Effect of restored freshwater inflow on macrofauna and meiofauna in upper Rincon Bayou, Texas, USA     

Paul A. Montagna  Richard D. Kalke  Christine Ritter 《Estuaries and Coasts》2002,25(6):1436-1447

Construction of two dams in 1958 and 1982 reduced freshwater inflow events to Rincon Bayou, part of the Nueces Delta near Corpus Christi, Texas, USA. Inflow reduction led to a reverse estuary, where low-salinity water flooded the delta on incoming tides and higher salinities were found near the Nueces River. Hypersaline conditions caused by high evaporation rates and low water levels were common during summer in the upper reaches. In October 1995, an overflow diversion channel was created by lowering the bank of the Nueces River to restore inflow events into Rincon Bayou, which is the main stem creek that runs through the center of the Delta. Hypersaline conditions occurred four times from mid-1994 to mid-1997 and only once after mid-1997. Lower, rather than higher, salinity conditions were found after August 1997 in the upper reaches. Benthic faunal recovery was monitored by changes in macrofauna and meiofauna communities. Macrofauna responded to inflow events with increased abundances, biomass, and diversity but decreased during hypersaline conditions. Meiofauna abundance also increased with increasing inflow. Benthic characteristics were different in Rincon Bayou than in a reference site, upstream from introduced inflow. As inflow events have increased due to the diversion, the opportunities for positive responses to increased flow have increased. Although the oveflow channel was filled in at the end of the demonstration project in fall 2000, the City of Corpus Christi reopened the channel in fall 2001 because the ecological benefits were credited toward the state-mandated minimum flow requirement for the Nueces Estuary.  相似文献   

Multimedia Risk-Based Soil Cleanup at a Gasoline-Contaminated Site Using Vapor Extraction     

William B. Mills  Kay M. Johnson  Sally Liu  John Y. Loh  Christine S. Lew 《Ground Water Monitoring & Remediation》1996,16(3):168-178

At a utility service center, gasoline from an underground storage tank had leaked into subsurface vadose zone soils for several years. To remediate the site, a soil vapor extraction (SVE) system was installed and operated. At the completion of the SVE operation, gasoline-containing residues in several confirmation soil borings exceeded agency-mandated cleanup levels. Rather than continue with SVE, a risk-based approach was developed to evaluate what levels of gasoline-containing residues could be left in the soil and still protect human health. The risk-based approach consisted of simulating the fate of chemical residues through the vadose zone and then into both the ground water and atmosphere. Receptor point concentrations were predicted, and health risks were assessed. The risk assessment concluded that ingestion of contaminated ground water and inhalation of air while showering were the largest potential contributors to risk, and that risks associated with inhalation of vapor-containing ambient air are small. However, all predicted risks are below the acceptable risk levels of 10⁻⁶ individual cancer risk probability and 1.0 hazard index. Therefore, the lead agency accepted the recommendation that the site requires no further remediation. The service center continues normal operations today.  相似文献   

The relationships of seabird assemblages to physical habitat features in Pacific equatorial waters during spring 1984-1991   总被引：1，自引：0，他引：1  

Ribic  Christine A.; Ainley  D. G. 《ICES Journal of Marine Science》1997,54(4):593-599

  相似文献   

Silicate determination in sea water: Toward a reagentless electrochemical method     

Marielle Lacombe  Vronique Garon  Maurice Comtat  Louise Oriol  Joël Sudre  Danile Thouron  Nadine Le Bris  Christine Provost 《Marine Chemistry》2007,106(3-4):489-497

Silicate has been determined in sea water by four different electrochemical methods based on the detection of the silicomolybdic complex formed in acidic media by the reaction between silicate and molybdenum salts. The first two methods are based on the addition of molybdate and protons in a seawater sample in an electrochemical cell. Cyclic voltammetry presents two reduction and two oxidation peaks giving four values of the concentration and therefore increasing the precision. Then chronoamperometry is performed on an electrode held at a constant potential. A semi-autonomous method has been developed based on the electrochemical anodic oxidation of molybdenum, the complexation of the oxidation product with silicate and the detection of the complex by cyclic voltammetry. This method is tested and compared with the classical colorimetric one during ANT XXIII/3 cruise across Drake Passage (January–February 2006). The detection limit is 1 μM and the deviation between both methods is less than 3% for concentrations higher than 10 μM. Finally a complete reagentless method with a precision of 2.6% is described based on the simultaneous formation of the molybdenum salt and protons in a divided electrochemical cell. This latter method should be very useful for developing a reagentless sensor suitable for long term in situ deployments on oceanic biogeochemical observatories.  相似文献   

Distribution of seabirds in the northern Gulf of Mexico in relation to mesoscale features: initial observations   总被引：1，自引：0，他引：1  

Ribic  Christine A.; Davis  Randall; Hess  Nancy; Peake  Dwight 《ICES Journal of Marine Science》1997,54(4):545-551

  相似文献   

Mantle Bouguer Anomaly Along an Ultra Slow-Spreading Ridge: Implications for Accretionary Processes and Comparison with Results from Central Mid-Atlantic Ridge     

Rommevaux-Jestin  Céline  Deplus  Christine  Patriat  Philippe 《Marine Geophysical Researches》1997,19(6):481-503

A three-dimensional analysis of gravity andbathymetry data has been achieved along the Southwest Indian Ridge (SWIR)between the Rodriguez Triple Junction (RTJ) and the Atlantis II transform,in order to define the morphological and geophysical expression ofsecond-order segmentation along an ultra slow-spreading ridge(spreading rate of 8 mm/yr), and to compare it with awell-studied section along a slow-spreading ridge (spreadingrate of 12.5 mm/yr): the Mid-Atlantic Ridge (MAR) between 28°and 31°30 N.Between the Atlantis II transform and theRTJ, the SWIR axis exhibits a deep axial valley with an 30°oblique trend relative to the north–south spreading direction. Onlythree transform faults offset the axis, so the obliquity has to beaccommodated by the second-order segmentation. Alongslow-spreading ridges such as the MAR, second-order segmentshave been defined as linear features perpendicular to the spreadingdirection, with a shallow axial valley floor at the segment midpoint,deepening to the segment ends, and are associated with Mantle BouguerAnomaly (MBA) lows. Along the SWIR, our gravity study reveals the presenceof circular MBA lows, but they are spaced further apart than expected. Thesegravity lows are systematically centred over narrow bathymetric highs, andinterpreted as the centres of spreading cells. However, along some obliquesections of the axis, the valley floor displays small topographicundulations, which can be interpreted as small accretionary segments frommorphological analysis, but as large discontinuity domains from thegeophysical data. Therefore, both bathymetry and MBA variations have to beused to define the second-order segmentation of an ultraslow-spreading ridge. This segmentation appears to be characterisedby short segments and large oblique discontinuity domains. Analysis of alongaxis bathymetric and gravimetric profiles exhibits three different sectionsthat can be related to the thermal structure of the lithosphere beneath theSWIR axis.The comparison between characteristics of segmentationalong the SWIR and the MAR reveals two major differences: first, the poorcorrelation between MBA and bathymetry variations and second, the largerspacing and amplitude of MBA lows along the SWIR compared to the MAR. Theseobservations seem to be correlated with the spreading rate and the thermalstructure of the ridge. Therefore, the gravity signature of the segmentationand thus the accretionary processes appear to be very different: there areno distinct MBA lows on fast-spreading ridges, adjacent ones on slowspreading ridges and finally separate ones on ultra slow-spreadingridges. The main result of this study is to point out that 2nd ordersegmentation of an ultra slow-spreading ridge is characterised bywide discontinuity domains with very short accretionary segments, suggestingvery focused mantle upwelling, with a limited magma supply through a cold,thick lithosphere. We also emphasise the stronger influence of themechanical lithosphere on accretionary processes along an ultra slow-spreading ridge.  相似文献   

Laxmi Ridge – A continental sliver in the Arabian Sea     

Talwani  Manik  Reif  Christine 《Marine Geophysical Researches》1998,20(4):259-271

Identification by Bhattacharya et al. (1994) of seafloor spreading type magnetic anomalies in the basin lying between Laxmi Ridge in the Arabian Sea and the Indian continent necessitates a change in plate tectonic reconstruction. Naini and Talwani (1982) named this basin the Eastern Basin and we will continue to use this term in this paper. Others, in the literature, have called this the Laxmi Basin. Previous reconstructions had assumed that the Eastern Basin is underlain by continental crust. The new reconstruction moves Seychelles' original location closer to India and ameliorates a space problem in the Mascarene Basin. A new rotation pole between anomaly 28 and 34 times avoids skipping of fracture zones resulting from rotation poles described earlier. The negative gravity anomaly over the Eastern Basin is a necessary consequence of a continental sliver lying between oceanic crust on either side. Seismic velocities that are slightly greater than 7 km s^–1 under the Eastern need not be necessarily interpreted as material that underplates continental crust.  相似文献   

Variability in terrigenous sedimentation processes off northwest Africa and its relation to climate changes: Inferences from grain-size distributions of a Holocene marine sediment record     

Christine Holz  Jan-Berend W. Stuut  Rüdiger Henrich  Helge Meggers 《Sedimentary Geology》2007,202(3):499-508

Variations in deposition of terrigenous fine sediments and their grain-size distributions from a high-resolution marine sediment record offshore northwest Africa (30°51.0′N; 10°16.1′W) document climate changes on the African continent during the Holocene. End-member grain-size distributions of the terrigenous silt fraction, which are related to fluvial and aeolian dust transport, indicate millennial-scale variability in the dominant transport processes at the investigation site off northwest Africa as well as recurring periods of dry conditions in northwest Africa during the Holocene. The terrigenous record from the subtropical North Atlantic reflects generally humid conditions before the Younger Dryas, during the early to mid-Holocene, as well as after 1.3 kyr BP. By contrast, continental runoff was reduced and arid conditions were prevalent at the beginning of the Younger Dryas and during the mid- and late Holocene. A comparison with high- and low-latitude Holocene climate records reveals a strong link between northwest African climate and Northern Hemisphere atmospheric circulation throughout the Holocene. Due to its proximal position, close to an ephemeral river system draining the Atlas Mountains as well as the adjacent Saharan desert, this detailed marine sediment record, which has a temporal resolution between 15 and 120 years, is ideally suited to enhance our understanding of ocean-continent-atmosphere interactions in African climates and the hydrological cycle of northern Africa after the last deglaciation.  相似文献   

Morphology and genesis of slow-spreading ridges—seabed scattering and seismic imaging within the oceanic crust     

Christine Peirce  Martin Sinha  Simon Topping  Christopher Gill 《Geophysical Journal International》2007,168(1):59-89

  相似文献   

Geographies of care: A commentary     

Christine Milligan  Sarah Atkinson  Mark Skinner  Janine Wiles 《New Zealand geographer》2007,63(2):135-140

  相似文献