Coupled radon, methane and nitrate sensors for large-scale assessment of groundwater discharge and non-point source pollution to coastal waters

We constructed a survey system of radon/methane/nitrate/salinity to find sites of submarine groundwater discharge (SGD) and groundwater nitrate input. We deployed the system in Waquoit Bay and Boston Harbor, MA where we derived SGD rates using a mass balance of radon with methane serving as a fine resolution qualitative indicator of groundwater. In Waquoit Bay we identified several locations of enhanced groundwater discharge, out of which two (Childs and Quashnet Rivers) were studied in more detail. The Childs River was characterized by high nitrate input via groundwater discharge, while the Quashnet River SGD was notable but not a significant source of nitrate. Our radon survey of Boston Harbor revealed several sites with significant SGD, out of these Inner Harbor and parts of Dorchester Bay and Quincy Bay had groundwater fluxes accompanied by significant water column nitrogen concentrations. The survey system has proven effective in revealing areas of SGD and non-point source pollution.     

Characterisation of submarine groundwater discharge offshore south-eastern Sicily

A complex approach in characterisation of submarine groundwater discharge (SGD) off south-eastern Sicily comprising applications of radioactive and non-radioactive tracers, direct seepage measurements, geophysical surveys and a numerical modelling is presented. SGD fluxes in the Donnalucata boat basin were estimated by direct seepage measurements to be from 4 to 12Ls(-1), which are comparable with the total SGD flux in the basin of 17Ls(-1) obtained from radon measurements. The integrated SGD flux over the Donnalucata coast estimated on the basis of Ra isotopes was around 60m(3)s(-1) per km of the coast. Spatial variations of SGD were observed in the Donnalucata boat basin, the average (222)Rn activity concentration in seawater varied from approximately 0.1kBqm(-3) to 3.7kBqm(-3) showing an inverse relationship with salinity. The continuous monitoring carried out at the site closest to the coast has revealed an inverse relationship of (222)Rn activity concentration on the tide. The (222)Rn concentrations in seawater varied from 2.3kBqm(-3) during high tides to 4.8kBqm(-3) during low tides, thus confirming an influence of the tide on submarine groundwater discharge. Stable isotopes (delta(2)H and delta(18)O) showed that SGD samples consist up to 50% of groundwater. Geo-electrical measurements showed a spatial variability of the salt/fresh water interface and its complex transformation in the coastal zone. The presented results imply that in the studied Donnalucata site there are at least two different sources of SGD, one superficial, represented by mixed fresh water and seawater, and the second one which originates in a deeper limestone aquifer.     

近年来江苏省海岸带土地利用/覆被变化时空动态研究

海岸带是陆海生态系统交错带,具有重要的经济与生态价值,其生态环境具有脆弱性特征。海岸带的开发利用使其地区生态环境发生变化,而土地利用/覆被变化是地区生态环境变化的重要组成部分和主要原因之一。取1980、2000、2005、2008年4个时相的TM遥感影像为数据源,通过土地利用结构、土地利用多样性以及土地利用程度指数分析江苏省1980年以来海岸带土地利用/覆被变化的时空动态特征,揭示地域差异与梯度分异特征。研究结果表明：（1）江苏省海岸带土地利用结构表现为生态用地占比高,城镇与农村居民点占比低的特征。1980年以来,不同土地利用类型数量不断变化而结构相对稳定;类型趋于多样化且利用强度增加。（2）江苏省海岸带土地利用存在地域差异特征。土地利用结构存在不同模式且变化相对稳定;土地利用程度在南北方向上存在高 低 高分布特征,但逐步被打破。（3）江苏省海岸带土地利用在陆海方向上存在梯度特征。土地利用多样性陆海方向呈现低 高 低模式,土地利用强度陆海方向呈现高 中 低模式。土地利用多样性高值区逐步向海岸带中部移动;海岸带各缓冲区土地利用程度分异逐步增大。以射阳河口作为分界点,南北地区梯度规律存在差异性     

Estimating the dynamics of groundwater input into the coastal zone via continuous radon-222 measurements

Submarine groundwater discharge (SGD) into the coastal zone has received increased attention in the last few years as it is now recognized that this process represents an important pathway for material transport. Assessing these material fluxes is difficult, as there is no simple means to gauge the water flux. To meet this challenge, we have explored the use of a continuous radon monitor to measure radon concentrations in coastal zone waters over time periods from hours to days. Changes in the radon inventories over time can be converted to fluxes after one makes allowances for tidal effects, losses to the atmosphere, and mixing with offshore waters. If one assumes that advective flow of radon-enriched groundwater (pore waters) represent the main input of 222Rn in the coastal zone, the calculated radon fluxes may be converted to water fluxes by dividing by the estimated or measured 222Rn pore water activity. We have also used short-lived radium isotopes (223Ra and 224Ra) to assess mixing between near-shore and offshore waters in the manner pioneered by. During an experiment in the coastal Gulf of Mexico, we showed that the mixing loss derived from the 223Ra gradient agreed very favorably to the estimated range based on the calculated radon fluxes. This allowed an independent constraint on the mixing loss of radon-an important parameter in the mass balance approach. Groundwater discharge was also estimated independently by the radium isotopic approach and was within a factor of two of that determined by the continuous radon measurements and an automated seepage meter deployed at the same site.     

Recent Cs deposition in sediments of Admiralty Bay, Antarctica

Cesium-137, radium-226 and lead-210 profiles of a 25 cm sediment core give an indication of recent changes in land-ocean interactions at a polar coastal environment (Admiralty Bay, King George Island, Antarctica). The linear sedimentation accumulation rate at the study site calculated from the unsupported ²¹⁰Pb profile was 6.7 mm/year from 1965 to 2005. A 3.5-fold increase in ¹³⁷Cs concentrations was observed in the top layer of this sediment core. This sharp increase seems to indicate a recent redistribution of fallout radionuclides previously deposited on soil, vegetation and snow. These results imply enhanced land-ocean interactions at this site likely as a result of climate change. Because our results are based on a single core, additional investigations are needed to confirm our observations.     

Time-series sampling of Ra and Ra at the inlet to Great South Bay (New York): a strategy for characterizing the dominant terms in the Ra budget of the bay

Ra isotopes are a powerful tool for quantifying the flux of submarine groundwater discharge (SGD) into the sea. Previous studies of ²²³Ra and ²²⁴Ra mass balances in coastal embayments have shown that the Ra balance is dominated by supply via SGD, exchange with the open ocean and radioactive decay. The current study shows that a single time series over a tidal cycle at the principal inlet to Great South Bay (NY, US) is sufficient to determine the net flux of Ra across the inlet, and also can be used to estimate the decay of short-lived Ra in the bay. Estimates of the net Ra flux obtained from a single tidal time-series by using three different approaches agree with those determined from a more time-consuming survey of Ra within the bay, and may represent a first step of estimating SGD in bays and coastal lagoons.     

Isotope tracing of submarine groundwater discharge offshore Ubatuba, Brazil: results of the IAEA–UNESCO SGD project

Results of groundwater and seawater analyses for radioactive (³H, ²²²Rn, ²²³Ra, ²²⁴Ra, ²²⁶Ra, and ²²⁸Ra) and stable (D and ¹⁸O) isotopes are presented together with in situ spatial mapping and time series ²²²Rn measurements in seawater, direct seepage measurements using manual and automated seepage meters, pore water investigations using different tracers and piezometric techniques, and geoelectric surveys probing the coast. This study represents first time that such a new complex arsenal of radioactive and non-radioactive tracer techniques and geophysical methods have been used for simultaneous submarine groundwater discharge (SGD) investigations. Large fluctuations of SGD fluxes were observed at sites situated only a few meters apart (from 0 cm d⁻¹ to 360 cm d⁻¹; the unit represents cm³/cm²/day), as well as during a few hours (from 0 cm d⁻¹ to 110 cm d⁻¹), strongly depending on the tidal fluctuations. The average SGD flux estimated from continuous ²²²Rn measurements is 17 ± 10 cm d⁻¹. Integrated coastal SGD flux estimated for the Ubatuba coast using radium isotopes is about 7 × 10³ m³ d⁻¹ per km of the coast. The isotopic composition (δD and δ¹⁸O) of submarine waters was characterised by significant variability and heavy isotope enrichment, indicating that the contribution of groundwater in submarine waters varied from a small percentage to 20%. However, this contribution with increasing offshore distance became negligible. Automated seepage meters and time series measurements of ²²²Rn activity concentration showed a negative correlation between the SGD rates and tidal stage. This is likely caused by sea level changes as tidal effects induce variations of hydraulic gradients. The geoelectric probing and piezometric measurements contributed to better understanding of the spatial distribution of different water masses present along the coast. The radium isotope data showed scattered distributions with offshore distance, which imply that seawater in a complex coast with many small bays and islands was influenced by local currents and groundwater/seawater mixing. This has also been confirmed by a relatively short residence time of 1–2 weeks for water within 25 km offshore, as obtained by short-lived radium isotopes. The irregular distribution of SGD seen at Ubatuba is a characteristic of fractured rock aquifers, fed by coastal groundwater and recirculated seawater with small admixtures of groundwater, which is of potential environmental concern and has implications on the management of freshwater resources in the region.     

Exerpts from the history of alpha recoils

Any confined air volume holding radon (²²²Rn) gas bears a memory of past radon concentrations due to ²¹⁰Pb (T_1/2 = 22 y) and its progenies entrapped in all solid objects in the volume. The efforts of quantifying past radon exposures by means of the left-behind long-lived radon progenies started in 1987 with this author’s unsuccessful trials of removing ²¹⁴Po from radon exposed glass objects. In this contribution the history and different techniques of assessing radon exposure to man in retrospect will be overviewed. The main focus will be on the implantation of alpha recoils into glass surfaces, but also potential traps in radon dwellings will be discussed. It is concluded that for a successful retrospective application, three crucial imperatives must be met, i.e. firstly, the object must persistently store a certain fraction of the created ²¹⁰Pb atoms, secondly, be resistant over decades towards disturbances from the outside and thirdly, all ²¹⁰Pb atoms analysed must originate from airborne radon only.For large-scale radon epidemiological studies, non-destructive and inexpensive measurement techniques are essential. Large-scale studies cannot be based on objects rarely found in dwellings or not available for measurements     

Some results from the demonstration of indoor radon reduction measures in block basement houses

Active soil ventilation techniques have been tested in 26 block-wall basement houses in eastern Pennsylvania with significantly elevated indoor radon concentrations, generally above 740 Bq/m³, and the results indicate that radon levels can be reduced substantially often below the U.S. Environmental Protection Agency (EPA) guideline of 148 Bq/m³, if effective suction can be drawn on the soil underneath the concrete slabs of these houses. Such effective suction appears achievable when either: 1) the house has a complete loop of drain tile around its footings for water drainage purposes, and suction is drawn on that loop; or 2) a sufficient number of suction pipes can be inserted at the proper locations into the crushed rock or the soil underneath the slab.     

Radon exhalation from building materials for decorative use

Long-term exposure to radon increases the risk of developing lung cancer. There is considerable public concern about radon exhalation from building materials and the contribution to indoor radon levels. To address this concern, radon exhalation rates were determined for 53 different samples of drywall, tile and granite available on the Canadian market for interior home decoration. The radon exhalation rates ranged from non-detectable to 312 Bq m⁻² d⁻¹. Slate tiles and granite slabs had relatively higher radon exhalation rates than other decorative materials, such as ceramic or porcelain tiles. The average radon exhalation rates were 30 Bq m⁻² d⁻¹ for slate tiles and 42 Bq m⁻² d⁻¹ for granite slabs of various types and origins. Analysis showed that even if an entire floor was covered with a material having a radon exhalation rate of 300 Bq m⁻² d⁻¹, it would contribute only 18 Bq m⁻³ to a tightly sealed house with an air exchange rate of 0.3 per hour. Generally speaking, building materials used in home decoration make no significant contribution to indoor radon for a house with adequate air exchange.     

Experimental study of effectiveness of four radon mitigation solutions, based on underground depressurization, tested in prototype housing built in a high radon area in Spain

The present paper discusses the results of an empirical study of four approaches to reducing indoor radon concentrations based on depressurization techniques in underground sumps. The experiments were conducted in prototype housing built in an area of Spain where the average radon concentration at a depth of 1 m is 250 kBq m⁻³.Sump effectiveness was analysed in two locations: underneath the basement, which involved cutting openings into the foundation, ground storey and roof slabs, and outside the basement walls, which entailed digging a pit alongside the building exterior. The effectiveness of both sumps was likewise tested with passive and forced ventilation methods.The systems proved to be highly efficient, lowering radon levels by 91-99%, except in the solution involving passive ventilation and the outside sump, where radon levels were reduced by 53-55%. At wind speeds of over 8 m/s, however, passive ventilation across an outside sump lowered radon levels by 95% due to a Venturi effect induced drop in pressure.     

Investigation of residence time and groundwater flux in Venice Lagoon: comparing radium isotope and hydrodynamical models

The four naturally-occurring isotopes of radium were coupled with a previously evaluated hydrodynamic model to determine the apparent age of surface waters and to quantify submarine groundwater discharge (SGD) into the Venice Lagoon, Italy.Mean apparent age of water in the Venice Lagoon was calculated using the ratio of ²²⁴Ra to ²²⁸Ra determined from 30 monitoring stations and a mean pore water endmember. Average apparent age was calculated to be 6.0 d using Ra ratios. This calculated age was very similar to average residence time calculated for the same period using a hydrodynamic model (5.8 d).A mass balance of Ra was accomplished by quantifying each of the sources and sinks of Ra in the lagoon, with the unknown variable being attributed to SGD. Total SGD were calculated to be 4.1 ± 1.5, 3.8 ± 0.7, 3.0 ± 1.3, and 3.5 ± 1.0 × 10¹⁰ L d⁻¹ for ^{223,224,226, 228}Ra, respectively, which are an order of magnitude larger than total mean fluvial discharge into the Venice Lagoon (3.1 × 10⁹ L d⁻¹). The SGD as a source of nutrients in the Venice Lagoon is also discussed and, though significant to the nutrient budget, is likely to be less important as the dominant control on SGD is recirculated seawater rather than freshwater.     

Inhalation dose assessment of indoor radon progeny using biokinetic and dosimetric modeling and its application to Jordanian population

High indoor radon concentrations in Jordan result in internal exposures of the residents due to the inhalation of radon and its short-lived progeny. It is therefore important to quantify the annual effective dose and further the radiation risk to the radon exposure. This study describes the methodology and the biokinetic and dosimetric models used for calculation of the inhalation doses exposed to radon progeny. The regional depositions of aerosol particles in the human respiratory tract were firstly calculated. For the attached progeny, the activity median aerodynamic diameters of 50 nm, 230 nm and 2500 nm were chosen to represent the nucleation, accumulation and coarse modes of the aerosol particles, respectively. For the unattached progeny, the activity median thermodynamic diameter of 1 nm was chosen to represent the free progeny nuclide in the room air. The biokinetic models developed by the International Commission on Radiological Protection (ICRP) were used to calculate the nuclear transformations of radon progeny in the human body, and then the dosimetric model was applied to estimate the organ equivalent doses and the effective doses with the specific effective energies derived from the mathematical anthropomorphic phantoms. The dose conversion coefficient estimated in this study was 15 mSv WLM⁻¹ which was in the range of the values of 6-20 mSv WLM⁻¹ reported by other investigators. Implementing the average indoor radon concentration in Jordan, the annual effective doses were calculated to be 4.1 mSv y⁻¹ and 0.08 mSv y⁻¹ due to the inhalation of radon progeny and radon gas, respectively. The total annual effective dose estimated for Jordanian population was 4.2 mSv y⁻¹. This high annual effective dose calculated by the dosimetric approach using ICRP biokinetic and dosimetric models resulted in an increase of a factor of two in comparison to the value by epidemiological study. This phenomenon was presented by the ICRP in its new published statement on radon.     

Challenges for marine spatial planning in the context of multiple sea uses,policy arenas and actors based on experiences from the German North Sea

Today, increasing use intensity and establishment of new sea uses such as offshore wind farming can be observed in coastal and marine waters. This development also increases the pressure on coastal and marine ecosystems. The exclusive economic zone of the German North Sea can serve as an example for this development, in particular illustrating the need to combine multiple uses and societal demands within a given sea area. In order to deal with the resulting conflicts and cumulative impacts, new planning tools and integrated approaches to planning and management are developing. While the sea becomes a contested but at the same time politically recognised area, also conflicts rooted in different perceptions, values and attitudes of coastal people can be observed. In order to deal with the current challenges in marine areas, marine spatial planning and similar tools for integrated planning need to be developed in the form of communication processes, which link diverse sets of information and span a dialogue between groups of society and across spatial scales including the transnational dimension.     

A theoretical approach to indoor radon and thoron distribution

A model based on the Finite Element Method was developed to simulate indoor behavior of radon ((222)Rn), thoron ((220)Rn) and their progeny, as well as, to calculate their spatial distributions. Since complex physical processes govern the distribution several simplifications were made in the presented model. Different locations of possible radon/thoron sources, diffusion of these gases, their radioactive decay, etc were taken into account. Influences of different parameters on thoron/radon as well as indoor distribution of their progeny, such as the geometry and room dimension, the presence of aerosols and their size distribution expressed through the diffusion coefficient, different kinds of ventilation, etc, were investigated. It has been found that radon is distributed homogeneously, while the thoron concentration is rather inhomogeneous and decreases exponentially with the distance from the source. Regardless of the source distribution, the distribution of radon was homogeneous, except at places near an air inlet and outlet. However, the distribution of thoron depends on the source distribution. If thoron emanates from walls or the floor, its concentration decreases with the distance from the wall. Moreover, the concentration gradient is much larger near walls. This suggests that the actual selection of the site effect should be taken into account when obtaining a representative value of indoor (220)Rn and their progeny for dose assessment. The simulation results of activities and their distribution were in accordance with the results of other studies and experiments.     

Two error components model for measurement error: application to radon in homes

In this paper, a simple model for analysing variability in radon concentrations in homes is tested. The approach used here involves two error components, representing additive and multiplicative errors, together with variation between-houses. We use a Bayesian approach for our analysis and apply this model to two datasets of repeat radon measurements in homes; one based on 3-month long measurements for which the original measurements were close to the current UK Radon Action Level (200 Bq m⁻³), and the other based on 6-month measurement data (from regional and national surveys), for which the original measurements cover a wide range of radon concentrations, down to very low levels. The model with two error components provides a better fit to these datasets than does a model based on solely multiplicative errors.     

Experience from indoor radon-daughter limitation schemes in Sweden

Sweden introduced limits and gave recommendations for decreasing the indoor radon daughter concentrations in 1980. The resulting experiences are summarized. From 1979 to 1987, measurements were carried out by the local authorities in about 58 000 out of 3.9 million homes in Sweden, and 5300 homes were found to have levels exceeding the limit for existing houses, or 400 Bq/m³ of equilibrium equivalent concentration of radon (EER). This may be about 13% of the estimated 40 000 homes with levels exceeding 400 Bq/m³. Very high levels, up to 28 000 Bq/m³, have been found. According to the local authorities, in one third of the homes found with levels exceeding the limit (1921 homes) certain reconstruction and other measures have been taken in order to decrease the levels. In reality, measures have been carried out in more houses. The methods depend on the radon source. The average reductions found for respective methods are reported. The local authorities can require a check of the radon daughter concentrations in newly built houses when they suspect that the concentrations exceed the limit of 70 Bq/m³. In 11% of the measured homes built during 1981 to 1985, the levels were above the limit for newly built houses. In 1.4% of these houses, the limit for existing houses, 400 Bq/m³, had been exceeded. The strategy to decrease both the collective dose to the population and the individual dose is discussed.     

Soil radium, soil gas radon and indoor radon empirical relationships to assist in post-closure impact assessment related to near-surface radioactive waste disposal

Least squares (LS), Theil’s (TS) and weighted total least squares (WTLS) regression analysis methods are used to develop empirical relationships between radium in the ground, radon in soil and radon in dwellings to assist in the post-closure assessment of indoor radon related to near-surface radioactive waste disposal at the Low Level Waste Repository in England. The data sets used are (i) estimated ²²⁶Ra in the <2 mm fraction of topsoils (eRa226) derived from equivalent uranium (eU) from airborne gamma spectrometry data, (ii) eRa226 derived from measurements of uranium in soil geochemical samples, (iii) soil gas radon and (iv) indoor radon data. For models comparing indoor radon and (i) eRa226 derived from airborne eU data and (ii) soil gas radon data, some of the geological groupings have significant slopes. For these groupings there is reasonable agreement in slope and intercept between the three regression analysis methods (LS, TS and WTLS). Relationships between radon in dwellings and radium in the ground or radon in soil differ depending on the characteristics of the underlying geological units, with more permeable units having steeper slopes and higher indoor radon concentrations for a given radium or soil gas radon concentration in the ground. The regression models comparing indoor radon with soil gas radon have intercepts close to 5 Bq m⁻³ whilst the intercepts for those comparing indoor radon with eRa226 from airborne eU vary from about 20 Bq m⁻³ for a moderately permeable geological unit to about 40 Bq m⁻³ for highly permeable limestone, implying unrealistically high contributions to indoor radon from sources other than the ground. An intercept value of 5 Bq m⁻³ is assumed as an appropriate mean value for the UK for sources of indoor radon other than radon from the ground, based on examination of UK data. Comparison with published data used to derive an average indoor radon: soil ²²⁶Ra ratio shows that whereas the published data are generally clustered with no obvious correlation, the data from this study have substantially different relationships depending largely on the permeability of the underlying geology. Models for the relatively impermeable geological units plot parallel to the average indoor radon: soil ²²⁶Ra model but with lower indoor radon: soil ²²⁶Ra ratios, whilst the models for the permeable geological units plot parallel to the average indoor radon: soil ²²⁶Ra model but with higher than average indoor radon: soil ²²⁶Ra ratios.     

Indoor radon levels in Greek schools

Radon and gamma dose rate measurements were performed in 512 schools in 8 of the 13 regions of Greece. The distribution of radon concentration was well described by a lognormal distribution. Most (86%) of the radon concentrations were between 60 and 250 Bq m⁻³ with a most probable value of 135 Bq m⁻³. The arithmetic and geometric means of the radon concentration are 149 Bq m⁻³ and 126 Bq m⁻³ respectively. The maximum measured radon gas concentration was 958 Bq m⁻³. As expected, no correlation between radon gas concentration and indoor gamma dose rate was observed. However, if only mean values for each region are considered, a linear correlation between radon gas concentration and gamma dose rate is apparent. Despite the fact that the results of radon concentration in schools cannot be applied directly for the estimation of radon concentration in homes, the results of the present survey indicate that it is desirable to perform an extended survey of indoor radon in homes for at least one region in Northern Greece.     

中国无船承运企业空间格局演化及影响因素

无船承运企业对国际货物流通领域和区域内社会经济系统的高效运转都具有重要的现实意义。选取2006~2013年中国无船承运业务经营者为研究样本,从宏观区域、省级行政区和城市等多层尺度来刻画和分析中国无船承运企业的分布特征,并从多种因素来探讨无船承运企业空间分布的影响因素。研究发现:在空间维度上,中国无船承运企业分布格局呈现出明显的空间差异性。沿海地区多于内陆,东部地区明显多于东北和中西部地区,东部沿海尤其上海与广东2省市集聚明显,而在城市尺度上非均衡性分布更加突出,已形成明显的集聚区和稀疏区。在时间维度上,中国无船承运企业总量和拥有无船承运企业城市数量都呈递增趋势,但区域间递增幅度有所差异。综合交通网络、区域外贸经济发育程度、区域经济发展水平和产业结构、商务支撑条件等是影响中国无船承运企业分布的主要因素。