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1.
《Continental Shelf Research》1999,19(9):1113-1141
Relationships among primary production, chlorophyll, nutrients, irradiance and mixing processes were examined along the salinity gradient in the Mississippi River outflow region. A series of six cruises were conducted during 1988–1992 at various times of year and stages of river discharge. Maximum values of biomass and primary production were typically observed at intermediate salinities and coincided with non-conservative decreases in nutrients along the salinity gradient. Highest values of productivity (>10 gC m−2 d−1) and biomass (>30 mg chlorophyll a m−3) were observed in April 1988, July–August 1990 and April–May 1992; values were lower in March and September 1991. Rates of primary production were apparently constrained by low irradiance and mixing in the more turbid, low salinity regions of the plume, and by nutrient limitation outside the plume. Highest values of primary production occurred at stations where surface nutrient concentrations exhibited large deviations from conservative mixing relationships, indicating that depletion of nutrients was related to phytoplankton uptake. Mixing and advection were important in determining the location and magnitude of primary production maxima and nutrient depletion. In addition to growth within plume surface waters, enhanced growth and/or retention of biomass may have occurred in longer residence time waters at the plume edge and/or beneath the surface plume. Vertical structure of some plume stations revealed the presence of subsurface biomass maxima in intermediate salinity water that was depleted in nutrients presumably by uptake processes. Exchange between subsurface water and the surface plume apparently contributed to the reduction in nutrients at intermediate salinities in the surface layer. DIN (=nitrate+nitrite+ammonium) : PO4 (=phosphate) ratios in river water varied seasonally, with high values in winter and spring and low values in late summer and fall. Periods of high DIN : PO4 ratios in river nutrients coincided with cruises when surface nutrient concentrations and their ratios indicated a high probability for P limitation. N limitation was more likely to occur at high salinities and during late summer and fall. Evidence for Si limitation was also found, particularly in spring.  相似文献   

2.
The effects from two winter rain storms on the coastal ocean of the Southern California Bight were examined as part of the Bight ‘03 program during February 2004 and February–March 2005. The impacts of stormwater from fecal indicator bacteria, water column toxicity, and nutrients were evaluated for five major river discharges: the Santa Clara River, Ballona Creek, the San Pedro Shelf (including the Los Angeles, San Gabriel, and Santa Ana Rivers), the San Diego River, and the Tijuana River. Exceedances of bacterial standards were observed in most of the systems. However, the areas of impact were generally spatially limited, and contaminant concentrations decreased below California Ocean Plan standards typically within 2–3 days. The largest bacterial concentrations occurred in the Tijuana River system where exceedances of fecal indicator bacteria were noted well away from the river mouth. Maximum nitrate concentrations (~40 μM) occurred in the San Pedro Shelf region near the mouth of the Los Angeles River. Based on the results of general linear models, individual sources of stormwater differ in both nutrient concentrations and the concentration and composition of fecal indicator bacteria. While nutrients appeared to decrease in plume waters due to simple mixing and dilution, the concentration of fecal indicator bacteria in plumes depends on more than loading and dilution rates. The relationships between contaminants (nutrients and fecal indicator bacteria) and plume indicators (salinity and total suspended solids) were not strong indicating the presence of other potentially important sources and/or sinks of both nutrients and fecal indicator bacteria. California Ocean Plan standards were often exceeded in waters containing greater than 10% stormwater (<28–30 salinity range). The median concentration dropped below the standard in the 32–33 salinity range (1–4% stormwater) for total coliforms and Enterococcus spp. and in the 28–30 salinity range (10–16% stormwater) for fecal coliforms. Nutrients showed a similar pattern with the highest median concentrations in water with greater than 10% stormwater. Relationships between colored dissolved organic matter (CDOM) and salinity and between total suspended solids and beam attenuation indicate that readily measurable, optically active variables can be used as proxies to provide at least a qualitative, if not quantitative, evaluation of the distribution of the dissolved, as well as the particulate, components of stormwater plumes. In this context, both CDOM absorption and the beam attenuation coefficient can be derived from satellite ocean color measurements of inherent optical properties suggesting that remote sensing of ocean color should be useful in mapping the spatial areas and durations of impacts from these contaminants.  相似文献   

3.
A quasi-synoptic survey of a eulerian small grid was carried out twice during mid-spring 2002 in the Gulf of Lions, NW Mediterranean Sea. Analysis of hydrological core parameters reveal for the first time, in the region of freshwater influence (ROFI) of the Rhone River, the presence of low-salinity water (LSW) lenses. The present work details the biogeochemical and ecological functioning of the two LSW lenses from a combined analysis of nutrients and organic matter content, taxonomic assemblages of phytoplankton, primary productivity measurements and nitrogen regeneration fluxes. During the first survey, the lens observed is only detached in part from the Rhone River plume and is considered as a juvenile lens. In contrast, the second lens is totally detached from the plume forming a confined 3D structure with a large vertical development and is considered as having a more advanced maturity. A second survey, 4 days later, provided the opportunity to propose a complete sequence of ecological functioning of the LSW lenses, from their formation to a late stage of maturity just before dispersion. Nitrate contents and dissolved organic matter remain in high concentrations during the juvenile stages while the little available phosphate is rapidly exhausted. In such, an unbalanced-nutrient environment picoplankton appear to out-compete bacterioplankton for phosphate and other resources such as ammonium. In turn, the dominance of such prokaryotic assemblages could have involved the rapid development of microzooplankton. The sudden increase in phosphate observed in a more advanced stage of lens maturity is attributed to intense P-regeneration driven by the large abundance of microzooplankton. This top-down control does not seem to enable the prokaryotic assemblages to bloom again but the high concentrations of phosphate and nitrate favour the development of larger phytoplankton. These autotrophic communities rapidly exhaust nutrients and then decline in the confined ecosystem of the LSW lens that subsequently evolves towards oligotrophic conditions. In the observed last stage, small-sized phytoplankton again dominates the microbial assemblages and the trophic regime is mainly based on regenerated production. The long lifetime of the LSW lens compared to that of the Rhone River plume enables a deep transformation of the initial characteristics of the Rhone River freshwaters both in terms of nutrients balance and microbial food webs, especially through trophic cascading effects. Hence, we show that the LSW lenses have the potential to transfer nutrients and organic matter offshore but the nature (inorganic vs. organic) of the dominant compound exported will depend on the maturity of the lens at the time of its dispersion.  相似文献   

4.
After 1990, external loads of Central European rivers with inorganic nutrients (nitrogen and phosphorus) and organic material were reduced because of changed environmental laws. However, in the eutrophic lowland River Warnow, North-Eastern Germany, nitrate concentrations remained high with 35–185 μmol l−1 without a significant decrease since 1992. In contrast, phosphate concentrations, varying between 0.3 and 5.2 μmol l−1 during the growth season 2002, decreased significantly over the years. However, its concentrations still exceeded 1 μmol l−1 regularly in the growth seasons. This load led to a substantial accumulation of organic matter additional to high terrestrial inputs. Despite the high organic load, the remineralising bacteria were mainly inactive in River Warnow. Therefore, the composition of the dissolved organic material, especially its bioavailability, were investigated during the growth season 2002 and discussed with other potential controlling factors. River Warnow carried a high load of dissolved organic carbon (14 mg l−1), especially of humic substances (5.5 mg C l−1). Bacterial abundance (12×106 ml−1) as well as production (1.7 μg C l−1 h−1) depended on temperature. During late spring and summer at constantly higher temperatures, bacterial production correlated positively to readily utilisable substrates and to humic compounds. Thus, the bacterial community in River Warnow may be well adapted or contain enough species using the available amino acids and carbohydrates as well as humic matter compounds. However, calculated from protozoan biomass, grazing may control bacterial biomass and perhaps community composition profoundly, what lead to the low percentages of active bacteria.  相似文献   

5.
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   

6.
Blooms of the toxic dinoflagellates, Karenia spp. occur nearly annually in the eastern Gulf of Mexico with cell abundances typically >105 cells L−1. Thermal and ocean color satellite imagery shows sea surface temperature patterns indicative of upwelling events and the concentration of chlorophyll at fronts along the west Florida continental shelf. Daily cell counts of Karenia show greater increases in cell concentrations at fronts than can be explained by Karenia's maximum specific growth rate. This is observed in satellite images as up to a 10-fold greater increase in chlorophyll biomass over 1–2 d periods than can be explained by in situ growth. In this study, we propose a model that explains why surface blooms of Karenia may develop even when nutrients on the west Florida shelf are low. In the summer, northward winds produce a net flow east and southeast bringing water and nutrients from the Mississippi River plume onto the west Florida shelf at depths of 20–50 m. This water mass supplies utilizable inorganic and organic forms of nitrogen that promote the growth of Karenia to pre-bloom concentrations in sub-surface waters in the mid-shelf region. In the fall, a change to upwelling favorable winds produces onshore transport. This transport, coupled with the swimming behavior of Karenia, leads to physical accumulation at frontal regions near the coast, resulting in fall blooms. Strong thermal fronts during the winter provide a mechanism for re-intensification of the blooms, if Karenia cells are located north of the fronts. This conceptual model leads to testable hypotheses on bloom development throughout the Gulf of Mexico.  相似文献   

7.
Satellite-derived chlorophyll-a fields have been used to investigate temporal and spatial variability of chlorophyll-a concentration over the continental shelf zone (25–40°S and 60–45°W) close to the La Plata River estuary. Ocean color data used in this study were obtained by the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and consisted of 368 weekly averaged Standard Mapped Images (SMI), from October 1997 to September 2005. Fourier harmonic and EOF analyses were used to study the variability of log-transformed chlorophyll-a concentration in the region. The harmonic analysis has shown that the annual cycle was the most dominant signal followed by the semi- and quadri-annual cycles, in certain areas. The strong annual cycle is mainly present in latitudes lower than 34°S where relatively high amplitudes (∼1.9 mg m−3) in pigment variation are seen over the southern Brazilian continental shelf. The semi-annual cycle is mainly associated with the Brazil–Malvinas frontal zone oscillation while the 4-year signal is related to positive La Plata discharge anomalies influenced by El Niño events. After removing the annual signal from the log-transformed chlorophyll anomalies, the EOF results showed that the first three modes captured 85.1% of the variability associated with the regional mean phytoplankton chlorophyll pattern in our smoothed data set. The first three modes explained, respectively, 63.4%, 14.1% and 7.6%. The EOF results showed that the long-term chlorophyll time/space patterns are associated with both La Plata discharge anomaly (mode 1) and alongshore wind stress (mode 2). A reconstruction of the chlorophyll anomaly fields has been made using the two leading EOF modes over two periods of high La Plata River discharge, during ENSO events. In the first event, the spatial patterns of high chlorophyll anomaly were confined to the southern portion of the region, associated with NE winds, which push the plume near the estuary mouth. The second period revealed an elongated tongue of positive chlorophyll anomalies over the Uruguayan and Brazilian middle continental shelves, associated with favorable SW winds. The analyses performed in this study allowed identification of the main modes of variability in SeaWiFS-derived chlorophyll in the region, which were consistent with modulations of important regional environmental forcing mechanisms.  相似文献   

8.
The tropical river ocean processes in coastal settings (TROPICS) program in Indonesia (Indotropics) was carried out in the Mamberamo estuary on May–June 1999 and August 2000. The Mamberamo River flows northward from the high mountains of West Papua to the narrow and steep continental slope of the Pacific Ocean. The data for the 1999 Mamberamo estuary cruises show the dispersal of fresh water coming out of the Mamberamo River into the Bismarck Sea, and the plume is clearly defined by the pattern of salinity, turbidity, and nutrient distribution. The Mamberamo River and other nearby rivers supply high concentrations of phosphate and nitrate to the New Guinea Coastal Current, so that nutrient concentrations are higher in the surface estuarine plume, compared to offshore areas. The distribution of fishes and benthic animals were also sampled over this area.  相似文献   

9.
Detailed knowledge of the flood period of Arctic rivers remains one of the few factors impeding rigorous prediction of the effect of climate change on carbon and related element fluxes from the land to the Arctic Ocean. In order to test the temporal and spatial variability of element concentration in the Ob River (western Siberia) water during flood period and to quantify the contribution of spring flood period to the annual element export, we sampled the main channel year round in 2014–2017 for dissolved C, major, and trace element concentrations. We revealed high stability (approximately ≤10% relative variation) of dissolved C, major, and trace element concentrations in the Ob River during spring flood period over a 1‐km section of the river channel and over 3 days continuous monitoring (3‐hr frequency). We identified two groups of elements with contrasting relationship to discharge: (a) DIC and soluble elements (Cl, SO4, Li, B, Na, Mg, Ca, P, V, Cr, Mn, As, Rb, Sr, Mo, Ba, W, and U) negatively correlated (p < 0.05) with discharge and exhibited minimal concentrations during spring flood and autumn high flow and (b) DOC and particle‐reactive elements (Al, Fe, Ti, Y, Zr, Nb, Cs, REEs, Hf, Tl, Pb, and Th), some nutrients (K), and metalloids (Ge, Sb, and Te), positively correlated (p < 0.05) with discharge and showed the highest concentrations during spring flood. We attribute the decreased concentration of soluble elements with discharge to dilution by groundwater feeding and increased concentration of DOC and particle‐reactive metals with discharge to leaching from surface soil, plant litter, and suspended particles. Overall, the present study provides first‐order assessment of fluxes of major and trace elements in the middle course of the Ob River, reveals their high temporal and spatial stability, and characterizes the mechanism of river water chemical composition acquisition.  相似文献   

10.
During four surveys at spring and neap tides in July and November 2005, continuous observations were conducted at four stations adjacent to the Changjiang (Yangtze River) mouth. The observation times lasted for 26 h that covered two consecutive semidiurnal cycles. Resuspension events and subsequently enhancements of suspended particulate matter (SPM) were commonly observed within a tidal cycle. Although nutrients (SiO32−, NO3−, and PO43−) were primarily governed by salinity, their statistically significant correlations with SPM could always be extracted after partial correlation analysis. Three parameter (salinity, SPM, nutrients) regressions generally produced better results of simulating nutrient concentrations than two parameter (salinity and nutrients) regressions, although compared to the latter, the former R2 values were elevated by no more than 13%. The partial correlation between SPM and a specific nutrient could be either positive or negative in different surveys, suggesting SPM influenced the nutrients in different ways under various conditions. The minor (albeit statistically significant) impacts of highly dynamic SPM on nutrients might be ascribed to the short duration time of resuspension events and estuarine mixing process, together with the complex nature of circulation in the Changjiang plume seawater.  相似文献   

11.
Ocean Dynamics - The analysis of a 28-year-long (1989–2016) series of monthly measurements of chlorophyll concentrations and primary production rates at a shelf station off A Coruña (NW...  相似文献   

12.
Based on literature data and shipboard observations, this study investigated the main environmental characteristics of the seafloor topography, current field, front, and upwelling that are closely related to hypoxia occurrence off the Changjiang estuary. The physical processes of the plume front and upwelling off the Changjiang estuary in summer were coupled. The vertical distribution pattern of the plume front was closely related to the upwelling. By reviewing and analyzing the historical summer hypoxia events off the Changjiang estuary, we statistically demonstrated the spatial structure of the horizontal distribution of the hypoxic zone and investigated the location of occurrence zone of the hypoxia. We found that the dissolved oxygen (DO) concentration on the inner continental shelf off the estuary showed a “V” shape in relation to station depth. Therefore, we noted that the hypoxic water on the inner continental shelf mostly occurred on the slopes with steep seafloor topography. Base on the current understanding of the hypoxic mechanisms off the Changjiang estuary, we analyzed the biogeochemical mechanisms that could cause the steep terrain off the Changjiang estuary to become the main areas prone to summer hypoxia and explained the internal relations between the location of the hypoxic zone on the slopes and the plume front and upwelling. The plume front and upwelling off the Changjiang estuary and their coupling were important driving forces of summer hypoxia. The continuous supply of nutrients affected by the interaction of the plume front extension of the Changjiang Diluted Water (CDW) and upwelling and the favorable light conditions were important mechanisms causing the phytoplankton blooms and benthic hypoxia off the Changjiang estuary in summer. By analyzing oxygen utilization, organic carbon mineralization, and nutrient regeneration in the hypoxic zone, we observed that the significant oxygen utilization process off the Changjiang estuary in summer also mainly occurred near the steep slopes with front and upwelling features and confirmed the apparent nutrient loss in the benthic hypoxic zone. Meanwhile, our analysis revealed that the sediment resuspension in the benthic boundary layer in the mud areas off the Changjiang estuary could also affect the oxygen utilization and mineralization of organic carbon and nutrient recycling and regeneration. This study also demonstrated that the steep terrain off the Changjiang estuary was the main location for summer acidification, and the coupling between the plume front and upwelling on the steep slopes was an important physical driving force inducing summer benthic acidification. Finally, we discussed issues to address in future studies of the hypoxic zone and water acidification off the Changjiang estuary.  相似文献   

13.
Oxygen depletion off the Changjiang (Yangtze River) Estuary   总被引：25，自引：0，他引：25  
In a survey on the Yellow Sea and the East China Sea on August 20-30 of 1999, we found a hypoxic zone (<2 mg/L) of 13700 km2 with an average thickness of 20m at the bottom of the Changjiang (Yangtze River) Estuary, with an oxygen minimum value of 1 mg/L. The extension of the dissolved oxygen deficiency extended to the 100m isobath in a southeastward direction along the bottom of the continental shelf of the East China Sea. During the last two decades, the minimum dissolved oxygen values in the low oxygen region of the Changjiang Estuary have decreased from 2.85 mg/L to 1 mg/L. In the hypoxic zone, the apparent oxygen utilization (AOU) was 5.8 mg/L and the total oxygen depletion approximately 1.59 × 106t. The strong halocline above the hypoxic zone, as a result of affluent water from the Changjiang, Taiwan Warm Current (TWC), and the high concentrations of particle organic carbon (POC) and nitrogen (PON) are the major factors causing the formation of the hypoxic zone. The POC: PON ratios and nutrient concentration distributions in the hypoxic zone suggest that the oxygen deficiency in the bottom water during the summer in the East China Sea off the Changjiang is the result of organic carbon production enhanced by nutrients from the Changjiang and fluvial organic matter input, followed by a shift in regeneration of nutrients in the East China Sea.  相似文献   

14.
Overlying bottom water samples were collected in the Vistula River plume, southern Baltic Sea, (Poland) and analysed for dissolved and labile particulate (1 M HCl extractable) Cu, Pb, Zn, Mn, Fe and Ni, hydrological parameters being measured simultaneously. Particulate organic matter (POM), chlorophyll a and dissolved oxygen are key factors governing the chemical behaviour of the measured metal fractions. For the dissolved Cu, Pb, Zn, Fe and Ni two maxima, in the shallow and in the deeper part of the river plume, were found. In the shallow zone desorption from seaward fluxing metal-rich riverine particles account for markedly increased metal concentrations, as confirmed also by high particulate metal contents. For Pb, atmospheric inputs were also considered to have contributed to the elevated concentrations of dissolved Pb adjacent to the river mouth. In the deep zone desorption from detrital and/or resuspended particles by aerobic decomposition of organic material may be the main mechanism responsible for enrichment of particle-reactive metals (Cu, Pb, Zn) in the overyling bottom waters. The increased concentrations of dissolved Fe may have been due to reductive dissolution of Fe oxyhydroxides within the deep sediments by which dissolved Ni was released to the water. The distribution of Mn was related to dissolved oxygen concentrations, indicating that Mn is released to the water column under oxygen reduced conditions. However, Mn transfer to the dissolved phase from anoxic sediments in deeper part of the Vistula plume was hardly evidenced suggesting that benthic flux of Mn occurs under more severe reductive regime than is consistent with mobilization of Fe. Behaviour of Mn in a shallower part has been presumably affected by release from porewaters and by oxidization into less soluble species resulting in seasonal removal of this metal (e.g. in April) from the dissolved phase. The particulate fractions represented from about 6% (Ni) and 33% (Mn, Zn, Cu) to 80% (Fe) and 89% (Pb) of the total (labile particulate plus dissolved) concentrations. The affinity of the metals for particulate matter decreased in the following order: Pb > Fe > Zn > or = > Cu > Mn > Ni. Significant relationships between particulate Pb-Zn-Cu reflected the affinity of these metals for organic matter, and the significant relationship between Ni-Fe reflected the adsorption of Ni onto Fe-Mn oxyhydroxides. A comparison of metal concentrations with data from other similar areas revealed that the river plume is somewhat contaminated with Cu, Pb and Zn which is in agreement with previous findings on anthropogenic origin of these metals in the Polish zone of southern Baltic Sea.  相似文献   

15.
Based on literature data and shipboard observations,this study investigated the main environmental characteristics of the seafloor topography,current field,front,and upwelling that are closely related to hypoxia occurrence off the Changjiang estuary.The physical processes of the plume front and upwelling off the Changjiang estuary in summer were coupled.The vertical distribution pattern of the plume front was closely related to the upwelling.By reviewing and analyzing the historical summer hypoxia events off the Changjiang estuary,we statistically demonstrated the spatial structure of the horizontal distribution of the hypoxic zone and investigated the location of occurrence zone of the hypoxia.We found that the dissolved oxygen(DO)concentration on the inner continental shelf off the estuary showed a"V"shape in relation to station depth.Therefore,we noted that the hypoxic water on the inner continental shelf mostly occurred on the slopes with steep seafloor topography.Base on the current understanding of the hypoxic mechanisms off the Changjiang estuary,we analyzed the biogeochemical mechanisms that could cause the steep terrain off the Changjiang estuary to become the main areas prone to summer hypoxia and explained the internal relations between the location of the hypoxic zone on the slopes and the plume front and upwelling.The plume front and upwelling off the Changjiang estuary and their coupling were important driving forces of summer hypoxia.The continuous supply of nutrients affected by the interaction of the plume front extension of the Changjiang Diluted Water(CDW)and upwelling and the favorable light conditions were important mechanisms causing the phytoplankton blooms and benthic hypoxia off the Changjiang estuary in summer.By analyzing oxygen utilization,organic carbon mineralization,and nutrient regeneration in the hypoxic zone,we observed that the significant oxygen utilization process off the Changjiang estuary in summer also mainly occurred near the steep slopes with front and upwelling features and confirmed the apparent nutrient loss in the benthic hypoxic zone.Meanwhile,our analysis revealed that the sediment resuspension in the benthic boundary layer in the mud areas off the Changjiang estuary could also affect the oxygen utilization and mineralization of organic carbon and nutrient recycling and regeneration.This study also demonstrated that the steep terrain off the Changjiang estuary was the main location for summer acidification,and the coupling between the plume front and upwelling on the steep slopes was an important physical driving force inducing summer benthic acidification.Finally,we discussed issues to address in future studies of the hypoxic zone and water acidification off the Changjiang estuary.  相似文献   

16.
《Marine pollution bulletin》2009,58(6-12):846-857
The objective of this study was to determine the concentrations and possible sources of heavy metals and persistent organic pollutants (POPs) in water and estuarine sediments from Gao-ping River in order to evaluate the environmental quality of aquatic system in southern Taiwan. High concentrations of heavy metals including Cr, Zn, Ni, Cu and As, ranging from 10.7 to 180 mg/kg-dry weight (dw), were detected in sediments from Gao-ping River. When normalized to the principal component analysis (PCA), swinery and electroplating wastewaters were found to be the most important pollution sources for heavy metals. Of various organochlorine pesticide (OCP) residues detected, aldrin and total-hexachlorocyclohexane (HCH) were frequently found in sediments. The total concentrations of OCPs were in the range 0.47–47.4 ng/g-dw. Also, the total-HCH, total-cyclodiene, and total-dichlorodiphenyltrichloroethane (DDT) were in the range 0.37–36.3, 0.21–19.0, and 0.44–1.88 ng/g-dw, respectively. The polychlorinated biphenyl (PCB) concentrations in sediments from Gao-ping River ranged between 0.37 and 5.89 ng/g-dw. The PCB concentrations are positively correlated to the organic contents of the sediment particles. α-HCH was found to be the dominant compound of HCH in the sediments, showing that long-range transport may be the possible source for the contamination of HCH in sediments from Gao-ping River. In summary, trace amounts of POPs in estuarine sediments from Gao-ping River were detected, showing that there still exist a wide variety of POP residues in the river sediments in Taiwan. These POP residues may be mainly from long-range transport and weathered agricultural soils, while heavy metal contamination is primarily from the swinery and industrial wastewaters.  相似文献   

17.
The ecological functioning of floodplain lakes is largely influenced by the interaction with the river mainstem. In this study, seasonal variation in water chemistry and the relationship with the river conditions were compared between floodplain lakes that differ in the level of connection to the Usumacinta River, the largest river of Mesoamerica. Samples for suspended solids, nutrients, and chlorophyll a were collected through the year in lakes permanently connected to the river and in lakes that only received water from the Usumacinta for a short period during peak flow. Floodplain lakes showed higher total suspended solids than the river during the dry season while during the rainy season greater differences were observed between the river and the lakes, probably explained by higher concentrations in the river and greater sedimentation in the lakes. Greater organic matter content in the suspended solids was observed in the floodplain lakes, particularly in the more isolated lakes, likely related to high algal biomass. Nitrate concentrations were always higher in the river than in the lakes and lower nitrate concentrations occurred at the isolated lakes, suggesting that processes that remove nitrate occur through the year and are a common feature of floodplain lakes. Phosphorus in the connected lakes was higher than in the river only during the dry season, while in the isolated lakes concentrations were always greater than in the river. Chlorophyll a concentrations were higher in the connected lakes than in the river only during the dry season, while the more isolated lakes exhibited higher values through the year, showing signs of eutrophication. Suspended organic matter, nitrate, and chlorophyll showed larger differences between lake and river sites in the more isolated lakes, probably related to greater water residence time and its influence on primary production. Less connected lakes are more vulnerable to flow alteration because the brief period of connection to the river can be compromised and the effects of eutrophication exacerbated.  相似文献   

18.
The present paper describes the chemical and biological characteristics of an upwelling filament off southern Iberia in October 2004, based on a total of 42 CTD casts, along with ADCP velocity measurements distributed by an almost regular grid of 15 km mean spacing. Stations were sampled from the surface to a maximum depth of 400 dbar, for nutrients (nitrate, phosphate and silicate) and chlorophyll a determination. The effect of cross-shelf exchange of nutrients and chlorophyll a between the coastal and oceanic waters was also investigated. Data revealed that, during the cruise conducted under relaxed winds, a relatively small filament was formed down to 75 m. However, an amount of 180 t of chlorophyll a was estimated there accompanied by low nutrient concentrations. The observed water properties reveal that SW Iberia is similar to NW Iberia, showing the continuity of the Canary Upwelling System along the Iberian Peninsula, one of poorest upwelling systems of the oceanic eastern boundaries. Nevertheless, the amounts of chlorophyll and nutrients transported through the filament are significant, revealing that those play a key role in the seaward export of matter with an important impact on the regional oceanography of this region. Considering the periods of strong upwelling events and the extent of their duration along the year, the amounts of exported matter must be hugely increased and responsible for the high productivity of these waters.  相似文献   

19.
Observations of the Hudson River plume were taken in the spring of 2006 in conjunction with the Lagrangian Transport and Transformation Experiment using mooring arrays, shipboard observations, and satellite data. During this time period, the plume was subjected to a variety of wind, buoyant, and shelf forcings, which yield vastly different responses in plume structure including a downstream recirculating eddy. During weak and downwelling winds, the plume formed a narrow buoyant coastal current that propagated downstream near the internal wave speed. Freshwater transport during periods when the downwelling wind was closely aligned with the coast was near the river discharge values. During periods with a cross-shore component to the wind, freshwater transport in the coastal current estimated by the mooring array is less than the river discharge due to a widening of the plume that leads to the internal Rossby radius scaling for the plume width to be invalid. The offshore detachment of plume and formation of a downstream eddy that is observed surprisingly persisted for 2 weeks under a variety of wind forcing conditions. Comparison between mooring, shipboard, and satellite data reveal the downstream eddy is steady in time. Shipboard transects yield a freshwater content equal to the previous 3 days of river discharge. The feature itself was formed due to a large discharge following a strong onshore wind. The plume was then further modified by a brief upwelling wind and currents influenced by the Hudson Shelf Valley. The duration of the detachment and downstream eddy can be explained using a Wedderburn number which is largely consistent with the wind strength index described by Whitney and Garvine (J Geophys Res 110:C03014 1997).  相似文献   

20.
Changes in the levels and spatial distribution of polycyclic aromatic hydrocarbons (PAHs) as a consequence of the Oder flood in the summer of 1997 were investigated in surface water samples and fluffy layer material from the Oder Lagoon and the Pomeranian Bight. The measurements of the contaminants were complemented by satellite data to describe the spreading of the Oder flood discharge including the distribution of the particulate material. During the flood elevated levels of PAHs were discussed in the surface water and fluffy layer material of the Oder River Estuary in comparison to the average values in this region. These increased concentrations were attributed to flooding of municipal and industrial waste disposal areas in the drainage area of the Oder River. The meteorological conditions during the sampling period were characterized by predominant easterly winds, which guided the river plume along the German coast into the Arkona Sea, as verified by satellite observations. The highest concentrations of PAHs were observed near the mouth of the Swina and along the main direction of the river plume. Elevated concentrations of PAHs were also found in fluffy layer samples taken from the Oder Lagoon in late August. As derived from satellite data the eastern and the western parts of the lagoon differed in their SPM load during the entire flood period. The eastern part was covered by Oder water, while the western part contained a mixture of Oder Lagoon water. The highest concentrations of PAHs were not observed in the western part with the highest suspended matter values, but in the eastern part where the flood water entered the lagoon. Despite the significantly increased PAH levels measured during the flood, all measured concentrations were below the values that are considered to pose a risk to the ecosystem.  相似文献   

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