Impacts of Oyster Reef Restoration on Primary Productivity and Nutrient Dynamics in Tidal Creeks of the North Central Gulf of Mexico     

Rochelle Plutchak  Kelly Major  Just Cebrian  C. Drew Foster  Mary-Elizabeth C. Miller  Andrea Anton  Kate L. Sheehan  Kenneth L. HeckJr.  Sean P. Powers 《Estuaries and Coasts》2010,33(6):1355-1364

The ability of oysters to remove large quantities of particulates from the water column, thereby potentially improving water quality, has been cited as one of the reasons for oyster reef restoration. However, this ability has not yet been effectively demonstrated in the field. As part of the Alabama Oyster Reef Restoration Project, this study was designed to assess impacts of restored eastern oyster (Crassostrea virginica) reefs on primary production, nutrient dynamics, and water quality in shallow tidal creeks. Using a Before–After-Control–Impact (BACI) design, we monitored tidal creeks around Dauphin Island, AL, for changes induced by the introduction of oyster reefs. Reef placement resulted in increased ammonium (NH₄⁺) in two of the three experimental creeks. Interestingly, oyster reefs did not seem to reduce water column particulates or have an impact on phytoplankton or microphytobenthic biomass or productivity. We do not believe that our data discount the importance and/or usefulness of oysters in modifying the water column. Rather, we acknowledge that it is difficult to detect these impacts/environmental services in this type of system (i.e., a tidal creek system), because they seem to be very localized and short-lived (i.e., not ecologically relevant on a creek-wide scale). This study highlights the need to consider location and habitat in planning oyster restoration projects. Also, it demonstrates that the types, magnitudes, and spatial extent of changes in ecosystem services that should be expected after reef restoration might need to be re-evaluated.  相似文献   

Two new eucrite breccias from Northwest Africa     

Sheryl A. SINGERLING  Aubrey L. MODI  Blake MCFERRIN  Emily A. WORSHAM  Harry Y. MCSWEEN JR.  Douglas RUMBLE III  Ryoji TANAKA  Lawrence A. TAYLOR 《Meteoritics & planetary science》2013,48(2):E1-E9

Abstract– This work describes two newly discovered eucrite breccias: three presumably paired meteorites, all named Northwest Africa (NWA) 6105, and NWA 6106. For each meteorite, major‐ and minor‐element compositions of minerals were determined using the electron microprobe. Pyroxene Fe‐Mn co‐variations and bulk‐rock oxygen isotope compositions confirm their classification as eucrites. Variations in mineral compositions and textures are attributed to differences in clast types present (i.e., basaltic or cumulate eucrite). The pyroxene compositions support the hypothesis that samples NWA 6105,1; 6105,2; and 6105,3 are paired polymict eucritic breccias, whereas sample NWA 6106 is a monomict basaltic eucritic breccia. Two‐pyroxene geothermometry yields temperatures too low for igneous crystallization. The variation in temperatures among samples suggests that metamorphism occurred prior to brecciation.  相似文献   

THE DRIVING FORCES OF LAND CHANGE IN THE NORTHERN PIEDMONT OF THE UNITED STATES     

ROGER F. AUCH  DARRELL E. NAPTON  STEVEN KAMBLY  THOMAS R. MORELAND JR.  KRISTI L. SAYLER 《Geographical review》2012,102(1):53-75

Driving forces facilitate or inhibit land‐use / land‐cover change. Human driving forces include political, economic, cultural, and social attributes that often change across time and space. Remotely sensed imagery provides regional land‐change data for the Northern Piedmont, an ecoregion of the United States that continued to urbanize after 1970 through conversion of agricultural and forest land covers to developed uses. Eight major driving forces facilitated most of the land conversion; other drivers inhibited or slowed change. A synergistic web of drivers may be more important in understanding land change than individual drivers by themselves.  相似文献   

The Supanberget area – basement imbrication and detached foreland thrusting in the Tertiary fold-and-thrust belt, Svalbard     

WINFRIED K. DALLMANN  HARMON D. MAHER  JR. 《Polar research》1989,7(2):95-107

The Supanberget area, situated in the southern part of the Tertiary Spitsbergen fold-and-thrust belt, occupies a position mainly within the central zone of the belt, characterized by basement-involved thrusting, but includes part of an eastern foreland zone of detached, thin-skinned thrust tectonics. The peculiar feature of Supanberget is the thrust- 'sliced' tectonic style that deforms a previously tightly folded basement-cover contact. Foreland structures indicate the additional presence of a subsurface detachment at a deeper structural level. Contrasts in magnitude and orientation of basement anisotropics may control lateral changes in tectonic style.  相似文献   

Evaluation of the Crystallization Conditions for the Calcalkaline Russian Peak Intrusive Complex, Klamath Mountains, Northern California     

COTKIN  SPENCER J.; MEDARIS  L. GORDON  JR. 《Journal of Petrology》1993,34(3):543-571

The mid-Jurassic calcalkaline Russian Peak intrusive complex,located in the Klamath Mountains of northern California, consistsof an elliptical peridotite-to-quartz diorite suite intrudedby two plutons of granodiorite. Several techniques were usedto decipher the crystallization conditions for ultramafic rocks,quartz diorite, and granodiorite, including comparison of parageneseswith crystallization experiments, application of geothermometersand barometers, and evaluation of phase equilibria. Contactmetamorphic assemblages, hornblende barometry, and amphibolesubstitution schemes indicate that pressures of intrusion were{small tilde}3 kbar. Plagioclase and pyroxene thermometry indicateintrusion temperatures of {small tilde}1000C for quartz dioriteand 900C for granodiorite. Phase equilibrium analysis for thereaction phlogopite+quartz=K-feldspar+enstatite+H₂O, coupledwith an estimate of the water-saturated quartz diorite solidus,suggests that the solidus of two-pyroxene quartz diorite wasat {small tilde}780C with a mole fraction of water of {smalltilde}0•55. The composition of granodiorite is very similarto that used in several crystallization experiments and indicatesa solidus of 70025C. Estimates of oxygen fugacity, obtainedfrom equilibrium relations of olivine, orthopyroxene, and spinelin ultramafic rocks, magnetite and ilmenite in quartz diorite,and magnetite, K-feldspar, and biotite in quartz diorite andgranodiorite are 2•1–2•5 and 1•0–1•3log units above the quartz-fayalite-magnetite (QFM) buffer forgranodiorite and quartz diorite at their respective solidustemperatures; and 1•0–4•0 log units above QFMfor ultramafic rocks and quartz diorite at subsolidus temperatures.Thus, the quartz diorite magma was hotter, drier, and slightlyreduced relative to the grandiorite magma, differences thatset important constraints on the genesis of the Russian Peakmagmas. These results also indicate that quartz diorite wasundersaturated with respect to H₂O as it reached its solidus,a condition that is consistent with the absence of deutericalteration in this unit. In contrast, granodiorite shows extensivedeuteric alteration and features pegmatites, quartz pods, andradial dikes as might be expected for H₂O-saturated conditions. Although calcalkaline plutonic complexes present serious difficultiesin estimating the intensive parameters of crystallization, judiciousapplication of appropriate methods may result in the successfulevaluation of the conditions of crystallization of such complexes.  相似文献   

Detecting genotoxicity using the Comet assay following chronic exposure of Manila clam Tapes semidecussatus to polluted estuarine sediments     

B. M. Coughlan  M. G. J. Hartl  S. J. O&#x;Reilly  D. Sheehan  C. Morthersill  F. N. A. M. van Pelt  J. O&#x;Halloran  N. M. O&#x;Brien 《Marine pollution bulletin》2002,44(12)

Sediments frequently cause damage to biota due to the accumulation of toxic compounds and the bioavailability of sediment-bound contaminants. Damage can be assessed using biomarkers, such as the degree of genotoxic impact following in vivo exposure to pollutants. Genotoxic damage, expressed as single-strand DNA breaks, was measured in cells isolated from haemolymph, gill and digestive gland from the clam Tapes semidecussatus, using the single cell gel electrophoresis (Comet assay). Clams were exposed for three weeks to sediment samples collected from a polluted site and a ‘clean’ reference site.The level of DNA damage was assessed using an image analysis package and expressed as Tail Moment. Throughout the study, significant differences in DNA damage were recorded for each tissue type between clams exposed to the two sediment samples. We conclude that the Comet assay is a useful tool for the detection of DNA damage in clams chronically exposed to polluted sediments.  相似文献   

An Oxygen and Hydrogen Isotope Study of the Skaergaard Intrusion and its Country Rocks: a Description of a 55 M.Y. Old Fossil Hydrothermal System   总被引：4，自引：4，他引：4  

TAYLOR  HUGH P.  JR.; FORESTER  RICHARD W. 《Journal of Petrology》1979,20(3):355-419

Oxygen isotope analyses have been obtained on rocks and coexistingminerals, principally plagioclase and clinopyroxene, from about400 samples of the Skaergaard layered gabbro intrusion and itscountry rocks. The ¹⁸O values of plagioclase decrease upwardin the intrusion, from ‘normal’ values of about+6.0 to +6.4 in the Lower Zone and parts of the Middle Zone,to values as low as –2.4 in the Upper Border Group. The¹⁸O depletions of the plagioclase all took place under subsolidusconditions, and were produced by the Eocene meteoric-hydrothermalsystem established by this pluton. Clinopyroxene, which is moreresistant to ¹⁸O exchange than is plagioclase, also underwentdepletion in ¹⁸O, but to a lesser degree (¹⁸O = +5.2 to +3.5).The ¹⁸O-depleted rocks typically show reversed ¹⁸Oplag–pxfractionations, except at the top of the Upper Zone, where thepyroxenes are very fine-grained aggregates pseudomorphous afterferrowollastonite; these inverted pyroxenes were much more susceptibleto subsolidus ¹⁸O exchange (¹⁸O = +3–9 to +0.7). D/H analysesof the chloritized basalt country rocks and of the minor quantitiesof alteration minerals in the pluton (D = –116 to –149)confirm these interpretations, indicating that the rocks interactedwith meteoric groundwaters having an original D –100.and ¹⁸O –14. Low D values ( –125) were also foundthroughout the biotites of the Precambrian basement gneiss,requiring that small amounts of water penetrated downward todepths of at least 6 to 10 km. These values, together with thelack of ¹⁸O depletion of the gneiss, imply that the overallwater/rock ratios were very small in that unit (<0.01), andthus that convective circulation of these waters was much morevigorous in the overlying highly jointed plateau basalts (¹⁸O –4.0 to +4–0) than in the relatively impermeablegneiss (¹⁸O +7–3 to +7–7). This contrast in permeabilitiesof the country rocks is also reflected in the distribution of¹⁸O values in the pluton; the plagioclases with ‘normal’¹⁸O values all lie stratigraphically beneath the projectionof the basalt-gneiss unconformity through the pluton. Elsewhere,the ¹⁸O depletions are correlated with abundance of fracturesand faults, particularly in the NE portion of the intrusion,where the Layered Series is very shallow-dipping and permeablebasalts underlie the gabbro. The transgressive granophyres in the lower part of the intrusivehave ¹⁸O values identical to those of the basement gneiss, indicatingthey were probably formed by partial melting of stoped blocksof gneiss. In the upper part of the intrusion these granophyredikes have ¹⁸O values similar to the adjacent host gabbro; thissuggests that much of the hydrothermal alteration occurred aftertheir emplacement. However, because of the rarity of low-temperaturehydrous alteration minerals, it is also clear that most of theinflux of H₂O into the layered gabbro occurred at very hightemperatures (>400–500 °C). Prior to flowing intothe gabbro, these fluids had exchanged with similar mineralassemblages in the basaltic country rocks, explaining the lackof chemical alteration of the gabbro. Xenoliths of roof rockbasalt and of Upper Border Group leucogabbro were strongly depletedin ¹⁸O by the hydrothermal system prior to their falling tothe bottom of the magma chamber and being incorporated in thelayered series. This proves that the hydrothermal system wasestablished very early, at the time of emplacement of the Skaergaardintrusion. However, no measurable ¹⁸O depletion of the gabbromagma could be detected, indicating that very little H₂O penetrateddirectly into the liquid magma, in spite of the fact that ahydrothermal circulation system totally enveloped the magmachamber for at least 100, 000 years during its entire periodof crystallization. Only as crystallization proceeded was thehydrothermal system able to collapse inward and interact withthe solidified and fractured portions of the gabbro. Neverthelesssome H₂O was clearly added directly to the magma by dehydrationof the stoped blocks of altered roof rock. It is also plausiblethat small amounts of meteoric water diffused directly intothe magma, most logically in the vicinity of major fracturezones that penetrated close to, or were underneath, the late-stagesheet of differentiated ferrodiorite magma. It is suggestedthat such influx of meteoric waters was responsible for manyof the gabbro pegmatite bodies that are common in the MarginalBorder Group; also, such H₂O might have produced local increasesin Fe⁺³/Fe⁺² in the magma that in turn could explain some ofthe asymmetric crystallization effects in the magma chamber.Local lowering of the liquidus temperature would also occur,perhaps leading to topographic irregularities on the floor ofthe magma chamber (e.g. the trough bands?).  相似文献   

Miocene goethitic and chamositic oolites, northeastern Colombia     

HAROLD E. JAMES  JR  FRANKLYN B. VAN  HOUTEN 《Sedimentology》1979,26(1):125-133

The late (?) Miocene non-marine to paralic Guayabo Group in northeastern Colombia and adjacent Venezuela contains as many as thirty-four thin (to 15 cm) goethitic and chamositic oolites and ooid-bearing sandstones in 1080 m of section. This eastward prograding deltaic complex consists mainly of chert-rich litharenite in fluvial, distributary channel, and shoreline facies, and of montmorillonite mudstone in floodplain and interdistributary embayment facies. Within this framework the oolites are restricted to a paralic association that developed during episodes of waning detrital sedimentation when distributary abandonment was followed by minor transgression across mudflats. Most of the multilayered and symmetrical ooids are composed of goethite, rarely with a small amount of chamosite. These are essentially spherical; many of the chamosite-rich ones have been plastically deformed. Goethitic ooids resemble those in a thin layer accumulating in brackish Lake Chad, central Africa. Chamositic ooids have affinities with those accumulating in a sea loch in western Scotland. Each of these examples is associated with detrital (silicate) sedimentation, apparently developed directly from colloidal ferric oxide and silicate precursors, and affords no evidence that primary aragonitic ooids were later placed by ironbearing oxide and clay.  相似文献   

Mineralogy and Petrology of the Metamorphosed Wabush Iron Formation, Southwestern Labrador     

KLEIN  CORNELIS  JR. 《Journal of Petrology》1966,7(2):246-305

The Wabush Iron Formation, of late Precambrian (Proterozoic)age is part of the Labrador Trough in southwestern Labrador,Canada. It is the regionally metamorphosed equivalent of lowgrade metamorphic (chlorite zone) iron-rich sediments of thecentral part of the Labrador Trough. The metamorphic grade iskyanite-staurolite zone, as concluded from conformably underlyingpelitic schist assemblages. Sedimentary textural features suchas very pronounced banding and a very rare occurrence of relicgranules are still preserved. The iron formation consists mainly of quartz, specularite, magnetite,cummingtonite-grunerite, and ferrodolomite-ankerite. Less commonare actinolite, anthophyllite, riebeckitetremolite, magnesioriebeckite,ferrosalite, orthopyroxene, aegirine-augite, aegirine, rhodonite,garnet (almandine, spessartine, calderite), siderite, rhodochrosite,calcite, and kutnahorite. Conventional wet chemical analyses or electron microprobe analyseshave been made of thirty-four phases belonging to the abovelist. Six additional electron probe analyses have been madeof phases from the underlying pelitic schists. All conventionallyanalyzed phases are characterized by complete optical, unitcell parameter, and density measurments. The analyzed assemblages from the silicate and silicate-carbonateiron formation include grunerite-ferrosalite, grunerite-eulite-siderite,grunerite-actinolite, grunerite-almandine, cummingtonite-spessartine,rhodonite-kutnahorite-calderite, aegirine-augite-riebeckite-tremolite,magnesioriebeckite-cummingtonite-rhodonite, aegirine-augite-rhodonite-rhodo-chrosite,and aegirine-rhodonite-calderite-rhodochrosite. The assemblages are concluded to be equilibrium assemblages.Of the volatile components, O₂, CO₂, and H₂O, O₂, is concludedto have behaved as an inert (buffered) component. Variationsin the activity of CO₂ are concluded to have existed betweensilicate-oxide and carbonate-oxide members of the iron formation.It is not clear, however, whether CO₂ has acted as a perfectlymobile component with strong aco₂ gradients throughout the area,or as an inert component in some parts of the area. H₂O is consideredto have been perfectly mobile. An increase in Mg/(Mg+Fe) ratioin ferromagnesian silicates is correlated with an increase inthe oxidation state of the assemblage. A similar increase in(Mg+Mn)/(Mg+Mn+Fe) is found in manganoan ferromagnesian silicateswith increasing activity of O₂. A number of ferromagnesian silicatescontain large amounts of Na⁺ and Fe³⁺ as a result of the verylow Al₂O₃ content of the iron formation. The P and T conditionsof metamorphism are deduced from experimental studies applicableto the underlying pelitic schists.  相似文献   

Anorthite--Forsterite and Anorthite--Enstatite Reactions and their bearing on the Basalt--Eclogite Transformation   总被引：3，自引：0，他引：3  

KUSHIRO  I.; YODER  H. S.  JR. 《Journal of Petrology》1966,7(3):337-362

The reactions betweeon anorthite and forsterite and betweenanorthite and enstatite have been studied at high pressuresand high temperatures with solid-media and gas-media apparatus.For the 1: 1 (molecular ratio) composition of anorthite andforsterite the following three assemblages have been obtainedwith increasing pressure at a constant temperature: anorthiteforsterite,clinopyroxeneorthopyroxenespinelanorthite, and garnet (pyropegrossulariteseries). Two univariant curves between these three assemblageshave been determined. The amounts of pyroxenes relative to spineland anorthite in the second assemblage increase and the contentsof the Tschermak's components in the pyroxenes increase withincreasing pressure. The 1:2 (molecular ratio) composition of anorthite and forsteritewas also studied, and the univariant curve for the reactionclinopyroxeneorthopyroxenespinel garnet (pyropegrossulariteseries)forsterite has been determined. For the 1: 2 (molecular ratio) composition of anorthite andenstatite the following assemblages have been obtained withincreasing pressure at a constant temperature: anorthiteenstatite,anorthiteorthopyroxeneclinopyroxenequartz, and garnet (pyrope-grossulariteseries)quartz. The univariant curve between the last two assemblageshas been determined. Both the pyroxenes in the second assemblagecontain Tschermak's components, which increase in content withincreasing pressure at the expense of anorthite. These experimental results suggest that basalts, either saturatedor undersaturated with silica, transform into aluminous pyroxene-richassemblages at lower pressures or higher temperatures than thestability field of eclogites, and that pyroxene-spinel symplectitesfound in some metamorphosed gabbro, troctolite, and norite mayhave formed in the stability field of the pyroxene-rich assemblages.The stability field of the pyroxene-rich assemblages is probablyincluded within the pressure-temperature conditions of the granulitefacies. It is also suggested that the garnet-free peridotites,such as the peridotite inclusions in basaltic rocks and theintrusive peridotites in the orogenic belts, are stable at lowerpressures or higher temperatures than garnet peridotites, suchas the inclusions in kimberlite and intrusive garnet peridotitein the orogenic belts.  相似文献