saale and Leipzig, Germany.  相似文献   

On the use of IPCC-class models to assess the impact of climate on Living Marine Resources     

Charles A. Stock  Michael A. Alexander  Nicholas A. Bond  Keith M. Brander  William W.L. Cheung  Enrique N. Curchitser  Thomas L. Delworth  John P. Dunne  Stephen M. Griffies  Melissa A. Haltuch  Jonathan A. Hare  Anne B. Hollowed  Patrick Lehodey  Simon A. Levin  Jason S. Link  Kenneth A. Rose  Ryan R. Rykaczewski  Jorge L. Sarmiento  Ronald J. Stouffer  Franklin B. Schwing  Francisco E. Werner 《Progress in Oceanography》2011,88(1-4):1-27

The study of climate impacts on Living Marine Resources (LMRs) has increased rapidly in recent years with the availability of climate model simulations contributed to the assessment reports of the Intergovernmental Panel on Climate Change (IPCC). Collaboration between climate and LMR scientists and shared understanding of critical challenges for such applications are essential for developing robust projections of climate impacts on LMRs. This paper assesses present approaches for generating projections of climate impacts on LMRs using IPCC-class climate models, recommends practices that should be followed for these applications, and identifies priority developments that could improve current projections. Understanding of the climate system and its representation within climate models has progressed to a point where many climate model outputs can now be used effectively to make LMR projections. However, uncertainty in climate model projections (particularly biases and inter-model spread at regional to local scales), coarse climate model resolution, and the uncertainty and potential complexity of the mechanisms underlying the response of LMRs to climate limit the robustness and precision of LMR projections. A variety of techniques including the analysis of multi-model ensembles, bias corrections, and statistical and dynamical downscaling can ameliorate some limitations, though the assumptions underlying these approaches and the sensitivity of results to their application must be assessed for each application. Developments in LMR science that could improve current projections of climate impacts on LMRs include improved understanding of the multi-scale mechanisms that link climate and LMRs and better representations of these mechanisms within more holistic LMR models. These developments require a strong baseline of field and laboratory observations including long time series and measurements over the broad range of spatial and temporal scales over which LMRs and climate interact. Priority developments for IPCC-class climate models include improved model accuracy (particularly at regional and local scales), inter-annual to decadal-scale predictions, and the continued development of earth system models capable of simulating the evolution of both the physical climate system and biosphere. Efforts to address these issues should occur in parallel and be informed by the continued application of existing climate and LMR models.  相似文献   

The California Current System in relation to the Northeast Pacific Ocean circulation     

Guillermo Auad  Dean Roemmich  John Gilson 《Progress in Oceanography》2011,91(4):576-592

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Size-differential feeding in Pinna nobilis L. (Mollusca: Bivalvia): Exploitation of detritus,phytoplankton and zooplankton     

John Davenport  Daria Ezgeta-Balić  Melita Peharda  Sanda Skejić  Živana Ninčević-Gladan  Slavica Matijević 《Estuarine, Coastal and Shelf Science》2011

The endangered fan shell Pinna nobilis is a large bivalve mollusc (<120 cm shell length) endemic to the Mediterranean that lives one-third buried in soft substrata, generally in shallow coastal waters. We hypothesised that P. nobilis of different sizes would ingest different food sources, because small fan shells will inhale material from closer to the substratum than do large fan shells. We studied stomach contents and faeces of 18 fan shells, 6 small (mean 23.0 cm length), 6 medium-sized (mean 41.5 cm length) and 6 large (mean 62.7 cm length) living in a small area of a low-energy coastal detritic bottom characterised by mud, sand and macroalgae at Mali Ston Bay, Croatia. We found that all P. nobilis ingested copious quantities of undetermined detritus (probably at least 95% of ingested material), phytoplankton, micro and mesozooplankton and pollen grains. Large P. nobilis stomach contents showed a preponderance of water column calanoid copepods, while small fan shells had higher numbers of bivalve larvae. All fan shells took in high numbers of harpacticoid copepods that are benthonic, feeding on microbial communities of detritus and benthic vegetation. There was also a significant selection of phytoplankton species, some apparently occurring between inhalation and ingestion. The stomach contents of small P. nobilis had a higher organic matter content than either medium-sized or large fan shells; this indicated that small fan shells ingested detritus of higher organic content than did larger P. nobilis. As the faeces of all P. nobilis had similar organic matter content, this also indicates higher assimilation efficiencies in small fan shells. The demonstration of differential dietary selectivity by different sized animals has implications for future trophic studies of this endangered species. This study also provides the first demonstration of predation on zooplankton by P. nobilis.  相似文献   

Appraisal of storm beach buffer width for cyclonic waves     

F.-C. Lee  John R.-C. Hsu  W.-H. Lin 《Coastal Engineering》2011

The loss of beach sand from berm and dune due to high waves and surge is a universal phenomenon associated with sporadic storm activities. To protect the development in a coastal hazard zone, hard structures or coastal setback have been established in many countries around the world. In this paper, the requirement of a storm beach buffer, being a lesser extent landward comparing with the coastal setback to ensure the safety of infrastructures, is numerically assessed using the SBEACH model for three categories of wave conditions in terms of storm return period, median sand grain size, berm width, and design water level. Two of the key outputs from the numerical calculations, berm retreat and bar formation offshore, are then analysed, as well as beach profile change. After having performed a series of numerical studies on selected large wave tank (LWT) test results with monochromatic waves using SBEACH, we may conclude that: (1) Berm erosion increases and submerged bar develops further offshore as the storm return period increases for beach with a specific sand grain size, or as the sand grain reduces on a beach under the action of identical wave condition; (2) Higher storm waves yield a large bar to form quicker and subsequently cause wave breaking on the bar crest, which can reduce the wave energy and limit the extent of the eroding berm; (3) A larger buffer width is required for a beach comprising small sand grain, in order to effectively absorb storm wave energy; and (4) Empirical relationships can be tentatively proposed to estimate the storm beach buffer width, from the input of wave conditions and sediment grain size. These results would benefit a beach nourishment project for shore protection or design of a recreational beach.  相似文献