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1.
Richard Dame Norbert Dankers Theo Prins Henk Jongsma Aad Smaal 《Estuaries and Coasts》1991,14(2):130-138
The uptake and release of materials by intertidal mussel beds were directly measured in two cultivated Dutch estuaries. Generally, chlorophylla, seston, and particulate organic carbon were taken up, while ammonium, orthophosphate, and silicate were released. The observed rates were higher than values computed from organismic observations and similar to those observed for intertidal oyster reefs in South Carolina. Specific estuarine material turnover rates varied from 1 week to 38 weeks when calculated with mussel bed fluxes. The fastest turnover rates were for chlorophylla and ammonium. These results support the idea that dense assemblages of bivalves are major components in the recycling of nutrients in estuaries. 相似文献
2.
Heat Flow in the Aegean Sea 总被引：3，自引：0，他引：3
Derk Jongsma 《Geophysical Journal International》1974,37(3):337-346
3.
Marine geological and geophysical data together with drilling information indicate that the North African passive continental margin has been subjected to extension and wrenching after it collided with the northern part of Sicily. The area of the Tripolitania Basin, Jarrafa Trough, Melita and Medina Bank and the Ragusa-Malta Plateau has formed part of a sinking passive margin since the dispersal of Gondwanaland at about 180 My ago as observed from geohistory diagrams. A record of rifting in a NW-SE direction accompanied by dextral shear along the southern troughs is observed in seismic reflection data. The rifting started during the Neocomian and lasted until the Eocene when activity became minor. A pre-Middle Miocene period of northward subduction of oceanic crust is inferred from the geology in NE Sicily. Uplift of the northern part of the African margin after collision in the Middle Miocene is seen in wells in southern Sicily. After the Messinian a rift and dextral shear zone established itself across the African Margin from the Strait of Sicily to the Medina Ridge in the lonian Basin. The zone is marked by up to 1.7 km deep grabens, narrow active wrench faulted channels, volcanic fissures and local uplifted ‘Keilhorsts’ such as Malta. This zone, which varies in width from 100 to 35 km, forms the southern boundary of a microplate which includes Sicily. We speculate that the present motion of this microplate is partly due to the eastward movement of the Calabrian Arc with the Sicilian block over the last remaining oceanic lithosphere in the Eastern Mediterranean. 相似文献
4.
The role of agency in overcoming path dependence and enabling sustainability transitions is receiving increasing attention. Currently lacking are more empirically derived explanations of the co-evolutionary dynamics between actors and institutional change that could potentially provide guidance on facilitating such transitions into the future. This paper investigates these dynamics through a longitudinal case analysis of Melbourne's transition to improved stormwater quality treatment. The complex data collection, analysis and validation approach, which included oral histories, semi-structured interviews, industry workshops and documentary analysis, examined the nuances of the actor-related strategies and institutional enabling processes throughout the different phases of the transition over the last fifty years. The results revealed the importance of a small group of loosely connected frontrunners from across government, private, community and scientific sectors who, through a mix of creating and disrupting institutional strategies, managed to facilitate a growing and diverse actor-network that steered this transition over decades. The establishment of networked bridging organisations was also instrumental because they formed different types of networks and alliances over time for protecting and deepening the reach of the transition dynamics across the city. The findings suggest there is no single cause–effect relationship nor one dominant intervention or action that shifted the urban stormwater management regime. Rather, it showed that the co-evolutionary processes between the broader transitional dynamics were played into by frontrunners and their actor-networks in such a way that emerging new narratives diffused, giving meaning to the evolving scientific agendas and on-the-ground experiments, which led to new institutional structures and enabling administrative tools. It seems as though each one of these dimensions is as crucial as the other in explaining the outcomes of this successful sustainability transition. 相似文献
5.
Stacie E. Crowe Paul T. Gayes Derk C. Bergquist Robert F. Van Dolah 《Marine pollution bulletin》2010,60(5):679-691
The deepening of shipping and entrance channels in Charleston Harbor (South Carolina, USA) was completed in April 2002 and placed an estimated 22 million cubic yards (mcy) of material in the offshore Charleston Ocean Dredged Material Disposal Site (ODMDS). To determine if sediments dispersed from the ODMDS were negatively affecting invertebrate and/or finfish communities at hard bottom reef areas around the disposal area, six study sites were established: three close to and downdrift of the ODMDS and three upcurrent and farther from the ODMDS. These sites were monitored biannually from 2000 to 2005 using diver surveys and annually using simultaneous underwater video tows and detailed sidescan-sonar. In general, the sediment characteristics of downdrift sites and reference sites changed similarly over time. Overall, the hard bottom reef areas and their associated communities showed little evidence of degradation resulting from the movement of sediments from the Charleston ODMDS during the study period. 相似文献
6.
Spherical translucent green glasses found in New Guinea for many years have the external appearance of stream abraded tektites, but are chemically distinct from known tektite groups. Their chemical composition is most similar to artificial glasses. If these objects are the source of reports of tektites occurring in New Guinea, the existence of New Guinea tektites must now be discounted. 相似文献
7.
D. Jongsma J.M. Woodside G.C.P. King J.E. van Hinte 《Earth and Planetary Science Letters》1987,82(1-2)
The Medina Wrenth in the central Mediterranean is a transform fault connecting the plate collision in northwest Africa and northern Sicily with that occurring at the Aegean plate boundary, south of Greece. The more than 800 km long crescent-shaped wrench zone is currently seismically quiet but exhibits major deformation since 5 Ma within a belt 30–100 km wide. It forms the southern boundary of two microplates moving eastward with respect to Africa and Europe. A simple plate rotation model constrained by recent paleomagnetic data indicates that a continental Iblean microplate and a hybrid continental/oceanic Ionian microplate, separated along the Malta Escarpment, have rotated anticlockwise by 11° and 12°, respectively, around poles in southern Italy. These rotations involved some 100 km of dextral eastward movement relative to Africa of the Ionian Basin north of the Medina Wrench since 5 Ma. Combining the published 26° clockwise rotation of the Peloponnesus and northwest half of the Aegean with the 12° anticlockwise rotation of the Ionian microplate results in (a) a 99% agreement between the length of the seismic Benioff Zone beneath Greece and the total convergence of the microplates, and (b) an average rate of convergence across the Aegean plate boundary southwest of the Peloponnesus of 6.6 ± 1cm a−1 since the Miocene. Relative motion between microplates in a collision zone thus may be as much as 6 times faster than convergence between the major plates which spawned them, and they can be considered rigid to the first order over the time span involved. 相似文献
8.
Derk C. Bergquist Jason A. Hale Patrick Baker Shirley M. Baker 《Estuaries and Coasts》2006,29(3):353-360
The Suwannee River watershed is one of the least developed in the eastern United States, but with increasing urbanization
it is facing potential long-term alterations in freshwater flow to its estuary in the Gulf of Mexico. The purpose of this
study was to develop biological indicators of oyster reef state along a natural salinity gradient in the Suwannee River estuary
in order to allow the rapid assessment of the effect of changing freshwater input to this system. Percent cover and density
of three size classes of living oysters, as well as the abundance of several predominant reef-associated invertebrates, were
measured along a broad salinity gradient in the estuary and were correlated with salinity estimates from a long-term database
for the preceding 12–24 mo. All eastern oyster,Crassostrea virginica, parameters (percent cover and density of three size classes) were significantly and negatively related to salinity. Data
from samples collected near the lower intertidal were more closely dependent upon salinity than were samples from the higher
intertidal at the same sites. Salinity differences were most closely reflected in differences in total oyster cover. This
relationship corresponded with a general decline in oyster habitat with increasing distance from the mouth of the Suwannee
River. Species richness was significantly and positively correlated with allC. virginica parameters (percent cover and density of three size classes), but the relationship explained only about half the variability.
Density data of the hooked mussel,Ischadium recurvum, and a mud crab,Eurypanopeus depressus, were positively and strongly correlated withC. virginica parameters, likely reflecting the abundance of habitat provided byC. virginica shells. All of the biological indicators measured responded similarly along the salinity gradient, indicating they provide
reliable indices of the effect of changing salinities in the Suwannee River estuary over the previous 1 or 2 yr. Some areas
of positive relief defined as reefs 30 years ago are no longer oyster habitat, suggesting an ongoing decline, but nearshoreC. virginica were abundant. *** DIRECT SUPPORT *** A02BY003 00002 相似文献
9.
Derk C. Bergquist Jason P. Andras Tim McNelis Sarah Howlett Mark J. van Horn & Charles R. Fisher 《Marine Ecology》2003,24(1):31-44
Abstract. The slow rate of change in hydrocarbon seep communities on the upper Louisiana slope prevents the use of direct observation in studying successional trends. We used a chronosequence consisting of three presumed stages – juvenile, adult and senescent – to test a previous model which proposed that sulfide availability and vestimentiferan growth and physiological health decline over the lifespan of a vestimentiferan aggregation. We replicated the chronosequence at two sites to simultaneously explore the influence of spatial heterogeneity on the characteristics of these communities. We determined environmental sulfide concentrations and vestimentiferan growth and condition in at least two vestimentiferan aggregations representative of each stage at each of these two sites. Hydrogen sulfide concentrations were highly variable both above and below the sediment's surface, and sulfide was present in high concentrations to sediment depths of 70 cm. Vestimentiferan growth and condition varied significantly on multiple spatial scales from sites separated by tens of kilometers, to aggregations separated by tens to hundreds of meters within a site, to individual vestimentiferans separated by tens of centimeters within an aggregation. The striking variability in both environmental sulfide and vestimentiferan growth and condition within individual aggregations suggests a crucial role for microhabitat variability in the persistence of vestimentiferan aggregations at these sites. Few significant successional trends in environmental sulfide or vestimentiferan growth and condition were found over the three stages tested. 相似文献
10.
Erik E. Cordes Derk C. Bergquist Meredith L. Redding & Charles R. Fisher 《Marine Ecology》2007,28(1):160-168
Seepiophila jonesi is a vestimentiferan tubeworm (Siboglinidae: Polychaeta) inhabiting the cold seeps of the upper slope of the Gulf of Mexico. It commonly co‐occurs with Lamellibrachia luymesi, which is among the most long‐lived non‐clonal animals known. The growth pattern of S. jonesi is best described by a model including a size‐specific probability of growth and an average growth rate that does not vary with individual size. This model, based on growth data from in situ staining and collection approximately 1 year later, predicts that S. jonesi is very slow growing and may attain ages comparable with L. luymesi. The efficacy of this model in describing L. luymesi growth rate was assessed, but the previously employed model of declining growth rate with individual size provided the better fit to the empirical data. Comparisons of both S. jonesi and L. luymesi growth rates among sites and among aggregations within a site indicate that there is some degree of habitat variability contributing to differences in growth rates. However, position of the anterior end of the worm within an aggregation did not have a significant effect on growth rate in comparisons among groups of L. luymesi from different distances from the center of an aggregation. The evolution of longevity in these species of vestimentiferans was favored by the relative stability of the seep habitat and sulfide sources, in contrast to the hydrothermal vent environment inhabited by relatively short‐lived and fast‐growing vestimentiferan species. 相似文献