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1.
用镭同位素评价海水滞留时间及海底地下水排泄   总被引：3，自引：0，他引：3  
海底地下水排泄(submarine groundwater discharge, SGD)难以直接测量, 镭同位素和氡-222等天然示踪剂使得间接评价SGD通量成为可能.为了评价五缘湾的水体滞留时间和SGD通量, 实测了湾内海水、湾外海水和地下水中224Ra和226Ra的活度, 利用224Ra和226Ra半衰期的差异, 采用224Ra与226Ra的活度比值计算湾内水团的年龄和平均滞留时间, 利用224Ra和226Ra的质量平衡模型计算SGD通量.五缘湾13个站位的水团年龄在0.6~2.4 d之间, 湾顶水团年龄相对较大, 平均海水滞留时间1.4 d.地下水输入五缘湾的224Ra和226Ra通量分别为5.17×106 Bq/d和5.28×106 Bq/d, 将该通量用地下水端元的活度转换成为SGD通量分别是0.21 m3/m2/d(224Ra平衡模型)和0.23 m3/m2/d(226Ra平衡模型), 两种模型的结果较接近, 其平均值0.22 m3/m2/d可作为五缘湾的海底地下水排泄通量.   相似文献   

2.
The “Water-Sediment Regulation Scheme” (WSRS) is critically important to the hydrologic evaluation of the Yellow River estuary since a huge pulse of water and sediment are delivered into the sea during a short period. We used the natural geochemical tracers radium (223Ra, 224Ra, 226Ra) and radon (222Rn) isotopes as well as other hydrological parameters to investigate the mixing variations and submarine groundwater discharge (SGD) in the Yellow River estuary under the influence of the 2013 WSRS. Dramatically elevated radium and radon isotopic activities were observed during this WSRS compared with activities measured during a non-WSRS period. Radium “water ages” indicated that the offshore transport rate nearly tripled when the river discharge increased from 400 to 3400 m3/s. We calculated the SGD flux in the Yellow River estuary based on a radium mass balance model as well as radium and radon time-series models. The SGD flux was estimated at 0.02~0.20 m/day during a non-WSRS period and 0.67~1.22 m/day during the 2013 WSRS period. The results also indicate that large river discharge tends to lead more intense SGD along the river channel direction with a large amount of fresh SGD.  相似文献   

3.
Lagrangian retention and flushing are examined by advecting neutrally buoyant point particles within a circulation field generated by a numerical ocean model of Tampa Bay. Large temporal variations in Lagrangian residence time are found under realistic changes in boundary conditions. Two 90-day time periods are examined. The first (P1) is characterized by low freshwater inflow and weak baroclinic circulation. The second (P2) has high freshwater inflow and strong baroclinic circulation. At the beginning of both time periods, 686,400 particles are released uniformly throughout the bay. Issues relating to particle distribution and flushing are examined at three different spatial scales: (1) at the scale of the entire bay, (2) the four major regions within the bay, and (3) at the scale of individual model grid cells. Two simple theoretical models for the particle number over time, N(t), are fit to the particle counts from the ocean model. The theoretical models are shown to represent N(t) reasonably well when considering the entire bay, allowing for straightforward calculation of baywide residence times: 156 days for P1 and 36 days for P2. However, the accuracy of these simple models decreases with decreasing spatial scale. This is likely due to the fact that particles may exit, reenter, or redistribute from one region to another in any sequence. The smaller the domain under consideration, the more this exchange process dominates. Therefore, definitions of residence time need to be modified for “non-local” situations. After choosing a reasonable definition, and removal of the tidal and synoptic signals, the residence times at each grid cell in P1 is found to vary spatially from a few days to 90 days, the limit of the calculation, with an average residence time of 53 days. For P2, the overall spatial pattern is more homogeneous, and the residence times have an average value of 26 days.  相似文献   

4.
A decade of studies of metal and nutrient inputs to the back-barrier area of Spiekeroog Island, NW German Wadden Sea, have concluded that pore water discharge provides a significant source of the enrichments of many components measured in the tidal channels during low tide. In this paper we add studies of radium isotopes to help quantify fluxes into and out of this system. Activities of radium isotopes in surface water from tidal channels in the back-barrier area exhibit pronounced changes in concert with the tide, with highest activities occurring near low tide. Other dissolved components: silica, total alkalinity (TA), manganese, and dissolved organic carbon (DOC) exhibit similar changes, with patterns matching the Ra isotopes. Uranium follows a reverse pattern with highest concentrations at high tide. Here we use radium isotope measurements in water column and pore water samples to estimate the fluxes of pore waters that enter the tidal channels during low tide. Using a flushing time of 4 days and the average activities of 224Ra, 223Ra, and 228Ra measured in the back-barrier surface and pore waters, we construct a balance of these isotopes, which is sustained by a deep pore water flux of (2-4) × 108 L per tidal cycle. This flux transports Ra and the other enriched components to the tidal channels and causes the observed low tide enrichments. An independent estimate of pore water recharge is based on the depletion of U in the tidal channels. The U-based recharge is about two times greater than the Ra-based discharge; however, other sinks of U could reduce the recharge estimate. The pore waters have wide ranges of enrichment in silica, alkalinity, manganese, DOC, and depletion of U with depth. We estimate concentrations of these components in pore water from the depth expected to contribute the majority of the pore water flux, 3.5 m, to determine fluxes of these components to the tidal channels. Samples from this depth have minimum concentrations of silica, alkalinity, manganese, and DOC. We also estimate the exports of these components (and import of U) due to mixing based on average measured concentrations in the tidal creeks and the 4-day flushing time. A comparison of these estimates reveals that the exports (negative in the case of U) equal or exceed the pore water fluxes. By using values slightly higher than the minimum concentrations at 3.5 m to calculate inputs, the two estimates could be forced to match. We conclude that pore water drainage is the major factor regulating fluxes of Ra isotopes, silica, alkalinity, manganese, DOC, and uranium in this system.  相似文献   

5.
The circulation patterns in St. Andrew Bay, Florida are revealed through the application of a well-tested, extensively used three-dimensional hydrodynamic model. A high resolution grid resolving both the horizontal and vertical directions is used with a systematically developed set of forcing functions to simulate conditions over a full year. Water levels at the three open boundaries are deduced from a year-long deployment of pressure gauges, and freshwater loadings are based upon drainage basin characteristics and precipitation measurements. Model validation involves comparisons with hydrographic casts taken at twelve stations distributed throughout the bay at monthly intervals. The relative average error between the observed and model-predicted salinity is 15% for the surface of the water column and 4% for the bottom. The annual net flow balance consists of an influx of water at the two Intracoastal Waterway open boundaries, with that water exiting to the Gulf of Mexico. An average of about 100 m3 s−1 enters from East Bay and about 40 m3 s−1 enters through West Bay. On shorter time scales, the flow balance is quite variable both in terms of magnitude and direction. This study also presents methods to overcome the paucity of data that is usually available for the development of such a model. These include techniques to take bottom pressure data sets with short gaps and create reliable sea surface elevation boundary conditions and to take precipitation data and drainage basin characteristics and produce estimates of freshwater inflows.  相似文献   

6.
Analyses have been made of many groundwater samples, some of which were collected from the vicinity of uranium deposits and others from unmineralized areas, for dissolved uranium and for the four naturally occurring isotopes of radium: 226Ra (238U decay series, y), 228Ra and 224Ra (232Th decay series, y and 3.8 d) and 223Ra (235U decay series, d). The radium isotopes 226Ra, 224Ra and 223Ra, are measured by alpha-spectrometry after extraction from a water sample soon after collection and 228Ra at a later time by determining the amount of ingrown 212Po.  相似文献   

7.
Land-based pollutants such as fertilizers and wastewater can infiltrate into aquifers and discharge into surrounding coastal water bodies as submarine groundwater discharge (SGD). Oceanic islands, with a large coast length to land area ratio, may be hot spots of SGD into the global ocean. Although SGD may be a major pathway of dissolved nutrients, carbon and metals to coastal waters, studies have been limited due to the difficulties in measuring this often diffuse process. This study used radium isotopes (223Ra, 224Ra, 226Ra) to investigate SGD and the associated fluxes of nutrients into Tauranga Harbour, New Zealand. We calculated the apparent water mass ages of the harbour to be between ~4.1 and 7.8 days, which was similar to a previous numerical model of ~2–8 days. A 226Ra mass balance was constructed to quantify SGD fluxes at the harbour scale. A minimum SGD flux rate of 0.53 cm day?1 was calculated by using the maximum groundwater end-member value from 22 sample sites. However, using the geometric mean from these samples as a representative end-member, a final value of 2.83 cm day?1 or a flux of 3.09 × 106 m3 day?1 was calculated. These values were between ~1 and 2.8 times greater than all the major river and creeks discharging into the harbour during the sampling period. Due to the higher observed nutrient concentrations in groundwater, the SGD-derived dissolved inorganic nitrogen (DIN), dissolved organic nitrogen (DON) and total dissolved phosphorus (TDP) fluxes were calculated to be 1.07, 0.87 and 0.05 mmol m2 day?1, respectively. These SGD inputs were ~5 times (for nitrogen) and ~8 times (for phosphorus) greater than the input from surrounding rivers and streams. The average N:P ratio in groundwater samples was 36:1 (which was greatly in excess of the Redfield ratio of 16). The harbour water had a N:P ratio of ~17:1. A positive relationship between radium isotopes and N:P ratios in the harbour further supported the hypothesis that SGD can have major implications for primary production, including recurrent algal bloom events which occur in the harbour. We suggest SGD as a major driver of nutrient dynamics in Tauranga Harbour and potentially other similar coastal lagoon systems and estuaries on oceanic islands.  相似文献   

8.
A nutrient mass balance for the tidal freshwater segment of the James River was used to assess sources of nutrients supporting phytoplankton production and the importance of the tidal freshwater zone in mitigating nutrient transport to marine waters. Monthly mass balances for 2007–2010 were based on riverine inputs, local point sources (including sewer overflow events), ungauged inputs, riverine outputs, and tidal exchange. The tidal freshwater James River received exceptionally high areal loads (446 mg TN m?2 day?1 and 55 mg TP m?2 day?1) compared to other estuaries in the region and elsewhere. P inputs were principally from riverine sources (84 %) whereas point sources contributed appreciably (54 %) to high N loads. Despite high loading rates and short water residence time, areal mass retention was high (143 mg TN m?2 day?1 and 33 mg TP m?2 day?1). Retention of particulate fractions occurred during high discharge, whereas dissolved inorganic fractions were retained during low discharge when chlorophyll-a concentrations were high. On an annualized basis, P was retained more effectively (59 %) than N (32 %). P was retained by abiotic mechanisms via trapping of particulate forms, whereas N was retained through biological assimilation of dissolved inorganic forms. Results from a limited suite of stable isotope determinations suggest that DIN from point sources was preferentially retained. Combined inputs from diffuse and point sources accounted for only 20 % and 36 % (respectively) of estimated algal N and P demand, indicating that internal nutrient recycling was important to sustaining high rates of phytoplankton production in the tidal freshwater zone.  相似文献   

9.
There is a net discharge of water and nutrients through Long Key Channel from Florida Bay to the Florida Keys National Marine Sanctuary (FKNMS). There has been speculation that this water and its constituents may be contributing to the loss of coral cover on the Florida Keys Reef tract over the past few decades, as well as speculation that changes in freshwater flow in the upstream Everglades ecosystem associated with the Comprehensive Everglades Restoration Plan may exacerbate this phenomenon. The results of this study indicate that although there is a net export of approximately 3,850 (±404) ton N year?1 and 63 (±7) ton P year?1, the concentrations of these nutrients flowing out of Florida Bay are the same as those flowing in. This implies that no significant nutrient enrichment is occurring in the waters of the FKNMS in the vicinity of Long Key Channel. Because of the effect of restricted southwestward water flow through Florida Bay by shallow banks and small islands, the volume of relatively high-nutrient water from central and eastern portions of the bay exiting through the channel is small compared to the average tidal exchange. Nutrient loading of relatively enriched bay waters is mediated by tidal exchange and mixing with more ambient concentrations of the western Florida Bay and Hawk Channel. System-wide budgets indicate that the contribution of Florida Bay waters to the inorganic nitrogen pool of the Keys coral reef is small relative to offshore inputs.  相似文献   

10.
Freshwater inflows to Texas estuaries vary widely due to regional climate fluctuations and are being substantially altered by human activities. The natural abundance stable isotope ratios of carbon and nitrogen in oyster adductor muscle were used to acquire a time-integrated view of freshwater and nitrogen contributions to the Mission-Aransas National Estuarine Research Reserve in South Texas. The study objective was to determine the influence of inputs from the San Antonio and Guadalupe rivers, which deliver approximately 1.6 km3 of water to the mid-Texas coastal region annually. A transect of sampling stations extending from the head of San Antonio Bay (northeast of the Reserve boundary) to the Aransas Pass ship channel (roughly 70 km to the southwest) was visited multiple times between 2009 and 2011. Carbon isotopic values increased from approximately ?25 to ?17‰ while δ15N values decreased from approximately +16 to +10‰ between the bay and ship channel. This range of carbon isotope values translates into time-integrated freshwater fractions as high as 0.8 (1 = 100% fresh) at the most inland sampling station to freshwater fractions around zero approaching the Gulf of Mexico. Contributions from the San Antonio and Guadalupe rivers to waters of the reserve vary between wet and dry years, but overall, the data suggest that these rivers are persistent and substantial sources of fresh water and nitrogen to the reserve. This study emphasizes the importance of connectivity and lateral exchanges among bays/lagoons when considering potential sources of fresh water and nitrogen that control ecosystem structure and function.  相似文献   

11.
The adsorption rate constants of Ra and Th were estimated from empirical data from a freshwater lake and its feeding saline springs. We utilized the unique setting of Lake Kinneret (Sea of Galilee, northern Israel) in which most of the Ra and Th nuclides are introduced into the lake by saline springs with high 226Ra activities and a high 224Ra/228Ra ratio of 1.5. The mixing of the Ra enriched saline waters and freshwater in the lake causes the 224Ra/228Ra ratio to drop down to 0.1 in the Kinneret due to preferential adsorption of 228Th. These conditions constitute a “natural experiment” for estimating adsorption rates. We developed a simple mass-balance model for the radionuclides in Lake Kinneret that accurately predicted the Ra isotope ratios and the 226Ra activity in the lake. The model is comprised of simultaneous equations; one for each radionuclide. The equations have one input term: supply of radionuclides from the saline springs; and three output terms: adsorption on particles in the lake, radioactive decay and outflow from the lake. The redundancy in the analytical solutions to the mass balance equations for the relevant nuclides constrained the values of Ra and Th adsorption rate constants to a very narrow range. Our results indicate that the adsorption rate constant for Ra is between 0.005 d−1 and 0.02 d−1. The rate constant for Th is between 0.5 d−1 and 1 d−1, about fifty to a hundred times higher. The estimated desorption rate coefficient for Ra is about 50-100 times larger than its adsorption rate constant. The mass-balance equations show that the residence times of all Ra isotopes (226Ra, 228Ra,223Ra, 224Ra) and of 228Th in the lake are about 95, 92, 14, 6 and 1 d, respectively. These residence times are much shorter than the residence time of water in the lake (about 5.5 y). The steady state activity ratios in Lake Kinneret depend mainly on the adsorption rate constants, decay constants, the outflow rate from the lake and the activity ratios in the saline springs. The activity ratios are independent of the saline springs flow rate.  相似文献   

12.
We analyzed 238U, 234U, 232Th, 230Th, and 226Ra by thermal ionization mass spectrometry (TIMS) and Ba by inductively coupled plasma optical emission spectrometry (ICP-OES) on eight Mn/Fe crusts from the Mecklenburg Bay (SW Baltic) and on one from the Bothnian Bay (N Baltic) to test the 226Raex/Ba ratio as potential geochronometer. 226Raex/Ba ratios decrease as a function of depth within the concretions in all analyzed profiles. Calculated diffusion coefficients are relatively low (∼9 · 10−7 cm2/yr for Ra and 5 · 10−7 cm2/yr for Ba) and suggest that diffusion is negligible for the Ra and Ba record. In addition, 226Raex/Ba ages are consistent and independent from the growth rate and growth direction within a crust. Thus, the decline in 226Raex/Ba ratio is most likely due to radioactive decay of 226Raex, although the influence of varying oxic conditions has still to be evaluated. 226Raex/Ba growth rates range from 0.021 to 0.0017 mm/yr and tend to be lower than those calculated and based on stratigraphic methods (1 to 0.013 mm/yr). 226Raex/Ba ages of concretions from shallow water environment (20 m depth, Mecklenburg Bay/SW Baltic) cover a time interval from 990 ± 140 yr to 4310 ± 310 yr BP corresponding to the stabilization of the sea level close to the present position about 5500 to 4500 yr ago. One sample from greater depth (70 m, Bothnian Bay-/N Baltic) showed a higher 226Raex/Ba age of 6460 ± 520 yr BP.  相似文献   

13.
Radium isotopes were used to determine the crustal residence times of hydrothermal fluids from two geothermal wells (Svartsengi and Reykjanes) from the Reykjanes Peninsula, Iceland. The availability of rock samples from the subsurface (to depths of 2400 m) allowed direct comparison of the radium isotopic characteristics of the fluids with those of the rocks within the high temperature and pressure reaction zone. The 226Ra activity of the Svartsengi fluid was ∼one-fourth of the Reykjanes fluid and the 228Ra/226Ra ratio of the Svartsengi fluid was ∼twice that of Reykjanes. The fluid isotopic characteristics were relatively stable for both sites over the 6 years (2000-2006) of the study. It was determined, using a model that predicts the evolution of the fluid 228Ra/226Ra ratio with time, that both sites had fluid residence times, from the onset of high temperature water-rock reaction, of less than 5 years. Measurement of the short-lived 224Ra and 223Ra allowed estimation of the recoil input parameter used in the model. The derived timescale is consistent with results from similar studies of fluids from submarine systems, and has implications for the use of terrestrial systems in Iceland as an exploited energy resource.  相似文献   

14.
Community Oxygen and Nutrient Fluxes in Seagrass Beds of Florida Bay, USA   总被引：1，自引：0，他引：1  
We used clear, acrylic chambers to measure in situ community oxygen and nutrient fluxes under day and night conditions in seagrass beds at five sites across Florida Bay five times between September 1997 and March 1999. Underlying sediments are biogenic carbonate with porosities of 0.7–0.9 and with low organic content (<1.6%). The seagrass communities always removed oxygen from the water column during the night and produced oxygen during daylight, and sampling date and site significantly affected both night and daytime oxygen fluxes. Net daily average fluxes of oxygen (?4.9 to 49 mmol m?2 day?1) ranged from net autotrophy to heterotrophy across the bay and during the 18-month sampling period. However, the Rabbit Key Basin site, located in the west-central bay and covered with a dense Thalassia testudinum bed, was always autotrophic with net average oxygen production ranging from 4.8 to 49 mmol m?2 day?1. In November 1998, three of the five sites were strongly heterotrophic and oxygen production was least at Rabbit, suggesting the possibility of hypoxic conditions in fall. Average ammonium (NH4) concentrations in the water column varied widely across the bay, ranging from a mean of 6.9 μmol l?1 at Calusa in the eastern bay to a mean of 0.6 μmol l?1 at Rabbit Key for the period of study. However, average NH4 fluxes by site and date (?240 to 110 μmol m?2 h?1) were not correlated with water column concentrations and did not vary in a consistent diel, seasonal, or spatial pattern. Concentrations of dissolved organic nitrogen (DON) in the water column, averaged by site (15–25 μmol l?1), were greater than mean NH4 concentrations, and the range of day and night DON fluxes (?920 to 1,300 μmol m?2 h?1), averaged by site and date, was greater than the range of mean NH4 fluxes. Average DON fluxes did not vary consistently from day to night, seasonally or spatially. Mean silicate fluxes ranged from ?590 to 860 μmol m?2 h?1 across all sites and dates, but mean net daily fluxes were less variable and most of the time contributed small amounts of silicate to the water column. Mean concentrations of filterable reactive phosphorus (FRP) in the water column across the bay were very low (0.021–0.075 μmol l?1); but site average concentrations of dissolved organic phosphorus (DOP) were higher (0.04–0.15 μmol l?1) and showed a gradient of increasing concentration from east to west in the bay. A pronounced gradient in average surficial sediment total phosphorus (1.1–12 μmol g DW?1) along an east-to-west gradient was not reflected in fluxes of phosphorus. FRP fluxes, averaged by site and date, were low (?5.2 to 52 μmol m?2 h?1), highly variable, and did not vary consistently from day to night or across season or location. Mean DOP fluxes varied over a smaller range (?8.7 to 7.4 μmol m?2 h?1), but also showed no consistent spatial or temporal patterns. These small DOP fluxes were in sharp contrast to the predominately organic phosphorus pool in surficial sediments (site means?=?0.66–7.4 μmol g DW?1). Significant correlations of nutrient fluxes with parameters related to seagrass abundance suggest that the seagrass community may play a major role in nutrient recycling. Integrated means of net daily fluxes over the area of Florida Bay, though highly variable, suggest that seagrass communities might be a source of DOP and NH4 to Florida Bay and might remove small amounts of FRP and potentially large amounts of DON from the waters of the bay.  相似文献   

15.
In shallow estuaries with strong river influence, the short residence time and pronounced gradients generate an environment for plankton that differs substantially in its dynamics from that of the open ocean, and the question arises “How is phytoplankton biomass affected?” This study assesses the small-scale spatial and temporal distribution of phytoplankton in Apalachicola Bay, a shallow bar-built estuary in the Florida Panhandle. Phytoplankton peaks were characterized to gain insights into the processes affecting spatial heterogeneity in biomass. Chlorophyll a (Chl a) distribution at 50-m spatial resolution was mapped using a flow-through sensor array, Dataflow©, operated from a boat that sampled four transects across the bay every 2 weeks for 16 months. Chl a peaks exceeding background concentrations had an average width of 1.3?±?0.7 km delineated by an average gradient of 3.0?±?6.0 μg Chl a L?1 km?1. Magnitude of E-W wind, velocity of N-S wind, tidal stage, and temperature affected peak characteristics. Phytoplankton contained in the peaks contributed 7.7?±?2.7% of the total integrated biomass observed along the transects during the study period. The river plume front was frequently a location of elevated Chl a, which shifted in response to river discharge. The results demonstrate that despite the shallow water column, river flushing, and strong wind and tidal mixing, distinct patchiness develops that should be taken into consideration in ecological studies and when assessing productivity of such ecosystems.  相似文献   

16.
The Choptank River, Chesapeake Bay’s largest eastern-shore tributary, is experiencing increasing nutrient loading and eutrophication. Productivity in the Choptank is predominantly nitrogen-limited, and most nitrogen inputs occur via discharge of high-nitrate groundwater into the river system’s surface waters. However, spatial patterns in the magnitude and quality of groundwater discharge are not well understood. In this study, we surveyed the activity of 222Rn, a natural groundwater tracer, in the Choptank’s main tidal channel, the large tidal tributary Tuckahoe Creek, smaller tidal and non-tidal tributaries around the basin, and groundwater discharging into those tributaries, measuring nitrate and salinity concurrently. 222Rn activities were <100 Bq m?3 in the main tidal channel and 100–700 Bq m?3 in the upper Choptank River and Tuckahoe Creek, while the median Rn activities of fresh tributaries and discharging groundwater were 1,000 and 7,000 Bq m?3, respectively. Nitrate-N concentrations were <0.01 mg L?1 throughout most of the tidal channel, 1.5–3 mg L?1 in the upper reaches, up to 13 mg L?1 in tributary samples, and up to 19.6 mg L?1 in groundwater. Nitrate concentrations in tributary surface water were correlated with Rn activity in three of five sub-watersheds, indicating a groundwater nitrate source. 222Rn and salinity mass balances indicated that Rn-enriched groundwater discharges directly into the Choptank’s tidal waters and suggested that it consists of a mixture of fresh groundwater and brackish re-circulated estuarine water. Further sampling is necessary to constrain the Rn activity and nitrate concentration of discharging groundwater and quantify direct discharge and associated nitrogen inputs.  相似文献   

17.
Water quality monitoring in Hanalei Bay, Kaua`i (Hawai`i, USA) has documented intermittent high concentrations of nutrients (nitrate, phosphate, silica, and ammonium) and fecal indicator bacteria (FIB, i.e., enterococci and Escherichia coli) in nearshore waters and spurred concern that contaminated groundwater might be discharging into the bay. The present study sought to identify and track sources of nutrients and FIB to four beaches in Hanalei Bay and one beach outside the bay, together representing a wide range of land uses. 223Ra and 224Ra activity, salinity, nutrient and FIB concentrations were measured in samples from the coastal aquifer, the nearshore ocean, springs, the Hanalei River, and smaller streams. In addition, FIB concentrations in beach sands were measured at each site, and the enterococcal surface protein (esp) gene assay was used to investigate whether the observed FIB originated from a human source. Nutrient concentrations in groundwater were significantly higher than in nearshore water, inversely correlated to salinity, and highly site specific, indicating local controls on groundwater quality. Fluxes of groundwater into Hanalei Bay were calculated using a mass-balance approach and represented at least 2–10% of river discharges. However, submarine groundwater discharge (SGD) may provide 2.7 times as much nitrate + nitrite to Hanalei Bay as does the Hanalei River. It may also provide significant fluxes of phosphate and ammonium, comprising 15% and 20% of Hanalei River inputs, respectively. SGD-derived silica inputs to the bay comprised less than 3% of Hanalei River inputs. FIB concentrations in groundwater were typically lower than those in nearshore water, suggesting that significant FIB inputs from SGD are unlikely. Positive esp gene assays suggested that some enterococci in environmental samples were of human fecal origin. Identifying how nutrients and FIB enter nearshore waters will help environmental managers address pressing water quality issues, including exceedances of the state Enterococcus water quality standard and nutrient loading to coral reefs.  相似文献   

18.
The estuarine environment can serve as either a source or sink of carbon relative to the coastal ocean carbon budget. A variety of time-dependent processes such as sedimentation, carbon supply, and productivity dictate how estuarine systems operate, and Mobile Bay is a system that has experienced both natural and anthropogenic perturbations that influenced depositional processes and carbon cycling. Sediments from eight box cores provide a record of change in bulk sediment accumulation and carbon burial over the past 110 years. Accumulation rates in the central part of the basin (0.09 g cm?2) were 60–80 % less than those observed at the head (0.361 g cm?2) and mouth (0.564 g cm?2) of the bay. Sediment accumulation in the central bay decreased during the past 90 years in response to both anthropogenic (causeway construction) and natural (tropical cyclones) perturbations. Sediment accumulation inevitably increased the residence time of organic carbon in the oxic zone, as observed in modeled remineralization rates, and reduced the overall carbon burial. Such observations highlight the critical balance among sediment accumulation, carbon remineralization, and carbon burial in dynamic coastal environments. Time-series analysis based solely on short-term observation would not capture the long-term effects of changes in sedimentation on carbon cycling. Identifying these relationships over longer timescales (multi-annual to decadal) will provide a far better evaluation of coastal ocean carbon budgets.  相似文献   

19.
An empirical scheme based on the concentrations of uranium and the three alpha-emitting radium isotopes 226Ra, 224Ra and 223Ra is proposed for rating the significance of ground waters with respect to uranium exploration. The scheme has been developed from the results for over 200 water samples from the vicinity of known uranium deposits and radium anomalies in areas of Australia with climates varying from arid to tropical. The scheme uses relative levels of the four factors to rate the potential of a sample as good, possible or poor. An example of the use of the system in ground-water exploration in the Frome Embayment, South Australia, is presented to illustrate the value of the scheme in rejecting falsely anomalous samples with high uranium concentrations whilst detecting nearby uranium mineralization from drill holes not intersecting mineralization.  相似文献   

20.
Groundwater may be highly enriched in dissolved carbon species, but its role as a source of carbon to coastal waters is still poorly constrained. Exports of deep and shallow groundwater-derived dissolved carbon species from a small subtropical estuary (Korogoro Creek, Australia, latitude ?31.0478°, longitude 153.0649°) were quantified using a radium isotope mass balance model (233Ra and 224Ra, natural groundwater tracers) under two hydrological conditions. In addition, air-water exchange of carbon dioxide and methane in the estuary was estimated. The highest carbon inputs to the estuary were from deep fresh groundwater in the wet season. Most of the dissolved carbon delivered by groundwater and exported from the estuary to the coastal ocean was in the form of dissolved inorganic carbon (DIC; 687 mmol m?2 estuary day?1; 20 mmol m?2 catchment day?1, respectively), with a large export of alkalinity (23 mmol m?2 catchment day?1). Average water to air flux of CO2 (869 mmol m?2 day?1) and CH4 (26 mmol m?2 day?1) were 5- and 43-fold higher, respectively, than the average global evasion in estuaries due to the large input of CO2- and CH4-enriched groundwater. The groundwater discharge contribution to carbon exports from the estuary for DIC, dissolved organic carbon (DOC), alkalinity, CO2, and CH4 was 22, 41, 3, 75, and 100 %, respectively. The results show that CO2 and CH4 evasion rates from small subtropical estuaries surrounded by wetlands can be extremely high and that groundwater discharge had a major role in carbon export and evasion from the estuary and therefore should be accounted for in coastal carbon budgets.  相似文献   

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