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.

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.

Submarine groundwater discharge and seasonal hypoxia off the Changjiang River Estuary

Hypoxia is a common phenomenon in the sea adjacent to the Changjiang River Estuary(CJE),one of the global major estuaries.Submarine groundwater discharge(SGD)is a widely recognized pathway for terrestrial materials entering the sea,and has been found to be significant off the CJE.We used a^(222)Rn mass balance model to estimate the SGD fluxes off the CJE and showed that it is linked to seasonal dissolved oxygen(DO)variations.Average SGD fluxes were estimated to be(0.012±0.010)m^(3)/(m^(2)·d)in winter,(0.034±0.015)m^(3)/(m^(2)·d)in summer,and(0.020±0.010)m^(3)/(m^(2)·d)in autumn.We found a significant negative correlation between DO concentrations and SGD rates with groundwater discharge being highest in the summer flood season.In addition,distribution patterns of SGD and hypoxia zones in summer are spatially overlapped,indicating that SGD is an important contributor to summer hypoxia in this region.

Distinguishing the main components of submarine groundwater and estimating the corresponding fluxes based on radium tracing method—taking the Maowei Sea for example

Submarine groundwater discharge(SGD)is an important part in the land-sea interactions,which mainly contains three components:submarine fresh groundwater discharge(SFGD),tidal flat recirculated saline groundwater discharge(tidal flat RSGD)and subtidal recirculated saline groundwater discharge(subtidal RSGD).In order to make a more accurate assessment of the impact of SGD on coastal ecological environment,it is necessary to distinguish the main components of SGD.In this study,the Maowei Sea,located in the northern part of the Beibu Gulf,was selected as the study area.Based on the radium(Ra)tracing method,we present a new analytical method for distinguishing the three main components of SGD in this area combined with field data.The average daily flow along the coastline of the Maowei Sea of tidal flat RSGD was slightly higher than that of SFGD,and both two were on the magnitude of 1×10^(5)m^(3)/d.The average daily flow for the subtidal RSGD of the entire subtidal zone of the Maowei Sea reached to the magnitude of 1×10^(6)-1×10^(7)m^(3)/d.The long-term variation trend of terrestrial SGD is a valuable information for the study of the influence of terrigenous material on the coastal ecological environment.Based on the results of four sampling periods,it is found that the fluxes of SFGD and tidal flat RSGD in the Maowei Sea had good linear correlation with the net precipitation.As an example,January 2015 to August 2022 were selected as the study periods,and the variation trends of SFGD and tidal flat RSGD were calculated by linear function with net precipitation as the independent variable.The results showed that the flux of tidal flat RSGD was slightly higher than that of SFGD,and the difference between the two is larger in flood season while smaller in dry season.In general,in the coastal range of China,the total SGD flux in the Maowei Sea area is at a high level,and the SFGD flux is at a medium level.

Submarine groundwater discharge enhances primary productivity in the Yellow Sea, China: Insight from the separation of fresh and recirculated components

Submarine groundwater discharge(SGD)is being increasingly recognized as a significant source of nutrient into coastal waters,and generally comprises two components:submarine fresh groundwater discharge(SFGD)and recirculated saline groundwater discharge(RSGD).The separate evaluation of SFGD and RSGD is extremely limited as compared to the conventional estimation of total SGD and associated nutrient fluxes,especially in marginal-scale regions.In this study,new high-resolution radium isotopes data in seawater and coastal groundwater enabled an estimation of SGD flux in a typical marginal sea of the Yellow Sea.By establishing 226Ra and 228Ra mass balance models,we obtained the SGD-derived radium fluxes,and then estimated the SFGD and RSGD fluxes through a two end-member model.The results showed that the total SGD flux into the Yellow Sea was equivalent to approximately 6.6 times the total freshwater discharge of surrounding rivers,and the SFGD flux accounted for only 5.2%–8.8%of the total SGD.Considering the nutrient concentrations in coastal fresh and saline groundwater,we obtained the dissolved inorganic nutrient fluxes(mmol m^(-2) yr^(-1))to be 52–353 for nitrogen(DIN),0.21–1.4 for phosphorus(DIP),34–226 for silicon(DSi)via SFGD,and 69–262 for DIN,1.0–3.9 for DIP,70–368 for DSi via RSGD,with the sum of nutrient fluxes equaling to(1.8–9.3)-fold,(1.3–5.6)-fold and(2.0–9.5)-fold of the riverine inputs.Compared to the conventional estimation of the total SGD flux,the nutrient fluxes derived from the separation of SFGD and RSGD were(1.6–2.1),(1.6–1.8)and(4.0–4.9)times lower for DIN,DIP and DSi,respectively,indicating that the estimates by separating SFGD and RSGD could be conservative and representative results of the Yellow Sea.Furthermore,we suggested that SGD played an important role in nutrient sources among all the traditional nutrient inputs sources,providing 15%–48%,33%–68%and 14%–43%of the total DIN,DIP and DSi input fluxes into the Yellow Sea,and the high nutrient stoichiometric ratios(i.e.,DIN/DIP)in SGD probably contributed to the increasing ratios in the Yellow Sea.In addition delivering large amounts of nutrient into the Yellow Sea,SGD would create primary productivity of 10–49,1.6–6.8 and 8.8–42 g C m^(-2)yr^(-1) based on N,P and Si,which were equivalent to 5.2%–27%,0.9%–3.7%and 4.7%–23%of the total primary productivity,respectively.In particular,the SFGD-derived DIN flux can be converted to primary productivity of 4.2–28 g C m^(-2)yr^(-1) thus demonstrating the disproportionately large role of SFGD in ecological environment of the Yellow Sea relative to its flux.Therefore,we conclude that SGD,particularly SFGD,plays an important role as a nutrient source for the Yellow Sea,and not only affects nutrient budgets and structures but also enhances the primary productivity.

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.

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.

Estimating submarine groundwater discharge and associated nutrient inputs into Daya Bay during spring using radium isotopes

Daya Bay, a semi-enclosed bay in the South China Sea, is well known for its aquaculture, agriculture, and tourism. In recent years, many environmental problems have emerged, such as the frequent(almost yearly) occurrence of harmful algal blooms and red tides. Therefore,investigations of submarine groundwater discharge(SGD) and associated nutrient inputs to this bay have important theoretical and practical significance to the protection of the ecological system. Such a study was conducted using short-lived radium isotopes ^(223)Ra and ^(224)Ra. The estimated SGD fluxes were 2.89 × 10~7 m^3/d and 3.05 × 10~7 m^3/d based on ^(223)Ra and ^(224)Ra, respectively. The average SGD flux was about 35 times greater than that of all the local rivers. The SGD-associated dissolved inorganic nitrogen(DIN) and dissolved inorganic phosphorus(DIP)fluxes ranged from 1.95 × 10~6 to 2.06 × 10~6 mol/d and from 5.72 × 10~4 to 6.04 × 10~4 mol/d, respectively. The average ratio of DIN to DIP fluxes in SGD was 34, much higher than that in local rivers(about 6.46), and about twice as large as the Redfield ratio(16). Our results indicate that SGD is a significant source of nutrients to the bay and may cause frequent occurrence of harmful algal blooms. This study provides baseline data for evaluating potential environmental effects due to urbanization and economic growth in this region.

Submarine groundwater discharge around Taiwan

A preliminary study shows that the submarine groundwater discharge（SGD） exists around Taiwan even though groundwater overdrawing on the island is serious. Fifteen of the 20 sites studied for major anions and cations recorded a clear SGD signal with freshwater outflow. A total of 278 salinity and major ion measurements were made. Sixteen nearly freshwater SGD（salinity≤1.0） samples were obtained, providing strong and direct evidence for the existence of fresh meteoric groundwater entering the ocean from Taiwan. The total SGD flux is estimated to be 1.07×1010 t/a which is about 14% of the annual river output. The freshwater component of the SGD is3.85×109 t which is about 5.2% of the annual river discharge in Taiwan. The collected SGD has a composition similar to seawater with an addition of Ca, CO3 and HCO3 due to dissolution of calcareous rocks. Some samples with high Cl/（Na＋K） may indicate pollution.

^(222)Rn指示北部湾北部近海SGD输送的时空特征初探

放射性同位素氡222(^(222)Rn)是来源于地层中铀衰变生成的惰性元素。由于其性质稳定,容易测量且在地下水和地表水中活度差异显著,近年来被用作示踪剂广泛应用在海底地下水排泄(submarine groundwater discharge,SGD)的研究中。本文选取北部湾北部海水的^(222)Rn活度作为研究对象,通过2021年8月—9月以及12月—次年1月在北部湾北部海域的两个航次采样,分析了北部湾北部海域水体^(222)Rn的空间分布和季节性变化特征,并结合^(222)Rn的质量平衡模型,估算了北部湾北部海域的SGD通量。结果表明,^(222)Rn分布特征受到季节变化和陆源SGD过程的显著影响,冬季^(222)Rn活度的平均值与夏季相比减少了约40%。夏季底层水^(222)Rn活度较高,断面特征显示SGD过程明显且多集中于研究区北部,而冬季底层水^(222)Rn活度较低,断面特征显示SGD过程较弱。通过构建^(222)Rn质量平衡模型,估算出北部湾北部海域夏季与冬季SGD速率分别为4.16 cm·d^(-1)和2.88 cm·d^(-1)。夏季SGD速率明显高于冬季,且夏季以近岸SGD过程为主,冬季以离岸SGD为主。北部湾北部海域存在着明显的SGD过程,而且由于该区域被陆地和岛屿三面环绕,SGD过程很可能是陆源物质向近岸海域输送的重要自然途径。

Linking bacterial and archaeal community dynamics to related hydrological,geochemical and environmental characteristics between surface water and groundwater in a karstic estuary

Subterranean estuaries(STEs)are characterized by the mixing of terrestrial fresh groundwater and seawater in coastal aquifers.Although microorganisms are important components of coastal groundwater ecosystems and play critical roles in biogeochemical transformations in STEs,limited information is available about how their community dynamics interact with hydrological,geochemical and environmental characteristics in STEs.Here,we studied bacterial and archaeal diversities and distributions with 16S rRNA-based Illumina MiSeq sequencing technology between surface water and groundwater in a karstic STE.Principal-coordinate analysis found that the bacterial and archaeal communities in the areas where algal blooms occurred were significantly separated from those in other stations without algal bloom occurrence.Canonical correspondence analysis showed that nutrients and salinity can explain the patterns of bacterial and archaeal community dynamics.The results suggest that hydrological,geochemical and environmental characteristics between surface water and groundwater likely control the bacterial and archaeal diversities and distributions in STEs.Furthermore,we found that some key species can utilize terrestrial pollutants such as nitrate and ammonia in STEs,indicating that these species(e.g.,Nitrosopumilus maritimus,Limnohabitans parvus and Simplicispira limi)may be excellent candidates for in situ degradation/remediation of coastal groundwater contaminations concerned with the nitrate and ammonia.Overall,this study reveals the coupling relationship between the microbial communities and hydrochemical environments in STEs,and provides a perspective of in situ degradation/remediation for coastal groundwater quality management.

厦门湾砂质潮间带海底地下水排泄的非均质性研究

以厦门岛南岸砂质海岸为研究对象,通过监测潮间带渗出面处地下水盐度、近岸海水盐度,并分析潮间带盐度空间分布规律,以探究厦门湾海底地下水排泄(SGD)的非均质性。结果显示:1)潮间带地下水、海水盐度变化可以间接指示海底地下淡水排泄量(SFGD)。2)垂直于海岸线方向,由内陆向海洋地下水盐度呈现先降低后升高的规律;沿海岸线方向,整个潮滩地下水盐度分布不均匀,差异性较大,具有明显的非均质性。3)通过对潮间带中部最低盐度区域进行加密监测,圈定了厦门湾潮间带高渗透天窗范围,推测高渗透天窗对SFGD影响较大。4)通过对典型剖面地下水、近岸海水盐度动态监测,发现潮汐对潮间带SFGD产生一定影响。

近岸海域^(226)Ra的时空变化与海底地下水排泄(SGD)估算

海底地下水排泄(submarine groundwater discharge,SGD)是沿海地区陆地物质向海洋输送的重要途径,中国具有漫长的海岸线,准确地评估我国沿海地区的SGD及其对沿海海洋生态环境的潜在影响具有重要的理论与实践意义。本文以浙江舟山朱家尖海湾为研究区域,通过冬、夏两季地下水和海水的同步采样分析,在研究地下水和海水中镭(226Ra)时空变化的基础上,利用226Ra的质量平衡原理,估算了研究区内SGD的通量为2.40×105～2.30×106 m3/d,根据12月份枯水期推算的全年保守通量为8.64×107～8.28×108 m3/a,另外,根据年平均降水量等水文参数估算的氮、磷和硅营养盐年平均的入海通量分别为3.256 t/a、0.029 t/a和52.775 t/a。

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.

基岩海岛地下水与海水相互作用研究

中国北方基岩海岛水文地质条件独特,气候变化和人类活动不同程度地影响着海岛地下水与海水相互作用过程,然而对包括海水入侵(SWI)和海底地下水排泄(SGD)的水文过程的定量认识比较缺乏。本研究基于2012—2016年我国北方某基岩群岛降水、地下水水位、水质动态监测数据,运用数理统计、空间插值和水力学方法,分析了基岩海岛地下水与海水相互作用的特征和影响因素。结果表明,降水和开采是影响地下水、海水相互作用的主要因素,地下水水位变化滞后于降水事件约10 d;南岛东北岸、南岸的大部分地区没有发生海水入侵,地下水向海排泄过程较稳定,2012—2016年SGD速率均值为0.2 m/d,向海NO3-N通量均值为81.8 mmol/(m^(2)·d);北岛东南地区是海水入侵的严重区域,地下水水位长期低于海平面且逐年下降,2012—2016年SWI速率均值为0.3 m/d,向陆NO3-N通量均值为69.6 mmol/(m^(2)·d)。分别计算南、北两岛枯水季(2014年4月)、丰水季(2013年9月)SGD水量,北岛SGD水量为3.5×10^(4)~4.5×10^(4)m^(3)/d,南岛SGD水量为0.4×10^(4)~1.1×10^(4)m^(3)/d。相关结果可为基岩海岛地下水资源管理和生态环境保护提供重要参考。

福建漳江口红树林湿地溶解无机碳横向输送的研究

红树林作为地球上最富碳的生态系统之一,是重要的蓝色碳汇。孔隙水/海底地下水排放(Submarine Groundwater Discharge,SGD)作为陆海交互作用的重要过程,是红树林碳横向输送的重要途径。本研究于2017年4月在福建省云霄县漳江口红树林潮沟处进行为期24 h的时间序列观测,并采集了河流(漳江)、孔隙水和生活污水样品,进行了镭(Ra)同位素、溶解无机碳(Dissolved Inorganic Carbon,DIC)、总碱度(Total Alkalinity,TA)、pH、流速的测定,量化了红树林溶解碳的横向输送(包括孔隙水输送和地表水输送)通量。结果表明,表层水体中DIC浓度与Ra活度(SGD示踪剂)呈正相关关系,孔隙水是潮沟DIC的重要来源,高于河流输入和污水排放。基于Ra质量平衡模型和潮动力模型估算的孔隙水交换速率为(0.2±0.1)m/d。红树林通过孔隙水交换输送至潮沟的单位红树林面积的DIC、TA、溶解有机碳(Dissolved Organic Carbon,DOC)和游离CO_(2)的通量分别为1013、1008、332和52 mmol/(m2·d);潮沟水体在潮汐作用下横向输送至河口的单位河道面积的DIC、TA、DOC和游离CO_(2)的通量分别是1136、1349、131和170 mmol/(m2·d),溶解碳主要以DIC的形式输出(占比82%)。漳江口红树林通过孔隙水向潮沟输送的溶解碳通量(3.9×104 mol/d)贡献了潮沟地表水横向输送DIC通量的89%,占红树林植被固碳量的23%,与漳江口红树林沉积物的碳埋藏量(3.2×104 mol/d)相当,是海岸带蓝碳收支的重要组成部分。

Quantifying tidal contribution to submarine groundwater discharges: A review

Submarine groundwater discharges (SGD), consisting of groundwater flow from both terrestrial and marine origins, is an important source of nutrients, contaminants, and other chemicals to the coastal waters, and has significant impacts and implications on coastal environment and ecology. This paper reviews the recent advances in quantifying the tide-induced SGD in various beach aquifers around the world by means of mathematical modeling, laboratory experiments, and field observations or their combinations. Numerous studies have shown that (1) the order of magnitude of SGD around the world estimated by radium isotope tracers typically ranges from 102 to 103m3d-1m-1 of the shoreline, (2) SGD is mainly of marine origin, i.e. the re-circulated seawater across the aquifer-sea interface, and (3) tide is one of the major forces driving seawater-groundwater circulation. The order of magnitude of the tidal contributions to SGD from beach aquifers reported in the literature is only 10m3d-1m-1 length of shoreline, at least one order of magnitude smaller than the total SGD estimated by radium isotope tracers. This is obviously in contradiction with (3). The possible reasons for this contradiction may include (1) underestimation of the shoreline length due to neglecting many headlands, bays and banks of tidal rivers, and (2) negligence of the seawater-groundwater exchange from the seabed ranging from the nearshore areas to the continental shelf. Further research is needed to understand more about the contradiction.

Spatial distribution and export of nutrients and metal elements in the subterranean estuary of Daya Bay

Subterranean estuaries(STE)are important seawater-groundwater mixing zones with complex biogeochemical processes,which play a vital role in the migration and transformation of dissolved materials.In this study,we first investigated the spatial distributions of dissolved inorganic nitrogen(DIN),dissolved inorganic phosphorous(DIP),dissolved inorganic silicon(DSi)and metal elements(As,Ba,Cr,Cu,Fe,Mn,Ni,Pb,and Zn)in STE including upper intertidal,seepage face and subtidal zones.We then estimated submarine groundwater discharge(SGD)and associated nutrient and metal element fluxes.From the generalized Darcy’s law method,SGD was estimated to be 30.13 cm/d,which was about 7 times larger than the inflow(4.16 cm/d).The nutrient and metal fluxes from SGD were estimated to be(5.33±4.99)mmol/(m^(2)·d)for DIN,(0.22±0.03)mmol/(m^(2)·d)for DIP,(16.20±2.05)mmol/(m^(2)·d)for DSi,(1325.06±99.10)μmol/(m^(2)·d)for Fe,(143.41±25.13)μmol/(m^(2)·d)for Mn,(304.06±81.07)μmol/(m^(2)·d)for Zn,(140.21±13.33)μmol/(m^(2)·d)for Cu,(84.49±2.94)μmol/(m^(2)·d)for Pb,(37.38±5.51)μmol/(m^(2)·d)for Ba,(27.88±3.89)μmol/(m^(2)·d)for Cr,(10.10±6.33)μmol/(m^(2)·d)for Ni,and(6.25±3.45)μmol/(m^(2)·d)for As.The nutrient and metal fluxes from SGD were relatively higher than those from the inflow,suggesting that nearshore groundwater acted as the sources of nutrients and metal elements discharging into the sea.The environmental potential pollution of coastal seawater was evaluated by pollution factor index(Pi),comprehensive water quality index(CWQI),and ecological risk index(ERI).Pb mainly caused potential danger of nearshore environment with considerable contamination(Pi=5.78±0.19),heavy pollution(CWQI=4.09)and high ecological risk(ERI=18.00).This study contributed to better understanding the behavior of nutrients and metal elements and improving the sustainable management of STE under the pressure of anthropogenic activities and climate change.

Using Rn-222 to Study Human-Regulated River Water-Sediment Input Event in the Estuary

The implementation of the water sediment regulation scheme(WSRS)is a typical example of artificially controlling land-source input.During WSRS,the water discharge of the Yellow River will increase significantly,and so will the input of terri-genous materials.In this study,we used a natural geochemical tracer 222Rn to quantify terrestrial inputs under the influence of the 2014 WSRS in the Yellow River Estuary.The results indicated that during WSRS the concentration of 222Rn in the estuary increased by about four times than in the period before WSRS.The high-level 222Rn plume disappeared quickly after WSRS,indicating that 222Rn has a very short‘memory effect’in the estuary.Based on the investigation conducted from 2015 to 2016,the concentration of 222Rn tended to be stable in the lower reaches of the Yellow River.During WSRS,the concentrations of 222Rn in the river water in-creased sharply at about 3–5 times greater than in the non-WSRS period.Based on the 222Rn mass balance model,the fluxes of 222Rn caused by submarine groundwater discharge(SGD)were estimated to be(3.5±1.7)×10^(3),(11±3.9)×10^(3),and(5.2±1.9)×10^(3)dpm m^(-2)d^(-1)in the periods before,during,and after WSRS,respectively.This finding indicated that SGD was the major source of 222Rn in the Yellow River Estuary,which can be significantly increased during WSRS.Furthermore,the SGD-associated nutrient fluxes were estimated to be 9.8×10^(3),2.5×102,and 1.1×10^(4)μmolm^(-2)d^(-1)for dissolved inorganic nitrogen,phosphorus,and silicon,respectively,during WSRS or about 2–40 times greater than during the non-WSRS period.

Measuring^(222)Rn in aquatic environment via Pulsed Ionization Chamber Radon Detector

Radon(Rn)is a naturally occurring radioactive inert gas in nature,and^(222)Rn has been routinely used as a powerful tracer in various aquatic environmental research on timescales of hours to days,such as submarine groundwater discharge.Here we developed a new approach to measure^(222)Rn in discrete water samples with a wide range of^(222)Rn concentrations using a Pulsed Ionization Chamber(PIC)Radon Detector.The sensitivity of the new PIC system is evaluated at 6.06 counts per minute for 1 Bq/L when a 500 mL water sample volume is used.A robust logarithmic correlation between sample volumes,ranging from 250 mL to 5000 mL,and system sensitivity obtained in this study strongly suggests that this approach is suitable for measuring radon concentration levels in various natural waters.Compared to the currently available methods for measuring radon in grab samples,the PIC system is cheaper,easier to operate and does not require extra accessories(e.g.,drying tubes etc.)to maintain stable measurements throughout the counting procedure.