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101.
Ammonium,nitrate and phytoplankton interactions in a freshwater tidal estuarine zone: potential effects of cultural eutrophication 总被引:2,自引:0,他引:2
Rita B. Domingues Ana B. Barbosa Ulrich Sommer Helena M. Galvão 《Aquatic Sciences - Research Across Boundaries》2011,73(3):331-343
Nitrate and ammonium are the most important nitrogen sources for phytoplankton growth. Differential utilization of inorganic
nitrogenous compounds by phytoplankton has been observed and may have significant impacts on primary productivity at local
scales. We used enrichment experiments with natural phytoplankton populations from the freshwater tidal zone of the Guadiana
estuary, a coastal ecosystem increasingly subjected to anthropogenic influences, to study the effects of nitrate and ammonium
on N-consumption and phytoplankton growth. In addition, we used combined additions of nitrate and ammonium to understand the
inhibitory effect of ammonium over nitrate uptake. Ammonium concentrations in the freshwater tidal reaches of the Guadiana
estuary throughout the sampling period were too low to exert an inhibitory effect on nitrate uptake or a toxic effect on phytoplankton
growth. Nitrate was clearly the main nitrogen source for phytoplankton at the study site. Overall, nitrate seemed to become
limiting at concentrations lower than 20 μM and N-limitation was particularly significant during summer. A trend of decreasing
nitrate uptake with increasing ammonium concentrations and uptake suggested an overall preference for ammonium. However, preference
for ammonium was group-specific, and it was observed mainly in green algae and cyanobacteria. In fact, cyanobacteria relied
only on ammonium as their N-source. On the contrary, diatoms preferred nitrate, and did not respond to ammonium additions.
The increasing eutrophication in the Guadiana estuary and particularly increased inputs of nitrogen as ammonium due to urban
waste effluents may result in a shift in phytoplankton community composition, towards a dominance of cyanobacteria and green
algae. 相似文献
102.
França S Vasconcelos RP Tanner S Máguas C Costa MJ Cabral HN 《Marine environmental research》2011,72(4):204-215
Stable carbon and nitrogen isotopes (δ13C, δ1?N) were used to analyse food web dynamics of two of the main estuaries of the Portuguese coast: Tejo and Mira. The ultimate sources of organic matter supporting production of some of the most abundant and commercially important fish species were determined; and seasonal, inter- and intra- estuarine differences in the trophic relations among producers and consumers were identified. Stable isotope analysis was performed in different producers, primary consumers (main prey items for fish) and fish species (Solea solea, Solea senegalensis, Pomatoschistus microps, Dicentrarchus labrax, Liza ramada, Diplodus vulgaris and Atherina presbyter) of two areas in each estuary, in July and October 2009. Model calculations showed that the main prey for the fish species in the Tejo estuary used mostly salt marsh-derived organic matter as nutritional sources, with no marked differences between the sampled months. Trophic levels of fish species from the same estuary differed at multiple scales: inter-species, seasonally and spatially (both between and within estuaries). Significant differences in isotopic composition of fish species were more pronounced spatially (between the two sampled areas in the estuary) than seasonally (between sampled months). Trophic relationships in both estuaries demonstrated that organic matter is transferred to higher trophic positions mainly through benthic pathways. This shows the flexibility of these species to share resources and to exploit temporary peaks in prey populations. The present results showed that extensive disturbance in intertidal habitats from both estuaries may potentially change the balance of organic matter in the base of these complex food webs. 相似文献
103.
104.
Seagrass beds have higher biomass, abundance, diversity and productivity of benthic organisms than unvegetated sediments. However, to date most studies have analysed only the macrofaunal component and ignored the abundant meiofauna present in seagrass meadows. This study was designed to test if meiobenthic communities, especially the free-living nematodes, differed between seagrass beds and unvegetated sediments. Sediment samples from beds of the eelgrass Zostera capricorni and nearby unvegetated sediments were collected in three estuaries along the coast of New South Wales, Australia. Results showed that sediments below the seagrass were finer, with a higher content of organic material and were less oxygenated than sediments without seagrass. Univariate measures of the fauna (i.e. abundance, diversity and taxa richness of total meiofauna and nematode assemblages) did not differ between vegetated and unvegetated sediments. However multivariate analysis of meiofaunal higher taxa showed significant differences between the two habitats, largely due to the presence and absence of certain taxa. Amphipods, tanaidacea, ostracods, hydrozoans and isopods occurred mainly in unvegetated sediments, while kinorhyncs, polychaetes, gastrotrichs and turbellarians were more abundant in vegetated sediments. Regarding the nematode assemblages, 32.4% of the species were restricted to Z. capricorni and 25% only occurred in unvegetated sediments, this suggests that each habitat is characterized by a particular suite of species. Epistrate feeding nematodes were more abundant in seagrass beds, and it is suggested that they graze on the microphytobenthos which accumulates underneath the seagrass. Most of the genera that characterized these estuarine unvegetated sediments are also commonly found on exposed sandy beaches. This may be explained by the fact that Australian estuaries have very little input of freshwater and experience marine conditions for most of the year. This study demonstrates that the seagrass and unvegetated sediments have discrete meiofaunal communities, with little overlap in species composition. 相似文献
105.
106.
ISO-SWS spectra of two Mira variables (R Cas and T Dra), taken at two different pulsational phases, are presented. We describe
the reduction of the data and the encountered problems. The dust features observed by ISO at different phases and with the
Low Resolution Spectrometer of IRAS are compared. We briefly discuss the results in terms of current models for the circumstellar
dust shells of AGB variables.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
107.
Josef Hron Walter Nowotny Rita Gautschy-Loidl Susanne Höfner 《Astrophysics and Space Science》2003,286(1-2):213-218
We present synthetic radii and visibilities in the IR, based on hydrostatic and dynamic model atmospheres of carbon stars.
The differences between these two sets of input models and to uniform disc models are discussed and compared to the expected
capabilities of the VLTI.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
108.
M.S. Fonseca J.S. Fisher J.C. Zieman G.W. Thayer 《Estuarine, Coastal and Shelf Science》1982,15(4):351-364
A salt-water flume was used to describe the mechanics of current flow around an articial Zostera marina meadow. Shear velocity and roughness height were positively correlated with seagrass surface area, and were positively/negatively correlated with current velocity. Current velocity intrusion into the meadow before diminution and maximum reduction (both at the 2 cm height line) proceed by factors of 1·25 and 2·07 cm into the meadow per cm s?1 of current velocity, respectively.Froude number was correlated with mean bending angle of the canopy as a whole. Maximum bending had occurred with Froude = 1, but most bending had taken place by Froude = 0·4, a velocity of 40–50 cm s?1 in this experiment.The meadow edge is the most dynamic zone of a seagrass meadow in regard to current flow. Bending of the shoot canopy is a mechanism for re-direction of current flow and in-canopy reduction of current velocity. Meadow dimensions may be regulated by scouring processes in different hydraulic regimes. Shoot bending and subsequent in-meadow current velocity reduction are mechanisms that affect self-shading and photosynthetic capabilities as well as providing habitat stability. 相似文献
109.
Rui Fonseca Domingos Barbosa Luis Cupido Ana Mouro Dinis M. dos Santos George F. Smoot Camilo Tello 《New Astronomy》2006,11(8):551-556
We probed for radio frequency interference (RFI) at three potential galactic emission mapping experiment (GEM) sites in Portugal using custom made omnidirectional disconic antennas and directional pyramidal horn antennas. For the installation of a 10-m dish dedicated to the mapping of polarized galactic emission foreground planned for 2005–2007 in the 5–10 GHz band, the three sites chosen as suitable to host the antenna were surveyed for local radio pollution in the frequency range 0.01–10 GHz. Tests were done to look for radio broadcasting and mobile phone emission lines in the radio spectrum. The results show one of the sites to be almost entirely RFI clean and showing good conditions to host the experiment. 相似文献
110.
Edoardo Barbero Luca Pandolfi Morteza Delavari Asghar Dolati Emilio Saccani Rita Catanzariti Valeria Luciani Marco Chiari Michele Marroni 《地学前缘(英文版)》2021,12(3):101106
The Durkan Complex is a key tectonic element of the Makran accretionary prism (SE Iran) and it has been interpreted as representing a continental margin succession. We present here a multidisciplinary study of the western Durkan Complex, which is based on new geological, stratigraphic, biostratigraphic data, as well as geochemical data of the volcanic and meta-volcanic rocks forming this complex. Our data show that this complex consists of distinct tectonic slices showing both non-metamorphic and very low-grade metamorphic deformed successions. Stratigraphic and biostratigraphic data allow us to recognize three types of successions. Type-I is composed by a Coniacian – early Campanian pelagic succession with intercalation of pillow lavas and minor volcaniclastic rocks. Type-II succession includes a volcanic sequence passing to a volcano-sedimentary sequence with Cenomanian pelagic limestones, followed by a hemipelagic sequence. This succession is characterized by abundant mass-transport deposits. Type-III succession includes volcanic and volcano-sedimentary sequences, which are stratigraphically covered by a Cenomanian platform succession. The latter is locally followed by a hemipelagic sequence. The volcanic rocks in the different successions show alkaline geochemical affinity, suggesting an origin from an oceanic within-plate setting. Our new results indicate that the western Durkan Complex represents fragments of seamounts tectonically incorporated in the Makran accretionary wedge during the latest Late Cretaceous–Paleocene. We propose that incorporation of seamounts in the frontal prism caused a shortening of the whole convergent margin and possibly contributed to controlling the deformation style in the Makran Accretionary Wedge during Late Cretaceous–Paleocene times. 相似文献