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1.
《Marine pollution bulletin》2012,64(5-12):385-395
The influence of different environmental stresses, including salinity (5–35‰), tidal cycle (6/6, 12/12 and 24/24 h of high/low tidal regimes) and nutrient addition (1–6 times background nitrogen and phosphorus content) on Bruguiera gymnorrhiza and Aegiceras corniculatum grown in sediment contaminated with spent lubricating oil (7.5 L m−2) were investigated. The oil-treated 1-year-old mangrove seedlings subject to low (5‰) and high (35‰) salinity had significantly more reduction in growth, more release of superoxide radical (O2−) and higher activity of superoxide dismutase (SOD) than those subject to moderate salinity (15‰). Extended flooding (24/24 h of high/low tidal regime) enhanced O2− release and malondialdehyde (MDA) content in both oil-treated species but had little negative effects on biomass production (P > 0.05) except the stem of A. corniculatum (P = 0.012). The addition of nutrients had no beneficial or even posed harmful effects on the growth and cellular responses of the oil-treated seedlings.  相似文献   

2.
《Continental Shelf Research》2005,25(9):1081-1095
The mesoscale distribution and seasonal variation of the size structure of phytoplankton biomass, as measured by chlorophyll a (chl a), was studied in the Ebro shelf area (NW Mediterranean) during three different seasons: autumn, winter and summer. In autumn and summer, when the water column was, respectively, slightly or strongly stratified and nutrient concentrations were low at surface, average total chl a values were 0.31 and 0.29 mg m−3, respectively. In winter, the intrusion of nutrients into the photic zone by intense vertical mixing and strong riverine inputs, produced an increase of the total autotrophic biomass (0.76 mg m−3). In the three seasons, the main contributor to total chl a was the picoplanktonic (<2 μm) size fraction (42% in winter and around 60% in autumn and summer). The nanophytoplankton (2–20 μm) contribution to total chl a showed the lowest variability amongst seasons (between 29% and 39%). The microplanktonic (>20 μm) chl a size fraction was higher in winter (27%) than in the other seasons (less than 13%). The maximum total chl a concentrations were found at surface in winter, at depths of 40 m in autumn and between 50 and 80 m in summer. The relative contribution of the <2 μm size fraction at these levels of the water column tended to be higher than at other depths in autumn and winter and lower in summer. In autumn and winter, nutrient inputs from Ebro river discharge and mixing processes resulted in an increase on the >2 μm contribution to total chl a in the coastal zone near the Ebro Delta area. In summer, the contribution of the <2 and >2 μm chl a size fractions was homogeneously distributed through the sampling area. In autumn and summer, when deep chl a maxima were observed, the total amount of the autotrophic biomass in the superficial waters (down to 10 m) of most offshore stations was less than 10% of the whole integrated chl a (down to 100 m or to the bottom). In winter, this percentage increased until 20% or 40%. The >2 μm chl a increased linearly with total chl a values. However, the <2 μm chl a showed a similar linear relationship only at total chl a values lower than 1 mg m−3 (in autumn and summer) or 2 mg m−3 (winter). At higher values of total chl a, the contribution of the <2 μm size fraction remained below an upper limit of roughly 0.5 mg m−3. Our results indicate that the picoplankton fraction of phytoplankton may show higher seasonal and mesoscale variability than is usually acknowledged.  相似文献   

3.
《Marine pollution bulletin》2012,64(5-12):255-261
Mussels were maintained for 4 weeks under different combinations of dissolved oxygen concentration (1.5, 3.0 and 6.0 mg O2 l−1) and salinity (15, 20, 25 and 30) in a 3 × 4 factorial design experiment. Clearance rate (CR), absorption efficiency (AE), respiration rate (RR) and scope for growth (SFG) decreased with decreasing salinity and dissolved oxygen concentration (DO), while excretion rate (ER) increased with decreasing salinity and increasing DO. The O:N ratio was <10 at salinities of 15 and 20, irrespective of DO levels. SFG was negative in most of the treatments, except for those under 6.0 mg O2 l−1 or at a salinity of 30 when DO was lower. The results may help explain the distribution pattern of Perna viridis in Hong Kong waters and provide guidelines for mussel culture site selection.  相似文献   

4.
The geochemical characteristics of mildly alkalic basalts (24–25 Ma) erupted in the southeastern Kerguelen Archipelago are considered to represent the best estimate for the composition of the enriched Kerguelen plume end-member. A recent study of picrites and high-MgO basalts from this part of the archipelago highlighted the Pb and Hf isotopic variations and suggested the presence of mantle heterogeneities within the Kerguelen plume itself. We present new helium and neon isotopic compositions for olivines from these picrites and high-MgO basalts (6–17 wt.% MgO) both to constrain the enriched composition of the Kerguelen plume and to determine the origin of isotopic heterogeneities involved in the genesis of Kerguelen plume-related basalts. The olivine phenocrysts have extremely variable 4He / 3He compositions between MORB and primitive values observed in OIB (∼90,000 to 40,000; i.e., R / Ra ∼8 to 18) and they show primitive neon isotopic ratios (average 21Ne / 21Neext ∼0.044). The neon isotopic systematics and the 4He / 3He ratios that are lower than MORB values for the Kerguelen basalts clearly suggest that the Kerguelen hotspot belongs to the family of primitive hotspots, such as Iceland and Hawaii. The rare gas signature for the Kerguelen samples, intermediate between MORB and solar, is apparently inconsistent with mixing of a primitive component with a MORB-like source, but may result from sampling a heterogeneous part of the mantle with solar 3He / 22Ne and with a higher (U, Th) / 3He ratio compared to typically high R / Ra hotspot basalts such as those from Iceland and Hawaii.  相似文献   

5.
《Marine pollution bulletin》2014,78(1-2):274-281
Nine macroalgal blooms were studied in five coastal lagoons of the SE Gulf of California. The nutrient loads from point and diffuse sources were estimated in the proximity of the macroalgal blooms. Chlorophyll a and macroalgal biomass were measured during the dry, rainy and cold seasons. Shrimp farms were the main point source of nitrogen and phosphorus loads for the lagoons. High biomasses were found during the dry season for phytoplankton at site 6 (791.7 ± 34.6 mg m−2) and during the rainy season for macroalgae at site 4 (296.0 ± 82.4 g m−2). Depending on the season, the phytoplankton biomass ranged between 40.0 and 791.7 mg m−2 and the macroalgal biomass between 1 and 296.0 g m−2. The bulk biomass (phytoplankton + macroalgal) displayed the same tendency as the nutrient loads entering the coastal lagoons. Phytoplankton and macroalgal biomass presented a significant correlation with the atomic N:P ratio.  相似文献   

6.
《Marine pollution bulletin》2009,58(6-12):313-324
This study investigated the seasonal and spatial dynamics of nutrients and phytoplankton biomass at 12 stations in Hong Kong (HK) waters during a three year period from 2004 to 2006 after upgraded sewage treatment and compared these results to observations before sewage treatment. Pearl River estuary (PRE) discharge significantly increased NO3 and SiO4 concentrations, particularly in western and southern waters when rainfall and river discharge was maximal in summer. Continuous year round discharge of sewage effluent resulted in high NH4 and PO4 in Victoria Harbour (VH) and its vicinity. In winter, spring and fall, the water column at all stations was moderately mixed by winds and tidal currents, and phytoplankton biomass was relatively low compared to summer. In summer, the mean surface phytoplankton chl biomass was generally >9 μg L−1 in most areas as a result of thermohaline stratification, and high nutrients, light, and water temperature. In summer, the potential limiting nutrient is PO4 in the most productive southern waters and it seldom decreased to limiting levels (∼0.1 μM), suggesting that phytoplankton growth may be only episodically limiting. The mean bottom dissolved oxygen (DO) remained >3.5 mg L−1 at most stations, indicating that the eutrophication impact in HK waters was not as severe as expected for such a eutrophic area. After the implementation of chemically enhanced primary sewage treatment in 2001, water quality in VH improved as indicated by a significant decrease in NH4 and PO4 and an increase in bottom DO. In contrast, there were an increase in chl a and NO3, and a significant decrease in bottom DO in southern waters in summer, suggesting that hypoxic events are most likely to occur in this region if phytoplankton biomass and oxygen consumption keep increasing and exceed the buffering capacity of HK waters maintained by monsoon winds, tidal mixing and zooplankton grazing. Therefore, future studies on the long-term changes in nutrient loading from PRE and HK sewage discharge will be crucial for developing future strategies of sewage management in HK waters.  相似文献   

7.
Meteorological extreme events (heavy rainfall, heat waves) may lead to fast changes in nutrient load and water temperature in temperate lakes. We conducted laboratory experiments with an artificial phytoplankton community to mimic a rapid temperature increase (from 21 °C to 29 °C) at low nutrient levels (‘heat wave scenario’), respectively temperature decrease (from 21 °C to 16 °C) and increased nutrient load (‘heavy rainfall scenario’). We hypothesised that there is a taxon specific nutrient x temperature interaction, leading to significant shifts in the phytoplankton community composition when both variables change. To separate the temperature effect from the nutrient effect, we performed another experimental series at a reduced temperature but without addition of nutrients. As expected, the nutrient effect was overall more important than temperature and significantly affected all five taxa tested that represented different algal classes. However, temperature also played an important role for community composition, because the cryptophyte Cryptomonas sp. and the dinoflagellate Peridinium sp. reached significantly higher biovolumes at lower temperatures. The nutrient x temperature interaction was significant in the green alga Scenedesmus obliquus. These findings suggest that our experimental results cannot be interpreted primarily by species competition for nutrients. Heterotrophic bacteria were present in all experiments. Bacterial biomass was significantly positively related to temperature and nutrients. However, relative to phytoplankton biovolume, bacterial biovolume decreased under nutrient replete conditions. In conclusion, our results demonstrate that short-term environmental change may significantly affect both the phytoplankton community (in terms of species dominance and total biomass) and the ratio between autotrophs and heterotrophs in temperate lakes.  相似文献   

8.
Satellite ocean color images were used to determine the space-time variability of the Amazon River plume from 2000–2004. The relationship between sea-surface salinity (SSS) and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) absorption coefficient for dissolved and detrital material (adg) (r2=0.76, n=30, rmse=0.4) was used to identify the Amazon River plume low-salinity waters (<34 psu). The plume's spatial information was extracted from satellite bi-weekly time series using two metrics: plume area and plume shape. These metrics identified the seasonal variability of plume dimensions and dispersion patterns. During the study period, the plume showed the largest areas from July to August and the smallest from December to January. The mean annual amplitude and the mean, maximum and minimum plume areas were 1020×103 km2, 680×103 km2, 1506×103 km2 and 268×103 km2, respectively. Three main shapes and dispersion pattern periods were identified: (1) flow to the northeastern South American coast, in a narrow band adjacent to the continental shelf, from January to April; (2) flow to the Caribbean region, from April to July; and (3) flow to the Central Equatorial Atlantic Ocean, from August to December. Cross-correlation techniques were used to quantify the relationship between the plume's spatial variability and environmental forcing factors, including Amazon River discharge, wind field and ocean currents. The results showed that (1) river discharge is the main factor influencing plume area variability, (2) the wind field regulates the plume's northwestward flow velocity and residence time near the river mouth, and (3) surface currents have a strong influence over river plume dispersion patterns.  相似文献   

9.
The seasonal pattern of size-fractionated phytoplankton biomass, primary production and respiration was investigated along the longitudinal axis of the Nervión–Ibaizabal estuary (Bay of Biscay) from April 2003 to September 2004. Environmental factors influencing phytoplankton dynamics were also studied. Chlorophyll a biomass showed a longitudinal pattern of increase from the outer Abra bay to the inner estuary. On a seasonal scale, in the intermediate and inner estuary phytoplankton biomass maxima were registered in summer, the warmest and driest season, whereas in the outer bay chlorophyll a peaks occurred in May 2004, but were delayed to August 2003, likely due to a very rainy spring. Data suggest that river flow exerts a marked influence on the timing of phytoplankton biomass maxima in this estuary, decreased river flows providing a lowering of turbidity and an increase in water residence time needed for chlorophyll a to build up. Nutrient concentrations were high enough not to limit phytoplankton growth throughout the annual cycle, except silicate and occasionally phosphate in the outer bay during summer. Silicate concentration correlated positively with river flow, whereas ammonium and phosphate maximum values were generally measured in the mid-estuary, suggesting the importance of allochthonous anthropogenic sources. In the intermediate and inner estuary phytoplankton biomass was generally dominated by >8 μm size-fraction (ca. 60%), but in August 2003 <8 μm size-fraction increased its contribution in the intermediate estuary. It is argued that the lower nutrient concentrations measured in August 2003 than in August 2004 could have played a role. This is the first study in which phytoplankton primary production rates have been measured along the longitudinal axis of the Nervión–Ibaizabal estuary. Throughout the annual cycle these rates ranged from 0.001 to 3.163 g C m?3 d?1 and were comparable to those measured in nearby small estuaries of the Basque coast and other larger estuaries on the Bay of Biscay. Surface plankton community respiration rate maxima were measured during the spring 2004 chlorophyll a peak in the Abra bay and in summer months at the mid and inner estuary, coinciding with chlorophyll a biomass and primary production maxima. In general, respiration rates showed a positive correlation with temperature. In order to compare results from the Nervión–Ibaizabal estuary with other nearshore coastal and estuarine ecosystems within the Bay of Biscay a review of existing information on phytoplankton biomass and primary production dynamics was performed.  相似文献   

10.
《Marine pollution bulletin》2014,83(1-2):155-166
Recently compiled databases facilitated estimation of basin-wide benthic organic biomass and turnover in the Strait of Georgia, an inland sea off western Canada. Basin-wide organic biomass was estimated at 43.1 × 106 kg C and production was 54.6 × 106 kg C yr−1, resulting in organic biomass turnover (P/B) of 1.27 × yr−1. Organic biomass and production for sub-regions were predictable from modified organic flux (r2 > 0.9). P/B declined significantly with increasing modified organic flux, suggesting greater biomass storage in high flux sediments. Biomass and production were highest, and P/B lowest near the Fraser River. Annual basin-wide benthic production was 60% of previously estimated oxidized organic flux to substrates, which agrees with proportional measurements from a recent, localized study.Deviations from expected patterns related to organic enrichment and other stressors are discussed, as are potential impacts to benthic biomass and production, of declining bottom oxygen, increasing bottom temperature and potential changes in riverine input.  相似文献   

11.
《Marine pollution bulletin》2013,66(10-12):478-489
Atoll lagoons display a high diversity of trophic states due mainly to their specific geomorphology, and probably to their level and mode of human exploitation. We investigated the functioning of the Ahe atoll lagoon, utilized for pearl oyster farming, through estimations of photosynthetic parameters (pulse amplitude modulation fluorometry) and primary production (13C incorporation) measurements of the size structured phytoplankton biomass (<2 μm and >2 μm). Spatial and temporal scales of variability were surveyed during four seasons, over 16 months, at four sites within the lagoon. While primary production (P) was dominated by the picophytoplankton, its biomass specific primary productivity (PB) was lower than in other atoll lagoons. The variables size fraction of the phytoplankton, water temperature, season, the interaction term station * fraction and site, explained significantly the variance of the data set using redundancy analysis. No significant trends over depth were observed in the range of 0–20 m. A clear spatial pattern was found which was persistent over the seasons: south and north sites were different from the two central stations for most of the measured variables. This pattern could possibly be explained by the existence of water cells showing different water residence time within the lagoon. Photoacclimation strategies of the two size fractions differed through their light saturation coefficient (higher for picophytoplankton), but not through their maximum photosynthetic capacity (ETRmax). Positive linear relationships between photosynthetic parameters indicated that their dynamic was independent of light availability in this ecosystem, but most probably dependent on nutrient availability and/or rapid changes in the community structure. Spatial and temporal patterns of the measured processes are then further discussed in the context of nutrient availability and the possible role of cultured oysters in nutrient recycling.  相似文献   

12.
《Continental Shelf Research》2007,27(10-11):1399-1407
The annual cycle of nutrient-phytoplankton dynamics in Bohai Sea (BS) is simulated using a coupled physical–biological model in this study. By comparison, the modeled seasonal variations of nutrients and primary productivity agree with observations rather well. Although the annual cycles of chlorophyll a and primary production are both characterized by a double-peak configuration, a structural difference is still apparent: the phytoplankton biomass reaches the highest value in spring while summer is characterized by the most productivity in the BS, which can be ascribed to the combined impact of seawater temperature and zooplankton-grazing pressure on the growth of algae. Based on the validated simulations, the annual budgets of carbon, nitrogen and phosphorus are estimated, and are about 0.82 mt C surplus, 39 kt N deficit and 12 kt P surplus, respectively, implying that the BS ecosystem is somewhat nitrogen limited. The contribution of two external nutrient sources, namely river discharges and resuspended sediments, to the growth of algae is also examined numerically, and it is found that the influence of river-borne nutrients mainly concentrates in estuaries, whereas the reduction of sediment-borne nutrients may significantly inhibit the onset of algae bloom in the whole BS.  相似文献   

13.
A double-spike method was used to obtain Mo isotope data for sediments and waters of the seasonally anoxic Chesapeake Bay, and its primary tributary, the Susquehanna River. The dissolved Mo distribution in the estuary is non-conservative, reflecting minor Mo loss to the sediments, although removal of Mo to the sediments does not have a large influence on the isotopic composition of the water column. The δ98Mo of dissolved Mo in most of the estuary is dominated by seawater. Six samples with salinity > 15 have an average δ98Mo = + 2.17‰ (± 0.12), which agrees well with a δ98Mo value for the CASS-4 seawater standard of + 2.23‰. A single sample of Susquehanna River water has a δ98Mo of + 1.02‰, consistent with recent findings of positive δ98Mo in rivers worldwide. Susquehanna river sediments, in contrast, have δ98Mo ～ ? 0.1‰. The difference between the river water and sediment values implies that isotopic fractionation occurs within the river basin. The δ98Mo values for estuarine sediments are offset from values in the overlying water. Most samples deposited before 1925 have δ98Mo less than 0‰, similar to the Susquehanna sediments. Subsequently, there is an increase in the variability of δ98Mo, with values ranging up to + 0.8‰. The transition to increased variability coincides with the onset of authigenic Mo deposition, which was previously attributed to escalating summertime anoxia. Authigenic Mo concentrations correlate poorly with δ98Mo in core samples, suggesting that independent mechanisms influence the two parameters. Authigenic Mo concentrations may be controlled by shifting pore water H2S levels, while δ98Mo may be primarily affected by annual variations in Mn refluxing.  相似文献   

14.
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   

15.
The Chilean Patagonian fjords region (41–56°S) is characterized by highly complex geomorphology and hydrographic conditions, and strong seasonal and latitudinal patterns in precipitation, freshwater discharge, glacier coverage, and light regime; all of these directly affect biological production in the water column. In this study, we compiled published and new information on water column properties (primary production, nutrients) and surface sediment characteristics (biogenic opal, organic carbon, molar C/N, bulk sedimentary δ13Corg) from the Chilean Patagonian fjords between 41°S and 55°S, describing herein the latitudinal pattern of water column productivity and its imprint in the underlying sediments. Based on information collected at 188 water column and 118 sediment sampling sites, we grouped the Chilean fjords into four main zones: Inner Sea of Chiloé (41° to ～44°S), Northern Patagonia (44° to ～47°S), Central Patagonia (48–51°S), and Southern Patagonia (Magellan Strait region between 52° and 55°S). Primary production in the Chilean Patagonian fjords was the highest in spring–summer, reflecting the seasonal pattern of water column productivity. A clear north–south latitudinal pattern in primary production was observed, with the highest average spring and summer estimates in the Inner Sea of Chiloé (2427 and 5860 mg C m?2 d?1) and Northern Patagonia (1667 and 2616 mg C m?2 d?1). This pattern was closely related to the higher availability of nutrients, greater solar radiation, and extended photoperiod during the productive season in these two zones. The lowest spring value was found in Caleta Tortel, Central Patagonia (91 mg C m?2 d?1), a site heavily influenced by glacier meltwater and river discharge loaded with glacial sediments. Biogenic opal, an important constituent of the Chilean fjord surface sediments (SiOPAL ～1–13%), reproduced the general north–south pattern of primary production and was directly related to water column silicic acid concentrations. Surface sediments were also rich in organic carbon content and the highest values corresponded to locations far away from glacier influence, sites within fjords, and/or semi-enclosed and protected basins, reflecting both autochthonous (water column productivity) and allochthonous sources (contribution of terrestrial organic matter from fluvial input to the fjords). A gradient was observed from the more oceanic sites to the fjord heads (west–east) in terms of bulk sedimentary δ13Corg and C/N ratios; the more depleted (δ13Corg ?26‰) and higher C/N (23) values corresponded to areas close to rivers and glaciers. A comparison of the Chilean Patagonian fjords with other fjord systems in the world revealed high variability in primary production for all fjord systems as well as similar surface sediment geochemistry due to the mixing of marine and terrestrial organic carbon.  相似文献   

16.
Our study summarizes data from six small water reservoirs in West Slovakia and analyzes the occurrence of zooplankton groups in relation to physico-chemical and catchment variables. The reservoirs are in two different catchments – of the Morava and Váh rivers. A total of 103 species were identified; 64 crustaceans (in both the pelagic and littoral zones) and 39 planktonic Rotifera in the pelagic zones. Significant differences were observed in species richness, abundance and biomass of planktonic crustaceans: 48 species were characteristic of the Váh catchment, while 53 were found in the Morava catchment. The density of zooplankton in the three reservoirs of the Váh River catchment ranged from 102 ind L?1 to 21,488 ind L?1 and the zooplankton biomass ranged from 0.12 mg L?1 to 103.29 mg L?1. The density of zooplankton in three Morava River catchment reservoirs ranged from 2 ind L?1 to 3928 ind L?1 and the zooplankton biomass ranged from 0.1 mg L?1 to 27.3 mg L?1. The differences were found to be related to catchment (altitude and catchment affiliation), chemical (BOD5, DO) and biological (Chromophyta, Chlorophyta) factors. Eutrophication of reservoirs in the Váh catchment was mainly due to agriculture and fish management, resulting in high nutrient concentrations. Species richness showed an unimodal response to BOD5 and N-NH4 with near optimum low values, 4.6 and 0.19 respectively. The relationship to oxygen content reflects preferences for less eutrophic waters and species richness tended to decrease with increasing DO and to decrease with increasing nutrient content.  相似文献   

17.
New geochemical and isotopic data are presented from the oldest part of the Cumbre Vieja volcano, La Palma (Canary Islands), located near the assumed emergence of the Canary mantle plume. The volcanics comprise a suite dominated by basanite flows with subordinate amounts of phono-tephrite, tephri-phonolite and phonolite flows and intrusives. Two compositionally different basanite groups have been identified, both with HIMU (high-μ)-type incompatible trace element characteristics: Primitive high-MgO basanites (10.7–12.1% MgO), found only at the base of a stratigraphic profile near Fuencaliente on the south coast, and intermediate-MgO basanites (6.0–7.3% MgO), exposed in the upper part of the profile and widespread on the east coast of La Palma. The high-MgO basanites are interpreted as near-primary mantle melts (primary composition 14–15% MgO) derived by progressive melting (2.9% to 4.5%) of a common lithospheric mantle source. Model calculations indicate that it is not possible to generate the intermediate-MgO basanites from the high-MgO group by crystal fractionation of observed phenocrysts. Relative to intermediate-MgO basanites, the high-MgO flows have lower concentrations of LIL and HFS elements, except for Ti, which is markedly enriched in the primitive rocks (3.7–4.7% TiO2 vs 3.4–3.9% TiO2). Fuencaliente volcanics display limited temporal isotopic variations suggested to be a result of mixing of melts originating from the rising plume and the metazomatized lithospheric mantle. 87Sr / 86Sr and 143Nd / 144Nd ratios range 0.70305–0.70311 and 0.51285–0.51291, respectively, while the corresponding ranges in Pb-isotope ratios are 206Pb / 204Pb = 19.46–19.64, 207Pb / 204Pb = 15.55–15.61, and 208Pb / 204Pb = 39.16–39.53. The overall variation of the Cumbre Vieja isotopic data can be accounted for by mixtures of three mantle components in the proportions 72–79% plume source (LVC = low velocity component), 9–16% depleted mantle (DM) and up to 12% enriched mantle (EMI). Negative Δ7 / 4 Pb (− 0.6 to − 5.4) in the Cumbre Vieja volcanics suggest derivation from a young HIMU mantle source. The relative abundance of plume source material increase in younger rocks in the Fuencaliente section, suggesting waning plume–lithosphere interaction during the emplacement of this part of the Cumbre Vieja volcano. The high-MgO volcanics define regular and systematic geochemical trends, interpreted as partial melting trends, when plotted against abundances of highly incompatible elements (P, Ce). Evaluation of minor and trace element variation in consecutive melts suggests control by residual amphibole, phlogopite, garnet and a Ti-bearing phase, possibly ilmenite. The melting mode changed gradually, allowing increasing input from residual phlogopite during partial melting. The residual mineralogy constrains the source region of the high-MgO basanites to the lowermost oceanic lithospheric mantle, presumably around 100 km depths.  相似文献   

18.
《Continental Shelf Research》1999,19(15-16):2041-2061
Three sampling cruises were conducted in the Seine Estuary from 1993 to 1995 in varying hydrological and seasonal conditions. The site included all of the lower part of the river under the influence of tidal dynamics and the dilution plume in the Baie de Seine. Chemical speciation of arsenic showed high seasonal variations, especially in September when AsIII represented around 50% of dissolved arsenic. The inclusion of organoarsenic compounds not accessible to direct analysis by hydride generation required preliminary mineralisation of the samples. The ratio of dissolved to particulate arsenic distribution was controlled mainly by the iron content of particles. Biological activity had an influence on chemical speciation and thus on the partition coefficient (KD 10−3=6±1 in September and 12±0.9 in February). The zone of conservative mixing used for Seine River flow calculations was limited to a salinity range of approximately 10–30. Dissolved arsenic concentrations extrapolated to null salinities were lower during the high-water period because of dilution (17.6±1.1 nM), and maximal during the low-water period in summer (35.7±0.9 nM). Mean arsenic export to the English Channel was estimated at 33.2±6 T yr−1 for dissolved arsenic. Observation of an arsenic output greater than the upstream input, as well as a simultaneous increase in dissolved and particulate arsenic concentrations during the mixing of freshwater with seawater, strongly suggested the existence of an important intra-estuarine source of arsenic, either of industrial origin or related to the transport and diagenesis of marine sediments.  相似文献   

19.
Three shallow basins in Huizhou West Lake, China, were compared with respect to phosphorus (P) cycling between sediment and water, binding forms of P in sediment, and macrophyte biomass. The basins had similar sediments and similar depths, but two of the basins were restored by carp fish removal and macrophyte transplantation. These two basins have had clear water, low Chl.a and high macrophyte coverage for seven and ten years, whilst the unrestored control basin had turbid water and higher Chl.a. Judged by diffusive ammonium efflux, sediments in restored basins had higher mineralization rates than the unrestored basin, but the release of total dissolved P were more similar. However, sediments of restored basins released primarily dissolved organic P, while the sediment from the unrestored basin only released dissolved inorganic P. One third of the P release in the unrestored basin occurred from resuspended sediment, while this pathway contributed less than 3% in restored basins where resuspension rates were 10 times lower and the surface sediments affinity for phosphate higher. Besides from the presence of carps in the unrestored basin, the main differences were a large pool of P (700–850 mg P m−2) in macrophyte biomass and a smaller pool (∼150 mg m−2) as loosely adsorbed P in the sediment of restored basins than in the unrestored (0 in macrophytes and 350 mg P m−2 as loosely adsorbed). Also, a tendency of higher concentrations of oxidized iron was observed in the surface sediment from restored basins. The study underlines the potential of trophic structure changes to alter internal nutrient cycling in shallow lakes.  相似文献   

20.
Paleoelevation constraints from fossil leaf physiognomy and stable isotopes of sedimentary carbonate suggest that significant surface uplift of the northern Andean plateau, on the order of 2.5 ± 1 km, occurred between ～ 10.3 and 6.4 Ma. Independent spatial and temporal constraints on paleoelevation and paleoclimate of both the northern and southern plateau are important for understanding the distribution of rapid surface uplift and its relation to climate evolution across the plateau. This study focuses on teeth from modern and extinct mammal taxa (including notoungulates, pyrotheres, and litopterns) spanning ～ 29 Ma to present, collected from the Altiplano and Eastern Cordillera of Bolivia (16.2°S to 21.4°S), and lowland Brazil. Tooth enamel of large, water-dependent mammals preserves a record of surface water isotopes and the type of plants that animals ingested while their teeth were mineralizing. Previous studies have shown that the δ18O of modern precipitation and surface waters decrease systematically with increasing elevations across the central Andes. Our results from high elevation sites between 3600 and 4100 m show substantially more positive δ18O values for late Oligocene tooth samples compared to < 10 Ma tooth δ18O values. Late Oligocene teeth collected from low elevation sites in southeast Brazil show δ18O values similar (within 2‰) to contemporaneous teeth collected at high elevation in the Eastern Cordillera. This affirms that the Andean plateau was at a very low elevation during the late Oligocene. Late Oligocene teeth from the northern Eastern Cordillera also yield consistent δ13C values of about ? 9‰, indicating that the environment was semi-arid at that time. Latitudinal gradients in δ18O values of late Miocene to Pliocene fossil teeth are similar to modern values for large mammals, suggesting that by ～ 8 Ma in the northern Altiplano and by ～ 3.6 Ma in the southern Altiplano, both regions had reached high elevation and established a latitudinal rainfall gradient similar to modern.  相似文献   

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