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1.
We measured the time-series variations in 222Rn activity at a fixed station in the Yeongsan River Estuary (YRE), Korea, where the upstream water is obstructed by an artificial dam, during November 18–24, 2008, and conducted a horizontal 222Rn survey in the Seomjin River Estuary (SRE), Korea, during December 16–18, 2008. In the YRE, we observed constantly low levels of 222Rn activity over the sampling period, relative to the summer in 2008. The 222Rn variations and 222Rn mass-balance modeling results indicate that the submarine groundwater discharge (SGD) in the YRE was relatively low and constant over the sampling period and that the temporal SGD variations were not related to tides or to the water elevation in the dam upstream. This low and constant SGD appears to be due to the lower water level in the dam relative to the local sea level during the study period, resulting in the SGD mostly from the surrounding land areas rather than from the dam. In the SRE, higher 222Rn activities were observed at upstream stations of the river (salinity: <5) and decreased as the salinity increased, but there were marked increases of 222Rn, together with dissolved inorganic silicate (DSi), at stations close to the river mouth (salinity: ～33). This suggests that the river has major groundwater inputs from the two extreme upstream and downstream areas. Because most chemical flux estimations via river discharge do not account for groundwater inputs from the downstream high-salinity zone, our results suggest that there is an important unaccounted source of river-driven chemical fluxes. Overall, our study shows that the continuous 222Rn monitoring system provides high-resolution information on SGD over different locations and times.  相似文献   

2.
海底地下水排放对典型红树林蓝碳收支的影响   总被引：1，自引：0，他引：1  
海底地下水排放(Submarine Groundwater Discharge，SGD)是陆海相互作用的重要表现形式之一，其携带的物质对近岸海域生源要素的收支有重要影响。本文利用222Rn示踪技术估算了我国典型红树林海湾—广西珍珠湾在2019年枯季(1月)SGD携带的碳通量。调查发现，地下水中222Rn活度、溶解无机碳(DIC)和溶解有机碳(DOC)的平均浓度均高于河水和湾内表层海水。利用222Rn质量平衡模型估算得到珍珠湾SGD速率为(0.36±0.36) m/d，SGD输入到珍珠湾的DIC和DOC通量分别为(2.41±2.63)×107 mol/d和(1.96±2.20)×106 mol/d。珍珠湾溶解碳的源汇收支表明，SGD携带的DIC和DOC分别占珍珠湾总DIC和总DOC来源的91%和89%。因此，SGD携带的DIC和DOC是珍珠湾DIC和DOC的主要来源，是海岸带蓝碳收支和生物地球化学循环过程中的重要组成。  相似文献   

3.
Stable isotopes, tritium, radium isotopes, radon, trace elements and nutrients data were collected during two sampling campaigns in the Ubatuba coastal area (south-eastern Brazil) with the aim of investigating submarine groundwater discharge (SGD) in the region. The isotopic composition (δD, δ18O, 3H) of submarine waters was characterised by significant variability and heavy isotope enrichment. The stable isotopes and tritium data showed good separation of groundwater and seawater groups. The contribution of groundwater in submarine waters varied from a few % to 17%. Spatial distribution of 222Rn activity concentration in surface seawater revealed changes between 50 and 200 Bq m−3 which were in opposite relationship with observed salinities. Time series measurements of 222Rn activity concentration in Flamengo Bay (from 1 to 5 kBq m−3), obtained by in situ underwater gamma-spectrometry showed a negative correlation between the 222Rn activity concentration and tide/salinity. This may be caused by sea level changes as tide effects induce variations of hydraulic gradients, which increase 222Rn concentration during lower sea level, and opposite, during high tides where the 222Rn activity concentration is smaller. The estimated SGD fluxes varied during 22–26 November between 8 and 40 cm d−1, with an average value of 21 cm d−1 (the unit is cm3/cm2 per day). The radium isotopes and nutrient data showed scattered distributions with offshore distance and salinity, which implies that in a complex coast with many small bays and islands, the area has been influenced by local currents and groundwater–seawater mixing. SGD in the Ubatuba area is fed by coastal contaminated groundwater and re-circulated seawater (with small admixtures of groundwater), which claims for potential environmental concern with implications on the management of freshwater resources in the region.  相似文献   

4.
The distributions of dissolved organic carbon (DOC), Ba, U, and a suite of naturally occurring radionuclides in the U/Th decay series (222Rn, 223,224,226,228Ra) were studied during high- and low-discharge conditions in the Loxahatchee River estuary, Florida to examine the role of submarine groundwater discharge in estuarine transport. The fresh water endmember of this still relatively pristine estuary may reflect not only river-borne constituents, but also those advected during active groundwater/surface water (hyporheic) exchange. During both discharge conditions, Ba concentrations indicated slight non-conservative mixing. Such Ba excesses could be attributed either to submarine groundwater discharge or particle desorption processes. Estuarine dissolved organic carbon concentrations were highest at salinities closest to zero. Uranium distributions were lowest in the fresh water sites and mixed mostly conservatively with an increase in salinity. Suspended particulate matter (SPM) concentrations were generally lowest (< 5 mg L− 1) close to zero salinity and increased several-fold ( 18 mg L− 1; low discharge) toward the seaward endmember, which may be attributed to dynamic resuspension of bottom sediments within Jupiter Inlet.Surface water-column 222Rn activities were most elevated (> 28 dpm L− 1) at the freshwater endmember of the estuary and appear to identify regions of the river most influenced by the discharge of fresh groundwater. Activities of four naturally occurring isotopes of Ra (223,224,226,228Ra) in this estuary and select adjacent shallow groundwater wells yield mean estuarine water-mass transit times of less than 1 day; these values are in close agreement to those calculated by tidal prism and tidal frequency. Submarine groundwater discharge rates to the Loxahatchee River estuary were calculated using a tidal prism approach, an excess 226Ra mass balance, and an electromagnetic seepage meter. Average SGD rates ranged from 1.0 to 3.8 × 105 m3 d− 1 (20–74 L m− 2 d− 1), depending on river-discharge stage. Such calculated SGD estimates, which must include both a recirculated as well as fresh water component, are in close agreement with results obtained from a first-order watershed mass balance. Average submarine groundwater discharge rates yield NH4+ and PO4− 3 flux estimates to the Loxahatchee River estuary that range from 62.7 to 1063.1 and 69.2 to 378.5 μmol m− 2 d− 1, respectively, depending on river stage. SGD-derived nutrient flux rates are compared to yearly computed riverine total N and total P load estimates.  相似文献   

5.
Transport between pore waters and overlying surface waters of Flamengo Bay near Ubatuba, Brazil, was quantified using natural and artificial geochemical tracers, 222Rn, Cl−, and SF6, collected from multi-level piezometers installed along a transect perpendicular to the shore. Eight sampling ports positioned along the length of the piezometers allowed sampling of pore waters at discrete depth intervals from 10 to 230 cmbsf (centimeters below seafloor). Small volume samples were collected from the piezometers using a peristaltic pump to obtain pore water depth profiles. Pore water 222Rn is deficient in shallow sediments, allowing application of a diffusion-corrected 222Rn exchange rate. This model estimates the magnitude of pore water exchange rates to be about 130–419 cm/day. An SF6-saturated fluorescein dye tracer was gently pumped into deep pore waters and exchange rates estimated from this method range from 29 to 185 cm/day. While absolute rates are higher using 222Rn than SF6, rates are of similar magnitudes and the trends with distance from shore are the same – flow is greatest 6 m from shore and decreases by more than 50% further offshore. A Cl− mass balance indicates the greatest fraction of fresh SGD occurs along an apparent preferential flow path in sediments within 5–7 m of the shoreline (87%). Recirculating bay waters through sediments dominate pore water advection at 10 m offshore where only 4% of the flow can be attributed to a freshwater source. Both fresh and marine sources combine to make up submarine groundwater discharge to coastal water bodies. The magnitude of fresh aquifer discharge is often a spatially variable and minor component of the total discharge.  相似文献   

6.
We report the results of an experiment in which we measured 222Rn (15,000 observations), CH4 (40,000 observations), and associated variables in seawater nearly continuously at a coastal site in the Gulf of Mexico for almost two years. Significant correlations between 222Rn and CH4 imply that they are derived from a common source, most likely groundwater. However, we were unable to explain the overall tracer variability as a single function of groundwater table height, temperature, tidal range, and wind speed, indicating multiple, overlapping controls on SGD dynamics at this site. Methane and radon concentrations may vary 2-fold in a given well in the subterranean estuary over tidal time scales, demonstrating the complexity of determining SGD endmember concentrations and suggesting that unaccounted for temporal changes in groundwater may explain some of the patterns observed in seawater. Surprisingly, the variability of 222Rn and CH4 in seawater over short (e.g., hourly) time scales was generally comparable to or even more pronounced than fluctuations over much longer (e.g., monthly) scales. While high tracer concentrations usually occurred during low tide and low tracer concentrations during high tide, this pattern was occasionally inverted or absent indicating that no single model can be used to describe the entire data set. We also describe a sequence of events in which SGD tracers were depleted in coastal waters during storms and regenerated afterwards. We found no increase in radon activities immediately after the largest storm (75 mm rainfall) perhaps because of the short residence times of groundwater in contrast to the ingrowth time of radon. Marine controls appeared to be the most important SGD drivers with only minor influence relating to the shallow and deep aquifers. This implies that seasonal investigations of SGD tracers in the coastal ocean may be masked by short-term variability.  相似文献   

7.
The input of groundwater-borne nutrients to Adelaide's (South Australia) coastal zone is not well known but could contribute to the ongoing decline of seagrass in the area. As a component of the Adelaide Coastal Waters Study (ACWS), the potential for using the radium quartet (223Ra, 224Ra, 226Ra and 228Ra) and 222Rn to evaluate submarine groundwater discharge (SGD) was evaluated. Potential isotopic signatures for SGD were assessed by sampling groundwater from three regional aquifers potentially contributing SGD to the ACWS area. In addition, intertidal groundwater was sampled at two sand beach sites. In general, the regional groundwaters were enriched in long-lived Ra isotopes (226Ra and 228Ra) and in 222Rn relative to intertidal groundwater. Radium activity (but not 222Rn activity) was positively correlated to salinity in groundwater from one of the regional aquifers and in intertidal groundwater. Radium isotope ratios (223Ra/226Ra, 224Ra/226Ra and 228Ra/226Ra) were less variable than individual Ra isotope activities within potential SGD sources. Recirculated seawater (estimated from the intertidal groundwater samples with seawater-like salinities) also had distinctly higher Ra isotope ratios than the regional groundwaters. The activities for all radioisotopes were relatively low in seawater. The activity of the short-lived 223Ra and 224Ra were highest at the shoreline and declined exponentially with distance offshore. In contrast, 228Ra and 226Ra activities had a weak linear declining trend with distance offshore. Rn-222 activity was at or near background in all seawater samples. The pattern of enrichment in short-lived Ra isotopes and the lack of 222Rn in seawater suggest that seawater recirculation is the main contributor to SGD in the ACWS area. Preliminary modeling of the offshore flux of 228Ra and 226Ra suggest that the SGD flux to the ACWS area ranges between 0.2 and 3 · 10− 3 m3 (m of shoreline)− 1 s− 1.  相似文献   

8.
The Yeongsan River estuary (YRE) is located downstream of a dam housing an artificial lake on the southwestern coast of Korea. Intermittent discharges of lake water through dam gates control the water level of the lake. This study compares fluxes of dissolved nutrients in discharged water with those of submarine groundwater discharge (SGD) occurring in the YRE in July and October 2008. With the exception of dissolved inorganic phosphorus (DIP) which limits primary production, nutrient concentrations in the YRE are controlled mainly by conservative mixing between lake water and open ocean water during periods of lake water discharge. In comparison with lake water discharge, the magnitude of SGD, based on a 222Rn mass balance model, is relatively small (about 1.5×105 m3 day?1 in July and about 30% higher in October) and dependent on the water elevation in the lake. However, SGD contributes considerably to the input of DIP when discharge of lake water is halted. Our study shows that SGD is more important in the delivery of biogeochemical components into estuaries that are obstructed by artificial dams.  相似文献   

9.
Algal blooms in Tolo Harbour, Hong Kong have received much attention and submarine groundwater discharge is speculated to be a significant pathway carrying nutrients into the constricted estuary. Plover Cove, a small cove in the Harbour, was selected for SGD analysis using 222Rn budget. The volumetric SGD rates are estimated to be about 8000 m3/day for neap tide and about 17,000 m3/day for spring tide. Result of nutrient analysis of the porewater indicates that the nutrient loading through this pathway is speculated to be crucial for eutrophication in Tolo Harbour. Current practice for the management of algal blooms in Hong Kong, in which nutrient loading through SGD was ignored, has to be reviewed and the control measures of groundwater contamination are obviously required.  相似文献   

10.
Submarine groundwater discharge (SGD) is now recognized as an important pathway for water and chemical species fluxes to the coastal ocean. In order to determinate SGD to the Gulf of Lion (France), we measured the activities of 226Ra and 228Ra by thermal ionization mass spectrometry (TIMS) in coastal waters and in the deep aquifer waters of the Rhone deltaic plain after pre-concentration of radium by MnO2. Compared to conventional counting techniques, TIMS requires lower quantities of water for the analyses, and leads to higher analytical precision. Radium isotopes were thus measured on 0.25–2 L water samples containing as little as 20 fg of 226Ra and 0.2–0.4 fg of 228Ra with precision equal to 2%. We demonstrate that coastal surface waters samples are enriched in 226Ra and 228Ra compared to the samples further offshore. The high precision radium measurements display a small but significant 226Ra and 228Ra enrichment within a strip of circa 30 km from the coast. Radium activities decrease beyond this region, entrained in the northern current along the shelf break or controlled by eddy diffusion. The radium excess in the first 30 km cannot be accounted for by the river nor by the early diagenesis. The primary source of the radium enrichment must therefore be ascribed to the discharge of submarine groundwater. Using a mass-balance model, we estimated the advective fluxes of 226Ra and 228Ra through SGD to be 5.2 × 1010 and 21 × 1010 dpm/d respectively. The 226Ra activities measured in the groundwater from the Rhone deltaic plain aquifer are comparable to those from other coastal groundwater studies throughout the world. By contrast, 228Ra activities are higher by up to one order of magnitude. Taking those groundwater radium activities as typical of the submarine groundwater end-member, a minimum volume of 0.24–4.5 × 1010 l/d is required to support the excess radium isotopes on the inner shelf. This has to be compared with the average rivers water runoff of 15.4 × 1010 l/d during the study period (1.6 to 29% of the river flow).  相似文献   

11.
Over a period of 5 days between August 12 and 17, 2005, we performed a gas exchange experiment using the dual tracer method in a tidal coastal ocean located off the southern coast of Korea. The gas exchange rate was determined from temporal changes in the ratio of3He to SF6 measured daily in the surface mixed layer. The measured gas exchange rate (k CO 2), normalized to a Schmidt number of 600 for CO2 in fresh water at 20°C, was approximately 5.0 cm h-1 at a mean wind speed of 3.9 m s-1 during the study period. This value is significantly less than those obtained from floating chamber-based experiments performed previously in estuarine environments, but is similar in magnitude to values obtained using the dual tracer method in river and tidal coastal waters and values predicted on the basis of the relationship between the gas exchange rate and wind speed (Wanninkhof 1992), which is generally applicable to the open ocean. Our result is also consistent with the relationship of Raymond and Cole (2001), which was derived from experiments carried out in estuarine environments using222Rn and chlorofluorocarbons along with measurements undertaken in the Hudson River, Canada, using SF6 and3He. Our results indicate that tidal action in a microtidal region did not discernibly enhance the measuredk CO 2 value.  相似文献   

12.
Both space and time variations in the 222Rn concentration in the atmospheric surface layer over continental Russia were analyzed on the basis of data obtained in the Transcontinental Observations into the Chemistry of the Atmosphere (TROICA) experiments. The measurements were taken from a mobile laboratory which was part of a passenger train moving along the Trans-Siberian Railway from Moscow to Vladivostok. The factors that affect the spatial distribution of both daily and seasonal variations in the concentrations of 222Rn in the surface air were determined: atmospheric vertical stability, geological features of the area under study, and atmospheric precipitation. The influence of temperature inversions on the accumulation of 222Rn in the atmospheric surface layer was analyzed. The fluxes of 222Rn from the soil into the atmosphere were estimated for different regions of Russia.  相似文献   

13.
A model for the Zambezi River plume, the largest on the Indian Ocean coast of Africa, is presented and the results of experiments with different discharges and wind forcings are analysed. Although the river plays an important role in the southern African economy through power generation on large dams, artisanal fisheries, and frequent flooding events that impact greatly on local populations, the plume has not been well studied. Observations during the period 2004–2007, when the winds were mainly easterly or south-easterly, indicated that the plume waters can extend both downstream (equatorwards) and upstream (polewards) of the Zambezi Delta with a recirculating bulge near the river mouth. The model is constructed using the Regional Ocean Modeling System (ROMS), with a 40-km long, 3-km wide river discharging into a rectangular coastal ocean with a linearly sloping bottom. When the model is forced only by a constant river discharge of 1 000?m3 s?1 (typical of observed discharge amounts in summer), the Kelvin and Froude numbers for the resulting plume imply a ‘large-scale’ buoyant discharge with a coastal current that is close to being in geostrophic balance with the across-shore pressure gradient and a recirculating ageostrophic bulge near the mouth. The distributions of the bulge and plume waters are found to be relatively insensitive to the discharge amount. Under constant wind forcing, the plume distribution changes dramatically. Northerly and easterly winds produce the largest changes with the latter able to deflect the plume up to 180° due to Ekman drift. When sea breeze-like winds are imposed, accumulation of water in the bulge occurs with substantial spreading upstream. Stronger sea breezes lead to less downstream spreading of the plume than gentle winds. When the winds are mainly across-shore, Ekman drift dominates, but the dynamics become almost geostrophic when the winds are roughly aligned to the coast. These experiments suggest that the Zambezi River plume is sensitive to the winds on diurnal to synoptic time-scales.  相似文献   

14.
自约 6ka前我国海岸轮廓形成以来 ,海岸线主要呈淤进状态。在距今 6～ 3ka前 ,因黄河等河流泥沙主要填淤平原洼地 ,岸线稳定微涨 ;在距今约 3ka至 2 0世纪 60年代 ,河流以巨量泥沙使海岸线 ,尤其是低平的平原海岸线迅速外移 ;最近 30 a来 ,因为黄河等河流入海水沙大量减少 ,造成目前除行水河口处淤涨外 ,多数岸段转为侵蚀或稳定 ,且被侵蚀岸线有逐渐扩大的趋势。这种变化导致了新淤土地的减少 ,也破坏了原有的沙滩、湿地资源 ,需要采取一些措施以减少海岸侵蚀带来的损失  相似文献   

15.
Distribution of coliform bacteria was surveyed monthly during July-1968 through December-1969 in Shimizu Harbor and Orido Bay. Among three significant rivers flowing into the coastal region, the water of Tomoe River was most microbiologically polluted. Throughout the period of investigation horizontal distribution of the bacterial density was highest at the estuary of the Tomoe River, and its density decreased toward Shimizu Harbor and Orido Bay.It was shown that the bacterial density decreased from surface to deeper layer. High density of bacteria was observed in bottom deposits at winter. The bacterial distribution might be disturbed by current caused by geographical features.Various types of coliform group were isolated in the surveyed areas. All types ofE. coli, E. freundii, A. aerogenes and Irregular appeared in the area of estuaries, and only limited types occurred in offshore.Bacterial number increased from upper stream toward the mouth of each river. The bacterial density differed from river to river. In the rivers flowing through the city the bacterial density changed with water temperature, whereas in the river running through agricultual district it might be affected with the rainfall.  相似文献   

16.
222Rn was measured in the near-bottom waters of the continental slope of the Mid-Atlantic Bight. Separate measurements of the 222Rn supported by dissolved 226Ra allowed the excess 222Rn that is derived from the underlying sediments to be distinguished. Measurements of production of 222Rn by the sediments were used to calculate fluxes of 222Rn from sediments that would be expected as a result of molecular diffusion. On the upper slope and on the lower slope excess 222Rn standing crops were, respectively, greater than and consistent with fluxes of radon from sediments by molecular diffusion as are typical of most ocean environments. On the middle slope, however, observed excess 222Rn concentrations and standing crops were significantly lower than what would be expected from the calculated fluxes from the underlying sediments. This unusual feature of low radon concentrations on the middle slope is referred to as the low-radon zone (LRZ). This LRZ was always present over several years and seasons, but was variable in intensity (excess-radon concentration and standing crop) and in location on the slope. Low concentrations of suspended particulate matter and low current velocities observed by others in the same region are consistent with low mixing as a possible cause of the LRZ. Radon profile shapes and recent work by others on near bottom mixing due to interactions between topography and internal waves, however, suggest that high mixing due to internal waves is a more likely cause of the LRZ.  相似文献   

17.
Hurricane Isabel made landfall along the North Carolina coast on September 18, 2003 (UTC 17:00) and the storm surge exceeded 2.0 m in many areas of the Chesapeake Bay and in the York River estuary. River flooding occurred subsequently, and the peak river discharge reached 317 and 104 m3 s−1 in the Pamunkey and Mattaponi rivers, respectively. The York River estuary experienced both storm surge and river flooding during the event and the estuary dynamics changed dramatically. This study investigates the hydrodynamics of the York River estuary in response to the storm surge and high river inflows. A three-dimensional model was used to investigate the changes of estuarine stratification, longitudinal circulation, salt flux mechanisms, and the recovery time required for the estuary to return to its naturally evolved condition without the storm. Results show that the salt flux was mainly caused by advection, which was induced by the barotropic gradient during the storm event. The net salt flux increased by a factor of 30 during the rise of the storm surge. However, the large amount of salt transported into the estuary was quickly transported out of the estuary as the barotropic gradient reversed during the descent of the storm surge. Subsequent high freshwater inflow influenced the estuarine circulation substantially. The estuary changed from a partially mixed estuary to a very stratified estuary for a prolonged period. The model results show that it will take about 4 months for the estuary to recover to its naturally evolved salinity distribution after the impacts of the storm surge and freshwater pulse.  相似文献   

18.
《Marine Chemistry》2007,103(1-2):131-145
We have investigated submarine groundwater discharge to Nueces Bay (Texas) using naturally occurring Ra isotopes. Dissolved Ra activities in Nueces Bay are among the highest observed in coastal estuaries; as great as 2600 dpm m− 3 for 228Ra and 1000 dpm m− 3 for 226Ra. Using a combination of salt and Ra mass balances, we demonstrate that river discharge and bay bottom sediments cannot supply the Ra needed to balance tidal export. In the case of 226Ra there is an additional source of 218 × 106 ± 105% dpm day− 1 which is 9 times the maximum supply from bay bottom sediments and 50 times the Ra supplied by the Nueces River. A groundwater flux of 310,000 m3 day− 1 is required to supply the needed 226Ra, based on the measured maximum Ra activity of local groundwater. Though as little as 10% of this flux may be advecting terrestrial groundwater this would still represent 160% of the Nueces River discharge. This makes it unlikely that groundwater discharge alone is supplying all of the additional 226Ra. Oil-field brine could potentially account for the remainder. Leakage of 6290 m3 day− 1 of oil-field brine from the submerged petroleum wells and pipelines within the bay could supply all of the needed 226Ra. Such large fluxes of brackish groundwater and oil-field brine could significantly affect bay nitrogen budgets, salinities, and dissolved oxygen concentrations and should be considered when determining the freshwater inflow requirements for Nueces Bay and similar estuaries.  相似文献   

19.
The nearshore shelf of the Beaufort Sea is defined by extreme physical and biological gradients that have a distinctive influence on its productivity and trophic structure. Massive freshwater discharge from the Mackenzie River, along with numerous smaller rivers and streams elsewhere along the coast, produce an environment that is decidedly estuarine in character, especially in late spring and summer. Consequently, the Beaufort coast provides a critical habitat for several species of amphidromous fishes, some of which are essential to the subsistence lifestyle of arctic native populations. Because of its low in situ productivity, allochthonous inputs of organic carbon, identifiable on the basis of isotopic composition, are important to the functioning of this arctic estuarine system. Coastal erosion and river discharge are largely responsible for introducing high concentrations of suspended sediment from upland regions into the nearshore zone. The depletion in the 13C content of invertebrate and vertebrate consumers, which drops about 4–5‰ eastward along the eastern Alaskan Beaufort Sea coast, may reflect the assimilation of this terrestrial organic matter into local food webs. In addition, the large range in 13C values of fauna collected in the eastern Beaufort (nearly 8‰) compared to the same species in the northeastern Chukchi (3‰), indicate a lower efficiency of carbon transfer between trophic levels in the eastern Beaufort. The wider spread in stable isotope values in the eastern Beaufort may also reflect a decoupling between benthic and pelagic components. Isotopic tracer studies of amphidromous fishes in the Simpson Island barrier island lagoon revealed that terrestrial (peat) carbon may contribute as much as 30–50% of their total dietary requirements. On the eastern Alaska Beaufort Sea coast, the δ13C values of arctic cod collected in semi-enclosed lagoons were more depleted, by 3–4‰, compared to fish collected in the coastal Beaufort Sea. Calculations from isotopic mixing equations indicate cod from lagoons may derive 70% of their carbon from terrestrial sources. The δ15N values of lagoon fish were also 4‰ lower than coastal specimens, reflective of the lower δ15N values of terrestrially derived nitrogen (0–1.5‰ compared to 5–7‰ for phytoplankton). The role of terrestrial carbon in arctic estuarine food webs is especially important in view of the current warming trend in the arctic environment and the role of advective processes that transport carbon along the nearshore shelf. Biogeochemical studies of the arctic coastal estuarine environment may provide more insights into the function of these biologically complex ecosystems.  相似文献   

20.
《Marine Chemistry》2007,103(1-2):172-184
Here we report on temporal changes in the concentration and composition of lignin phenols in high molecular weight (< 0.2 μm, > 1 kDa) dissolved organic matter (HMW DOM) collected from the lower Mississippi and Pearl Rivers (MR and PR) (USA). Monthly water samples were collected at a station in the lower reach in each river from August 2001 to August 2003. Significantly higher concentrations of lignin and Λ8 values (mg lignin phenols in 100 mg organic carbon) in the Pearl River than in the Mississippi River, reflected sporadic inputs of terrestrial DOM during rainstorm events from wetlands and forest soils. Larger seasonal variations in lignin concentration and composition in the Pearl River, compared to the Mississippi River, were attributed to shifts in organic matter sources from topsoil inputs during rainstorm events to groundwater inputs and in situ production during base flow in this small river. Conversely, lower Λ8 and vanillic acid to vanillin ratios [(Ad/Al)v] in the HMW DOM of the lower Mississippi River may be a result of a lower export rate of lignin from agricultural soils due to lower carbon storage in the expansive agricultural systems of the Mississippi River watershed, as well as dilution of phytoplankton DOM inputs. Large seasonal changes in lignin concentration and Λ8 (linked at times with river discharge), and minimal variability in the composition of lignin phenols, likely represented an integrated signal of soil-derived vascular inputs from the upstream drainage basin. If we are to better understand the controls of organic matter delivery to the coastal zone from both small and large rivers, sampling strategies need to be adjusted to account for the different scales of hydrologic response time and in situ processing associated with different residence times.  相似文献   

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