钦州湾河流沉积物中镭的解吸行为

放射性镭同位素在海底地下水排放（SGD）等海洋物质变化过程的研究中具有优良的示踪作用,估算SGD通量时需要计算河流悬浮颗粒物的解吸通量。因此,对河流沉积物/悬浮颗粒物中镭同位素解吸行为的研究不可或缺,而目前对于粒度较小范围内镭同位素的解吸特征及其机理的研究依然不足。本文选用钦州湾河流沉积物,通过室内实验探究粒度和盐度对沉积物中镭同位素解吸行为的影响。结果表明,在沉积物平均粒径0.9~136.0 μm范围内,随着粒径增大,沉积物中镭同位素在海水（盐度为33.9）中解吸活度逐渐减小,且变化趋势也逐渐变缓,平均粒径大于43.7 μm后,解吸量几乎不变;在海水盐度4.9~33.9范围内,随着盐度增大,沉积物中镭同位素解吸活度逐渐增大,盐度大于24.9后,解吸量趋于不变。本文创新性地建立了沉积物表面分形结构的镭解吸理论模型,拟合得到钦州湾河流沉积物表面最大可交换态224Ra、226Ra和228Ra活度分别为1.13 dpm/g、0.17 dpm/g和0.85 dpm/g,以干重计;沉积物中224Ra、226Ra和228Ra最大解吸比分别为30%、7%和18%。钦州湾河流沉积物颗粒表面最大可交换态224Ra和226Ra活度分别处于全球中等水平和较低水平,而其最大解吸比分别处于全球较高水平和较低水平。本研究结果有助于更好地理解镭同位素的解吸行为,以帮助更准确地估算SGD通量。     

苏北浅滩海底地下水排放及其对海域营养盐通量的贡献

海底地下水排放(SGD)是近海海域的一个重要的营养盐来源。本研究借助多种天然镭同位素对春季苏北浅滩海域的SGD及其携带入海的营养盐通量进行量化评估。研究发现:苏北浅滩海域的~(224)Ra、~(223)Ra和~(226)Ra等镭同位素的浓度水平较高,呈现近岸高、远岸低的分布趋势;根据~(224)Ra/~(226)Ra的"表观年龄模型"估算的水龄的分布情况推断,春季该海域表层水体主体流向为东北向,流速约为0.1m/s,这与前人物理海洋数值模拟结果一致;最终利用226Ra质量平衡模型发现海域的SGD通量为(46±29)cm/d,由其携带入海的溶解态无机氮、磷、硅营养盐(DIN、 DIP、 DSi)等的通量分别为(2.6±3.1)×1~09、(3.0±2.5)×10~6和(5.5±4.2)×10~8mol/d。     

海底地下水排放对典型红树林蓝碳收支的影响

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。     

盐度对镭同位素在海南红树林沉积物解吸行为的影响

天然放射性镭同位素在沉积物上的解吸行为是影响其在陆-海交换过程中的关键所在。采用沉积物室内解吸实验和现场采集间隙水测量224Ra含量两种方法,对水体盐度梯度控制镭在海南八门湾红树林沉积物的解吸行为进行了讨论。结果表明:沉积物上可交换态224Ra的最大量为0.44dpm/g,解吸比为35%。利用间隙水的224Ra含量确定镭的分配比Kd与水体盐度S呈反比例函数:Kd=8.4×102/S,与室内解吸实验的结果相比更能代表镭在沉积物上的真实解吸行为。在深度25—40cm内,湿地沉积物的224Ra处于与其母体228Th的平衡状态,但223Ra很可能处于相对其母体227Th亏损状态。     

用镭同位素评价胶州湾水体表观年龄及地下水入海通量

为评价胶州湾水体表观年龄和地下水入海通量,2011年9—10月在胶州湾地区分别采集地下水、河水和海水样品,对水样的224Ra和226Ra活度进行测量。基于224Ra和226Ra半衰期的差异,运用224Ra与226Ra的活度比值计算了胶州湾水体表观年龄;采用三端元混合模型计算了胶州湾海水中地下水、河水与湾外海水的混合比例;在水体表观年龄和混合比例的基础上,计算了地下水入海通量。结果表明:研究期间胶州湾水体表观年龄分布范围为3.2—39.4d,平均值为14.7d,呈现从湾顶到湾口年龄逐渐增大的趋势,地下水的平均混合比例是11.0%,地下水的入海通量为7.29×106m3/d,海底地下水排泄速率为3.8cm/d。     

秋季红沿河核电站海域水龄分布及其对水母丰度分布的影响

本研究调查了秋季红沿河核电站海域镭、氡同位素的活度水平及分布情况,结合镭同位素表观年龄模型计算该海域的水体年龄,进而得出研究区域的水体运移方向,初步探讨了水母丰度分布与水体运移的相关关系。得到结论如下:(1)红沿河核电站海域表层水体中224Ra、226Ra及222Rn的活度水平分别为2.9～62.4 dpm/(100 L),11.9～57.4 dpm/(100 L)及0.1～1.3 dpm/L,镭同位素活度呈现出近岸高、远岸低的分布趋势,氡同位素的分布则更大程度上受水温控制;(2)通过224Ra/226Ra表观年龄模型计算得出红沿河海域表层水体年龄范围介于0～16 d,平均年龄(10.9±3.6) d,水体主体流向为北偏东方向,流速为7.2 cm/s;(3)水母丰度分布与水体流向呈现出较为一致的对应关系,在主体流向方向上,水体年龄较大的海域水母丰度最高。     

桑沟湾不同形态锰的分布、季节变化及影响因素

利用催化动力学分光光度法和两步提取法对2011年4月（春）、8月（夏）、10月（秋）和2012年1月（冬）桑沟湾海域溶解态无机锰(DIMn)和表层沉积物中的锰的含量进行测定。结果表明,桑沟湾4个季节（春季至冬季,后同）DIMn浓度呈现出近岸高、远岸低的分布特点,其平均浓度分别为(60.5±43.1) nmol/L、(42.0±30.5) nmol/L、(23.4±11.2) nmol/L和(18.2±13.5) nmol/L,呈现出明显的季节变化,即春季最高,夏季、秋季次之,冬季最低;与相邻的俚岛湾和爱莲湾相比,桑沟湾春季、夏季DIMn的浓度较高,秋季、冬季则没有显著性差异。桑沟湾表层沉积物中总Mn在4个季节的含量分别为(861±308) mg/kg、(915±322) mg/kg、(589±108) mg/kg、(653±185) mg/kg,表层沉积物中醋酸提取态Mn在4个季节的含量分别为(500±272) mg/kg、(502±232) mg/kg、(322±81) mg/kg、(345±91) mg/kg,两者均表现出近岸高、远岸低的分布特点。醋酸提取态Mn的含量在春季、夏季要显著高于秋季、冬季。悬浮颗粒物的吸附和浮游生物的利用是影响桑沟湾DIMn浓度与分布的重要因素。桑沟湾DIMn的源主要包括河流及地下水输送、大气输送、沉积物?水界面释放;汇主要包括养殖生物的清除、向黄海的输送等。简单箱式模型收支计算结果显示,桑沟湾DIMn的源略大于汇,表明除了养殖生物的清除和向黄海的输送,桑沟湾DIMn还存在其他汇。本研究的结果为桑沟湾DIMn的生物地球化学循环的深入认识提供了基础数据。     

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 2.3×10⁸ cm     

桑沟湾溶解态铝的分布、季节变化及影响因素

基于2011-04,2011-08,2011-10和2012-01对桑沟湾海域大面调查的资料,利用改进的荧光镓(LMG)分子荧光光谱分析法测定溶解态铝的含量,研究了桑沟湾溶解态铝的分布和季节变化特征。结果表明,4个航次桑沟湾溶解态铝的平均浓度分别是(47.3±14.4),(56.0±14.6),(64.5±11.3)和(32.1±6.0)nmol/L,呈现出明显的季节变化,即秋季最高,夏季、春季次之,冬季最低。除几个异常站位外,溶解态铝的分布大致呈现随离岸距离的增加其浓度逐渐降低的趋势。夏季表层溶解态铝的浓度在近岸出现低值,夏、秋季湾口北部均出现高值。影响桑沟湾溶解态铝分布的主要因素包括与黄海的水交换、河流及地下水、浮游植物和养殖生物、悬浮颗粒物。根据简单箱式模型对桑沟湾溶解态铝的通量进行了估算,结果显示,除了河流和大气沉降外,桑沟湾溶解态铝还存在其他的源。与相邻的爱莲湾和俚岛湾相比,桑沟湾溶解态铝的浓度在春季较高,在夏季较低。与世界大洋相比,桑沟湾溶解态铝的浓度全年均较高。     

桑沟湾沉积碳库年汇入速率的长期变化及其区域性差异

对取自桑沟湾北西南三根柱样近200 a碳来源及埋藏通量的解析,分析了湾内不同站位各形态碳的差异性,进而对全湾碳埋藏进行了估算。湾内环流、贝藻养殖等造成湾内不同区域碳埋藏的差异;桑沟湾总碳（TC）平均量1.79%,有机碳（TOC）平均量0.54%,无机碳（TIC）平均量1.25%,TOC含量相对较小,为海陆混合来源,以陆源有机碳（C_t）为主,大规模人工养殖后,海源有机碳（C_a）有明显增加的趋势。桑沟湾碳埋藏通量平均为228.9 g/（m2·a）,以无机碳为主要埋藏形式（约占70%）,高的沉积速率及生物残骸沉降使桑沟湾养殖区碳的来源及埋藏区别于其他陆架海域。     

226Ra and 228Ra in the mixing zones of the Pee Dee River-Winyah Bay,Yangtze River and Delaware Bay Estuaries

²²⁶Ra and ²²⁸Ra have non-conservative excess concentrations in the mixing zones of the Pee Dee River-Winyah Bay estuary, the Yangtze River estuary, and the Delaware Bay estuary. Laboratory experiments, using Pee Dee River sediment, indicate desorption of ²²⁶Ra to increase with increasing salinities up to 20‰. In Winyah Bay desorption from river-borne sediments could contribute almost all of the increases for both isotopes. Desorption adds only a portion of the excess ²²⁸Ra measured in the Yangtse River and adjacent Shelf waters and Delaware Bay. In the Yangtze River the mixing zone extends over a considerable portion of the Continental Shelf where ²²⁸Ra is added to the water column by diffusion from bottom sediments, while ²²⁶Ra concentrations decrease from dilution. Diffusion of ²²⁸Ra from bottom sediments in Delaware Bay primarily occurs in the upper part of the bay (< 22‰ water) where fine grained sediments predominate. A diffusive flux for ²²⁸Ra of 0·33 dpm cm^?2 year was determined for Delaware Bay.     

Submarine groundwater discharge to Great South Bay, NY, estimated using Ra isotopes

There is increasing evidence that submarine groundwater discharge (SGD) in many areas represents a major source of dissolved chemical constituents to the coastal ocean. In Great South Bay, NY, previous studies have shown that the discharge of nutrients with SGD may cause harmful algal blooms. This study estimates SGD to Great South Bay during August 2006 by performing a mass balance for each of the dissolved Ra isotopes (²²⁴Ra, ²²³Ra, ²²⁸Ra, ²²⁶Ra). The budget indicates a major unknown source (between 30 and 60% of the total input) of Ra to the bay. This imbalance can be resolved by a flux of Ra-enriched groundwater on the order of 3.5–4.5 × 10⁹ L d^− 1, depending on the Ra isotope. The Ra-estimated SGD rates compare well with those previously estimated by models of flow that decreases exponentially away from shore. Compared to previous reports of fresh groundwater discharge to the bay, the Ra-estimated discharge must comprise approximately 90% recirculated seawater. The good agreement between Ra- and model-estimated flow rates indicates that the primary SGD endmember may be best sampled at shallow depths in the sediments a short distance bayward of the low tide line.     

九龙江河口区水体中224Ra的分布及其应用

研究了九龙江河口区表层水体中224Ra的分布,发现同世界其他河口一样,224Ra在九龙江河口区呈非保守行为;同时发现224Ra-Ss关系受季节变化的影响显着;与世界其他河口相比,九龙江河口表层水体中224Ra含量偏高;用九龙江河口区海端溶解态224Ra估算九龙江河口水流向外海的流速在夏季为2.5cm/s,冬季为0.91cm/s.     

228Ra, 226Ra, 224Ra and 223Ra in potential sources and sinks of land-derived material in the German Bight of the North Sea: implications for the use of radium as a tracer

Activities of the naturally occurring radium nuclides ²²⁸Ra, ²²⁶Ra, ²²⁴Ra and ²²³Ra were determined in waters of the open German Bight and adjacent nearshore areas in the North Sea, in order to explore the potential use of radium isotopes as natural tracers of land–ocean interaction in an environment characterised by extensive tidal flats, as well as riverine and groundwater influx. Data collected at various tidal phases from the Weser Estuary (²²⁸Ra: 46.3 ± 4.6; ²²⁶Ra: 17.1 ± 1.1; ²²⁴Ra: 26.1 ± 8.2 to 36.5 ± 6.1; ²²³Ra: 1.8 ± 0.1 to 4.0 ± 0.4), tidal flats near Sahlenburg (²²⁸Ra: 39.3 ± 3.8 to 46.0 ± 4.5; ²²⁶Ra: 15.5 ± 1.5 to 16.5 ± 1.7; ²²⁴Ra: 34.3 ± 2.2 to 85.3 ± 6.3; ²²³Ra: 3.6 ± 0.5 to 8.0 ± 1.2), freshwater seeps on tidal flats near Sahlenburg (²²⁸Ra: 42.1 ± 4.1; ²²⁶Ra: 21.3 ± 2.2; ²²⁴Ra: 5.1 ± 0.9; ²²³Ra: 2.6 ± 1.3) and also in permanently inundated parts of the North Sea (²²⁸Ra: 23.0 ± 2.3 to 28.2 ± 2.8; ²²⁶Ra: 8.2 ± 0.8 to 11.8 ± 1.2; ²²⁴Ra: 3.1 ± 1.0 to 10.1 ± 0.9; ²²³Ra: 0.1 ± 0.02 to 0.9 ± 0.05; units: disintegrations per minute per 100 kg water sample) reveal that, except for the fresh groundwater, the potential end-members of nearshore water mass mixing have quite similar radium signatures, excluding a simple discrimination between the sources. However, the decreasing activities of the short-lived ²²⁴Ra and ²²³Ra isotopes recorded towards the island of Helgoland in the central German Bight show a potential to constrain fluxes of land-derived material to the open North Sea. The largest source for all radium isotopes is generally found on the vast tidal flats and in the Weser Estuary. Future work could meaningfully combine this so-called radium quartet approach with investigations of radon activity. Indeed, preliminary data from a tidal flat site with fresh groundwater seepage reveal a ²²²Rn signal that is clearly lower in seawater.     

Estimating submarine groundwater discharge around Isola La Cura, northern Venice Lagoon (Italy), by using the radium quartet

The four naturally-occurring radium isotopes (²²³Ra, ²²⁴Ra, ²²⁶Ra and ²²⁸Ra) were used to estimate the submarine groundwater discharge (SGD) in the Isola La Cura marsh area in the northern Venice Lagoon (Italy). By determining the radium contributors to the study area (river, coastal ocean and sediments) the radium excess in the lagoon water was quantified through a mass balance model. This radium excess is attributed to a submarine groundwater discharge source and represents the most important input of radium. Possible endmembers were considered from analysis of groundwater samples (subtidal and marsh piezometers, marsh wells and seepage meters) that were enriched in Ra by one to two orders of magnitude relative to surface waters. In particular, a permeable layer at 80 cm depth in the surrounding marsh is considered to be representative of the most likely SGD source, although similar radium activities were measured in other subtidal porewater samples collected in the Isola La Cura area. The estimated SGD flux to the study area ranged from 1 · 10⁹ to 6 · 10⁹ L·d^− 1, the same order of magnitude as the overall riverine input to the lagoon (3 · 10⁹ L·d^− 1). A major fraction of this SGD flux is likely recirculated seawater, as evidenced by the endmember salinity. The water residence time of 2 days was estimated by both using the shortest-lived radium isotope and estimating the volume of water exchanged between the lagoon and the open sea during a tidal cycle (tidal prism approach). This SGD flux could be used to estimate the input of other chemical species (metals, nutrients, etc.) via SGD which might affect the Venice Lagoon ecosystem.     

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 ~(224)Ra and ~(223)Ra,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 ~(224)Ra and ~(223)Ra,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.     

Radium and radon radioisotopes in regional groundwater, intertidal groundwater, and seawater in the Adelaide Coastal Waters Study area: Implications for the evaluation of submarine groundwater discharge

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.     

224,223Ra和137Cs在吕宋海峡及周边海域的分布以及其对“彩虹”台风的响应

本文报道2015年9月和2016年5月期间天然放射性核素²²⁴Ra和²²³Ra在吕宋海峡及周边海域表层和垂向水体的分布特征。为理解日本福岛核事故的影响,本文亦分析研究区域内人工放射性核素¹³⁷Cs的分布特征。结果表明,^224,223Ra和¹³⁷Cs比活度水平均处于我国南海海洋天然放射性本底变化范围之内。²²⁴Ra在吕宋海峡以西南海北部海域比活度较高,在吕宋海峡以东菲律宾海域比活度较低。¹³⁷Cs没有明显的分布趋势。基于三站位（LS3,LS5和LS8）²²⁴Ra、¹³⁷Cs以及温盐的垂向分布特征,本文揭示²²⁴Ra和¹³⁷Cs在热带表层水、次表层水和中-深层水中比活度水平和梯度变化的差异特征。彩虹台风事件扭转了整个吕宋海峡及周边海域的海流循环过程。大量以低水平²²⁴Ra为特征的西太平洋海水涌入南海,降低水体²²⁴Ra比活度水平。但是,西太平洋和南海北部海域水体¹³⁷Cs比活度水平没有明显差异,台风导致的海流变化对水体¹³⁷Cs比活度没有明显影响。