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1.
We present sub-crystal-scale 238U–230Th zircon ages and 238U–230Th–226Ra plagioclase ages of bulk mineral separates from the Holocene (2.0–2.3 ka) eruptions of the Rock Mesa (RM) and Devil's Hills (DH) rhyolites at South Sister volcano, Oregon. We link these age data with sub-crystal trace-element analyses of zircon and plagioclase to provide insight into the subvolcanic system at South Sister, as an example of a small-volume continental arc volcano. Our results document the presence of coeval yet physically-distinct regions within the magma reservoir and constrain the timescales over which these heterogeneities existed. Zircons from the RM and DH dominantly record ages from 20 to 80 ka, with some grains recording ages > 350 ka, whereas plagioclase records 230Th–226Ra ages of 2.3–6.8 ka (RM) and 4.0–9.6 ka (DH-3) and a 238U–230Th age of 10 ± 34 ka (DH-3). We interpret zircons with ages < 350 ka as antecrysts inherited from a longer lived upper-crustal magma reservoir from which the rhyolites were generated, based on crystallization ages coeval with earlier periods of silicic volcanism at South Sister, the undersaturated nature of the RM and DH magmas with respect to zircon, and Ti-in-zircon temperatures consistent with low-temperature (< 815 °C) crystallization. In contrast, plagioclase ages are near the eruption age and dominantly preserve information about the recent (< 10 ka), higher-temperature evolution of the host magmas. Although zircon and plagioclase record different crystallization ages, each phase crystallized over the same time period in the RM compared to DH rhyolites. Linking these crystal age data with sub-crystal trace-element analyses demonstrates that zircon and plagioclase have distinct trace-element characteristics between eruptions, which require that the RM and DH crystals (and therefore magmas) were derived from distinct regions that had evolved independently for > 50 ka within a heterogeneous magmatic system and coexisted as physically-distinct, dominantly-liquid bodies prior to eruption. Thus, we favor a model where rhyolites are generated in independent batches by accumulation of evolved liquids in a heterogeneous, largely crystalline reservoir. Similarities in crystal age and chemical data to that at other young silicic systems (e.g., Mount St. Helens, Okataina Caldera Complex) suggest that this model may be more generally applicable to silicic magmas.  相似文献   

2.
Calcitic crusts of calcareous red algae could be suitable material for age determination of raised marine deposits and palaeothermometry at annual to sub-annual resolution. We examined the potential of U–Th dating of cold-water calcareous algae by analysing fossil specimens (n=10) from Kapp Ekholm (Svalbard) and recent specimens from Norway (n=3) and Scotland (n=1). After initial measurements using α-spectrometry, thermal ionisation mass spectrometry (TIMS) was used to study the material in more detail. Recent specimens contain 0.19–1.55 μg g−1 U, and the measured (234U/238U) activity ratios vary between 1.12 and 1.30. Fossil specimens contain 1–168 μg g−1 U, and display variable and highly elevated initial (234U/238U) activity ratios. In general, the TIMS results show increasing (234U/238U) activity ratios and concentrations of U and Th with increasing stratigraphic age. From this it is evident that marine calcareous red algae contain U in-vivo and they experience substantial post-mortem uptake of U. We conclude that direct U–Th dating of fossil calcareous algae from raised marine deposits is not viable without further geochemical understanding of the in-vivo uptake and post-depositional pathways of U and Th in such deposits. Despite the convincing open-system behaviour of the material, comparison with previously published chronostratigraphy from the site shows that the calcareous algae generally yield ages that are too old. This is in contrast to the expected result based on simple continuous post-mortem U accumulation and calls for a complex model comprising migration of U and multi-component addition of Th (detrital/colloidal) to explain the observed trends.  相似文献   

3.
The activities of the natural radionuclides (238U, 232Th, 226Ra and 40K) of the surface sediments in the Yangtze Estuary were determined and used to evaluate radiation hazards in the study area. The of activities of 238U, 232Th, 226Ra and 40K ranges from 14.1 to 62.3, 26.1 to 71.9, 13.7 to 52.3, and 392 to 898 Bq kg? 1, respectively, which were comparable to values of other regions in China. The activities of 232Th, 40K and 226Ra were clearly different from the global recommended values. The radium equivalent activity was less than the recommended limit of 370 Bq kg? 1; therefore, the sediment in this area can be safely used for reclamation. The external hazard index values were less than one. The average absorbed gamma dose rate and annual effective dose equivalent values were slightly greater than the world average value. 226Ra/238U and 232Th/238U ratios could potentially be applied for tracing sediment source.  相似文献   

4.
Marine and eolian carbonate deposits, grouped under the name “Tamala Limestone”, have been investigated along thousands of kilometers of coastal Western Australia (WA). Relative-age diagenetic features of carbonate sand dunes or “eolianites” indicate that coastal ridges decrease in age seaward, reflecting coastal accretion during successive sea-level stands. Yellow- to red-stained quartz sands are associated with eolianites as pits, lenses, extensive beds, and even 40-m-high dunes.A regional survey using whole-rock and land snail amino acid epimerization geochronology confirms the eolianite succession and provides a means of correlating widespread deposits along a steep climatic gradient and 16° of latitude. AMS 14C and uranium–thorium (U/Th) ages provide independent radiometric calibration of the amino acid ratios, and eolianite ages can be estimated using a parabolic kinetic model.Over 90% of the sampled eolianite deposits comprise Aminozones A, C, E (125 ka), F?, G, and H, and correlate with interglacials from <10 ka (Holocene) to ca. 500 ka. In contrast, at the type locality of the Tamala Limestone along the Zuytdorp Cliffs, the upper eolianite-paleosol units are characterized by advanced stages of cavernous weathering, pedogenesis, and recrystallization. In the same units, sediment and snail samples generally yield very low or non-detectable levels of amino acids. These factors along with the stratigraphic complexity of the deposits reflect an age much greater than a large majority of sites along the WA coastline. These findings encourage a revision of the existing classification and nomenclature of Quaternary carbonate deposits in WA, as well as a reexamination of the underlying mechanisms related to the formation and emplacement of both carbonate and quartz dunes.  相似文献   

5.
《Marine pollution bulletin》2012,65(12):2857-2859
Baseline Hg concentration in bycatch fish from the SE Gulf of California were determined in muscle and liver of 19 species. Levels of Hg in muscle were compared with legal limits of this element in national and international legislation. Considering all fish species, mean concentrations in liver (2.458 ± 1.997 μg g−1) were significantly higher (p < 0.05) than in muscle (0.993 ± 0.670 μg g−1). The sequence of averaged Hg concentrations in most ichthyofauna was liver > muscle. Highest level of Hg in muscle (2.556 μg g−1) and liver (7.515 μg g−1) corresponded to Diapterus peruvianus and Ophioscion strabo, respectively. Considering muscle samples, none of the species had levels of Hg above the limit (1.0 μg g−1 wet weight) in the Mexican legislation; with respect to the Japanese (0.4 μg g−1 wet weight) and British (0.3 μg g−1 wet weight) legislations, 26.3% and 31.6% of the species respectively, were above the corresponding limits.  相似文献   

6.
Nanoparticle contamination in freshwater habitat leads to the drastic reduction in the population of freshwater micro crustaceans. Both Ceriodaphnia cornuta and Moina micrura were considered as the potential biological bio-tracers of freshwater ecosystem. This study describes the chemical synthesis of zinc oxide nanoparticles (ZnO NPs) using zinc nitrate as the starting material. The physico-chemical characterization of ZnO NPs was made by UV–Vis spectroscopy, X-Ray Diffraction (XRD), Fourier Transform Infra Red (FTIR) and Transmission Electron Microscopy (TEM). ZnO NPs elicited 100% and 76% mortality of freshwater crustaceans, Ceriodaphnia cornuta and Moina micrura at 160 μg L−1 respectively. The accumulation of ZnO NPs in the intestine and loss of antennae and carapace were clearly visualized through light microscopy. The exposure of C. cornuta and M. micrura neonates at 160 μg L−1 of ZnO NPs showed abnormal swimming behaviour after 12 h. However, chitosan significantly reduced the mortality and enhanced the survival of C. cornuta and M. micrura at 100 μg ml−1. This study concludes the protective effect of chitosan against the hazardous effect of ZnO NPs in C. cornuta and M. micrura.  相似文献   

7.
We present a 10Be production-rate calibration derived from an early Holocene debris-flow deposit at about 1000 m above sea level in the central Southern Alps, New Zealand, in the mid-latitude Southern Hemisphere. Ten radiocarbon ages on macrofossils from a soil horizon buried by the deposit date the deposit to 9690 ± 50 calendar years before AD2008. Surface 10Be concentrations of seven large boulders partially embedded in the stable surface of the deposit are tightly distributed, yielding a standard deviation of ～2%. Conversion of the 10Be measurements to sea level/high-latitude values using each of five standard scaling methods indicates 10Be production rates of 3.84 ± 0.08, 3.87 ± 0.08, 3.83 ± 0.08, 4.15 ± 0.09, and 3.74 ± 0.08 atoms g?1 a?1, relative to the ‘07KNSTD’ 10Be AMS standard, and including only the local time-integrated production-rate uncertainties. When including a sea level high-latitude scaling uncertainty the overall error is ～2.5% (1σ) for each rate. To test the regional applicability of this production-rate calibration, we measured 10Be concentrations in a set of nearby moraines deposited before 18 060 ± 200 years before AD2008. The 10Be ages are only consistent with minimum-limiting 14C age data when calculated using the new production rates. This also suggests that terrestrial in situ cosmogenic-nuclide production did not change significantly from Last Glacial Maximum to Holocene time in New Zealand. Our production rates agree well with those of a recent calibration study from northeastern North America, but are 12–14% lower than other commonly adopted values. The production-rate values presented here can be used elsewhere in New Zealand for rock surfaces exposed during or since the last glacial period.  相似文献   

8.
Currently, nanotechnology has gained much interest due to the unique properties of nanomaterials in science and technology. Different types of metallic nanoparticles are routinely synthesized. However, their release into the aquatic environments is a major ecotoxicological concern. In this scenario, it is important to study the potential impact of engineered nanoparticle in aquatic organisms especially freshwater microcrustaceans, such as Ceriodaphnia cornuta. In this study, ZnO NPs were synthesized using the aqueous leaf extracts of Musa paradisiaca and physico-chemically characterized by UV–Vis spectroscopy, X-ray diffraction (XRD), Fourier transform infra red (FTIR), scanning electron microscopy (SEM) and atomic force microscopy (AFM). UV–Vis spectroscopy recorded the absorbance peak of ZnO NPs at 338 nm. XRD analysis showed the various Bragg’s reflection peaks at 100, 002, 101, 102, 110, 103, 200, 112, 201, 004 and 202 lattice planes. FTIR spectroscopy outlined sharp intense peaks at 3416 cm−1, 1388 and 1416 cm−1. SEM showed the spherical shape of ZnO NPs with mean particle size of 23.3 nm. AFM confirmed the spherical shape, nanosize and 3D topography of NPs. The ecotoxicity of ZnO NPs was tested on the freshwater crustacean C. cornuta. ZnO NPs were comparatively less toxic than zinc acetate. ZnO NPs caused 42% mortality of C. cornuta at 50 μg mL−1. However, 80% mortality was observed at 50 μg mL−1 of zinc acetate after 24 h. Light and confocal laser scanning microscopic images evidenced the uptake and accumulation of ZnO NPs in the gut of C. cornuta at 50 μg mL−1 after 24 h. Structural deformities were observed on C. cornuta after treatment with 50 μg mL−1 of ZnO NPs. Overall, this study describes the potential impact of the biologically synthesized ZnO NPs in comparison with zinc acetate in the freshwater crustacean C. cornuta.  相似文献   

9.
《Marine pollution bulletin》2012,64(5-12):516-522
Surface and core sediments collected from six mariculture farms in the Pearl River Delta (PRD) were analyzed to evaluate contamination levels of polychlorinated biphenyls (PCBs). The ∑PCBs (37 congeners) concentrations ranged from 5.10 to 11.0 ng g−1 (mean 7.96 ng g−1) in surface and 3.19 to 22.1 ng g−1 (mean 7.75 ng g−1) in core sediments, respectively. The concentrations were significantly higher than that measured in the sediments of their corresponding reference sites, whereby the average enrichment percentages were 62.0% and 42.7% in surface and core sediments, respectively. Significant correlations (R2 = 0.77, p < 0.05) of PCB homologue group proportions between fish feeds and surface mariculture sediments suggested that fish feed input was probably the main source for the enrichment of PCBs. Due to the fact that PCBs could be transferred along food chains, PCB contamination in fish feeds and mariculture sediments should not be overlooked.  相似文献   

10.
《Marine pollution bulletin》2009,58(6-12):575-586
Irgarol 1051 (2-methythiol-4-tert-butylamino-6-cyclopropylamino-s-triazine) is an algaecide commonly used in antifouling paints. It undergoes photodegradation which yields M1 (2-methylthio-4-tert-butylamino-6-amino-s-triazine) as its major and most stable degradant. Elevated levels of both Irgarol and M1 have been detected in coastal waters worldwide; however, ecotoxicity effects of M1 to various marine autotrophs such as cyanobacteria are still largely unknown. This study firstly examined and compared the 96 h toxicities of Irgarol and M1 to the cyanobacterium Chroococcus minor and two marine diatom species, Skeletonema costatum and Thalassiosira pseudonana. Our results suggested that Irgarol was consistently more toxic to all of the three species than M1 (96 h EC50 values: C. minor, 7.71 μg L−1 Irgarol vs. >200 μg L−1 M1; S. costatum, 0.29 μg L−1 Irgarol vs. 11.32 μg L−1 M1; and T. pseudonana, 0.41 μg L−1 Irgarol vs. 16.50 μg L−1 M1). Secondly, we conducted a meta-analysis of currently available data on toxicities of Irgarol and M1 to both freshwater and marine primary producers based on species sensitivity distributions (SSDs). Interestingly, freshwater autotrophs are more sensitive to Irgarol than their marine counterparts. For marine autotrophs, microalgae are generally more sensitive to Irgarol than macroalgae and cyanobacteria. With very limited available data on M1 (i.e. five species), M1 might be less toxic than Irgarol; nonetheless this finding warrants further confirmation with additional data on other autotrophic species.  相似文献   

11.
IRSL single-aliquot dating of three feldspar fractions from a Howieson's Poort (SA) industry site has been investigated. In the case of the plagioclase fraction (ρ > 2.62 g cm?3) equivalent dose is similar to that of the other fractions (i.e. ρ < 2.58 g cm?3, high-K-feldspar; and 2.58 < ρ < 2.62 g cm?3; low-K-feldspar). However, the g values measured for this fraction is such that the fading-corrected age is overestimated. The K content of each fraction was estimated by SEM. The DRC-corrected ages for the two lighter feldspar fractions are consistent with the archaeological interpretation. This study shows that reliable single-aliquot luminescence ages can be obtained using K-feldspar and Na-plagioclase.  相似文献   

12.
Landfill leachates that contain persistent organic pollutants (POPs) are a big threat to groundwater systems and are projected to have hazardous effects in the long term if proper management strategies of the landfills are not put in place by those responsible. Monitoring the levels of POPs in landfill leachates is very crucial. This work presents an amperometric biosensor for determination of selected POPs in landfill leachates. The biosensor is based on kinetic inhibition of horseradish peroxidase (HRP). The enzyme was immobilised by electrostatic attachment on a polyaniline-modified Pt electrode surface. Selected POPs inhibited HRP enzyme activity and the decrease in the enzyme activity was used to determine these environmental pollutants. Selected polybrominated diphenyl ethers (PBDEs), polybrominated biphenyls (PBBs) and polychlorinated biphenyls (PCBs) were the analytes of choice because they are commonly found in South Africa water systems. Limits of detection for the amperometric biosensor were established as 0.014, 0.018, 0.022, 0.016 and 0.019 μg l−1 for BDE-100, PBB-1, PCB-1, PCB-28 and PCB-101, respectively. The HRP biosensor system gave different linear ranges for; BDE-100 (0.424–25.8 μg l−1), PBB-1 (0.862–13.4 μg l−1), PCB-1 (0.930–18.1 μg l−1), PCB-28 (0.730–15.7 μg l−1) and PCB-101 (0.930–27.1 μg l−1). Inhibition studies on HRP biosensor response toward the reduction of H2O2 in the absence and presence of the selected POPs were carried out to investigate the inhibition kinetics and its mechanism. The results obtained indicated that the inhibition mechanism was competitive for PBDEs and non-competitive for biphenyls (PCBs and PBBs). The application of the biosensor was tested on wastewater samples obtained from landfill leachate for determination of selected POPs. The leachate samples were found to contain PCB-28 (0.28 ± 0.03 μg l−1) and PCB-101 (0.31 ± 0.02 μg l−1). The samples were also analysed by GC–MS as a cross-check method and the two sets of results were in close agreement.  相似文献   

13.
《Continental Shelf Research》2007,27(10-11):1477-1500
Constraining the exchange of water from the shoreline to the mid-shelf is necessary for the development of accurate and predictive models of nearshore circulation. Ra isotopes, which emanate from sediments and have a variety of half-lives, may be useful in measuring cross-shelf mixing rates. The distributions of Ra isotopes were measured in transects extending perpendicular from the shoreline at Sunset Beach and Huntington Beach, CA. The average inventory at Sunset Beach was four times greater than at Huntington Beach. Building on previous research on Ra inputs and circulation in San Pedro Bay, a two-dimensional model for surface water Ra was developed to identify the importance of onshore flow and cross-shelf mixing near Huntington Beach. For the mean summertime conditions, the eddy diffusivity (Kh) was 1.4±0.4 m2 s−1, with 8% of the water from Sunset Beach moving down the coast. The remaining water must be low-Ra water that has moved onshore. At time scales greater than a week, the short-lived Ra inventory at Huntington Beach varied by 50%, which reflects changes in the fractions of water moving down-coast and/or in the longshore advection rate. The shoreline Ra concentration varied on time scales of hours, which may be generated by tidal changes in the Ra input at the shoreline and short-period fluctuations in the mixing rate. The low Kh observed in this study in comparison to higher values measured further offshore is evidence that Kh increases with distance offshore. When scale-dependent mixing beyond 455 m offshore is incorporated into the model, the results are consistent with the observed data for 223Ra, 224Ra, and 228Ra. Using the model, the 228Ra input flux to the summertime mixed layer was between 3.4×106 and 4.0×106 atoms s−1 (m shoreline)−1.  相似文献   

14.
The production rate of cosmogenic 3He in apatite, zircon, kyanite and garnet was obtained by cross-calibration against 10Be in co-existing quartz in glacial moraine boulders from the Nepalese Himalaya. The boulders have 10Be ages between 6 and 16 kyr and span elevations from 3200 to 4800 m. In all of these minerals 3He correlates with 10Be and is dominantly cosmogenic in origin. After modest correction for non-cosmogenic components, 3He/10Be systematics imply apparent sea-level high-latitude (SLHL) apparent production rates for 3He of 226 atoms g? 1 yr? 1 in zircon, 254 atoms g? 1 yr? 1 in apatite, 177 atoms g? 1 yr? 1 in kyanite, and 153 atoms g? 1 yr? 1 in garnet. These production rates are unexpectedly high compared with rates measured elsewhere in the world, and also compared with proposed element-specific production rates. For apatite and zircon, the data are sufficient to conclude that the 3He/10Be ratio increases with elevation. If this reflects different altitudinal scaling between production rates for the two isotopes then the SLHL production rates estimated by our approach are overestimates. We consider several hypotheses to explain these observations, including production of 3He via thermal neutron capture on 6Li, altitudinal variations in the energy spectrum of cosmic-ray neutrons, and the effects of snow cover. Because all of these effects are small, we conclude that the altitudinal variations in production rates of cosmogenic 3He and 10Be are distinct from each other at least at this location over the last ～ 10 kyr. This conclusion calls into question commonly adopted geographic scaling laws for at least some cosmogenic nuclides. If confirmed, this distinction may provide a mechanism by which to obtain paleoelevation estimates.  相似文献   

15.
Contamination with As, Cd and Hg, their spatial and temporal distribution are reported from the coastal wetland sediments of the northern Beibu Gulf, South China Sea. The content of As, Cd, Hg and TOC in surface sediments is 8.1 ± 5.8 μg g?1, 0.08 ± 0.14 μg g?1, 0.034 ± 0.028 μg g?1 and 0.45 ± 0.39%, respectively. The mean sedimentation rates are 0.93–1.37 cm year?1 during 1920s to 2008 determined by 210Pb and 137Cs dating in three cores. The vertical profiles of As, Cd and Hg content in the cores retrieved from Qin and Nanliu River estuaries show increasing trends during 1985–2008 due to anthropogenic impact caused by local economic development. Locally the surface sediments have potential ecological risk of As to benthos according to the NOAA sediment quality guidelines.  相似文献   

16.
《Marine pollution bulletin》2012,64(5-12):417-423
Sediment samples were collected from 12 locations of Kaohsiung Harbor, Taiwan and analyzed for polycyclic aromatic hydrocarbons (PAHs). Total PAH concentrations varied from 472 to 16,201 ng g−1 dry weight. The highest PAH concentrations were from the industrial zone docks situated in south Kaohsiung Harbor. Diagnostic ratios showed that the possible source of PAHs in the industrial zone dock could be coal combustion while in the other zones it could be petroleum combustion. The toxic equivalent concentrations (TEQcarc) of PAHs varied from 55 to 1964 ng TEQ g−1 dry weight. Higher total TEQcarc values were found at industrial zone docks (from 1404 to 1964 ng TEQ g−1 dry weight). As compared with the US Sediment Quality Guidelines (SQGs), the observed levels of PAHs at industrial zone docks exceeded the effects range low (ERL), and could thus cause acute biological damage. However, the lower levels of PAHs at the other zones would probably not exert adverse biological effects.  相似文献   

17.
《Marine pollution bulletin》2012,65(12):2663-2670
This study evaluated embryotoxicity and genotoxicity of two dissolved metals copper and cadmium (Cu and Cd) and two pesticides (metolachlor and irgarol) occurring in Arcachon Bay (SW France) in Pacific oyster (Crassostrea gigas) larvae and investigated the relationship between those two endpoints. Embryotoxicity was measured by calculating the percentage of abnormal D-shaped larvae and genotoxicity was evaluated with DNA strand breaks using the comet assay. After 24 h exposure, significant increases of the percentage of abnormal D-larvae and the DNA strand breaks were observed from 0.1 μg L−1 for Cu, 10 μg L−1 for Cd and 0.01 μg L−1 for both irgarol and metolachlor in comparison with the controls. A strong positive relationship between embryotoxicity and genotoxicity was recorded for Cu, Cd and metolachlor. The current study suggests that copper, irgarol and metolachlor can induce larval abnormalities and DNA damage in a population of exposed oysters at environmentally relevant concentrations.  相似文献   

18.
《Journal of Geodynamics》2007,43(1):170-186
Stratigraphic and sedimentological studies indicate that Iceland has experienced over 20 glaciations during the last 4–5 Myr, in reasonable agreement with the number of glaciations reconstructed from the ∂18O record in deep-sea sediment. The pattern of glacial erosion was to a large part controlled by constructive volcanic processes resulting in increased topographic relief after 2.5 Myr. Between 2.5 and 0.5 Ma valleys up to 400 m deep were excavated into the Tertiary basalts of eastern and south Iceland with an average erosion rate of 10–20 cm ka−1. During the last 0.5 million years rates of erosion increased to 50–175 cm ka−1, with an additional 200 to over 1000 m of valley excavation. Previous estimates of the rate of landscape erosion during the Holocene vary widely, from 5 to 70,000 cm ka−1. We present new studies that define the rates of landscape denudation during the major part of the Holocene (the last 10,200 years): one based on the Iceland shelf sediment record, the other from the sediment record in the glacier-fed lake, Hvítárvatn. Both studies indicate average Holocene erosion rates of about 5 cm ka−1 similar to our erosion rate estimate for 4–5 Ma old strata that has not been subjected to regional glaciation.  相似文献   

19.
We characterized the seasonal cycle of productivity in Reloncaví Fjord (41°30′S), Chilean Patagonia. Seasonal surveys that included measurements of gross primary production, community respiration, bacterioplankton secondary production, and sedimentation rates along the fjord were combined with continuous records of water-column temperature variability and wind forcing, as well as satellite-derived data on regional patterns of wind stress, sea surface temperatures, and surface chlorophyll concentrations. The hydrography and perhaps fjord productivity respond to the timing and intensity of wind forcing over a larger region. Seasonal changes in the direction and intensity of winds, along with a late-winter improvement in light conditions, may determine the timing of phytoplankton blooms and potentially modulate productivity cycles in the region.Depth-integrated gross primary production estimates were higher (0.4–3.8 g C m?2 d?1) in the productive season (October, February, and May), and lower (0.1–0.2 g C m?2 d?1) in the non-productive season (August). These seasonal changes were also reflected in community respiration and bacterioplankton production rates, which ranged, respectively, from 0.3 to 4.8 g C m?2 d?1 and 0.05 to 0.4 g C m?2 d?1 during the productive and non-productive seasons and from 0.05 to 0.6 g C m?2 d?1 and 0.05 to 0.2 g C m?2 d?1 during the same two periods. We found a strong, significant correlation between gross primary production and community respiration (Spearman, r=0.95; p<0.001; n=12), which suggests a high degree of coupling between the synthesis of organic matter and its usage by the planktonic community. Similarly, strong correlations were found between bacterioplankton secondary production and both gross primary production (Spearman, r=0.7, p<0.05, n=9) and community respiration (Spearman, r=0.8, p<0.05, n=9), indicating that bacterioplankton may be processing an important fraction (8–59%) of the organic matter produced by phytoplankton in Reloncaví Fjord. In winter, bacterial carbon utilization as a percentage of gross primary production was >100%, suggesting the use of allochthonous carbon sources by bacterioplankton when the levels of gross primary production are low. Low primary production rates were associated with a greater contribution of small cells to autotrophic biomass, highlighting the importance of small-sized plankton and bacteria for carbon cycling and fluxes during the less productive winter months. Fecal pellet sedimentation was minimal during this period, also suggesting that most of the locally produced organic carbon is recycled within the microbial loop. During the productive season, on the other hand, the area exhibited a great potential to export organic matter, be it to higher trophic levels or vertically towards the bottom.  相似文献   

20.
The demand for clean water is on the increase as the population increases. One of the ways to address the water shortage is to treat the polluted water through removal of the contaminants. The use of adsorbents for pollutant removal is one of the promising methods. Seaweed is an aquatic plant and its sorption ability for selected metals in water was investigated in this study. We report the performance of the seaweed (Caulerpa serrulata) before and after modification with ethylenediamine (EDA), on adsorption of copper, lead and cadmium in aqueous solution. The adsorption capacities for Cu, Cd and Pb were 5.27 mg g−1, 2.12 mg g−1 and 2.16 mg g−1, respectively, with the EDA-modified seaweed, and 3.29 mg g−1, 4.57 mg g−1 and 1.06 mg g−1, with the unmodified weed, respectively. The pH for maximum adsorption was found to be within the range of pH 4–pH 6. In a separate investigation, it was found that 0.1 g of dried seaweed leached 20 mg of dissolved organic carbon (DOC) using 100 ml of distilled-deionised water. The resulting solution was green. The leaching phenomenon contributes to secondary pollution. Modification of the seaweed with EDA reduced the DOC content by half (50%) and also removed the green colouration. Kinetic studies showed that the adsorbent was able to take up to 95% of the metals (in synthetic standard solutions) in less than 10 min. The adsorbed metals were then stripped using a solution of 0.5 M HNO3 indicating that the adsorbent can be regenerated. In addition, the study revealed that modification improved the thermal stability of the adsorbent such that even when the temperature was raised to 1000 °C, more than 80% (compared to <50% for unmodified weed) of the modified adsorbent was not degraded, indicating that modification had a significant influence on the thermal stability of seaweed. The modified seaweed has been shown to have great potential for the removal of metals and DOC in polluted water. The modified adsorbent can therefore be applied for the removal of metals in polluted waters hence suitable for treatment of water for domestic consumption at a point of use.  相似文献   

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