Using radium isotopes to evaluate the uncertainty of submarine groundwater discharge in the northeast and entirety of Daya Bay

Submarine groundwater discharge(SGD),which can be traced using naturally occurring radium isotopes,has been recognized as a significant nutrient source and land-ocean interaction passage for the coastal waters of the Daya Bay,China.However,uncertainties in assessing SGD fluxes must still be discussed in detail.In this study,we attempted to utilize the Monte Carlo method to evaluate the uncertainties of radium-derived SGD flux in the northeast and entirety of the Daya Bay.The results show that the uncertainties of the SGD estimate in the northeast bay are very sensitive to variations in excess radium inventories as well as radium inputs from bottom sediments,while the uncertainties of the SGD estimate for the entire bay are strongly affected by fluctuations in radium inputs from bottom sediments and radium end-members of SGD.This study will help to distinguish the key factors controlling the accuracy of SGD estimates in similar coastal waters.

Optimization of enrichment and pretreatment of low-activity radium isotopes in the open ocean

In the open ocean,radium isotopes are useful tracers of residence time and water-mass mixing.However,limited by the measurement resolution of commonly used gamma counters,the low activity of radium in the open ocean makes it necessary to enrich radium from large volumes of seawater and pretreat radium-enriched carriers prior to measurements.The commonly applied method of radium enrichment and pretreatment,however,has limitations of uneven coating of MnO_(2)on cartridges,relatively expensive cartridges,time-consuming issues during cartridge-ashing,ash loss during transfer,and changes of gamma counters efficiency caused by different ash weights.To address these issues,in this study we optimized the enrichment and pretreatment of low-activity radium prior to measurements.Firstly,we replaced commonly used acrylic cartridges with cheaper polypropylene cartridges,which took 6 h to be ashed,42 h shorter than for acrylic cartridges.Secondly,MnO_(2)-coated cartridges were prepared with a circulating hot acidic KMnO_(4)solution to ensure homogeneous coating.The radium extraction efficiency of this MnO_(2)-coated cartridge was 20%-61%higher than that prepared by directly immersing cartridges in the solution.The radium delayed coincidence counter efficiency for MnO_(2)-coated cartridge was stable with a moisture content of 0.05-1.Lastly,after ashing cartridges,instead of directly transferring the ash to a measurement vial,a mixture of hydroxylamine hydrochloride and hydrochloric acid was used to completely leach the ash for long-lived radium,followed by coprecipitation by BaSO_(4),to avoid potential loss of ash during transfer and variations in measurement geometry due to different ash weights.And the recovery of long-lived radium pretreatment was 94%-102%,which improved by 11%compared with the common method.In addition,the radium extraction efficiency of the MnO_(2)-coated cartridge varied from 3%to 4%within the in situ pump working flow rate of 4-7 L/min,which fell within the measurement errors.

Using radium isotopes to quantify submarine groundwater discharge at different scales in the Huanghe River Estuary,China

As an important land-ocean interaction process,submarine groundwater discharge(SGD)is composed of multiple dynamical processes at different scales and plays an important role in the study of coastal ocean geochemical budgets.However,most of the existing studies focus on the quantification of the total groundwater discharge,few studies are about the differentiation and quantification of groundwater discharge processes at different scales(i.e.,short-scale SGD and long-scale SGD).As a world-class river,the Huanghe River is highly turbid and heavily regulated by humans.These natural and anthropogenic factors have a significant impact on groundwater discharge processes in the Huanghe River Estuary(HRE).In this study,the distribution patterns of the natural geochemical tracer radium isotopes(^(224)Ra and^(223)Ra)and other hydrological parameters in the HRE were investigated during four cruises.By solving the mass balance of^(224)Ra and^(223)Ra in the HRE,the long-scale SGD flux was quantified as 0.01−0.19 m/d,and the short-scale SGD flux was 0.03−0.04 m/d.The rate of short-scale SGD remained essentially constant among seasons,while the rate of long-scale SGD varied considerably at different periods and showed a synchronous trend with the variation of river discharge.The results of this study are significant for understanding the SGD dynamics in the HRE and the contribution of SGD to the ocean geochemical budgets.

Features and factors of radium isotopes in Tianjin’s typical estuaries

In order to characterize the features of radium isotopes in estuaries of Tianjin,a continuous survey and sampling of typical estuaries were conducted from 2013 to 2017 in this study.The activities of natural radioactive radium isotopes(^(223)Ra,^(224)Ra,and ^(228)Ra)in groundwater and surface water were measured by the radium-delayed coincidence counting(RaDeCC)system.The non-conservative behavior of the radium isotopes was investigated under hydrogeochemical conditions and urbanization.The results indicated that in terms of horizontal distribution,the activities of radium in groundwater(Hangu,Tanggu,and Dagang)showed an upward trend from north to south and demonstrated a higher figure than surface water(Haihe River and Duliujian River).Concerning the vertical distribution,the activitives of radium at a 15 m burial depth was higher than that at a 30 m burial depth in all measurements.The activities of radium isotopes in the study area increased with the increase of total dissolved solids,and their desorption behavior on Fe-Mn oxides was constrained by the redox intensity.Different hydrogeological conditions resulted in variations in the vertical profile of radium activities.The activity of radium was regulated by seasonal variation and precipitation in groundwater and surface water.In addition,the rapid urbanization has caused a significant impact on the features of radium isotopes in typical estuaries of Tianjin.Meanwhile,radium isotopes can be applied to reflect the impact of urbanization on surface watergroundwater systems.Clarifying and cleverly utilizing the relationship between behavior of radium isotopes and urbanization will promote the development of the Tianjin Binhai New Area in a healthy way.

Evaluation of shallow groundwater discharge fluxes and nutrient fluxes in the west of Qinghai Lake using radium isotopes

We collected 14 samples and 9 samples for surface water in Quan bay and the north bay of Qinglai Lake respectively,as well as 11 samples for groundwater and 3 samples for river water.First the water samples were filtered through a

Radium isotopes assess water mixing processes and its application in the Zhujiang River estuary

Radium （Ra） isotopes are useful for tracing water mass transport and examining estuarine hydrological dynamics. In this study, several hydrological parameters, nutrients, ehlorophyll-a （ehl-a）, suspended particulate matter （SPM） and Ra isotopes （223Ra, 224Ra and 226Ra） of surface waters of the Zhujiang （Pearl） River estuary （ZRE） were measured. This was done for both winter （December） and summer （July） seasons, to quantitatively understand the seasonal characteristics of river plume flow rate and trajectories, as well as the ecological response. The results show that Ra concentrations in summer were higher than in winter, especially Z24Ra （about 2-5 times higher）. The spatial distribution of three Ra isotopes and relative Ra water ages indicated that river water mainly flushed out of ZRE through the western side in winter, where the water transport was about 5 days faster than in the eastern zone. In summer, diluted river water expended to the east side, resulting in fairly similar water ages for both sides of the river mouth. Although nutrients were higher during the summer season, lower chl-a concentrations indicated that reduced primary production might be caused by high SPM （low light penetration）. The results obtained from this study will provide knowledge needed for effectively developing and managing the ZRE.

Radium Isotopes in an Oil-Field Produced Lake near Baku, Azerbaijan

An assessment of radiologically enhanced residual materials generated during oil and gas production in near Baku, Azerbaijan, was conducted. Distribution of the 228Ra/226Ra Activity Ratio (AR) with depth in a sediment core from radium lake was examined. The dashed line represented ingrowth assuming that 228Ra was below equilibrium with 232Th in the young sediments near the top and reached equilibrium at a depth around 10 cm. In this study the radium isotopic data are used to provide estimates of the age of formation of the radiobarite contaminant and age of oil field lake. The results indicate that, the upper two layers in the core (up to 4 cm) contain fallout 137Cs so at least these layers are no older than about 40 yrs. Formation waters that are sent to disposal ponds may consist of accumulated heavy hydrocarbons, paraffin, inorganic solids, and heavy emulsions. We report here results of chemical and radiochemical measurements from formation waters separated from oil pumped from approximately 700 m below ground near Baku, Azerbaijan. Our results also include data from a formation water storage pond (“radium lake”) where the waters are temporarily stored after oil is separated and then eventually disposed of by pumping into the Caspian Sea. We also analyzed the associated sediment for radiochemical components. Our study was intended to investigate how radium fractionated between the pond water and sediments.

Analysis of Radium Isotopes in Surface Waters nearby a Phosphate Mining with NORM at Santa Quiteria,Brazil

The radium isotopes 226Ra and 228Ra were analyzed in surface water at six points in the neighborhood of a mine of phosphate, associated with uranium, in the region of Santa Quitéria, state of Ceará, Brazil. Water samples were collected during twenty months, filtered and the concentrations of activity determined in the soluble and particulate phases. The results were analyzed using the Principal Component Analysis (PCA) for ordination of environmental data, and also by ANOVA, Tukey and Z tests to compare sets of data considering the radionuclides, the two analyzed phases and the six collecting points. The PCA identified four groups that included all collecting points, using aggregation features such as radionuclide and analyzed phase. The first group is composed by the samples of 226Ra in the soluble phase;the second group by samples of 226Ra in the particulate phase;the third one by 228Ra in the soluble phase, and finally, the fourth group by 228Ra in the particulate phase. This last group has two discrepant points (01 and 06). Statistical analysis identified differences between the concentrations of activity of radionuclides (228Ra higher than 226Ra) and in analyzed phases (soluble phase higher than the particulate one) but showed no differences between sampled points.

Submarine groundwater discharge and associated nutrient fluxes in the Greater Bay Area, China revealed by radium and stable isotopes

The estuary-bay system is a common and complex coastal environment.However,quantifying submarine groundwater discharge(SGD)and associated nutrient fluxes in the complex coastal environment is challenging due to more dynamic and complicated riverine discharge,ocean processes and human activities.In this study,SGD and SFGD(submarine fresh groundwater discharge)fluxes were evaluated by combining stable and radium isotopes in the Guangdong-Hong Kong-Macao Greater Bay Area(GBA),a typical estuary-bay system.We first built a spatially distributed radium mass balance model to quantify SGD fluxes in coastal areas of GBA integrating the Pearl River Estuary(PRE),bays and shelf.We then used the stable water isotope(d2 H and d18O)end-member mixing model to distinguish submarine fresh groundwater discharge(SFGD)from SGD.Based on the 228Ra mass balance,the estimated SGD fluxes in the PRE,adjacent bay,and shelf areas were(6.14±2.74)×10^(8) m^(3) d^(-1),(3.00±1.11)×10^(7) m^(3) d^(-1),and(5.00±5.64)×10^(8) m^(3) d^(-1),respectively.Results showed that the largest area-averaged SGD was in the PRE,followed by that in the adjacent shelf and the bay.These differences may be mainly influenced by ocean forces,urbanization and benthic topographies controlling the variability of groundwater pathways.Further,the three end-member mixing model of ^(228)Ra and salinity was developed to confirm the validity of the estimated SGD using the Ra mass balance model.In the two models,groundwater endmember and water apparent age estimation were the main sources of uncertainty in SGD.The estimated SFGD flux was(1.39±0.76)108 m^(3) d^(-1),which accounted for approximately 12%of the total SGD.Combining stable and radium isotopes was a useful method to estimate groundwater discharge.Moreover,the estimated SGD associated dissolved inorganic nitrogen(DIN)flux was one order of magnitude higher than other DIN sources.SGD was considered to be a significant contributor to the DIN loading to the GBA.The findings of this study are expected to provide valuable information on coastal groundwater management and environmental protection of the GBA and similar coastal areas elsewhere.

Radium-traced nutrient outwelling from the Subei Shoal to the Yellow Sea:Fluxes and environmental implication

The Subei Shoal is the largest sandy ridge in the southern Yellow Sea and is important source for nutrient loading to the sea.Here,the nutrient fluxes in the Subei Shoal associated with eddy diffusion and submarine groundwater discharge(SGD)were assessed to understand their impacts on the nutrient budget in the Yellow Sea.Based on the analysis of 223 Ra and 224 Ra in the field observation,the offshore eddy diffusivity mixing coefficient and SGD were estimated to be 2.3×10^(8)cm^(2)/s and 2.6×10^(9)m^(3)/d(16 cm/d),respectively,in the Subei Shoal.Combined the significant offshore decreasing gradients of nutrient in seawater of the Subei Shoal,the spatially integrated nutrient outwelling fluxes to the Yellow Sea were 262-1465μmol/(m^(2)·d)for DIN,5.2-21μmol/(m^(2)·d)for DIP and711-913μmol/(m^(2)·d)for DSi.Compared to the riverine input,atmospheric deposition and mariculture,nutrient outwelling from the Subei Shoal might play an important role in nutrient budget of the Yellow Sea.These nutrient fluxes could provide 4.1%-23%N and 1.3%-5.3%P requirements for the primary productivity,and the deviated DIN/DIP ratios have the potential to affect the growth of phytoplankton in the marine ecosystem of the Yellow Sea.

Measurement of ^(224)Ra, ^(226)Ra and ^(228)Ra in seawater using Mn-fiber adsorption-γ spectrum method

The specific activities of ^(224) Ra, ^(226)Ra and ^(228)Ra were determined by measuring γ-ray of their daughters with HPGe γ spectrometer after preconcentrating Ra isotope with Mn-fiber adsorption from large volume seawater. The calculating formulas of specific activities of the three nuclides were de rived. The methods of sample preparation and spectrum analysis were discussed. The advantages of the method are simple, rapid and three nuclides can be determined simultaneously.

Estimating submarine groundwater discharge at a subtropical river estuary along the Beibu Gulf,China

In certain regions,submarine groundwater discharge(SGD)into the ocean plays a significant role in coastal material fluxes and their biogeochemical cycle;therefore,the impact of SGD on the ecosystem cannot be ignored.In this study,SGD was estimated using naturally occurring radium isotopes(^(223)Ra and ^(224)Ra)in a subtropical estuary along the Beibu Gulf,China.The results showed that the Ra activities of submarine groundwater were approximately 10 times higher than those of surface water.By assuming a steady state and using an Ra mass balance model,the SGD flux in May 2018 was estimated to be 5.98×10^(6) m^(3)/d and 3.60×10^(6) m^(3)/d based on 224Ra and 223Ra,respectively.At the same time,the activities of Ra isotopes fluctuated within a tidal cycle;that is,a lower activity was observed at high tide and a higher activity was seen at low tide.Based on these variations,the average tidal pumping fluxes of SGD were 1.15×10^(6) m^(3)/d and 2.44×10^(6) m^(3)/d with 224Ra and 223Ra,respectively.Tidaldriven SGD accounts for 24%-51%of the total SGD.Therefore,tidal pumping is an important driving force of the SGD in the Dafengjiang River(DFJR)Estuary.Furthermore,the SGD of the DFJR Estuary in the coastal zone contributes significantly to the seawater composition of the Beibu Gulf and the material exchange between land and sea.

Submarine groundwater discharge and benthic biogeochemical zonation in the Huanghe River Estuary

Submarine groundwater discharge(SGD)has received increasing attention by studies on coastal areas;however,its effects on biogeochemical zonation have not been investigated to date.The Huanghe River Estuary(HRE)is a world class river estuary with high turbidity,and heavy human regulation.This study investigated how SGD is related to the benthic biogeochemistry of the HRE.Based on the distribution of several parameters(e.g.,salinity,temperature,dissolved oxygen(DO)levels,p H,radium isotopes,and nutrients),the HRE was subdivided into six different zones,and the SGD fluxes within each zone were quantified and compared.The highest SGD flux was found in the northwest nearshore zone,where it was more than one order of magnitude higher than in the offshore zone.High SGD resulted in low DO and p H,but high nutrient levels in the benthic boundary layer.The southeast nearshore zone was also characterized by high SGD flux,but benthic waters were more oxic because of the dominating inputs by the Huanghe River.These data suggest that such a zonation would help to understand benthic biogeochemical processes.High SGD may not only contribute to the estuarine nutrient budget,but may also contribute to the formation of hypoxia and acidification.

The significant role of submarine groundwater discharge in an Arctic fjord nutrient budget

Under global climate change,water flow and related nutrient biogeochemistry in the Arctic are changing at an unprecedented rate,and potentially affect nutrient cycling in the Arctic Ocean.However,nutrient fluxes via submarine groundwater discharge(SGD)are potentially important yet poorly understood in the Arctic.Here we quantified that nutrient fluxes through radium-derived SGD were three orders of magnitude higher than those from the local river and constituted 25%-96%of the total nutrient inputs into the Kongsfjorden.These large groundwater nutrient fluxes with high NIN/DIP molar ratio(average 99)may change the biomass and community structure of phytoplankton.Meanwhile,combining other SGD study cases around the Arctic region,SGD rates tend to increase over the past three decades,possibly on account of the effects of global warming.The SGD-derived nutrient may cause the increase of net primary productivity in the Arctic Ocean.The results will provide important basic data for land-ocean interactions in the typical fjord of the Arctic under the influence of global warming.

Advances in the study of submarine groundwater discharge(SGD)in China

Submarine groundwater discharge(SGD)is a critical land-ocean process in coastal areas and an essential component of the global hydrological cycle.Thus,hydrologists and oceanographers are paying more attention to SGD.SGD transports large amounts of materials into the ocean,including nutrients,carbon,and metals,and thus plays a vital role in the cycling of marine materials and affects the ecological environments of nearshore areas.This study examined the research status of SGD and its environmental effects in China,including a systematic analysis of radium activities and nutrient contents in groundwater,SGD rates,and the contribution of SGD to nutrients in various coastal ecosystems(bays,estuaries,continental shelves,and lagoons).The results showed the median concentrations of groundwater nutrients(dissolved inorganic nitrogen DIN,dissolved inorganic phosphorus DIP,and dissolved inorganic silicon DSi),SGD rates,and SGD-derived DIN and DIP in estuarine areas far exceeded those in the other three ecosystems studied.This result could be attributed to the complex hydrodynamic conditions of estuary areas as well as the considerable influence of human activities.Conversely,the lowest SGD rates and three inorganic nutrient species via SGD were observed in large scale continental shelves.SGD-derived nutrient fluxes were comparable to riverine inputs along the entire coast of China,which significantly affected the nutrient budget,nutrient composition,and primary productivity of coastal waters.Finally,this review suggests further research of SGD in three aspects:(1)accurate assessment,(2)its environmental effects,and(3)its regulatory strategies.