Succession of microphytobenthos in a restored coastal wetland     

Christopher N. Janousek  Carolyn A. Currin  Lisa A. Levin 《Estuaries and Coasts》2007,30(2):265-276

Sediment microphytobenthos, such as diatoms and photosynthetic bacteria, are functionally important components of food webs and are key mediators of nutrient dynamics in marine wetlands. The medium to long-term recovery of benthic microproducers in restored habitats designed to improve degraded coastal wetland sites is largely unknown. Using taxon-specific photopigments, we describe the composition of microphytobenthic communities in a large restoration site in southern California and differences in the temporal recovery of biomass (chlorophylla), composition, and taxonomic diversity between vegetatedSpartina foliosa salt marsh and unvegetated mudflat. Visually distinct, spatially discreet, microphytobenthic patches appeared after no more than 7 mo within the restoration site and were distinguished by significant differences in biomass, taxonomic diversity, and the relative abundance of cyanobacteria versus diatoms. Sediment chlorophylla concentrations within the restored site were similar to concentrations in nearby natural habitat 0.2–2.2 yr following marsh creation, suggesting rapid colonization by microproducers. RestoredSpartina marsh very rapidly (between 0.2 and 1.2 yr) acquired microphytobenthic communities of similar composition and diversity to those in naturalSpartina habitat, but restored mudflats took at least 1.6 to 2.2 yr to resemble natural mudflats. These results suggest relatively rapid recovery of microphytobenthic communities at the level of major taxonomic groups. Sediment features, such as pore water salinity andSpartina density, explained little variation in microphytobenthic taxonomic composition. The data imply that provision of structural heterogeneity in wetland construction (such as pools and vascular plants) might speed development of microproducer communities, but no direct seeding of sediment microfloras may be necessary.  相似文献   

Possible nature of the seismic boundary at a depth of 70 km     

B. W. Levin  M. V. Rodkin  E. V. Sasorova 《Doklady Earth Sciences》2007,414(1):578-581

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A one-dimensional model of the atmospheric electric field near the Venusian surface     

I. Tzur  Z. Levin 《Icarus》1982,52(2):346-353

A numerical model is used to simulate the buildup of an electric field from below the Venusian cloud layer to the surface. The steady-state profiles of the ion concentration, net space charge, diffusion and conduction current, and electric field are calculated. Two electric field sources are considered. The first is that produced by the higher diffusivity of positive ions relative to negative ions, which results in charging the surface with a net positive charge. The results show that the magnitude of the electric field and the net space charge developed near the surface are mainly dependent on the mixing conditions in the boundary layer. However, even in the case of relatively strong mixing, the maximum electric field is found to be 1.5 V m^?1 and it decays rapidly above 100 m. The second source of an electric field is assumed to be charge separation inside Venusian clouds. A steady-state conduction current in the region below the layer of clouds which represents the intensity of charge separation inside the clouds is used as a parameter. When this parameter is assumed to be 10^?12 A m^?2, which is about the fair-weather conduction current in the atmosphere of Earth, an electric field of 5 kV m^?1 is developed near the surface. This electric field exists up to a few kilometers, decreases by an order of magnitude at about 20 km, and then decays rapidly.  相似文献   

A Comparison of Seismic Array Processing Methods     

P. E. Green Jr.  E. J. Kelly  Jr.  M. J. Levin 《Geophysical Journal International》1966,11(1):67-84

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The petrochemical method for recognizing geodynamic formation settings of igneous rocks (Shmidt Terrane,Sakhalin)     

V. M. Grannik  B. V. Levin 《Doklady Earth Sciences》2011,441(2):1607-1610

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New insights on the trophic ecology of bathyal communities from the methane seep area off Concepción,Chile (~36° S)     

Germán Zapata‐Hernández  Javier Sellanes  Andrew R. Thurber  Lisa A. Levin  Frédéric Chazalon  Peter Linke 《Marine Ecology》2014,35(1):1-21

Studies of the trophic structure in methane‐seep habitats provide insight into the ecological function of deep‐sea ecosystems. Methane seep biota on the Chilean margin likely represent a novel biogeographic province; however, little is known about the ecology of the seep fauna and particularly their trophic support. The present study, using natural abundance stable isotopes, reveals a complex trophic structure among heterotrophic consumers, with four trophic levels supported by a diversity of food sources at a methane seep area off Concepción, Chile (~36° S). Although methanotrophy, thiotrophy and phototrophy are all identified as carbon fixation mechanisms fueling the food web within this area, most of the analysed species (87.5%) incorporate carbon derived from photosynthesis and a smaller number (12%) use carbon derived from chemosynthesis. Methane‐derived carbon (MDC) incorporation was documented in 22 taxa, including sipunculids, gastropods, polychaetes and echinoderms. In addition, wide trophic niches were detected in suspension‐feeding and deposit‐feeding taxa, possibly associated with the use of organic matter in different stages of degradation (e.g. from fresh to refractory). Estimates of Bayesian standard ellipses area (SEA_B) reveal different isotopic niche breadth in the predator fishes, the Patagonian toothfish Dissostichus eleginoides and the combtooth dogfish Centroscyllium nigrum, suggesting generalist versus specialist feeding behaviors, respectively. Top predators in the ecosystem were the Patagonian toothfish D. eleginoides and the dusky cat shark, Bythaelurus canescens. The blue hake Antimora rostrata also provides a trophic link between the benthic and pelagic systems, with a diet based primarily on pelagic‐derived carrion. These findings can inform accurate ecosystem models, which are critical for effective management and conservation of methane seep and adjacent deep‐sea habitats in the Southeastern Pacific.  相似文献   

Alteration of benthic communities associated with copper contamination linked to boat moorings     

Carlos Neira  Lisa A. Levin  Guillermo Mendoza  Alberto Zirino 《Marine Ecology》2014,35(1):46-66

Although copper (Cu) is an essential element for life, leaching from boat paint can cause excess environmental loading in enclosed marinas. The effects of copper contamination on benthic macrofaunal communities were examined in three San Diego Bay marinas (America's Cup, Harbor Island West and East) in Southern California, USA. The distribution of Cu concentration in sediments exhibited a clear spatial gradient, with hotspots created by the presence of boats, which in two marinas exceeded the effect range medium (ERM). Elevated sediment Cu was associated with differences in benthic assemblages, reduced species richness and enhanced dominance in America's Cup and Harbor Island West, whereas Harbor Island East did not appear to be affected. At sites without boats there were greater abundances of some amphipods such as the species Desdimelita sp., Harpinia sp., Aoroides sp., Corophium sp., Podocerus sp., bivalves such as Lyonsia californica, Musculista senhousia, Macoma sp., and polychaetes such as Diplocirrus sp. In contrast, at sites with boats, densities of Pseudopolydora paucibranchiata, Polydora nuchalis, Euchone limnicola, Exogone lourei, Tubificoides spp. were enhanced. The limited impact on Harbor Island East suggests not only lower Cu input rates and increased water flushing and mixing, but also the presence of adequate defense mechanisms that regulate availability and mitigate toxic impacts. At all three marinas, Cu in tissues of several macrobenthic species exhibited Cu bioaccumulation above levels found in the surrounding environment. The annelids Lumbrineris sp. and Tubificoides spp., and the amphipod Desdimelita sp. contained high levels of Cu, suggesting they function as Cu bioaccumulators. The spionid polychaetes Polydora nuchalis and Pseudopolydora paucibranchiata had much lower Cu concentrations than surrounding sediments, suggesting they function as Cu bioregulators. The macrobenthic invertebrates in San Diego Bay marinas that tolerate Cu pollution (e.g. P. nuchalis, P. paucibranchiata, Euchone limnicola, Typosyllis sp., Tubificoides sp.) may function as indicators of high‐Cu conditions, whereas the presence of Cu‐sensitive species (e.g. Podocerus sp., Aoroides sp., Harpinia sp., Macoma sp., Lyonsia californica) may indicate healthier conditions (less Cu‐stressed). Parallel responses by faunas of Shelter Island Yacht Basin, also in San Diego Bay, suggest potential for development of regional Cu contamination assessment criteria, and call for functional comparisons with other marinas and coastal water bodies.  相似文献   

New data about tsunami evidence on Russia’s Pacific coast based on instrumental measurements for 2009–2010     

Shevchenko  G. V.  Ivel’skaya  T. N.  Kovalev  P. D.  Kovalev  D. P.  Kurkin  A. A.  Levin  B. V.  Likhacheva  O. N.  Chernov  A. G.  Shishkin  A. A. 《Doklady Earth Sciences》2011,438(2):893-898

Doklady Earth Sciences -  相似文献   

Connectivity clues from short-term variability in settlement and geochemical tags of mytilid mussels     

F. Joel Fodrie  Bonnie J. Becker  Lisa A. Levin  Kristen Gruenthal  Pat A. McMillan 《Journal of Sea Research》2011,65(1):141-150

The use of geochemical tags in calcified structures of fish and invertebrates is an exciting tool for investigating larval population connectivity. Tag evaluation over relatively short intervals (weeks) may detect environmental and ecological variability at a temporal scale highly relevant to larval transport and settlement. We collected newly settled mussels (Mytilus californianus and M. galloprovincialis) weekly during winter/spring of 2002 along the coast of San Diego, CA, USA, at sites on the exposed coast (SIO) and in a protected coastal bay (HI), to investigate temporal patterns of geochemical tags in mussel shells. Analyses of post-settlement shell via LA-ICP-MS revealed statistically significant temporal variability for all elements we examined (Mg, Mn, Cu, Sr, Cd, Ba, Pb and U). Despite this, our ability to distinguish multielemental signatures between sites was largely conserved. Throughout our 13-week study, SIO and HI mussels could be chemically distinguished from one another in 78–87% of all cases. Settlement varied between 2 and 27 settlers gram-byssus^?1 week^?1 at SIO and HI, and both sites were characterized by 2–3 weeks with “high” settlement. Geochemical tags recorded in early larval shell of newly settled mussels differed between “high” and “low” settlement weeks at both sites (MANOVA), driven by Mg and Sr at SIO (p = 0.013) and Sr, Cd, Ba and Pb at HI (p < 0.001). These data imply that shifts in larval sources or transport corridors were responsible for observed settlement variation, rather than increased larval production. In particular, increased settlement at HI was observed concurrent with the appearance of geochemical tags (e.g., elevated Cd), suggesting that those larvae were retained in upwelled water near the mouth of the bay. Such shifts may reflect short-term changes in connectivity among sites due to altered transport corridors, and influence the demography of local populations.  相似文献   

Non-linear r‐modes in a spherical shell: issues of principle     

Yuri Levin  Greg Ushomirsky 《Monthly notices of the Royal Astronomical Society》2001,322(3):515-522

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