Assessment of radon transportation and uranium content in the tectonically active zone of Himalaya, India

The study shows how geology and tectonic activity affect the soil gas 222Rn concentration. The tectonically active zone, namely the Ghuttu region, which is located within the Himalayan seismic belt, was studied to decipher its impact on soil gas 222Rn concentrations. A soil gas 222Rn study was performed in the soil at a depth of 30 cm, and it varied from 426 ± 156 Bq m-3 to 24,057 ± 1110 Bq m-3 with an average of 5356.5 ± 1634.6 Bq m-3, and at 60 cm below the soil surface, the concentration varied from 1130 ± 416 Bq m-3 to 30,236 ± 1350 Bq m-3 with an average of 8928.5 ± 2039.5 Bq m-3. These concentrations vary in soil from -3.4 % to 437.3 % as the depth moves from 30 cm to 60 cm. The variation in uranium content also shows anomalies, and higher values of uranium content in the soil affect the radon concentration in the study area. The average soil gas 222Rn concentration in the Ghuttu window was found to be higher than that in its surrounding region. This is likely due to transportation from daughter products of uranium. 222Rn mass exhalation rate measurements were also carried out, and a weak correlation with the soil gas 222Rn concentration was observed. A significant variation in the mass exhalation rate was noticed in tectonically active areas. This study is vital to understanding the behavior of radon and uranium in tectonic regions.

Seasonal characteristics of groundwater discharge controlled by precipitation and its environmental effects in a coal mining subsidence lake, eastern China

Many regions have formed subsidence lakes due to underground mining in the world. However, seasonal variations of lacustrine groundwater discharge (LGD) rate and solute fluxes in the coal mining subsidence were rarely reported. In this study, we conducted four seasonal samplings in a coal mining subsidence, during which samples for stable water (δ18O) and radioactive (222Rn) isotopes were collected to quantify the seasonal dynamics of LGD rates. The LGD rates estimated from the 222Rn mass balance model were 10.2 ± 8.7, 5.5 ± 3.2, 11.5 ± 7.8, and 7.8 ± 4.5 mm d-1 in summer, autumn, winter and spring, respectively. According to the 18O mass balance model, the corresponding LGD rates were 15.1, 7.3, 15.6, and 11.3 mm d-1 in summer, autumn, winter and spring, respectively. We found a significant correlation between precipitation and LGD rates, suggesting precipitation was recognized as the main control factor for seasonal variations of LGD rates. Based on this correlation, the extrapolated LGD rates over a year ranged from 3.1 to 12.7 mm d-1 with an average of 8.8 mm d-1. Moreover, the fluxes of dissolved silicon (DSi), iron (Fe), and manganese (Mn) from LGD in autumn were (1.6 ± 0.9) × 105, (1.9 ± 1.1) × 104, and (1.1 ± 0.6) × 104 mol a-1, respectively. Correspondingly, in winter they were (3.5 ± 2.4) × 105, (4.1 ± 2.8) × 103, and (2.8 ± 1.9) × 103 mol a-1, respectively. This study demonstrated significantly seasonal variations of LGD, with precipitation being the main control factor of LGD in the coal mining subsidence lake. The fluxes of dissolved substance (DSi, Fe, Mn) from LGD need to be emphasized because they may have important impacts on the ecological stability in coal mining subsidence lakes.

Characteristics of 222Rn and 220Rn equilibrium factors in the indoor environments

Humans receive a significant portion (˃50%) of the total dose attributed to all the natural radiation sources from indoor radon (222Rn), thoron (220Rn), and their progeny. While progeny contributes an overwhelming part to the dose, in most surveys, only radon gas is measured because of the simplicity of measurement. Progeny concentration is usually estimated by multiplying gas concentration with an assumed factor, called the equilibrium factor, and taken from literature. Recently, results of the measurements of equilibrium factors for 222Rn and 220Rn were reported from various parts of the globe. In India, many such studies have been conducted in the current decade. The studies show a wide variation of equilibrium factors which suggests that they depend on environmental factors and measurement conditions. Therefore, they should be determined site specifically if accurate site-specific dose estimation is targeted. This paper summarizes concepts, definitions, and methods to determine equilibrium factors and reviews literature about reported equilibrium factors worldwide, focusing on data reported from India.

Towards a radon-in-water primary standard at LNHB

Despite widespread radon-in-water measurements, no primary radon-in-water standards currently exist. This work aims to bridge this gap by developing a system to produce radon-in-water reference materials. The system relies on cryogenic, loss-free transfer of radon, which is standardized through defined solid angle measurements, to a radon standard in water. It allows for preparation of liquid scintillation and gamma-ray spectrometry samples with traceable radon-in-water concentrations. The system's design, functionality, and the results of pilot performance tests are described.

Using isotopic tracers to enhance routine watershed monitoring - Insights from an intensively managed agricultural catchment

Experimental (research-based) and non-research-based watershed monitoring programs often differ with respect to sampling frequency, monitored variables, and monitoring objectives. Isotopic variables, which are more commonly incorporated in research-based programs, can provide an indication of water sources and the transit time of water in a catchment. These variables may be a valuable complement to traditional water quality monitoring variables and have the potential to support improved hydrologic process-related insights from long term monitoring programs that typically have low resolution sampling. The purpose of this investigation is to explore the utility of incorporating isotopic variables (specifically δ18O, δ2H, and 222Rn) into routine monthly sampling regimes by comparing insights gained from these variables to monitoring only specific conductivity and chloride. A complete annual cycle of monthly groundwater and surface water monitoring data collected from the Upper Parkhill watershed in southwestern Ontario, Canada was used to characterize baseline watershed conditions, evaluate watershed resilience to climate change, and examine contamination vulnerability. Study results provide an improved understanding of appropriate tracer use in agricultural regions with isotopic variables able to provide important insights into the seasonality of hydrologic phenomena, such as the timing of groundwater recharge. A comparison of monitoring variables to present-day hydro-meteorological conditions suggests the importance of a winter dominated hydrologic regime and the potential influence of changes in precipitation on groundwater-surface water interactions. Estimated transit time dynamics indicate the likelihood for rapid contaminant transport through surface and shallow subsurface flow and highlight the possible effects of agricultural tile drainage. The sampling approach and data analysis methods adopted in this study provide the basis for improving routine watershed monitoring programs in agricultural regions.

222Radon reduction in small-scale water supply systems using low-technology reduction methods in the Republic of Korea: A field research and mass balance model approach

In rural areas, low-technology radon reduction methods are essential for safe access to clean groundwater. This study monitored the radon reduction rates in small-scale groundwater-based water supply systems in the Republic of Korea and also presented a mass balance equation using physical environmental conditions from three radon reduction methods. The mass balance results showed that the radon reduction rate would be affected by the groundwater flow rate (m³/day), capacity of the drainage facility (m³), surface area of air-water interface (m²), air-water ratio (dimensionless), and ventilation system. The radon reduction order was as follows: simultaneously powered and non-powered aeration method (free-fall (60.0 %) > aeration (19.6 %) > decay (0.9 %) > diffusion (0.2 %)), low-technology non-powered aeration (free-fall (60.0 %) > decay (3.4 %) > diffusion (0.9 %)), and only storage (free-fall (35.5 %) > decay (4.4 %) > diffusion (1.1 %)). Overall, non-powered aeration using the maximum free-fall effect has the potential for use as a low-technology reduction method and natural decay during water storage is the most important factor underlying seasonal variations in the reduction effect.

Uncertainty due to primary sampling of 222Rn in analyses of water

Measurement uncertainty is an important variable, to be accounted for when decisions have to be made based on measurement results. Measurement uncertainty is composed of two main components; one is related to the primary sampling, the other to the sample preparation and the subsequent analysis of the sample. The component related to the sample preparation and the analysis is commonly well evaluated in proficiency testing while there is generally no straightforward similar approach to evaluate sampling uncertainty. ISO 17025:2017 explicitly requires that testing laboratories performing sampling and analyses determine the uncertainty related to the primary sampling. In order to determine uncertainty arising in the primary sampling of ²²²Rn in water destined for human consumption, three laboratories IRE (BE), DiSa (LU) and SCK CEN (BE) initiated a joined sampling and measurement campaign. The dual split sample method in combination with ANOVA was used to evaluate the primary sampling uncertainty (precision) of the different methods. The tests showed that sampling bias is very probably, but that with good laboratory practice the sampling uncertainty precision and respectively bias can be kept below 5%.

Indoor radon survey in Greenland and dose assessment

Indoor radon and its decay products are the primary sources of the population's exposure to background ionizing radiation. Radon decay products are one of the leading causes of lung cancer, with a higher lung cancer risk for smokers due to the synergistic effects of radon decay products and cigarette smoking. A total of 459 year-long radon measurements in 257 detached and semi-detached residential homes in southwest and south Greenland were carried out, and a dose assessment for adults was performed. The annual arithmetic and geometric means of indoor radon concentrations was 10.5 ± 0.2 Bq m^-3 and 8.0 ± 2.3 Bq m^-3 in Nuuk, 139.0 ± 1.0 Bq m^-3 and 97.3 ± 2.1 Bq m^-3 in Narsaq, and 42.1 ± 0.7 Bq m^-3 and 22.0 ± 3.1 Bq m^-3 in Qaqortoq. Arithmetic and geometric mean radon concentration of 79.0 Bq m^-3 and 50.3 Bq m^-3 were estimated for adult, person-weighted living in south Greenland. The total number of detached and semi-detached residential homes where indoor radon is exceeding 100 Bq m^-3, 200 Bq m^-3, and 300 Bq m^-3 is 37 homes (15.0%), 13 homes (5.2%), and 8 homes (3.2%), respectively. A positive correlation between indoor air radon concentrations and underlying geology was observed. The indoor radon contribution to the annual inhalation effective dose to an average adult was 0.5 mSv in Nuuk, 6.5 mSv in Narsaq, 2.0 mSv in Qaqortoq, and 4.0 mSv for south Greenland adult person weighted. The estimated annual average effective dose to adults in Narsaq is higher than the world's average annual effective dose of 1.3 mSv due to inhalation of indoor radon. Cost-efficient mitigation methods exist to reduce radon in existing buildings, and to prevent radon entry into new buildings.

Using 222Rn temporal and spatial distributions to estimate the groundwater discharge rate and associated nutrient fluxes into high salinity lakes in Badain Jaran Desert, Northwest China

Groundwater is the main source of water and salt recharge for to lakes in arid regions. Quantifying the groundwater discharge and its nutrient input is important in the evolution of lake environments in the Badain Jaran Desert (BJD), Northwest China. In this study, ten BJD lakes were sampled for ²²²Rn in April and September 2021, and the ²²²Rn mass balance model was used to quantify the groundwater discharge rates and derived nutrient fluxes to these lakes. The results showed that the ²²²Rn activity and the groundwater recharge rate of lake water both present a positively correlated with lake water depth. The hot points of high ²²²Rn activity in the lake water were consistent with the locations of groundwater discharge areas. According to the ²²²Rn temporal and spatial distributions, the mean groundwater recharge rates for the ten lakes in April and September were 5.4 ± 0.6 and 7.7 ± 1 mm/d, respectively, and the annual mean groundwater discharge rates varied between 1.1 ± 0.2 and 14.6 ± 1.6 mm/d, with a mean of 7 ± 0.9 mm/d. Given that all the perennial lakes in the BJD have the same groundwater recharge rate as the mean recharge rate of the ten studied lakes, the annual mean groundwater recharge amount received by the lakes in the entire BJD is (5.6 ± 0.7) × 10⁷ m³/a. According to the groundwater recharge amount, the inputs of dissolved inorganic nitrogen, dissolved inorganic phosphorus, dissolved inorganic silicon, total nitrogen, and total phosphorus to the BJD lakes from groundwater were (4.7 ± 0.6) × 10⁵, (3.8 ± 0.5) × 10⁴, (7.9 ± 1) × 10⁵, (7.2 ± 0.9) × 10⁵, (2.5 ± 0.3) × 10⁴ kg/a, respectively. This study provides a reference for quantifying of groundwater discharge rates into salt lakes in other arid regions.

Greenhouse gases emissions and dissolved carbon export affected by submarine groundwater discharge in a maricultural bay, Hainan Island, China

Greenhouse gases (GHG) emissions in coastal areas are influenced by both mariculture and submarine groundwater discharge (SGD). In this study, we first conducted a comprehensive investigation on carbon dioxide (CO₂) and methane (CH₄) emissions affected by SGD in a typical maricultural bay in north-eastern Hainan Island, China. A radon (²²²Rn) mass balance model revealed considerable high SGD rates (179 ± 92 cm d^-1) in the bay, and the fluxes of SGD-derived dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) were 150.36 and 3.65 g C m^-2 d^-1, respectively. Time-series measurement results, including those for ²²²Rn, CH₄, CO₂, and physicochemical parameters, indicated that GHG dynamics in the maricultural bay mainly varied with tidal fluctuations, and isotopic evidence further revealed that acetate fermentation was the main mechanism of methanogenesis in the maricultural waters. The water-air fluxes in the maricultural area were 1.05 ± 0.32 and 9.49 ± 3.96 mmol m^-2 day^-1 for CH₄ and CO₂, respectively, implying that Qinglan Bay was a potential source of GHG released into the atmosphere. At the bay-scale, the CO₂ emissions followed a spatial pattern, and the CH₄ emissions were mainly affected by mariculture. The high CH₄ emissions in the maricultural waters caused by maricultural activities, SGD, high temperature, and special hydrology resulted in the formation of the CH₄-dominated total CO₂-equivalent emissions model. Our study highlights the importance of considering the link between SGD and GHG emissions in maricultural bays when constraining global GHG fluxes.

Unravelling groundwater and surface water sources in the Esteros del Iberá Wetland Area: An isotopic approach

In the Esteros del Iberá Wetland Area (EIWA, NE Argentina), the southern sector of the transboundary Guarani Aquifer System (SAG) is overlain by the Ramsar listed Iberá Wetlands and several rivers, that combined extend across 37,930 km² and represent one of the largest freshwater systems on the South American continent. Previous hydrogeological studies encompassing the entire SAG proposed preferential discharge of groundwater of various origins and ages to the EIWA. In this study, a multi-tracer study using major ionic species, δ¹⁸O, δ²H and ²²²Rn was conducted in lagoons, rivers, wells, and boreholes in the EIWA to confirm if discharge from the transboundary SAG is contributing to the surface water system. End-member Mixing Analysis (EMMA) determined the existence of four main end-members: groundwater from the SAG, more saline groundwater from the deeper Pre-SAG, and two poorly mineralised end-members from shallow, Post-SAG. EMMA calculations clearly illustrated complex binary and ternary mixing patterns involving the four end-members and highlighted the role of geological structures, specifically regional steep faults, in controlling the mixing patterns. ²²²Rn activities allowed in-situ identification of preferential deep groundwater discharge into both surface waters and shallow groundwaters. These findings provide strong evidence for the widespread existence of upward flows along major faults in this sector of the SAG, inducing complex mixing flow patterns and explaining the presence of old groundwater in shallow aquifers. Mapping the sources of water and the hydrological interactions are relevant for improving water balance estimates and develop management policies towards the preservation of these wetlands.

Delineating E. coli occurrence and transport in the sandy beach groundwater system by radon-222

Fecal pollution poses a global threat to environmental safety and ecosystem, but the mechanism of microbial transport and occurrence in the beach groundwater system is still poorly explored. Here, we leveraged one-year field data of Escherichia coli (E. coli) and radon-222 (²²²Rn) and found that E. coli occurrence and transport in the sandy beach groundwater system can be delineated by ²²²Rn. The underlying mechanism behind this phenomenon is due to similar half-lives of ²²²Rn and E. coli in the sandy beach groundwater system. Thus, the unique relationship between ²²²Rn and E. coli can provide additional critical context to the microbial water quality assessments and ecosystem resilience. Also, the beach aquifer in this study is found to be a vital compartment for E. coli removal. The net E. coli removal/production capacity is identified to be highly impacted by submarine groundwater discharge. Finally, a conceptual model is constructed for a better understanding of the occurrences and characteristics of E. coli and ²²²Rn at multiple spatial scales. These findings are constructive to mitigate the hazardous influences of microbe on water quality, especially in recreational sandy beaches and mariculture zones.

Using geochemistry to identify and quantify the sources, distribution, and fluxes of baseflow to an intermittent river impacted by climate change: The upper Wimmera River, southeast Australia

Documenting the distribution, sources and fluxes of baseflow discharge into rivers is important for their management and for maintaining ecosystem health. This study uses major ion geochemistry, ²²²Rn, and ³H to differentiate between the input of low-salinity near-river waters (bank storage and return waters and/or interflow) and regional groundwater in an intermittent river from southeast Australia that is undergoing long-term changes in flow resulting from climate change. Baseflow discharge calculated by ²²²Rn mass balance was up to 1.3 m³/m/day in the high flow period in July 2019 and up to 0.1 m³/m/day at low flow conditions in November 2019. The distribution of ²²²Rn activities implies higher baseflow fluxes in the upper and middle reaches that have relatively steep topography and higher hydraulic gradients. The lower reaches received less baseflow due to subdued topography and fine-grained sediments. The observation that Cl concentrations did not increase uniformly downstream, however, implies that much of the baseflow may comprise bank return flow or interflow. This conclusion is also consistent with water mass balance calculations and the observation that ³H activities (1.85-3.00 TU) in the river were higher than in the groundwater (<0.45 TU). Intermittent streams are likely to be less well connected to regional groundwater, and thus near-river water stores will be more important in sustaining streamflow during dry periods than regional groundwater. These rivers and their ecosystems may be less susceptible to the impacts of groundwater extraction and the near-river waters will provide a buffer zone from potentially contaminated regional groundwater. However, these near river stores are vulnerable to short-term climate variability, and changes to flow regimes resulting from climate change may significantly impact water supplies and ecosystem health.

Rapid sequential determination of 222Rn and 226Ra in drinking water by liquid scintillation counting

Since daily drinking water is one of the major source for the ingestion of radiotoxic ²²²Rn and ²²⁶Ra, the demand for a simple method to determine these two radionuclides has significantly increased. In the present study, a rapid, simple sequential analysis method for determining ²²²Rn and ²²⁶Ra in drinking water using a liquid scintillation counter was developed. The method employs solvent extraction and correction equations for the effect of native ²²²Rn for ²²⁶Ra analysis. Validation and examination of applicability for drinking water analysis were conducted using ²²²Rn-injected water and ²²⁶Ra standard source. Minimum required counting times for examining drinking water on Quantulus 1220 and Hidex 300SL were estimated via minimum detectable activity depending on the counting time. In addition, the correction method, including an equation for reducing analysis time by more than 10 days, was suggested based on the analytical results for different elapsed times between sampling and measurement.

Effect of NAPL mixture and alteration on 222Rn partitioning coefficients: Implications for NAPL subsurface contamination quantification

Soils and groundwater are often contaminated by complex organic mixtures also called Non Aqueous Phase Liquids (NAPLs). Several techniques such as drilling, monitoring of soil gas or injection of tracers are traditionally used to quantify NAPLs in aquifers but are complex to perform. The use of natural soil gas such as ²²²Rn could be an easy and cheap alternative. This method requires the knowledge of the radon NAPL-water partitioning coefficients (K_n-w.). Once spilled on soil, NAPL will undergo degradation (evaporation, effects of sun light among others) and this degradation could impact the K_n-w. This study aims at investigating the partitioning coefficients of complex NAPLs such as commercial diesel fuel and gasoline in relation to degradation such as evaporation and UV-degradation. For that purpose, batch experiments and GCMS investigations were carried out. The results show different K_n-w for the commercial diesel fuel (60.7 ± 6.1) and gasoline (37.4 ± 5.6). The results also show different K_n-w behaviors in relation with degradation. Degraded diesel fuel display opposite K_n-w values (74.8 ± 7.5 and 25.1 ± 2.5 for UV degraded and evaporated diesel fuel, respectively), compared to fresh one. Degraded gasoline shows no significant variations of the K_n-w compared to fresh one. The molecular investigation reveals the removal of the most volatile fraction for the evaporation treatment, whereas UV-degradation do not have pronounced effects on the chromatogram pattern. For the gasoline molecular investigation, no difference is observed between the treatments excepted a very slight removal of the lightest compounds under evaporation. These results show that NAPL degradation have effects on the K_n-w for diesel fuel and no significant effects for gasoline, at least with these degradation paths. This K_n-w variation will have in fine effects on ²²²Rn activity interpretation and NAPL subsurface quantification.

Characterization of a NAPL-contaminated site using the partitioning behavior of noble gases

Noble gases have been used for oil field exploration due to their partitioning behavior in oil-water systems. However, their application to study sites contaminated with non-aqueous phase liquids (NAPL) has been limited, except for ²²²Rn, which has been traditionally used as a partitioning tracer for contaminated sites. This study applied natural noble gas components such as ²²²Rn, He, Ne, Ar, Kr, and Xe to the characterization of a field site contaminated with trichloroethylene (TCE) located in Wonju, Korea. Groundwater at the site showed a maximum level of TCE that exceeded 1000 μg/L, with an approximate average of 400 μg/L, indicating the presence of residual TCE in the subsurface system even after remediation. The traditional tracer (i.e., ²²²Rn) was first used to characterize residual TCE. However, its heterogeneous distribution throughout the fractured bedrock aquifer negated its usefulness as a TCE indicator. The use of radiogenic ⁴He was also limited by the wide distribution of radiogenic sources on the site. By contrast, changes in the TCE level had clear effects on the conditions of other noble gases, such as Ne, Ar, and Xe, making them useful for characterization of the TCE-contaminated site. Furthermore, calculation of the TCE/water ratio including residual TCE was achieved, but identification of the TCE originating from the vadose zone was relatively hard. The results of this study indicate that based on their partitioning behavior, naturally-occurring noble gases can be used to delineate and quantify residual TCE.

Are surface water characteristics efficient to locate hyporheic biodiversity hotspots?

Location of river-groundwater exchange zones and biodiversity hotspot is essential for a river management plan, especially for Mediterranean karstic rivers. This location is often difficult and time-consuming when long river sectors are considered. We studied a 13 km-long sector of the Cèze River (Southern France) located in a karstic canyon. We compared five indicators of river-groundwater exchanges: longitudinal profiles of temperature, electrical conductivity and ²²²Rn concentrations in the surface water of the river, chemical characteristics of the hyporheic water and hyporheic biodiversity. Upwelling zones occurred downstream of geomorphological heterogeneities (here at the tail of gravel bars). Surface water chemistry, especially electrical conductivity and ²²²Rn concentrations, clearly traces large scale gaining sections, which were not associated to valley narrowing but with lateral springs, suggesting a crucial role of the geological structuration of the karstic plateau of Méjanne-le-Clap. Hyporheic water chemistry fits with the large-scale hydrological pattern, but with a high variability corresponding to local heterogeneities. The stygobite fauna (obligate groundwater organisms) and benthic EPTC (Ephemeroptera, Plecoptera, Trichoptera and Coleoptera) occurred preferentially in the gaining sections fed by groundwater, likely because of oligotrophic water and cooler temperature. The spatial distribution of river-groundwater exchange zone and hyporheic biodiversity may be thus predicted using changes in surface water chemistry, especially for electrical conductivity and ²²²Rn concentrations.

Excessive radon-based radiation in indoor air caused by soil building materials in traditional homes on Đồng Văn karst plateau, northern Vietnam

Radon-based radiation from natural soil building materials is an important factor likely influencing residents' health as a contributing source of natural radiation. This survey aims to quantify the nuclide-specific α-radiation of isotopes ²²²Rn and ²²⁰Rn in common types of houses in a region of northern Vietnam, Đồng Văn karst plateau, to preliminarily (i) evaluate the total annual effective dose rates and (ii) assess the relative risk of cancer induction from indoor α-radiation for inhabitants. The average ²²²Rn concentrations in all house types were lower than 100 Bq m^-3, but ²²⁰Rn abundances were far higher than ²²²Rn, even up to >1000 Bq m^-3 in air close to a wall of unfired-soil bricks. The estimated total annual effective dose rates from indoor ²²²Rn and ²²⁰Rn and their progenies to residents with daily exposure of 13 h in the various types of houses range from 3.1 to 4.3 mSv a^-1 for houses constructed with modified materials, but up to higher than 6 mSv a^-1 in houses with raw building materials. The average risk of developing lung cancer as a consequence of a lifetime exposure to indoor α-radiation in affected homes ranges from 3.9% to 14.6%. ²²⁰Rn and its metallic progenies contribute more than 80% of the total average lung cancer risk from total radon, being responsible for a range of 2.7-14.6% of the risk of developing lung cancer.

222Rn, 210Pb and 210Po in coastal zone groundwater: Activities, geochemical behaviors, consideration of seawater intrusion effect, and the potential radiation human-health risk

Groundwater quality in human-influenced coastal landscapes is receiving novel attention. Radionuclides have been recognized as another important monitoring indicator in many developed countries due to the discovery of extremely high level of natural ²¹⁰Po (up to 10,000 Bq/m³) and radium and radon isotopes. This study aims to evaluate the groundwater quality in the Beibu Bulf-Guangxi coast from radiological point of view. ²¹⁰Po, ²¹⁰Pb and ²²²Rn activities in 20 wells ranged from 0.24 ± 0.05 to 6.96 ± 1.62 Bq/m³, 2.17 ± 0.12 to 13.08 ± 0.74 Bq/m³ and 1500 ± 200 to 31,800 ± 900 Bq/m³, respectively. Compared with research data of other countries, groundwaters in this area have ²¹⁰Po, ²¹⁰Pb and ²²²Rn activity within low levels. The large deficiencies of ²¹⁰Po and ²¹⁰Pb relative to ²²²Rn in groundwaters implied that ²¹⁰Po and ²¹⁰Pb are strong particle-reactive radionuclides and they might be controlled by similar scavenging processes in groundwaters due to a good positive correlation between ²¹⁰Pb and ²¹⁰Po (R² = 0.67, p < 0.01). The concentrations of ²¹⁰Po and ²¹⁰Pb decreased with increasing pH values and salinity, which indicated that geochemical behaviors of ²¹⁰Po and ²¹⁰Pb in groundwater were influenced by seawater intrusion and pH changing. Groundwater ²²²Rn activity concentrations decreased with increasing salinity in coastal zone, which may be caused by dilution due to seawater intrusion or intensified ²²²Rn escaping from well-developed pores in coastal zone. The estimated annual ingestion doses for infants, children and adults were well below the recommended reference dose level (RDL) of 0.2-0.8 mSv/a, suggesting that consumption of analyzed groundwaters is safe from radiological point of view.

Does submarine groundwater discharge contribute to summer hypoxia in the Changjiang (Yangtze) River Estuary?

The Changjiang (Yangtze) River Estuary (CJE) is one of the largest and most intense seasonal hypoxic zones in the world. Here we examine the possibility that submarine groundwater discharge (SGD) may contribute to the summer hypoxia. Spatial distributions of bottom water ²²²Rn suggest a hotspot discharge area in the northern section of the CJE. SGD fluxes were estimated based on a ²²²Rn mass balance model and were found to range from 0.002 ± 0.004 to 0.022 ± 0.011 m³/m²/day. Higher SGD fluxes were observed during summer hypoxia period. The well-developed overlap of the distribution patterns for SGD flux and dissolved oxygen (DO) implies that SGD could be an important contributor to summer hypoxia in the region off the CJE. We suggest that SGD contributes to the seasonal hypoxia either: (1) directly via discharge of anoxic groundwaters together with reducing substances; and/or (2) indirectly by delivering excess nutrients that stimulate primary productivity with consequent consumption of DO during organic matter decomposition.

Laboratory-scale experimental and modelling investigations of 222Rn profiles in chemically heterogeneous LNAPL contaminated vadose zones

The potential of LNAPL delineation by ²²²Rn soil-gas monitoring in a chemically heterogeneous vadose zone was investigated in this study based on laboratory (batch and columns) experiments and numerical modelling. An enhanced version of the MIN3P reactive transport code was used to simulate Rn transport in both uncontaminated and NAPL-contaminated vadose zones and results were validated against analytical solutions and laboratory experiments. Results show that ²²²Rn activity profiles are mainly controlled by porous media ²²²Rn production, vadose zone fluid saturations and especially the type and distribution of NAPL in contaminated areas. The results also show that decreases in ²²²Rn activity and variations in activity gradients provide evidence for the presence and saturation of NAPL. This study demonstrates that LNAPL delineation via ²²²Rn gas surveys at contaminated sites works best, if gas measurements extend as deep as possible and include regions where ²²²Rn activity decreases due to elevated NAPL content. In addition, collection and analysis of depth-discrete gas samples allows the characterization of vertical NAPL distribution based on the ²²²Rn activity gradient. The determination of ²²²Rn production in the unsaturated zone, as well as water capillary pressure curves are of key importance in enabling the discrimination of an uncontaminated from a NAPL-contaminated area.

Characteristics of groundwater discharge to river and related heavy metal transportation in a mountain mining area of Dabaoshan, Southern China

Groundwater discharge to river and the related heavy metal transportation were estimated for Dabaoshan, a mountain mining area where extensive mining activities had been conducted over 40 years. In the lower reach of the mining area, shallow aquifers were contaminated by varies heavy metals due to the discharge of acid mine drainage. Polluted aquifers act as long-term pollution sources to the surrounding gaining rivers, even after the mining activities were stopped. The natural tracer ²²²Rn was measured for river water of the Hengshi River and groundwater adjacent to the river channel in both wet and dry seasons. The total groundwater discharge rate was estimated to be 17.4-26.7 × 10³ m³ day^-1 in wet season and 1.9-2.1 × 10³ m³ day^-1 in dry season; and the river recharge was 5.6 ± 1.0 × 10³ m³ day^-1 in wet season and 2.1 ± 1.0 × 10³ m³ day^-1 in dry season. Compared with other mining and natural/artificial factor influenced areas, groundwater discharge rate in Dabaoshan was much lower, but the magnitudes of groundwater-borne Cu, Zn, Mn and Co fluxes were comparable or even much higher. This suggested that groundwater-derived heavy metal fluxes were significant pollution sources to river in the mountain mining area. Meanwhile, the results also suggested that concentrations of Cd, Pb, Cu, Ni, Mn, Fe, Zn and Tl in groundwater increased where the recharge of river water to groundwater occurred, suggesting the recharge of river water can affect heavy metal concentrations of the beneath aquifers, even in a gaining river.

High 222Rn concentrations and dynamics in Shawan Cave, southwest China

Cave ²²²Rn has been a major health issue and subject of scientific debate for decades. While the basics of natural ventilation physics are well understood, it is difficult to make blind predictions of ²²²Rn concentrations in a given cave due to the complexity of cave systems. In-situ continuous observation is necessary to improve our ability to quantify radiation dose exposure and reduce radiation hazard to cave users, and trace the air exchange patterns occurring in caves. In this study, continuous monitoring using a RAD7 radon detector revealed high ²²²Rn concentrations and large fluctuations in ²²²Rn concentration in a small karst cave in southwest China, Shawan Cave. From August 2016 to July 2017, the average annual concentration was 47,419 Bqm^-3 and ranged between 3720 and 123,000 Bqm^-3, with lower values during summer than other seasons. Taking Shawan Cave as a case study, we suggest a framework to evaluate the potential dose exposure, allowing cave users to minimize risk of exposure to hazardous levels of ²²²Rn. Furthermore, we comparing results from this study with other studies in 35 caves worldwide, and conclude that there are three patterns of seasonal ²²²Rn variation. They were classified into five types of ventilation mode based on diversity of cave locations, geometry and connectivity of bed rock fracture networks, together with temperature differences between outside atmosphere and cave air.

Evaluation of groundwater discharge into surface water by using Radon-222 in the Source Area of the Yellow River, Qinghai-Tibet Plateau

Understanding hydrological processes in the Source Area of the Yellow River (SAYR), Qinghai-Tibet Plateau, is vital for protection and management of groundwater and surface water resources in the region. In situ water measurements of exchange rates between surface water and groundwater are, however, hard to conduct because of the harsh natural conditions of the SAYR. We here present an indirect method using in situ ²²²Rn measurements to estimate groundwater discharge into rivers and lakes in the SAYR. ²²²Rn was measured in rivers, lakes, groundwater and springs during three sampling periods (2014-2016), and the results indicate large variability in the concentration of the isotope. The data also indicate decreasing ²²²Rn trends in groundwater in the cold season (the Feb-2015 sampling period) which may be linked to frequency of capturing ²²²Rn in the frozen ground caused by geocryogenic processes. In addition, permafrost spatial extent and freeze-thaw processes have strongly affected the hydrological conditions in the region.

Stack releases of radionuclides from an integrated steel plant in China

Crude steel production in China made up the majority of the global output, at 49.5% in 2014. High temperature smelting processes result in the release of natural radionuclides, including radon gas and other air pollutants into the atmosphere. This paper conducts an analysis of the raw materials, end products and flue gas sampled from an integrated steel plant from within China's Jiangxi Province, with annual production of 8.50 Mt of crude steel. Normalized stack emissions factors of radionuclides from steel production were first reported in China. The results showed that sintering was the main process that released natural radionuclides, and the main radionuclides released into the atmosphere were ²²²Rn (86.4 GBq/Mt), ²¹⁰Pb (13.4 GBq/Mt), and ²¹⁰Po (1.71 GBq/Mt). The results provided essential basic data for radiological impact assessment of steel production, as well as that of nuclear energy chain, coal chain and other electricity sources.

Numerical modeling of the sources and behaviors of 222Rn, 220Rn and their progenies in the indoor environment-A review

²²²Rn, ²²⁰Rn and their short-lived progenies are well known radioactive indoor pollutants, identified as the leading environmental cause of lung cancer next to smoking. Apart from the conventional measurement methods, numerical modeling methods are developed to simulate their physical and decay processes in ²²²Rn and ²²⁰Rn's life cycle, estimate their levels, concentration distributions, as well as effects of control strategies in the indoor environment. In this article, we summarized the numerical models used to illustrate the physical processes of each source of ²²²Rn and ²²⁰Rn entry into the indoor environment, and the application of Jacobi room models and CFD (Computational Fluid Dynamic) models used to present the behaviors of indoor ²²²Rn, ²²⁰Rn and their progenies. Furthermore, we consider that the development of numerical modeling of ²²²Rn and ²²⁰Rn would have a bright prospect in the directions of stochastic methods based on a steady-state model, the fine simulation of the time-dependent model as well as the multi-dimension model.

Detecting the leakage source of a reservoir using isotopes

A good monitoring method is vital for understanding the sources of a water reservoir leakage and planning for effective restoring. Here we present a combination of several tracers (²²²Rn, oxygen and hydrogen isotopes, anions and temperature) for identification of water leakage sources in the Pushihe pumped storage power station which is in the Liaoning province, China. The results show an average ²²²Rn activity of 6843 Bq/m³ in the leakage water, 3034 Bq/m³ in the reservoir water, and 41,759 Bq/m³ in the groundwater. Considering that ²²²Rn activity in surface water is typically less than 5000 Bq/m³, the low level average ²²²Rn activity in the leakage water suggests the reservoir water as the main source of water. Results of the oxygen and hydrogen isotopes show comparable ranges and values in the reservoir and the leakage water samples. However, important contribution of the groundwater (up to 36%) was present in some samples from the bottom and upper parts of the underground powerhouse, while the leakage water from some other parts indicate the reservoir water as the dominant source. The isotopic finding suggests that the reservoir water is the main source of the leakage water which is confirmed by the analysis of anions (nitrate, sulfate, and chloride) in the water samples. The combination of these tracer methods for studying dam water leakage improves the accuracy of identifying the source of leaks and provide a scientific reference for engineering solutions to ensure the dam safety.

Testing the usefulness of 222Rn to complement conventional hydrochemical data to trace groundwater provenance in complex multi-layered aquifers. Application to the Úbeda aquifer system (Jaén, SE Spain)

The Úbeda aquifer system is a multi-layered aquifer intensively exploited for irrigation. It covers 1100km² and consists of piled up sedimentary aquifer and aquitard layers from Triassic sandstones and clays at the bottom, to Jurassic carbonates (main exploited layer) in the middle, and Miocene sandstones and marls at the top. Flow network modification by intense exploitation and the existence of deep faults favour vertical mixing of waters from different layers and with distinct chemical composition. This induces quality loss and fosters risk of quantity restrictions. To support future groundwater abstraction management, a hydrogeochemical (major and some minor solutes) and isotopic (²²²Rn) study was performed to identify the chemical signatures of the different layers and their mixing proportions in mixed samples. The study of 134 groundwater samples allowed a preliminary identification of hydrochemical signatures and mixtures, but the existence of reducing conditions in the most exploited sector prevents the utility of sulphate as a tracer of Triassic groundwater in the Jurassic boreholes. The potential of ²²²Rn to establish isotopic signatures and to trace groundwater provenance in mixtures was tested. ²²²Rn was measured in 48 samples from springs and boreholes in most aquifer layers. At first, clear correlations were observed between ²²²Rn, Cl and SO₄ in groundwater. Afterwards, very good correlations were observed between ²²²Rn and the chemical facies of the different layers established with End Member Mixing Analysis (EMMA). Using ²²²Rn as part of the signatures, EMMA helped to identify end-member samples, and to quantify the mixing proportions of water from the Triassic and the Deep Miocene layers in groundwater pumped by deep agricultural wells screened in the Jurassic. The incorporation of ²²²Rn to the study also allowed identifying the impact of irrigation returns through the association of moderate NO₃, Cl, and Br contents with very low ²²²Rn activities.

Radon in harvested rainwater at the household level, Palestine

The main objective of this study was to assess Radon concentration in the harvested rainwater (HRW) at the household level in Yatta area, Palestine. HRW is mainly used for drinking as it is the major source of water for domestic uses due to water scarcity. Ninety HRW samples from the household cisterns were collected from six localities (a town and five villages) and Radon concentrations were measured. The samples were randomly collected from different households to represent the Yatta area. Fifteen samples were collected from each locality at the same day. RAD7 device was used for analysis and each sample was measured in duplicate. Radon concentrations ranged from 0.037 to 0.26 Bq/L with a mean ± standard deviation of 0.14 ± 0.06 Bq/L. The estimated annual effective radiation doses for babies, children and adults were all far below the maximum limit of 5 mSvy^-1 set by the National Council on Radiation Protection and Measurements.

Measuring radon-222 in soil gas with high spatial and temporal resolution

In order to exploit ²²²Rn as a naturally-occurring tracer in soils we need to sample and measure radon isotopes in soil gas with high spatial and temporal resolution, without disturbing in situ activity concentrations and fluxes. Minimisation of sample volume is key to improving the resolution with which soil gas can be sampled; an analytical method is then needed which can measure radon with appropriate detection limits and precision for soil gas tracer studies. We have designed a soil gas probe with minimal internal dead volume to allow us to sample soil gas volumes of 45 cm³. Radon-222 is extracted from these samples into a mineral oil-based scintillation cocktail before counting on a conventional liquid scintillation counter. A detection limit of 320 Bq m^-3 (in soil gas) is achievable with a 1 h count. This could be further reduced but, in practice, is sufficient for our purpose since ²²²Rn in soil gas typically ranges from 2000-50,000 Bq m^-3. The method is simple and provides several advantages over commonly used field-portable instruments, including smaller sample volumes, speed of deployment and reliability under field conditions. The major limitation is the need to count samples in a liquid scintillation counter within 2-3 days of collection, due to the short (3.824 day) radioactive half-life of ²²²Rn. The method is not applicable to the very short-lived (55 s half-life) ²²⁰Rn.

Radon in soil gas in Kosovo

An assessment of the radiological situation due to exposure to radon and gamma emitting radionuclides was conducted in southern Kosovo. This study deals with sources of radon in soil gas. A long-term study of radon concentrations in the soil gas was carried out using the SSNTDs (CR-39) at 21 different locations in the Sharr-Korabi zone. The detectors were exposed for an extended period of time, including at least three seasonal periods in a year and the sampling locations were chosen with respect to lithology. In order to determine the concentration of the natural radioactive elements ²³⁸U and ²²⁶Ra, as a precursor of ²²²Rn, soil samples were collected from each measuring point from a depth of 0.8 m, and measured by gamma spectrometry. The levels (Bq kg^-1) of naturally occurring radionuclides and levels (kBq m^-3) of radon in soil gas obtained at a depth 0.8 m of soil were: 21-53 for ²²⁶Ra, 22-160 for ²³⁸U and 0.295-32 for ²²²Rn. With respect to lithology, the highest value for ²³⁸U and ²²⁶Ra were found in limestone and the highest value for ²²²Rn was found in metamorphic rocks. In addition, the results showed seasonal variations of the measured soil gas radon concentrations with maximum concentration in the spring months.

Exploring 222Rn as a tool for tracing groundwater inflows from eskers and moraines into slope peatlands of the Amos region of Quebec, Canada

Peatlands can play an important role in the hydrological dynamics of a watershed. However, interactions between groundwater and peat water remain poorly understood. Here, we present results of an exploratory study destined to test radon (²²²Rn) as a potential tracer of groundwater inflows from fluvioglacial landform aquifers to slope peatlands in the Amos region of Quebec, Canada. ²²²Rn occurs in groundwater but is expected to be absent from peat water because of its rapid degassing to the atmosphere. Any ²²²Rn activity detected in peat water should therefore derive from groundwater inflow. ²²²Rn activity was measured in groundwater from municipal, domestic wells and newly drilled and instrumented piezometers from the Saint-Mathieu-Berry and Barraute eskers (n = 9), from the Harricana Moraine (n = 4), and from the fractured bedrock (n = 3). Forty measurements of ²²²Rn activity were made from piezometers installed in five slope peatlands, along six transects oriented perpendicular to the fluvioglacial deposits. The relationship between ²²²Rn and total dissolved solids (TDS) measured in water from the mineral deposits underlying the peat layer suggests that ²²²Rn is introduced by lateral inflow from eskers and moraine together with salinity. This input is then diluted by peat water, depleted in both TDS and ²²²Rn. The fact that a relationship between TDS and ²²²Rn is visible calls for a continuous inflow of groundwater from lateral eskers/moraines, being ²²²Rn rapidly removed from the system by radioactive decay. Although more research is required to improve the sampling and tracing techniques, this work shows the potential of ²²²Rn tracer to identify groundwater inflow areas from granular aquifers found in eskers and moraines to slope peatlands.

Estimating the input of submarine groundwater discharge (SGD) and SGD-derived nutrients in Geoje Bay, Korea using (222)Rn-Si mass balance model

In order to evaluate the main source of nutrients for maintaining the high production in shellfish farming bay, we have measured (222)Rn activities and the concentrations of nutrients in stream water, seawater, and coastal groundwater around Geoje Bay, one of the largest cultivation areas of oyster in the southern sea of Korea in April 2013. Using the (222)Rn and Si mass balance model, the residence time of bay seawater was about 5days and the submarine groundwater discharge (SGD) into the bay was estimated to be approximately 1.8×10(6)m(3) d(-1). The SGD-derived nutrient fluxes contributed approximately 54% for DIN, 5% for DIP, and 50% for DSi of total nutrient input entering into the bay. Thus, our results suggest that SGD is the major source of nutrients in Geoje Bay, and SGD-derived nutrients are very important to support the biological production of this shellfish farming bay.

Atmospheric stability effects on potential radiological releases at a nuclear research facility in Romania: Characterising the atmospheric mixing state

A radon-based nocturnal stability classification scheme is developed for a flat inland site near Bucharest, Romania, characterised by significant local surface roughness heterogeneity, and compared with traditional meteorologically-based techniques. Eight months of hourly meteorological and atmospheric radon observations from a 60 m tower at the IFIN-HH nuclear research facility are analysed. Heterogeneous surface roughness conditions in the 1 km radius exclusion zone around the site hinder accurate characterisation of nocturnal atmospheric mixing conditions using conventional meteorological techniques, so a radon-based scheme is trialled. When the nocturnal boundary layer is very stable, the Pasquill-Gifford "radiation" scheme overestimates the atmosphere's capacity to dilute pollutants with near-surface sources (such as tritiated water vapour) by 20% compared to the radon-based scheme. Under these conditions, near-surface wind speeds drop well below 1 m s(-1) and nocturnal mixing depths vary from ∼ 25 m to less than 10 m above ground level (a.g.l.). Combining nocturnal radon with daytime ceilometer data, we were able to reconstruct the full diurnal cycle of mixing depths. Average daytime mixing depths at this flat inland site range from 1200 to 1800 m a.g.l. in summer, and 500-900 m a.g.l. in winter. Using tower observations to constrain the nocturnal radon-derived effective mixing depth, we were able to estimate the seasonal range in the Bucharest regional radon flux as: 12 mBq m(-2) s(-1) in winter to 14 mBq m(-2) s(-1) in summer.

Outdoor (222)Rn-concentrations in Germany - part 1 - natural background

To determine the natural radiation exposure due to outdoor radon ((222)Rn) and its short-lived decay products in Germany, the Federal Office for Radiation Protection (BfS) conducted a measuring programme over three years. The annual mean radon concentration at 1.5 m above ground level was measured with solid-state track etch detectors at 173 measuring points in an even grid with a grid length of approx. 50 km. Furthermore, annual mean values of the equilibrium-equivalent radon concentration (EEC) and the equilibrium factor were estimated on the basis of the activity concentrations of (214)Pb and (214)Bi measured at 27 stations of the German Meteorological Service (DWD). Our study yielded a spatial mean outdoor radon concentration for Germany of 9 ± 1 Bq m(-3) (median: 8 (-0.5/+1.0) Bq m(-3)), with regional means varying from 4.5 Bq m(-3) in Hamburg to 14 Bq m(-3) in Bavaria. The determined EEC are in a range from 1.4 to 11 Bq m(-3).

Radon-222 activity flux measurement using activated charcoal canisters: revisiting the methodology

The measurement of radon ((222)Rn) activity flux using activated charcoal canisters was examined to investigate the distribution of the adsorbed (222)Rn in the charcoal bed and the relationship between (222)Rn activity flux and exposure time. The activity flux of (222)Rn from five sources of varying strengths was measured for exposure times of one, two, three, five, seven, 10, and 14 days. The distribution of the adsorbed (222)Rn in the charcoal bed was obtained by dividing the bed into six layers and counting each layer separately after the exposure. (222)Rn activity decreased in the layers that were away from the exposed surface. Nevertheless, the results demonstrated that only a small correction might be required in the actual application of charcoal canisters for activity flux measurement, where calibration standards were often prepared by the uniform mixing of radium ((226)Ra) in the matrix. This was because the diffusion of (222)Rn in the charcoal bed and the detection efficiency as a function of the charcoal depth tended to counterbalance each other. The influence of exposure time on the measured (222)Rn activity flux was observed in two situations of the canister exposure layout: (a) canister sealed to an open bed of the material and (b) canister sealed over a jar containing the material. The measured (222)Rn activity flux decreased as the exposure time increased. The change in the former situation was significant with an exponential decrease as the exposure time increased. In the latter case, lesser reduction was noticed in the observed activity flux with respect to exposure time. This reduction might have been related to certain factors, such as absorption site saturation or the back diffusion of (222)Rn gas occurring at the canister-soil interface.

Liquid scintillation counting of polycarbonates: a sensitive technique for measurement of activity concentration of some radioactive noble gases

This work explores the application of the liquid scintillation counting of polycarbonates for measurement of the activity concentration of radioactive noble gases. Results from experimental studies of the method are presented. Potential applications in the monitoring of radioactive noble gases are discussed.

Radon emanation from low-grade uranium ore

Estimation of radon emanation in uranium mines is given top priority to minimize the risk of inhalation exposure due to short-lived radon progeny. This paper describes the radon emanation studies conducted in the laboratory as well as inside an operating underground uranium mine at Jaduguda, India. Some of the important parameters, such as grade/(226)Ra activity, moisture content, bulk density, porosity and emanation fraction of ore, governing the migration of radon through the ore were determined. Emanation from the ore samples in terms of emanation rate and emanation fraction was measured in the laboratory under airtight condition in glass jar. The in situ radon emanation rate inside the mine was measured from drill holes made in the ore body. The in situ(222)Rn emanation rate from the mine walls varied in the range of 0.22-51.84 × 10(-3) Bq m(-2) s(-1) with the geometric mean of 8.68 × 10(-3) Bq m(-2) s(-1). A significant positive linear correlation (r = 0.99, p < 0.001) between in situ(222)Rn emanation rate and the ore grade was observed. The emanation fraction of the ore samples, which varied in the range of 0.004-0.089 with mean value of 0.025 ± 0.02, showed poor correlation with ore grade and porosity. Empirical relationships between radon emanation rate and the ore grade/(226)Ra were also established for quick prediction of radon emanation rate from the ore body.

Using 222Rn to estimate submarine groundwater discharge (SGD) and the associated nutrient fluxes into Xiangshan Bay, East China Sea

Continuous radon ((222)Rn) monitoring was conducted at two stations (site A and site B) with different perpendicular distance from the shoreline in Xiangshan Bay, East China Sea. Based on a (222)Rn balance model (various sources and sinks of (222)Rn in coastal water), the average rate of SGD was estimated to be 0.69 cm/day and 0.23 cm/day for site A and site B, respectively. The results from a nutrient analysis of the groundwater indicate that the associated nutrients fluxes loading through the SGD pathway were 4.27×10(6) mol/day for DIN, 2.24×10(4) mol/day for DIP and 1.82×10(6) mol/day for DSi, respectively, which were comparable to or even higher than the levels observed in the local streams. Therefore, adequate attention should be paid to the importance of SGD as one source of nutrients during the eutrophication control process in this area.