首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 578 毫秒
1.
Herein we present results from one of the first extensive bay-wide oceanographic surveys of Manila Bay, wherein 31 stations were sampled during the northeast monsoon (cold and dry season). A band of hypoxic bottom water (dissolved oxygen<2.8 mg/L) spanned the midsection of the bay from east to west. Bottom nitrate concentrations (5.7-16.8 μM; avg. 11.1 μM) and total organic carbon values in sediments (1.7-3.1%; avg. 2.4%) were high in the midsection, which coincided with the band of hypoxic bottom water. Physical processes and site-specific accumulation of organic material likely lead to hypoxic conditions in Manila Bay, even during the northeast monsoon period when the water column is relatively well mixed. The results of this study complement the previously reported widespread hypoxia that occurs during the rainy season. Thus, hypoxia may be pervasive in the bay throughout the year, although it varies in intensity and spatial extent.  相似文献   

2.
To study the correlation between nutrient enrichment derived from fish farming activities and changes in macrobenthic assemblages, a one-year field study was conducted in Kau Sai Bay marine fish culture zone of Hong Kong. Bimonthly sediment samples were collected at six stations: two at the fish cages, two near the boundary of the fish culture area, and two reference sites further away from the culture area. Sediment physico-chemical characteristics in terms of silt/clay fraction, moisture content, total organic carbon (TOC), total Kjeldahl nitrogen (TKN) and total phosphorus (TP) were analyzed. The macrobenthos (>0.5 mm) present in the sediment were sorted, identified and enumerated. On average, TOC, TKN and TP levels at the fish cage stations were 82.8%, 128.5% and 1315.7% higher than those at the reference stations, respectively. As a result, the N:P molar ratio was greatly reduced from 8.75 at the reference stations to 1.83 at the fish cage stations. Univariate and multivariate analyses revealed that diversity of macrofauna was significantly reduced and community structure differed at the fish cage stations relative to the reference sites. The intermediary stations near the fish culture area showed a transitional state of disturbance. Faunal diversity was negatively correlated with nutrient level, reflecting the adverse impacts of nutrient enrichment derived from fish farming activities on the benthic assemblages. Whilst in subtropical Asia-Pacific trash fish is the major feed for fish culture resulting in a higher nutrient loading and nutrient ratio accumulated in the sediment beneath the fish rafts, the effects of nutrient enrichment on macrobenthic assemblages are comparable to that in temperate waters owing to relatively high sediment metabolism rate and smaller fish culture scale in Hong Kong.  相似文献   

3.
《Marine pollution bulletin》2012,64(5-12):243-248
Herein we present results from one of the first extensive bay-wide oceanographic surveys of Manila Bay, wherein 31 stations were sampled during the northeast monsoon (cold and dry season). A band of hypoxic bottom water (dissolved oxygen <2.8 mg/L) spanned the midsection of the bay from east to west. Bottom nitrate concentrations (5.7–16.8 μM; avg. 11.1 μM) and total organic carbon values in sediments (1.7–3.1%; avg. 2.4%) were high in the midsection, which coincided with the band of hypoxic bottom water. Physical processes and site-specific accumulation of organic material likely lead to hypoxic conditions in Manila Bay, even during the northeast monsoon period when the water column is relatively well mixed. The results of this study complement the previously reported widespread hypoxia that occurs during the rainy season. Thus, hypoxia may be pervasive in the bay throughout the year, although it varies in intensity and spatial extent.  相似文献   

4.
It has recently been shown that inner shelf waters of NE Monterey Bay, California function as an “extreme bloom incubator”, frequently developing dense “red tide” blooms that can rapidly spread. Located within the California Current upwelling system, this open bay is strongly influenced by oceanographic dynamics resulting from cycles of upwelling favorable winds and their relaxation and/or reversal. Different wind forcing causes influx of different water types that originate outside the bay: cold nutrient-rich waters during upwelling and warm nutrient-poor waters during relaxation. In this study, we examine how the bay's bloom incubation area can interact with highly variable circulation to cause red tide spreading, dispersal and retention. This examination of processes is supported by satellite, airborne and in situ observations of a major dinoflagellate bloom during August and September of 2004. Remote sensing of high spatial, temporal and spectral resolution shows that the bloom originated in the NE bay, where it was highly concentrated in a narrow band along a thermal front. Upwelling circulation rapidly spread part of the bloom, mixing cool waters of an upwelling filament with warm bloom source waters as they spread. Vertical migration of the dinoflagellate populations was mapped by autonomous underwater vehicle surveys through the spreading bloom. Following bloom expansion, a two-day wind reversal forced intrusion of warm offshore waters that dispersed much of the bloom. Upwelling winds then resumed, and the bloom was further dispersed by an influx of cold water. Throughout these oceanographic responses to changing winds, an intense bloom persisted in sheltered waters of the NE bay, where extreme blooms are most frequent and intense. Microscopic examination of surface phytoplankton samples from the central bay showed that spreading of the bloom from the NE bay and mixing with regional water masses resulted in significantly increased abundance of dinoflagellates and decreased abundance of diatoms. Similar dinoflagellate bloom incubation sites are indicated in other areas of the California Current system and other coastal upwelling systems. Through frequent bloom development and along-coast transports, relatively small incubation sites may significantly influence larger regions of the coastal marine ecosystems in which they reside.  相似文献   

5.
Hydrographic conditions, and particularly current speeds, have a strong influence on the management of fish cage culture. These hydrodynamic conditions can be used to predict particle movement within the water column and the results used to optimise environmental conditions for effective site selection, setting of environmental quality standards, waste dispersion, and potential disease transfer. To this end, a 3D hydrodynamic model, MOHID, has been coupled to a particle tracking model to study the effects of mean current speed, quiescent water periods and bulk water circulation in Mulroy Bay, Co. Donegal Ireland, an Irish fjard (shallow fjordic system) important to the aquaculture industry. A Lagangrian method simulated the instantaneous release of “particles” emulating discharge from finfish cages to show the behaviour of waste in terms of water circulation and water exchange. The 3D spatial models were used to identify areas of mixed and stratified water using a version of the Simpson-Hunter criteria, and to use this in conjunction with models of current flow for appropriate site selection for salmon aquaculture.The modelled outcomes for stratification were in good agreement with the direct measurements of water column stratification based on observed density profiles. Calculations of the Simpson-Hunter tidal parameter indicated that most of Mulroy Bay was potentially stratified with a well mixed region over the shallow channels where the water is faster flowing. The fjard was characterised by areas of both very low and high mean current speeds, with some areas having long periods of quiescent water. The residual current and the particle tracking animations created through the models revealed an anticlockwise eddy that may influence waste dispersion and potential for disease transfer, among salmon cages and which ensures that the retention time of waste substances from cages is extended.The hydrodynamic model results were incorporated into the ArcViewTM GIS system for visualisation and interrogation of results and to allow effective holistic environmental management and site selection for fish cage aquaculture.  相似文献   

6.
Variability in water-exchange time between Tokyo Bay and the Pacific Ocean during winter is investigated based on the results of intensive field observation from November 2000 to March 2001. Water-exchange time between Tokyo Bay and the Pacific Ocean during winter mainly depends on the strength of northerly monsoon, being about 16 days under the weak monsoon and about 12 days under the strong monsoon. Moreover, it becomes longer by about 1 day in spring tide and shorter in neap tide due to the coupling effect of estuarine circulation and vertical mixing. Water-exchange time also varies depending on the open-ocean condition. When the warm water mass approaches from the Pacific Ocean to the mouth of Tokyo Bay through the eastern channel of Sagami Bay, which connects Tokyo Bay and the Pacific Ocean, water-exchange time becomes longer by about 2 days because the warm water mass is blocked in the surface layer at the bay mouth. On the other hand, when the warm water mass approaches to the mouth of Tokyo Bay through the western channel of Sagami Bay, water-exchange time becomes shorter by about 1 day because the warm water mass intrudes into the middle or lower layers of Tokyo Bay. Such different behavior of warm water mass at the mouth of Tokyo Bay is due to the difference in density of approaching warm water masses, that is, the density of the warm water mass through the eastern channel is smaller than that of the warm water mass through the western channel of Sagami Bay.Responsible Editors: Yens Kappenberg  相似文献   

7.
Langevin CD 《Ground water》2003,41(6):758-771
Variable density ground water flow models are rarely used to estimate submarine ground water discharge because of limitations in computer speed, data availability, and availability of a simulation tool that can minimize numerical dispersion. This paper presents an application of the SEAWAT code, which is a combined version of MODFLOW and MT3D, to estimate rates of submarine ground water discharge to a coastal marine estuary. Discharge rates were estimated for Biscayne Bay, Florida, for the period from January 1989 to September 1998 using a three-dimensional, variable density ground water flow and transport model. Hydrologic stresses in the 10-layer model include recharge, evapotranspiration, ground water withdrawals from municipal wellfields, interactions with surface water (canals in urban areas and wetlands in the Everglades), boundary fluxes, and submarine ground water discharge to Biscayne Bay. The model was calibrated by matching ground water levels in monitoring wells, baseflow to canals, and the position of the 1995 salt water intrusion line. Results suggest that fresh submarine ground water discharge to Biscayne Bay may have exceeded surface water discharge during the 1989, 1990, and 1991 dry seasons, but the average discharge for the entire simulation period was only approximately 10% of the surface water discharge to the bay. Results from the model also suggest that tidal canals intercept fresh ground water that might otherwise have discharged directly to Biscayne Bay. This application demonstrates that regional scale variable density models are potentially useful tools for estimating rates of submarine ground water discharge.  相似文献   

8.
The GEF/UNDP/IMO/PEMSEA project identifies Manila Bay as among the marine pollution hot spots in the Seas of East Asia. 210Pb dating of its sediment can provide a historical perspective of its pollution loading. However, the validity of 210Pb dating in a complex dynamic coastal system of Manila Bay may come into question. Land-based sediment input can be high and physical and biological processes can possibly disturb the sediment layers. In this report, the 210Pb profiles of sediment cores from different parts of the bay are presented. The linear sedimentation rates are shown to be higher in the recent past and are also variable across the bay. The largest change in sedimentation rate, coincided with the occurrence of a volcanic eruption in 1991 and is shown by applying a variant of the CIC model in sedimentation rate calculations. The data suggest that 210Pb dating can be useful in estimating relative magnitudes of sedimentation rates, even in a complex dynamic coastal system like Manila Bay.  相似文献   

9.
A suite of 36 surface sediment samples, taken between 10 and 100 m water depth in Mejillones Bay (Northern Chile), were analyzed for mineralogy, grain size, total organic carbon, Al, and heavy metal content (Cd, Zn, Ni, Mn, V, Mo). Quartz and feldspars were the main lithogenic minerals and carbonate the predominant biogenic mineral. Sediments were fine sands in the shallow zone and organic silt in the deeper zone. Enrichment Factor and Factor Analysis approach showed that the presence of Mn in the marine sediment of Mejillones is due to a partial influence of continental input, while all other metals are not supported by lithogenic debris. Although all metals showed high concentrations in the marine sediment of Mejillones Bay, comparison between metal concentration in surface sediments and preindustrial levels in this bay, show that present values agree with natural levels.  相似文献   

10.
A suite of 36 surface sediment samples, taken between 10 and 100 m water depth in Mejillones Bay (Northern Chile), were analyzed for mineralogy, grain size, total organic carbon, Al, and heavy metal content (Cd, Zn, Ni, Mn, V, Mo). Quartz and feldspars were the main lithogenic minerals and carbonate the predominant biogenic mineral. Sediments were fine sands in the shallow zone and organic silt in the deeper zone.

Enrichment Factor and Factor Analysis approach showed that the presence of Mn in the marine sediment of Mejillones is due to a partial influence of continental input, while all other metals are not supported by lithogenic debris. Although all metals showed high concentrations in the marine sediment of Mejillones Bay, comparison between metal concentration in surface sediments and preindustrial levels in this bay, show that present values agree with natural levels.  相似文献   


11.
Murchison Bay in the Northern part of Lake Victoria has for decades received a daily wastewater load of 0.2% of its volume from Kampala City, through the Nakivubo channel. In spite of this, the Water Treatment Works abstracts raw water from this bay and has been able to produce drinking water of sufficient quality for the capital. This study monitored various physical−chemical components within the bay during 2000−2003 to understand the processes responsible for the acceptable quality of raw water. Four sampling stations were located along a transect from the channel mouth towards the open lake.Resultsshowed that the wastewater did not accumulate in the bay, instead was already strongly diluted 2.5 km from the channel mouth. This caused an abrupt reduction in conductivity and the concentrations of the nutrients total phosphorus (Tot-P), orthophosphate (PO4-P) and total nitrogen (Tot-N).Inshore−offshore exchange of water was mediated by flows from daily and sub-daily water level fluctuations and wind-driven currents. As a daily average, 2% of the Murchison Bay flowed in and out and the incoming wastewater was diluted 9.7 times.During the dry season from June to August (D2), when the weather was influenced by the south-east monsoon, the thermal stratification in the main lake disappeared and cooler and deoxygenated water from deeper depths entered the bay influencing its water quality.The daily flushing of water in and out of the bay due to water level variation was identified as the main factor diluting the bay water.  相似文献   

12.
Surveys of stranded marine debris around Motupore Island, a small island in Bootless Bay, Papua New Guinea, revealed exceptionally high loads (up to 78.3itemsm(-2)), with major concentrations in mangrove-dominated, depositional areas. The worst affected, 50-m stretch of shore was estimated to contain >37.000 items with a combined weight of 889kg. Consistent with studies elsewhere, plastics comprised by far the majority of debris across all sites (89.7%). The lack of centralised waste collection and limited village-based resources, coupled with an increasing population, suggests that this issue is a long way from solution. High debris loads thwart attempts to rehabilitate depleted mangrove forests through smothering of seedlings, perpetuating run-off and water quality issues in the bay. Addressing marine debris is thus of fundamental importance for the sustainability of Bootless Bay and its resources, and a critical step in promoting ecosystem resilience.  相似文献   

13.
An in situ monitoring of the sediment characteristics and macrobenthic communities was undertaken at a marine fish culture site in subtropical waters of Hong Kong before and after the deployment of biofilters which were made of cement concrete artificial reef (AR) structures. According to the distance to the boundary of the fish cages, 6 points were selected as sampling stations: 2 at the fish cages, 2 near the boundary of the fish culture area, and 2 reference sites further away from the culture area. Bimonthly sediment samples were collected for analysis of silt-clay fraction (SCF), moisture content (MC), total organic carbon (TOC), total Kjeldahl nitrogen (TKN) and total phosphorus (TP). The macrobenthos (>0.5mm) present in the sediment were sorted, identified and enumerated. TOC, TKN and TP levels at the fish cage stations were consistently higher than those at the reference stations over the 1-year pre-AR and 2-year post-AR deployment monitoring period. The diversity of macrofauna was significantly reduced at the fish cage stations relative to the reference sites. The intermediary stations near the fish culture area showed a transitional state of disturbance. Over the 2-year post-AR deployment period, TOC, TKN and TP showed a decreasing trend at the fish cage and intermediary stations. More diverse macrofaunal communities were recorded at the fish cage stations, with species diversity H'increasing from 0-1 at the beginning of the AR deployment to H'>2 at the end of the study. The present results demonstrated that artificial reefs can improve the benthic abiotic environment and biotic conditions beneath fish rafts which are deteriorated due to farming activities.  相似文献   

14.
Nagahama Bay of Satsuma Iwo‐Jima Island, southwest Japan, is an excellent place for studying sedimentation of iron‐oxyhydroxides by shallow‐marine low‐temperature hydrothermal activity. Its fishing port has a narrow entrance that limits exchange of seawater between the bay and open ocean, allowing the accumulation of fine‐grained precipitates of iron‐bearing materials (Fe‐oxyhydroxides) on the seafloor. The fishing port is usually filled with orange‐ to brown‐colored Fe‐rich water, and deposits >1.5 m thick Fe‐rich sediments. To elucidate the movement and depositional processes of the Fe‐rich precipitates in the bay, we conducted continuous profiling of turbidity throughout the tidal cycle and monitoring of surface water. The results showed that clear seawater entered the bay during the rising tide, and turbid colored water flowed into the ocean during the ebb tide. Neap tide was found to be an optimal condition for sedimentation of Fe‐oxyhydroxides due to weak tidal currents. Storms and heavy rains were also found to have influenced precipitation of Fe‐oxyhydroxides. Storm waves disturbed the bottom sediments, resulting in increased turbidity and rapid re‐deposition of Fe‐oxyhydroxides with an upward‐fining sequence. Heavy rain carried Fe‐oxyhydroxides originally accumulated in nearby beach sands to the bay. Our findings provide information on optimal conditions for the accumulation of Fe‐rich sediments in shallow‐marine hydrothermal settings.  相似文献   

15.
Puerto Galera Bay is a coastal lagoon with a variety of marine habitats and high species diversity. It is an area in the Phillippines where the growing influence of human activities is affecting the quality of its marine resources. This study examined the distribution and behaviour of nutrients and the physical hydrography of Puerto Galera Bay and determined how its physico-chemical nature affected the condition of biotic components in the bay. The relative importance of the nitrogen and phosphorus signals were used as indicators to implicate the influence of sewage and run-off into the bay. A nutrient pool accumulated in the bay as a result of low flushing rates. The interaction of hydrodynamic forcing with the biota have implications on the phytoplankton production and coral communities in the area.  相似文献   

16.
We applied stable carbon isotopes, ultraviolet-visible absorption(UV-Vis), fluorescence excitation-emission matrices spectroscopy(EEMs), and Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR-MS) to investigate the chemical composition and sources of the dissolved organic matter(DOM) in both the water column and pore water in Xiangshan Bay, a representative semi-enclosed and eutrophic bay in Zhejiang Province, China. One protein-like fluorescent component(C1) and two humic-like fluorescent components(C2 and C3) were identified by PARAFAC modeling. The concentration of dissolved organic carbon(DOC), the relative intensities of C2, C3, and black carbon-like compounds are all negatively correlated with salinity, indicating that there is a dilution effect of terrestrial signals by seawater in Xiangshan Bay. The differences in light penetration ability of Xiangshan Bay cause different degrees of photo-degradation, which may play an important role in the transformation of organic matter in Xiangshan Bay. The weak correlation between the C1 fluorescent component and salinity indicates that autochthonous sources cannot dominate the protein-like FDOM in the Xiangshan Bay drainage area. Multiple sources(such as anthropogenic inputs and release of pore water) also affect the distribution of the protein-like fluorescent component under eutrophication conditions. The relative proportion of the protein-like fluorescent component in Xiangshan Bay is on a medium level in China and anthropogenic inputs may be a significant source of DOM in coastal bays.  相似文献   

17.
《Marine pollution bulletin》2009,58(6-12):652-661
An in situ monitoring of the sediment characteristics and macrobenthic communities was undertaken at a marine fish culture site in subtropical waters of Hong Kong before and after the deployment of biofilters which were made of cement concrete artificial reef (AR) structures. According to the distance to the boundary of the fish cages, 6 points were selected as sampling stations: 2 at the fish cages, 2 near the boundary of the fish culture area, and 2 reference sites further away from the culture area. Bimonthly sediment samples were collected for analysis of silt-clay fraction (SCF), moisture content (MC), total organic carbon (TOC), total Kjeldahl nitrogen (TKN) and total phosphorus (TP). The macrobenthos (>0.5 mm) present in the sediment were sorted, identified and enumerated. TOC, TKN and TP levels at the fish cage stations were consistently higher than those at the reference stations over the 1-year pre-AR and 2-year post-AR deployment monitoring period. The diversity of macrofauna was significantly reduced at the fish cage stations relative to the reference sites. The intermediary stations near the fish culture area showed a transitional state of disturbance. Over the 2-year post-AR deployment period, TOC, TKN and TP showed a decreasing trend at the fish cage and intermediary stations. More diverse macrofaunal communities were recorded at the fish cage stations, with species diversity H′increasing from 0–1 at the beginning of the AR deployment to H′ > 2 at the end of the study. The present results demonstrated that artificial reefs can improve the benthic abiotic environment and biotic conditions beneath fish rafts which are deteriorated due to farming activities.  相似文献   

18.
To assess risks of chemically-dispersed oil to marine organisms, oil concentrations in the water were simulated using a hypothetical spill accident in Tokyo Bay. Simulated oil concentrations were then compared with the short-term no-observed effect concentration (NOEC), 0.01 mg/L, obtained through toxicity tests using marine diatoms, amphipod and fish. Area of oil concentrations higher than the NOEC were compared with respect to use and non-use of dispersant. Results of the simulation show relatively faster dispersion near the mouth of the bay compared to its inner sections which is basically related to its stronger water currents. Interestingly, in the inner bay, a large area of chemically-dispersed oil has concentrations higher than the NOEC. It seems emulsifying oil by dispersant increases oil concentrations, which could lead to higher toxicity to aquatic organisms. When stronger winds occur, however, the difference in toxic areas between use and non-use of dispersant is quite small.  相似文献   

19.
A combination of geophysical methods including continuous electrical resistivity and high-resolution Chirp sub-bottom profiling were utilized to characterize geologic controls on pore fluid salinity in the nearshore of Long Bay, SC. Resistivity values ranged from less than 1 Ω m to greater than 40 Ω m throughout the bay. Areas of elevated electrical resistivity suggest the influence of relatively fresher water on pore water composition. Geophysical evidence alone does not eliminate all ambiguity associated with lithological and porosity variations that may also contribute to electrical structure of shallow marine sediments. The anomalous field is of sufficient magnitude that lithological variation alone does not control the spatial distribution of elevated electrical resistivity zones. Geographical distribution of electrical anomalies and structures interpreted from nearby sub-bottom profiles indicates abrupt changes in shallow geologic units control preferential pathways for discharge of fresh water into the marine environment. Shore parallel resistivity profiles show dramatic decreases in magnitude with increasing distance from shore, suggesting a significant portion of the terrestrially driven fresh SGD in Long Bay is occurring via the surficial aquifer within a few hundred meters of shore.  相似文献   

20.
The environmental impact of marine fish culture: Towards a sustainable future   总被引：42，自引：0，他引：42  
The environmental impact of marine fish-farming depends very much on species, culture method, stocking density, feed type, hydrography of the site and husbandry practices. In general, some 85% of phosphorus, 80–88% of carbon and 52–95% of nitrogen input into a marine fish culture system as feed may be lost into the environment through feed wastage, fish excretion, faeces production and respiration. Cleaning of fouled cages may also add an organic loading to the water, albeit periodically. Problems caused by high organic and nutrient loadings conflict with other uses of the coastal zone. The use of chemicals (therapeutants, vitamins and antifoulants) and the introduction of pathogens and new genetic strains have also raised environmental concerns.

Despite the high pollution loadings, results from various studies show that some 23% of C, 21% of N and 53% of P of feed input into the culture system is being accumulated in the bottom sediments and the significant impact is normally confined to within 1 km of the farm. The major impact is on the sea bottom, where high sediment oxygen demand, anoxic sediments, production of toxic gases and a decrease in benthic diversity may result. Decreases in dissolved oxygen and increases in nutrient levels in the water are also evident but are normally confined to the vicinity of the farm. Tributyltin (TBT) contamination and the development of antibiotic-resistant bacteria have been reported near fish farms. The stimulating effects of vitamins/fish wastes on growth of red tide species have been demonstrated in a number of laboratory studies. Nevertheless, there is no evidence to support the suggestion that the present use of therapeutants, vitamins and antibiotics and the introduction of pathogens and new genetic strains would pose a significant threat to the environment.

Marine fish culture can be a sustainable development, provided pollution loadings generated by fish farms are kept well below the carrying capacity of the water body. Effects can be significantly reduced by careful site selection, control of stock density, improved feed formulation and integrated culture (with macroalgae, filter-feeders and deposit-feeders). An example of the application of computer modelling in mariculture management is demonstrated. Environmental impact assessment and monitoring should also be carried out to ensure culture activities are environmentally sustainable.  相似文献   


设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号