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1.
Domestic and industrial sewage is discharged at a depth of 60 m near Whites Point on the San Pedro Shelf, Southern California borderland. A density-stratified thermocline, above the outfall at a depth of 20 to 30 m, is thought to prevent most effluent particles from reaching shallower depths and recreational facilities. In this investigation, measurement of the natural abundance of nitrogen isotopes (15N14N) is used to determine the level of sewage contribution to flocculent suspended material persisting at water depths of 7, 13 and 20 m. Organic nitrogen at 20 m depth was shown to be predominantly of sewage-origin and at 7 m, predominantly of marine origin. Organic nitrogen at 13 m depth and within 3 km of the outfall pipes is predominantly sewage in origin.Stable isotope composition of sulphur (32S34S) in the flocculent material indicates that the effluent particles contain metabolic sulphur, incorporated from dissolved seawater, as well as bacterially produced mineral sulphide.  相似文献   

2.
Moored sediment traps were deployed from January 2004 through December 2007 at depths of 550 and 800 m in San Pedro Basin (SPB), CA (33°33.0′N, 118°26.5′W). Additionally, floating sediment traps were deployed at 100 and 200 m for periods of 12-24 h during spring 2005, fall 2007, and spring 2008. Average annual fluxes of mass, particulate organic carbon (POC), ??13Corg, particulate organic nitrogen (PON), ??15N-PON, biogenic silica (bSiO2), calcium carbonate (CaCO3), and detrital material (non-biogenic) were coupled with climate records and used to examine sedimentation patterns, vertical flux variability, and organic matter sources to this coastal region. Annual average flux values were determined by binning data by month and averaging the monthly averages. The average annual fluxes to 550 m were 516±42 mg/m2 d for mass (sdom of the monthly averages, n=117), 3.18±0.26 mmol C/m2 d for POC (n=111), 0.70±0.05 mmol/m2 d for CaCO3 (n=110), 1.31±0.21 mmol/m2 d for bSiO2 (n=115), and 0.35±0.03 mmol/m2 d for PON (n=111). Fluxes to 800 and to 550 m were similar, within 10%. Annual average values of ??13Corg at 550 m were −21.8±0.2‰ (n=108), and ??15N averages were 8.9±0.2‰ (n=95). The timing of both high and low flux particle collection was synchronous between the two traps. Given the frequency of trap cup rotation (4-11 days), this argues for particle settling rates ≥83 m/d for both high and low flux periods. The moored traps were deployed over one of the wettest (2004-2005, 74.6 cm rainfall) and driest (2006-2007, 6.6 cm) rain years on record. There was poor correlation (Pearson's correlation coefficient, 95% confidence interval) of detrital mass flux with: Corg/N ratio (r=0.10, p=0.16); ??15N (r=−0.19, p=0.02); and rainfall (r=0.5, p=0.43), suggesting that runoff does not immediately cause increases in particle fluxes 15 km offshore. ??13Corg values suggest that most POC falling to the basin floor is marine derived. Coherence between satellite-derived chlorophyll a records from the trap location (±9 km2 resolution) and SST data indicates that productivity and export occurs within a few days of upwelling and both of these parameters are reasonable predictors of POC export, with a time lag of a few days to 2 weeks (with no time lag—SeaWiFS chlorophyll a and POC flux, r=0.25, p=0.0014; chlorophyll a and bSiO2 flux, r=0.28, p=0.0002).  相似文献   

3.
High primary productivity on the Pacific coast of the Baja California Peninsula is usually related to coastal upwelling activity that injects nutrients into the euphotic zone in response to prevailing longshore winds (from the northwest to north). The upwelling process has maximum intensity from April to June, with the coastal upwelling index varying from 50 to 300 m3/s per 100 m of coastline. Along the entire coast of the peninsula, the upwelling intensity changes in accordance with local wind conditions and bottom topography. Spatial variability can also be modulated by the influence of mesoscale meanders of the California Current. We have identified the seasonal and synoptic variability of upwelling signatures on the Baja California shelf, using averaged monthly and weekly sea surface temperature (SST) distributions obtained from remote sensing imagery from the Advanced Very High Resolution Radiometer in the period from 1996 to 2001. Analysis of SST distribution and direct experimental data on temperature and nutrient concentration shows that the areas with the coldest SST anomalies were closely related to the bottom slope, shelf width, and coastline orientation relating to wind direction. We also assume that the nutrient transport into the coastal lagoons may be forced by the coupling of coastal upwelling and tidal pumping of surface waters into the lagoon system. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

4.
During more than 60 years, sedimentation on the Palos Verdes Shelf has been dominated by time-varying inputs of municipal wastewater from the Los Angeles County Sanitation Districts (LACSD) and debris from the Portuguese Bend Landslide (PBL). The present study examines the depositional history of wastewater-derived organic contaminants at a site approximately 6–8 km downcurrent from the outfall system. Sediments at this location are impacted by contributions from both sources, but the relative influence of the sources has changed over time. Two classes of hydrophobic organic contaminants (chlorinated hydrocarbons, long-chain alkylbenzenes) were determined in sediment cores collected in 1981 and 1992. Using molecular stratigraphy, we determined average sedimentation rates (cm/year) and mass accumulation rates (g cm−2 year−1) for the following periods: 1955–1965, 1965–1971, 1971–1981 and 1981–1992. The results show that sedimentation and mass accumulation rates increased from 1955 to 1971 and decreased from 1971 to 1981. These trends are consistent with historical information on the emission of suspended solids from the outfall system, indicating that the discharge of wastes dominated sedimentation at the site during this period. In the 1980s and early 1990s, however, mass accumulation rates increased in spite of continually decreasing emissions of wastewater solids. Several lines of evidence indicate that this increase was due to mobilization of debris from the PBL during and after unusually strong winter storms in the 1980s. As a result, heavily contaminated sediments deposited during the years of greatest waste emissions (i.e. 1950–1970) have been buried to greater sub-bottom depths, thereby reducing their availability for mobilization to the overlying water column. These results highlight the dynamic nature of sedimentation in contaminated coastal ecosystems and its importance to the long-term fate and effects of toxic substances.  相似文献   

5.
Municipal wastes discharged through deepwater submarine outfalls since 1937 have contaminated sediments of the Palos Verdes Shelf. A site approximately 6–8 km downcurrent from the outfall system was chosen for a study of the diagenetic fate of organic contaminants in the waste-impacted sediments. Concentrations of three classes of hydrophobic organic contaminants (DDT+metabolites, polychlorinated biphenyls (PCBs), and the long-chain alkylbenzenes) were determined in sediment cores collected at the study site in 1981 and 1992. Differences between the composition of effluent from the major source of DDT (Montrose Chemical) and that found in sediments suggests that parent DDT was transformed by hydrolytic dehydrochlorination during the earliest stages of diagenesis. As a result, p,p′-DDE is the dominant DDT metabolite found in shelf sediments, comprising 60–70% of ΣDDT. The p,p-DDE/p,p′-DDMU concentration ratio decreases with increasing sub-bottom depth in sediment cores, indicating that reductive dechlorination of p,p′-DDE is occurring. Approximately 9–23% of the DDE inventory in the sediments may have been converted to DDMU since DDT discharges began ca. 1953. At most, this is less than half of the decline in p,p′-DDE inventory that has been observed at the study site for the period 1981–1995. Most of the observed decrease is attributable to remobilization by processes such as sediment mixing coupled to resuspension, contaminant desorption, and current advection. Existing field data suggest that the in situ rate of DDE transformation is 102–103 times slower than rates determined in recent laboratory microcosm experiments (Quensen, J.F., Mueller, S.A., Jain, M.K., Tiedje, J.M., 1998. Reductive dechlorination of DDE to DDMU in marine sediment microcosms. Science, 280, 722–724.). This explains why the DDT composition (i.e. o,p′-, p,p′-isomers of DDE, DDD, DDT) of sediments from this site have not changed significantly since at least 1972. Congener-specific PCB compositions in shelf sediments are highly uniform and show no evidence of diagenetic transformation. Apparently, the agents/factors responsible for reductive dechlorination of DDE are not also effecting alteration of the PCBs. Two types of long-chain alkylbenzenes were found in the contaminated sediments. Comparison of chain length and isomer distributions of the linear alkylbenzenes in wastewater effluent and surficial sediment samples indicate that these compounds undergo biodegradation during sedimentation. Further degradation of the linear alkylbenzenes occurs after burial despite relatively invariant isomer compositions. The branched alkylbenzenes are much more persistent than the linear alkylbenzenes, presumably due to extensive branching of the alkyl side chain. Based on these results, p,p′-DDE, PCBs, and selected branched alkylbenzenes are sufficiently persistent for use in molecular stratigraphy. The linear alkylbenzenes may also provide information on depositional processes. However, their application as quantitative molecular tracers should be approached with caution.  相似文献   

6.
Larval fishes were sampled from the nearshore region of the Southern California Bight off San Onofre for 29 months and analyzed with a Curtis-Bray Cluster Analysis to determine temporal assemblages and species associations. Two major assemblages of larvae were found: members of the winter-spring (December-May) assemblage were most abundant from January to May; members of the summer-fall (June-November) assemblage were most abundant from July to September. The winter-spring assemblage was composed primarily of Engraulis mordax, Genyonemus lineatus, Sebastes spp. and Paralichthys californicus; some abundant taxa in the summer-fall assemblage were Seriphus politus, Paralabrax spp., and Hypsoblennius spp., although E. mordax again predominated. Demersal spawners tended to have spawning seasons of longer duration than pelagic spawners; winter-spring spawners generally had longer spawning seasons than summer-fall spawners.We suggest that temperature is an important determinant in the seasonal pattern of larval fish occurrence. The annual ocean temperature cycle near San Onofre was a good indicator of the seasonal occurrence of fish larvae in this area. Larvae found in the cooler months were generally offspring of adults whose northern ranges extend to Canada. Warm-water larvae were offspring of adults whose northern ranges extend to Point Conception or northern California.  相似文献   

7.
Benthic fluxes of dissolved inorganic carbon, total alkalinity, oxygen, nutrients, nitrous oxide and methane were measured in situ at three sites of Río San Pedro salt marsh tidal creek (Bay of Cádiz, SW Spain) during three seasons. This system is affected by the discharges of organic carbon and nutrients from the surrounding aquaculture installations. Sediment oxygen uptake rates and inorganic carbon fluxes ranged respectively from 16 to 79 mmol O2 m? 2 d? 1 and from 48 to 146 mmol C m? 2 d? 1. Benthic alkalinity fluxes were corrected for the influence of NH4+ and NO3? + NO2? fluxes, and the upper and lower limits for carbon oxidation rates were inferred by considering two possible scenarios: maximum and minimum contribution of CaCO3 dissolution to corrected alkalinity fluxes. Average Cox rates were in all cases within ± 25% of the upper and lower limits and ranged from 40 to 122 mmol C m? 2 d? 1. Whereas carbon mineralization did not show significant differences among the sites, Cox rates varied seasonally and were correlated with temperature (r2 = 0.72). During winter and spring denitrification was estimated to account for an average loss of 46% and 75%, respectively, of the potentially recyclable N, whereas during the summer no net removal was observed. A possible shift from denitrification to dissimilatory nitrate reduction to ammonium (DNRA) during this period is argued. Dissolved CH4 and N2O fluxes ranged from 5.7 to 47 μmol CH4 m? 2 d? 1 and 4.3 to 49 μmol N–N2O m? 2 d? 1, respectively, and represented in all cases a small fraction of total inorganic C and N flux. Overall, about 60% of the total particulate organic matter that is discharged into the creek by the main fish farm facility is estimated to degrade in the sediments, resulting in a significant input of nutrients to the system.  相似文献   

8.
Bioaccumulation of endocrine disruptors in marine mammals positioned at the top of the food chain is of toxicological concern. Livers from four pups and ten adult harbor seals (Phoca vitulina) stranded in San Francisco Bay (SFB) and the Gulf of Maine (GOM) were analyzed for polychlorinated biphenyls (PCBs) and their hydroxylated metabolites (OH-PCBs). We used GC–ECD and GC–NCI/MS to investigate the presence of 28 PCBs and 8 OH-PCB metabolites, respectively. Σ28PCB concentrations (di- to octa-CBs) ranged from 1.81 to 35.9 μg/g lipid with a median of 6.53 for the seal pups and 2.31 to 249 μg/g lipid with a median of 28.9 for the adult seals. Σ8OH-PCB concentrations (penta- to hepta-OH-PCBs) ranged from 0.02 to 0.69 μg/g lipid with a median of 0.04 for the adult seals, i.e., at much lower concentrations than those for PCBs. Ratios of OH-PCBs to PCBs (0.24% on average) were comparable to those in beluga whale, but were lower than ratios in human livers. The OH-PCB profiles were slightly different between SFB and GOM seal livers, although similar PCB congener patterns were observed. Generally, 4-OH-CB107 was found predominantly in seal livers and was the only OH-PCB detectable in most of seal pup livers. This study provides information on OH-PCBs in seals, adding to the scarce exposure data for these chemicals.  相似文献   

9.
This paper analyses the diagenetic evolution of sandstones belonging to the Bajo Barreal Formation (Cretaceous) in the Golfo de San Jorge Basin (Patagonia, Argentina). The Bajo Barreal Formation includes the main reservoirs, which are located along the western area of the basin and is composed of sandstones, conglomerates, mudstones, tuffaceous mudstones and some layers of tuffs. The principal reservoirs comprise medium-to coarse-grained sandstones, which are dominated by feldspathic litharenites and contain minor amounts of litharenites and lithic arkoses. The authigenic minerals include kaolinite, smectite, chlorite, quartz overgrowths, microquartz and calcite, with minor proportions of megaquartz, siderite, analcime, laumontite, feldspar overgrowths and illite/smectite and chlorite/smectite mixed layers. Secondary porosity is much more important than primary porosity and is produced by the dissolution of feldspar, lithic clasts and clay cements. The diagenetic history of the Bajo Barreal sandstones can be divided into seven diagenetic stages, each of which is characterized by a specific assemblage of authigenic minerals and diagenetic processes. Eogenetic conditions occur in stages 1, 2, 3 and 4. Stage 1 corresponds to shallow burial characterized by the physical reduction of primary porosity by compaction; during stage 2, rim clay cements of chlorite, smectite and clinoptilolite, as well as thin quartz overgrowths, were formed. The precipitation of pore-filling cements of kaolinite, chlorite and smectite occurred during stage 3, while stage 4 records the intense dissolution of feldspar, lithic fragments and kaolinite cements. Mesogenesis occurs in diagenetic stages 5 and 6. The former corresponds to a new phase of authigenic kaolinite, while the latter records the significant dissolution of feldspar, lithic clasts and previous cements, which produced the highest values of secondary porosity. Finally, stage 7 corresponds to the highest degree of diagenesis in the Bajo Barreal Formation (mesogenesis), which resulted in the precipitation of cements of zeolites and calcite, as well as quartz and plagioclase overgrowths.  相似文献   

10.
11.
《Marine Policy》2005,29(1):75-83
In its capacity to lead and facilitate the development and implementation of integrated management plans under the 1997 Oceans Act, Fisheries and Oceans Canada is working with a range of stakeholders through a collaborative process—the Eastern Scotian Shelf Integrated Management (ESSIM) Initiative—to develop and implement an integrated ocean management plan for the eastern Scotian Shelf off Nova Scotia. Stakeholders include federal and provincial departments, aboriginal communities, municipal and local planning authorities, ocean industry and resource use sectors, coastal communities, environmental interest groups, and university researchers. This large ocean management area possesses important living and non-living marine resources, high biological productivity and diversity, and increasing levels of multiple use and competition for ocean space and resources. The ESSIM vision is to achieve environmental, economic, social/community, and institutional sustainability in the eastern Scotian Shelf.The ESSIM Initiative is building a collaborative planning process that involves all interested and affected parties. Ongoing information sharing and dialogue with stakeholder groups is providing capacity building and important input to current proposals for a collaborative planning structure and the ocean management plan. A joint federal-provincial working group has been established to move the Initiative forward within government and to address policy and regulatory coordination for ocean management. The future ocean management plan will include a balanced set of environmental, social, economic and institutional objectives, indicators and management strategies, as well as spatial and temporal planning approaches to address multiple ocean use.This article provides an overview of the ESSIM Initiative, including an assessment of ocean use, ecosystem understanding, and ocean management and planning requirements. The design of a collaborative management and planning structure and process will be discussed, as well as the key elements of the future integrated ocean management plan.  相似文献   

12.
Icefish populations continue to decline. Historical as well as current over-exploitations of stocks aggravated by climate change are frequently seen as res  相似文献   

13.
陆架沙丘(波)活动量级和稳定性标志研究   总被引:4,自引:0,他引:4  
陆架底流包含定时变向的潮流、定时定向的洋流和偶发性的暴风浪流,水下沙丘的塑造和运动是潮、浪动力共同作用的结果.用水文计算法计算沙丘迁移速率时应充分考虑陆架各动力要素的作用,并与定位观测速率相对照.按陆架水下沙丘的运动量级和发育过程可划分为强运动、弱运动、不运动(残留)和消亡(或埋藏)沙丘等4种类型,它们的稳定性标志,表现于海底状况、外部形态、粒度结构、水动力和迁移速率等方面.  相似文献   

14.
15.
The structure of the plankton community and fatty acid composition of nano-, micro- and zooplankton are described during four seasons of 1994 from the San Lorenzo Channel. During August, the warmest temperature in the surface water was observed and a thermocline developed between 20 and 30 m. In the remaining months, a well-mixed layer occurred in the upper 30 m. The chlorophyllacontent of the nanoplankton fraction (<38 μm) was higher than the microplanktonic fraction (38–200 μm) year round. Maximal chlorophyll values (1·5–3 μ l−1) occurred in January, which may be associated with organic matter, since phytoplankton was lower than at other seasons. The relative abundance of diatoms increased from January (57% of phytoplankton) to November (99%). The increment was mainly due toNitzschiaandChaetoceros. Dinoflagellates were always low (0·03–1·36 cells ml−1). Copepods (mainlyEucalanus) dominated the zooplankton in winter and fall, while in spring and summer, the abundance of doliolids was similar to the copepods (Nannocalanus minordominated).Four fatty acids (16:0, 16:1, 18:0, 18:1) were the most conspicuous in the plankton, representing usually between 40 and 80% of the total fatty acids throughout the water column. In winter, higher fatty acid content and higher relative amounts of 16:0 and 16:1 were observed than in the warm months. Stearic acid (18:0) peaked during fall. The major seasonal differences occurred in the nanoplankton, which had peaks of 20:5 during January, and 16:4 in April. A strong decrease in polyunsaturated fatty acids (PUFA) occurred during the warm months. The fatty acid composition of microplankton and larger zooplankton was similar in winter–spring. Individual copepods of selected species (Eucalanus sewelli,Rhincalanus nasutus,Centropages furcatusandLabidocera acuta) showed fatty acid profiles similar to the mixed zooplankton, with some differences in content of PUFA.  相似文献   

16.
The Vallecitos syncline is a westerly structural extension of the San Joaquin Basin. The Vallecitos oil field, comprised of eight separate areas that produce from Cretaceous and Paleogene reservoirs, accounted for 5.4 MMB of oil and 5.6 BCF associated of gas through 2010. However, exploration for oil and gas in the Vallecitos area is challenging due to structural complexity and limited data. The purpose of this study is to evaluate whether source rocks are actively generating petroleum in the Vallecitos syncline and to improve our understanding of burial history and timing of hydrocarbon generation. We conducted biomarker analysis on twenty-two oil samples from the Vallecitos syncline. Source-related biomarkers show two genetic groups of oil, which originated from two different source rocks. These results differ from earlier published interpretations in which the Kreyenhagen Formation is the only source rock in the Vallecitos syncline, and suggest that the Cretaceous Moreno Formation in the syncline also is an active source rock.Stratigraphic evidence and modeling suggest that late Cenozoic episodes of erosion due to folding and uplift removed significant overburden on the flanks of the syncline. To better understand the petroleum systems and clarify the total active source rocks in the area, 2D burial histories were generated through the Vallecitos syncline. A published cross-section through the deepest part of the syncline was selected to conduct thermal history, basin evolution, and migration analyses. The 2D model results indicate that the lower Kreyenhagen Formation has various maturities within the formation at different locations in the present-day syncline. The basal part of the Kreyenhagen Formation is in the dry gas window and maturity decreases away from the central part to the flanks. It remains immature along shallow portions of the present-day flanks. In contrast, the basal part of the Moreno Formation achieved extremely high maturity (past the gas generation zone) but is in the oil generation zone on the flanks of the syncline at shallow depth. All of our geochemical and 2D model results suggest that there are two active source rocks in the Vallecitos syncline. Accordingly, we propose that there are two active petroleum systems in the Vallecitos syncline.  相似文献   

17.
陆架沙丘(波)形成发育的环境条件   总被引:9,自引:0,他引:9  
陆架大、中、小、巨沙丘(沙波)发育的动力机制与河流沙波有相似之处,也有许多差异,前者含定时多向的潮流、持续定向的洋流和偶发性的暴风浪流,后者为单向持续水流。20~100cm/s的底流速是发育沙丘的动力因素,水流的多向性和浪流的偶发性又常常制约沙丘发育的强度和迁移的速度;陆架浅水区(小于18m)受破浪的影响,沙丘尺度与水深呈微弱负相关,深水区水深的影响甚微。陆架输沙量是沙丘发育的物质条件,特别是细、中砂底质,在此粒度范围内沙波尺度与粒径呈微弱正相关,平缓广阔的地形在沙丘发育中也起一定的作用。  相似文献   

18.
Tide gauge observations usually include temperature and density measurements. As an example of such data, a time series of sea surface temperature (SST) from 1855 to 1877 and from 1921 to 1993 at Fort Point, San Francisco, California (the longest U.S. record), and mean air temperature at Mission Dolores (San Francisco), California, from 1936 to 1990, were analyzed. Annual mean Fort Point SST increased at a rate of 0.3°C per century, but the coefficient of determination (r2) was below 0.06; for air temperature the results were 1.6°C per century and r2 = 0.16 respectively. Evidence of El Niño were found in the periodogram of the mean annual SST but not in the air temperature. The annual and semiannual peaks in the monthly time‐series analysis of SST and air temperature dominate their periodograms, and the cross‐correlation between them has r2 = 0.47. Of the 1.3 mmlyr sea level rise over the same time period. 0.003°C/yr accounts for 0.04 mmlyr in thermal expansion if the upper 100 m of the water column were uniformly warmed.  相似文献   

19.
20.
California sea lions (Zalophus californianus) off the coast of Southern California are known to damage both commercial and recreational fishing activities, causing decreases to fish catch and damage to gear. Their increasing population has intensified the potential for conflict between sea lions and anglers, likely requiring changes to current legislation. The recreational fishing community in Southern California is a valuable and largely underutilized source for information and potential solutions to management and legislative problems. This recreational fishing survey-based study conducted in 2013 utilized personal interviews, conducted in the field with recreational anglers and commercial passenger fishing vessel (CPFV) crews in Southern California, to gather data on: (a) the occurrence and impact of sea lion depredation on the local fishing, (b) angler awareness and opinions on current legislation, and (c) the conflict between fishing activities and conservation efforts. Results show that surveyed CPFV operators and private boaters had the most conflict with sea lions and perceive them as more of a problem than anglers on piers, jetties or kayaks. The conflict was also reportedly more prevalent in San Diego County compared to the other counties surveyed (Orange, Los Angeles and Ventura). Participating CPFV operators were overwhelmingly in support of a government culling program for sea lions, while recreational angler respondents did not feel that a control program was necessary. These CPFV operators reported more money lost, and were willing to pay more for an effective deterrent device. There was also a consensus among respondents that fish catch is declining, yet anglers were unsatisfied with the effectiveness of current legislation designed to increase fish stocks. These data will provide a better understanding of California sea lion depredation in Southern California and its effect on recreational anglers in order to aid future mitigation efforts. Additionally, these results provide stakeholder feedback on local marine protected areas and other fisheries management legislation, and build a foundation for future conservation and education programs.  相似文献   

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