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1.
Understanding the behaviour and variability of environmental tracers is important for their use in estimating groundwater discharge to rivers. This study utilizes a multi‐tracer approach to quantify groundwater discharge into a 27 km upland reach of the Gellibrand River in southwest Victoria, Australia. Ten sampling campaigns were conducted between March 2011 and June 2012, and the distribution of 222Rn activities, Cl and 3H concentrations imply the river receives substantial groundwater inflows. Mass balances based on 222Rn, Cl and 3H yield estimates of groundwater inflows that agree to within ± 12%, with cumulative inflows in individual campaigns ranging from 24 346 to 88 467 m3/day along the studied river section. Groundwater discharge accounts for between 10 and 50% of river flow dependent on the time of year, with a high proportion (>40 %) of groundwater sustaining summer flows. Groundwater inflow is largely governed by regional groundwater flowpaths; between 50 and 90% of total groundwater inflows occur along a narrow 5–10 km section where the river intersects the Eastern View Formation, a major regional aquifer. Groundwater 222Rn activities over the 16 month period were spatially heterogeneous across the catchment, ranging between 2000 Bq/m3 and 16 175 Bq/m3. Although groundwater 222Rn activities display temporal variation, spatial variation in groundwater 222Rn is a key control on 222Rn mass balances in river catchments where groundwater and river 222Rn activities are within an order of magnitude of each other. Calculated groundwater discharges vary from 8.4 to 15 m3/m/day when groundwater 222Rn activities are varied by ± 1 σ. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

2.
Yong Hwa Oh  Guebuem Kim 《水文研究》2016,30(14):2525-2532
Activities of radon (222Rn) in groundwater were continuously monitored in a saline aquifer from September 2010 to July 2011. The activities of 222Rn ranged from 200 to 4300 Bq m?3, with a large seasonal variation. Because the activity of 222Rn in seawater is low, 222Rn in saline groundwater must be produced in the aquifer from radium (226Ra) in rocks and sediments. The 222Rn activities were higher in the warm‐dry seasons (September–November 2010 and April–May 2011) when the saline aquifer was stable. In contrast, the lowest 222Rn activities were observed in the cold‐dry season (December 2010 and January–March 2011), because of the effective exchange between groundwater and seawater. In addition, sudden decreases of 222Rn activities coincided with episodic drops in groundwater temperatures. These results reveal that lower seawater temperature in winter may result in density‐driven seawater intrusion. During the wet season (June–July 2011), 222Rn activities were more clearly affected by semi‐monthly and diurnal tidal pumping, showing higher 222Rn activities during low and spring tides. Such a tidal effect was not clearly observed during the warm‐dry and cold‐dry seasons. This result implies that the residence time of SGD in coastal zones is significantly affected by seasonal changes in driving forces such as tidal pumping and seawater intrusion. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

3.
Discharge in mountain streams may be a mixture of snowmelt, water from surface runoff, and deep return flow through valley bottom alluvia. We used δ18O and δ2H, solute concentrations, and 222Rn to determine water sources of a headwater stream located at the McDonald Creek watershed, Glacier National Park, USA, during summer recession flow period. We analysed minimal water isotope ranges of ?17.6‰ to ?16.5‰ and ?133‰ to ?121‰ for δ18O and δ2H, respectively, potentially due to dominance of snow‐derived water in the stream. Likewise, solute concentrations measured in the stream through the watershed showed minimal variation with little indication of subsurface water input into the stream. However, we observed 222Rn activities in the stream that ranged from 39 to 2646 Bq/m3 with the highest value measured in middle of the watershed associated with channel constriction corresponding to changes in local orientation of underlying rocks. Downstream from this point, 222Rn activity decreased from 581 to 117 Bq/m3 in a series of punctuated steps associated with small rapids and waterfalls that we hypothesized to cause radon degassing with a maximum predicted loss of 427 Bq/m3 along a 400 m distance. Based on mass balance calculations using 222Rn activity values, streamflow, and channel characteristics, we estimated that groundwater contributed between 0.3% and 29% of total flow. Overall, we estimated a 5.9% of groundwater contribution integrated for stream reach measured at McDonald Creek during recession flow period. Finally, a lower mean hyporheic flux of 14 m3/day was estimated compared to the groundwater flux of 70 710 m3/day. These assessments highlight the potential for radon as a conservative tracer that can be used to estimate subsurface water contribution in mountain streams within a complex geologic setting. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

4.
The field radiometric and laboratory measurements were performed at the Sin Quyen copper deposit in North Vietnam. The field gamma-ray spectrometry indicated the concentration of uranium ranging from 5.5 to 87 ppm, thorium from 5.6 to 33.2 ppm, and potassium from 0.3 to 4.7%. The measured dose rates ranged from 115 to 582 nGy/h, the highest doses being at the copper ore. Concentrations in the solid samples were in the range of 20–1700 Bq/kg for uranium, 20–92.7 Bq/kg for thorium, and 7–1345 Bq/kg for potassium. The calculated doses were from 22 to 896 nGy/h; both measured and calculated dose rates are mostly related to uranium. Concentrations of radium in water samples were below 0.17 Bq/L. Uranium in water samples was significantly higher than the hydrogeological background; the maximum of 13 Bq/L was at the waste zone pool, but neither radium nor uranium were present in tap water. Radon concentration in the dwelling air was from 42 to 278 Bq/m3 for 222Rn and from 8 to 193 Bq/m3 for 220Rn. The estimated committed dose rates were principally related to 222Rn concentration and ranged from 1.1 to 8.1 mSv/y.  相似文献   

5.
Submarine groundwater discharges (SGD) were investigated in a marine watershed in south‐eastern Korea using water budget analysis and a 222Rn mass balance model. Multi‐layered TOPMODEL added hydrological assumption was used to estimate groundwater components in the water budget analysis. Field observations of soil moisture, rainfall, runoff and groundwater fluctuations were used for calibration and validation of the hydrologic model. Based on observed hydrological data and terrain analyses, parameters for the hydrologic model were delineated and used to describe several hydrologic responses in the watershed. SGD estimations by 222Rn mass balance method were also performed at Il‐Gwang bay in July, 2010, and May, June, July and Nov. 2011. The estimated groundwater through hydrologic modeling and water balance analysis was 1.3x106 m3/year, which rapidly increased during typhoon season due to heavy rainfall and permeable geologic structure. The estimated groundwater was approximately 3.7–27.1% of SGD as evaluated by 222Rn mass balance method ranges 3.44 and 17.45 m3m?2year?1. Even though SGD is predominantly influenced by tide fluctuation, the head gradient (difference) from hydrologic processes associated with heavy rainfalls can also have extra significant influences. Comprehensive understanding of SGD evaluation can be improved through a simultaneous application of both these approaches. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

6.
Continuous radon (222Rn) monitoring was conducted at two stations (site A and site B) with different perpendicular distance from the shoreline in Xiangshan Bay, East China Sea. Based on a 222Rn balance model (various sources and sinks of 222Rn in coastal water), the average rate of SGD was estimated to be 0.69 cm/day and 0.23 cm/day for site A and site B, respectively. The results from a nutrient analysis of the groundwater indicate that the associated nutrients fluxes loading through the SGD pathway were 4.27 × 106 mol/day for DIN, 2.24 × 104 mol/day for DIP and 1.82 × 106 mol/day for DSi, respectively, which were comparable to or even higher than the levels observed in the local streams. Therefore, adequate attention should be paid to the importance of SGD as one source of nutrients during the eutrophication control process in this area.  相似文献   

7.
In the Long Valley caldera, where seismicity has continued essentially uninterrupted since mid-1980 and uplift is documented, samples of water from hot, warm, and cold springs have been collected since September, 1982, and their222Rn concentrations analyzed. Concurrently, rocks encompassing the hydrologic systems feeding the springs were analyzed for their radioelement contents, because their uranium is the ultimate source of the222Rn in the water.The222Rn concentration in the springs varies inversely with their temperature and specific conductance. High concentrations (1500 to 2500 picocuries per liter) occur in dilute cold springs on the margins of the caldera, while low contents (12 to 25 pCi/l) occur in hot to boiling springs. Springwater radon concentrations also correlate slightly with the uranium content of the encompassing rocks.A continuous monitoring system was installed in August, 1983, at a spring issuing from basalt, to provide hourly records of radon concentration. A gamma detector is submerged in a natural pool, and we have observed that the radioactivity measured in this manner is due almost entirely to the222Rn concentration of the water. Initial operation shows diurnal and semidiurnal variations in the222Rn concentration of the springwater that are ascribed to earth tides, suggesting that those variations are responding to small changes in stress in the rocks encompassing the hydrologic system.  相似文献   

8.
Semiarid rivers are often characterized by chains of small pools connected by riffles and wet meadows. The pools can be maintained by wet season surface runoff, groundwater discharge, or some combination thereof. Using synoptic surveys for several environmental tracers (δD and δ18O of H2O, specific electrical conductance at 25°C [EC], chloride and 222Rn), we evaluated the groundwater—surface water connectivity of the Light River (South Australia) along an 8 km section in the vicinity of a proposed mining development. In all three surveys (representing spring, summer and winter conditions), the pools were maintained by regional groundwater discharge based on an elevated surface water EC (9–12 dS m−1) similar to regional groundwater, elevated radon-222 activities (0.09–3.0 Bq L−1) and low rainfall. Most pools were perennial, either because they directly received groundwater discharge or, indirectly, had an inflow originating from upstream groundwater-fed pools. The elevated salinity of regional groundwater is a key factor for the maintenance of perennial pools in the Light River because the potential for baseflow depletion by groundwater pumping is more limited.  相似文献   

9.
The objective of this study was to investigate whether 222Rn in groundwater can be used as a tracer for light non‐aqueous phase liquid (LNAPL) quantification at a field site treated by dual‐phase LNAPL removal. After the break of a pipeline, 5 ha of soil in the nature reserve Coussouls de Crau in southern France was contaminated by 5100 m3 of crude oil. Part of this oil seeped into the underlying gravel aquifer and formed a floating oil body of about 3.9 ha. The remediation consists of plume management by hydraulic groundwater barriers and LNAPL extraction in the source zone. 222Rn measurements were performed in 21 wells in and outside the source zone during 15 months. In uncontaminated groundwater, the radon activity was relatively constant and remained always >11 Bq/L. The variability of radon activity measurements in wells affected by the pump‐and‐skim system was consistent with the measurements in wells that were not impacted by the system. The mean activities in wells in the source zone were, in general, significantly lower than in wells upgradient of the source zone, owing to partitioning of 222Rn into the oil phase. The lowest activities were found in zones with high non‐aqueous phase liquid (NAPL) recovery. LNAPL saturations around each recovery well were furthermore calculated during a period of high groundwater level, using a laboratory‐determined crude oil–water partitioning coefficient of 38.5 ± 2.9. This yielded an estimated volume of residual crude oil of 309 ± 93 m3 below the capillary fringe. We find that 222Rn is a useful and cheap groundwater tracer for finding zones of good LNAPL recovery in an aquifer treated by dual‐phase LNAPL removal, but that quantification of NAPL saturation using Rn is highly uncertain.  相似文献   

10.
The dynamics of size-fractionated phytoplankton along the salinity gradient in the Pearl River Estuary and the adjacent near-shore oceanic water was investigated using microscopic, flow cytometric, and chlorophyll analyses in the early spring (March) and early autumn (September) of 2005. In the inner part of the estuary where salinity was less than 30, the phytoplankton community was dominated by micro- and nano-sized (3–200 μm) cells, particularly the diatom Skeletonema costatum, both in early spring and early autumn. In areas where salinity >30, including the mixing zone and nearshore oceanic water, micro- and nano-sized cell populations dominated the phytoplankton assemblage during early spring when influence of river discharge was minimal, whereas pico-sized (≤3 μm) cell populations were dominant during early autumn as a result of strong river discharge in the summer, with Synechococcus and pico-eukaryotes being predominant. Picophytoplankton were two orders of magnitude more abundant in early autumn (106 cells mL−1) than in early spring in the nearshore oceanic water. Nutrients delivered by freshwater input to the estuary were pushed toward high salinity (>30) areas as a result of short residence time, exerting a strong influence on phytoplankton abundance, especially picophytoplankton in the nearshore, otherwise oligotrophic, water. Influenced by high abundance of DIN and limitation in phosphorus, picophytoplankton in the adjacent nearshore oceanic water rose to prominence seasonally. Our results indicate that eutrophication in the Pearl River Estuary not only stimulates the growth of S. costatum in the nutrient-rich areas of the estuary but also appears to promote the growth of Synechococcus and pico-eukaryotes in the adjacent usually oligotrophic oceanic water at least during our autumn cruise.  相似文献   

11.
Groundwater discharge flux into rivers (riverine groundwater discharge or RGD) is essential information for the conservation and management of aquatic ecosystems and resources. One way to estimate area-integrated groundwater discharge into surface water bodies is to measure the concentration of a groundwater tracer within the water body. We assessed groundwater discharge using 222Rn, a tracer common in many surface water studies, through field measurements, surface water 222Rn mass balance model, and groundwater flow simulation, for the seldom studied but ubiquitous setting of a flooding river corridor. The investigation was conducted at the dam-regulated Lower Colorado River (LCR) in Austin, Texas, USA. We found that 222Rn in both the river water and groundwater in the river bank changed synchronously over a 12-hour flood cycle. A 222Rn mass balance model allowed for estimation of groundwater discharge into a 500-m long reach of the LCR over the flood. The groundwater discharge ranged between negative values (indicating recharge) to 1570 m3/h; groundwater discharge from groundwater flow simulations corroborated these estimates. However, for the dynamic groundwater discharge estimated by the 222Rn box model, assuming whether the groundwater 222Rn endmember was constant or dynamic led to notably different results. The resultant groundwater discharge estimates are also highly sensitive to river 222Rn values. We thus recommend that when using this approach to accurately characterize dynamic groundwater discharge, the 222Rn in near-stream groundwater should be monitored at the same frequency as river 222Rn. If this is not possible, the 222Rn method can still provide reasonable but approximate groundwater discharge given background information on surface water-groundwater exchange time scales.  相似文献   

12.
Extensive mud deposits superimposed on the predominantly sandy inner continental shelf adjacent to the Patos Lagoon estuary, indicates that the Lagoon is a potential source of fine sediments to the coastal sedimentary system. The lagoon is large and shallow, and the water movement is mainly controlled by wind-driven set-up and set-down. The mean river inflow is around 2000 m3 s−1, although peak flow rates exceeding 20,000 m3 s−1 have been observed during El Niño periods. Though the tidal elevations are small, tidal velocities in the lagoon's inlet can be significant due to the large extension of the backwaters. Moreover, significant exchange flows can be generated between the estuary and coastal area due to barotropic pressure gradients established as a function of wind and freshwater discharge. The predominant net flow is seawards, but opposite near-bed flows due to pronounced vertical salinity stratification can also be observed. The coastal area is characterized by small tidal effects, large scale ocean circulation, wind-induced residual flows and wave-driven currents, where the waves originate from swell or are locally generated.  相似文献   

13.
Given that the concentration of 222Rn in groundwater is much higher than that in surface water and that its radioactive half‐life (3.83 d) is short, 222Rn is an effective tracer of groundwater–surface water interactions. In this study, a new mass balance method is presented, which can be used to estimate specific groundwater–surface water interactions within a river reach. Three possible situations of interaction between groundwater and surface water are considered, and equations based on the mass conservation of 222Rn are formulated for judging specific groundwater–surface water interaction processes and for calculating water flux. A case study was conducted for the Nalenggele River, Northwest China, to demonstrate the usefulness of this method. Samples of river water and groundwater containing 222Rn were collected from the study area to estimate the interactions between groundwater and surface water. The amount of water exchanged during these interactions was estimated and the results show that transformations between groundwater and surface water are frequent along the stream. The 222Rn mass balance method is highly sensitive for studying such interactions, even in areas for which conventional hydrologic data are sparse. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

14.
Two sampling cruises conducted in the Seine estuary (France) under low-water and flood conditions produced high resolution profiles for dissolved cadmium, lead, copper, zinc and nickel concentrations versus salinity. The distribution of dissolved trace metals differed depending on hydrologic conditions, partly because of the dilution of upstream inputs during flood periods. Daily fluxes of these dissolved trace metals were estimated for the two sampling periods (September 1994 and February 1995) by extrapolating the dilution lines observed in higher salinity waters to salinity=0 and then multiplying the effective freshwater concentrations thus obtained by the corresponding freshwater flow. Several procedures were subsequently applied to deduce each daily flux for the year studied from data for these two periods. A consensus was found among these procedures, allowing the determination of net fluxes of dissolved trace metals with a precision of 20–35%. The net fluxes thus estimated were 4 T yr−1 for Cd, 4 T yr−1 for Pb, 40 T yr−1 for Cu, 130 T yr−1 for Zn and 50 T yr−1 for Ni.  相似文献   

15.
The air–sea ice CO2 flux was measured over landfast sea ice in the Chukchi Sea, off Barrow, Alaska in late May 2008 with a chamber technique. The ice cover transitioned from a cold early spring to a warm late spring state, with an increase in air temperature and incipient surface melt. During melt, brine salinity and brine dissolved inorganic carbon concentration (DIC) decreased from 67.3 to 18.7 and 3977.6 to 1163.5 μmol kg−1, respectively. In contrast, the salinity and DIC of under-ice water at depths of 3 and 5 m below the ice surface remained almost constant with average values of 32.4±0.3 (standard deviation) and 2163.1±16.8 μmol kg−1, respectively. The air–sea ice CO2 flux decreased from +0.7 to −1.0 mmol m−2 day−1 (where a positive value indicates CO2 being released to the atmosphere from the ice surface). During this early to late spring transition, brought on by surface melt, sea ice shifted from a source to a sink for atmospheric CO2, with a rapid decrease of brine DIC likely associated with a decrease in the partial pressure of CO2 of brine from a supersaturated to an undersaturated state compared to the atmosphere. Formation of superimposed ice coincident with melt was not sufficient to shut down ice–air gas exchange.  相似文献   

16.
Pore water radon (222Rn) distributions from Indian River Lagoon, Florida, are characterized by three zones: a lower zone where pore water 222Rn and sediment-bound radium (226Ra) are in equilibrium and concentration gradients are vertical; a middle zone where 222Rn is in excess of sediment-bound 226Ra and concentration gradients are concave-downward; and an upper zone where 222Rn concentration gradients are nearly vertical. These 222Rn data are simulated in a one-dimensional numerical model including advection, diffusion, and non-local exchange to estimate magnitudes of submarine groundwater discharge components (fresh or marine). The numerical model estimates three parameters, fresh groundwater seepage velocity, irrigation intensity, and irrigation attenuation, using two Monte Carlo (MC) simulations that (1) ensure the minimization algorithm converges on a global minimum of the merit function and the parameter estimates are consistent within this global minimum, and (2) provide 90% confidence intervals on the parameter estimates using the measured 222Rn activity variance. Model estimates of seepage velocities and discharge agree with previous estimates obtained from numerical groundwater flow models and seepage meter measurements and show the fresh water component decreases offshore and varies seasonally by a factor of nine or less. Comparison between the discharge estimates and precipitation patterns suggests a mean residence time in unsaturated and saturated zones on the order of 5 to 7 months. Irrigation rates generally decrease offshore for all sampling periods. The mean irrigation rate is approximately three times greater than the mean seepage velocity although the ranges of irrigation rates and seepage velocities are the same. Possible mechanisms for irrigation include density-driven convection, wave pumping, and bio-irrigation. Simulation of both advection and irrigation allows the separation of submarine groundwater discharge into fresh groundwater and (re)circulated lagoon water.  相似文献   

17.
We calculated statistical average of thermal data to speculate regional thermal structure of the forearc area of the Japanese Islands. The three thermal statistical averages show a difference of a high thermal regime in the western part of forearc inner zone and a low in the Kanto forearc outer zone. The Kanto zone marks 18 K km−1 for mean geothermal gradient, 44 mW m−2 for mean heat flow, while the western inner zone shows 27 K km−1 for mean geothermal gradient, 63 mW m−2 for mean heat flow. The geothermal gradients of the Nobi Plain and the Osaka Plain in the western inner zone are 29 and 36 K km−1, respectively, while the value of the Kanto Plain in the Kanto zone is 21 K km−1. Taking account of the effect of accumulation of sediments, we see the difference in the thermal regime between the plains and conclude that the difference is significant. Heat flux in the crust depends on the volume of granite rich in radioactive elements. There are few granitic rocks in the Kanto zone, while granitic rocks are dominant in the western inner zone. The heat flow of 20 mW m−2 is attributed to the granitic rocks of about 8 km in thickness. There are two oceanic plate subductions of the Pacific plate and the Philippine Sea plate under the Kanto zone, while only the Philippine Sea plate has been subducting under the western inner zone. The model simulation based on thermal and subduction model shows a heat flow ranging 50-60 mW m−2 in the southwest Japan forarc area and a low value of about 20 mW m−2 in the northeast Japan forearc area. The heat flux from the cooling oceanic lithosphere depends on the age of plate. The Shikoku Basin, a part of the Philippine Sea plate, off the western inner zone is 15-30 Ma, while the Pacific plate off the Kanto zone is 122-132 Ma. Theoretically, heat flux values of 15 and 50 Ma oceanic plates range 60-120 mW m−2 and those of 122-132 Ma could be about 10 mW m−2. If the heat flux contribution from the Philippine Sea plate under the Kanto zone is smaller than the plate under the western inner zone, there could be a thermal regime difference in order of several tens of mW m−2. Conclusively, the cause of the difference of heat flux could be the uneven granitic rocks distribution and/or the difference of heat flux between the two subducting plate.  相似文献   

18.
The physical aspects of the Subtropical Shelf Front (STSF) for the Southwest Atlantic Continental Shelf were previously described. However, only scarce data on the biology of the front is available in the literature. The main goal of this paper is to describe the physical, chemical and biological properties of the STSF found in winter 2003 and summer 2004. A cross-section was established at the historically determined location of the STSF. Nine stations were sampled in winter and seven in summer. Each section included a series of conductivity-temperature-depth (CTD) stations where water samples from selected depths were filtered for nutrient determination. Surface samples were taken for chlorophyll a (Chl-a) determination and plankton net tows carried out above and below the pycnocline. Results revealed that winter was marked by an inner-shelf salinity front and that the STSF was located on the mid-shelf. The low salinity waters in the inner-shelf indicated a strong influence of freshwater, with high silicate (72 μM), suspended matter (45 mg l−1), phosphate (2.70 μM) and low nitrate (1.0 μM) levels. Total dissolved nitrogen was relatively high (22.98 μM), probably due to the elevated levels of organic compound contribution close to the continental margin. Surface Chl-a concentration decreased from coastal well-mixed waters, where values up to 8.0 mg m−3 were registered, to offshore waters. Towards the open ocean, high subsurface nutrients values were observed, probably associated to South Atlantic Central Waters (SACW). Zooplankton and ichthyoplankton abundance followed the same trend; three different groups associated to the inner-, mid- and outer-shelf region were identified. During summer, diluted waters extended over the shelf to join the STSF in the upper layer; the concentration of inorganic nutrients decreased in shallow waters; however, high values were observed between 40 and 60 m and in deep offshore waters. Surface Chl-a ranged 0.07–1.5 mg m−3; winter levels were higher. Three groups of zoo and ichthyoplankton, separated by the STSF, were also identified. Results of the study performed suggest that the influence of freshwater was stronger during winter and that abundance distribution of Chl-a, copepods and ichthyoplankton was related to the Plata Plume Waters (PPW), rather than to the presence of the STSF. During summer, when the presence of freshwater decreases, plankton interactions seem to take place in the STSF.  相似文献   

19.
Conductivity-temperature-depth (CTD) observations taken in the Great Australian Bight (GAB) during ORV Franklin cruise Fr 07/94 in July 1994 indicated the presence of a dense bottom layer at the head of the GAB, which flowed along the sea floor towards the shelf-break as a gravity current The north central region of the GAB was stratified with a maximum salinity difference of between 0.4 and 0.5. The outflow was confined to the shelf and was directed in a south-easterly direction with little evidence of cross-shelf transport. The flow exhibited a well-defined bottom interface evident from the head of the GAB to near the mouth of Spencer Gulf (SG), where the surface-bottom salinity difference was about 0.3. The mean thickness of the outflow was about 15 m. An estimate of the speed of the outflow at the discharge over the shelf-break was made using the zero entrainment assumption. This yielded a speed of <16 cm s−1, which remarkably was consistent with near bottom current meter measurements (16 cm s−1) on the continental shelf edge, reported south of the Eyre Peninsula. A mass budget analysis indicated that the outflow, which probably is partially maintained by the gravity current and partly by a wind-driven circulation would exist over the period, July–December, with a peak transport of about 106 m3s−1 (1 Sverdrup) which is approximately twenty times that of the bottom outflow from the adjoining Spencer Gulf.  相似文献   

20.
To investigate how salinity changes with abrupt increases and decreases in river discharge, three surveys were conducted along six sections around the Yellow River mouth before, during and after a water regulation event during which the river discharge was increased from ∼200 to >3000 m3 s−1 for the first 3 days, was maintained at >3000 m3 s−1 for the next 9 days and was decreased to <1000 m3 s−1 for the final 4 days. The mean salinity in the Yellow River estuary area during the event varied ∼1.21, which is much larger than its seasonal variation (∼0.50) and interannual variation (∼0.05). Before the event, a small plume was observed near the river mouth. During the event, the plume extended over 24 km offshore in the surface layer in the direction of river water outflow. After the event, the plume diminished in size but remained larger than before the event. The downstream propagation of the plume (as in a Kelvin wave sense) was apparent in the bottom layer during the second survey and in both the surface and bottom layers during the third survey. The plume sizes predicted by the formulas from theoretical studies are larger than those we observed, indicating that factors neglected by theoretical studies such as the temporal variation in river discharge and vertical mixing in the sea could be very important for plume evolution. In addition to the horizontal variation of the plume, we also observed the penetration of freshwater from the surface layer into the bottom layer. A comparison of two vertical processes, wind mixing and tidal mixing, suggests that the impact of wind mixing may be comparable with that of tidal mixing in the area close to the river mouth and may be dominant over offshore areas. The change in Kelvin number indicates an alteration of plume dynamics due to the abrupt change in river discharge during the water regulation event.  相似文献   

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