Effects of soil heterogeneity and preferential flow on the water flow and isotope transport in an experimental hillslope

Soil water movement plays vital roles in hillslope runoff generation and groundwater and surface water interaction. However, there are still knowledge gaps about the impacts of soil heterogeneity and preferential flow on the internal water flow and transport process. In this study, the vertical soil heterogeneity focused on the variations in soil retention capacity, and the consideration of lateral preferential flow emphasized the higher hydraulic conductivity. We combined isotopic tracing and numerical modeling in an artificial hillslope, focusing on monitored processes of the artificial rainfall and isotopic tracing experiment. The results showed that the soil moisture quickly accumulated at the bottom of the hillslope during rainfall events, while the 2H enrichment occurred in the topsoil derived from enriched isotope injection in the second artificial rainfall. The evaporation process slowed down the mixing of new water in the topsoil and old water in the lower layer. We found that the vertical soil heterogeneity had significant influences on the internal water and isotope transport paths within the hillslope. The lateral preferential flow played an important role in the water flux and transport time to the seepage face. The coupling of isotopic tracing, which reflects the water transport and mixing with the hillslope, effectively improved the model simulation and mechanism analysis of hillslope water flow. Our findings provide new insights into the mechanisms governing soil water flow and transport dynamics in hillslopes, taking into account vertical soil heterogeneity and lateral preferential flow.

Geological and hydrochemical controls on water chemistry and stable isotopes of hot springs in the Three Parallel Rivers Region, southeast Tibetan Plateau: The genesis of geothermal waters

The Three Parallel Rivers Region (TPRR) is a tectonically active area in the middle segment of the Sanjiang Tethys Orogen, southeast Tibetan Plateau, characterized by many hot springs. This area is up-and-coming for producing geothermal energy, a CO2-free energy source, which will help China in reducing the effects of climate change. We report here the results of 37 geothermal springs that have been sampled to investigate the physical and chemical characteristics of the thermal water and evolution patterns. These springs are drained along three major N-S faults zones (the Lujiang Fault, the Lancangjiang Fault and the Jinshajiang-Red River Fault) to the interior of the Lanping Basin. Five hydrochemical water facies were recognized with Na-HCO3 being the primary type. Fluorine and boron that are produced through water-rock interactions are commonly enriched in these waters, and their concentrations are further controlled by secondary hydrochemical processes during water migration. The water's stable isotopes (δ18O and δD) suggest the meteoric origin of all thermal waters in the TPRR. The estimated reservoir temperatures range between 61 °C and 118 °C with the relatively hot reservoirs (> 100 °C) generally developed in major shear zones. These results indicate variable water circulation depth exceeding 3000 m, implying that the large-scale shearing displacement plays a vital role in heat acquisition. Conductive cooling and possible mixing of the thermal water with near-surface cold water occurred as the thermal water ascended along the fault systems and was ejected along the outlets of the springs. This study adds insights into hydrogeochemical constrains on evolution of water solutes over a large-scale hydrological cycle in the TPRR.

Geochemistry and Sr, S, and O stable isotopes of Miocene Abu Dhabi evaporites, United Arab Emirates

This study investigates for the first time the subsurface Miocene evaporite facies (Gachsaran Formation) in Abu Dhabi, United Arab Emirates. Forty-five evaporite rock samples were selected for petrographic, mineralogical, and geochemical investigations and stable isotope analyses to decipher their origin and constrain their age. Secondary gypsum with anhydrite relics dominates the investigated evaporitic rocks, with minor amounts of clays, dolomicrite, Fe/Ti oxides, and celestite. These samples are characterized by their excellent purity and low variability in geochemical composition. The distribution of trace element concentrations is significantly influenced by continental detrital intake. The main focus of the study is to determine the strontium, sulfur, and oxygen stable isotope compositions. The measured ⁸⁷Sr/⁸⁶Sr values of 0.708411-0.708739 are consistent with Miocene marine sulfates and indicate ∼21.12-15.91 Ma (Late Aquitanian-Burdigalian). The δ³⁴S and δ¹⁸O values are 17.10‰-21.59‰ and 11.89‰-19.16‰, respectively. These values are comparable to those of Tertiary marine evaporites. The relatively low values of δ³⁴S suggest that non-marine water possesses little influence on S distribution. The geochemical composition and Sr, S, and O isotope distributions of the Abu Dhabi gypsum facies from the Gachsaran Formation reveals that their source brines were marine (coastal saline/sabkha) with subordinate continental input.

Effects of groundwater and distilled water on the durability of evaporitic rocks

Evaporitic rock durability induced by groundwater cause several construction challenges, but representative experimental studies to evaluate such conditions are still missing. Therefore, this study intended to provide better and more realistic degradability features of evaporites with groundwater besides a comparison with distilled water as slaking fluids. Forty-eight evaporitic rock blocks were collected from Abu Dhabi area, United Arab Emirates. 96 slake durability index (SDI) tests were performed, 48 with each of the slaking fluids; groundwater and distilled water, and their textural, mineralogical, and geochemical attributes were also examined before and after the SDI tests. In comparison to mineralogical and textural modifications, slaking fluid had a greater impact on the chemical composition of evaporitic rock. The study shows that the degradability of evaporites with groundwater and distilled water indicates a wide range from very low to high. The mean weight loss values after four cycles with groundwater and distilled water vary from 11 to 77 and from 4 to 81 wt.%, respectively. Consequently, slaking with groundwater illustrates a wide range compared to the slaking with distilled water. This could be due to quick interactions between groundwater and evaporites and fast hydration-dehydration process than distilled water due to the chemical composition of the groundwater. It is recommended to investigate the attributes of evaporitic rocks as well as groundwater geochemistry for safe, cost-effective, and sustainable structures.

127I and 129I species in the English Channel and its adjacent areas: Uncovering impact on the isotopes marine pathways

Radioactive iodine-129 has been released from the La Hague nuclear fuel reprocessing facility (NRF) into the English Channel, but the distribution and transformation of the isotope species, and environmental consequences have not been fully characterized in the Channel. Here we present data on iodine isotopes (¹²⁹I and ¹²⁷I) species in surface water of the English Channel and the southern Celtic Sea. Compared to ¹²⁷I species, the concentrations of ¹²⁹I^- and ¹²⁹IO₃^- show more variations, but iodate is the major species for both ¹²⁹I and ¹²⁷I. Our data provide new information regarding iodide-iodate inter-conversion showing that water dilution and mixing are the main factors affecting the ¹²⁷I and ¹²⁹I species distribution in the Channel. Some reduction of iodate occurs within the English Channel and mainly in the west part because of biotic processes. The ¹²⁹I species transformation is overall insignificant, especially in the eastern Channel, where a constant value of ¹²⁹IO₃^-/¹²⁹I is observed, which might characterize the La Hague wastewater signal. In the Celtic Sea, oxidation of iodide can be traced by ¹²⁷I and ¹²⁹I species. On a larger scale, ¹²⁹I generally experienced an oxidation process in the Atlantic Ocean, while in the coast of shallow shelf seas, new produced ¹²⁹I^- can be identified, especially in the German Bight and the Baltic Sea. The data of ¹²⁹I species in the English Channel can provide estimate of redox rates in a much broader marine areas if the transit time of ¹²⁹I from La Hague is well-defined. Furthermore, estimate of inventories for ¹²⁹I and its species in the Channel, and fluxes of ¹²⁹I species from the English Channel to the North Sea add important information to the geochemical cycle of ¹²⁹I.

Anthropogenic 236U and 233U in the Baltic Sea: Distributions, source terms, and budgets

The Baltic Sea receives substantial amounts of hazardous substances and nutrients, which accumulate for decades and persistently impair the Baltic ecosystems. With long half-lives and high solubility, anthropogenic uranium isotopes (²³⁶U and ²³³U) are ideal tracers to depict the ocean dynamics in the Baltic Sea and the associated impacts on the fates of contaminants. However, their applications in the Baltic Sea are hampered by the inadequate source-term information. This study reports the first three-dimensional distributions of ²³⁶U and ²³³U in the Baltic Sea (2018-2019) and the first long-term hindcast simulation for reprocessing-derived ²³⁶U dispersion in the North-Baltic Sea (1971-2018). Using ²³³U/²³⁶U fingerprints, we distinguish ²³⁶U from the nuclear weapon testing and civil nuclear industries, which have comparable contributions (142 ± 13 and 174 ± 40 g) to the ²³⁶U inventory in modern Baltic seawater. Budget calculations for ²³⁶U inputs since the 1950s indicate that, the major ²³⁶U sources in the Baltic Sea are the atmospheric fallouts (∼1.35 kg) and discharges from nuclear reprocessing plants (> 211 g), and there is a continuous sink of ²³⁶U to the anoxic sediments (589 ± 43 g). Our findings also indicate that the limited water renewal endows the Baltic Sea a strong "memory effect" retaining aged ²³⁶U signals, and the previously unknown ²³⁶U in the Baltic Sea is likely attributed to the retention of the mid-1990s' discharges from the nuclear reprocessing plants. Our preliminary results demonstrate the power of ²³⁶U-¹²⁹I dual-tracer in investigating water-mass mixing and estimating water age in the Baltic Sea, and this work provides fundamental knowledge for future ²³⁶U tracer studies in the Baltic Sea.

A multi-isotopic evaluation of groundwater in a rapidly developing area and implications for water management in hyper-arid regions

Management of water resources in hyper-arid areas faces vital challenges in a global climate change context. Consequently, understanding the effects on groundwater sources can help mitigating the problem of water scarcity and the negative impact of human intervention on the environment. A case study area in the hyper-arid climate of the United Arab Emirates, was tackled here with the focus on applying stable isotopes as tools for evaluating groundwater sources and quality assessment. The results of major ions indicate variable increase in groundwater salinity moving away from Al Hajar Mountains recharge areas to the discharge areas (Arabian Gulf coast). The data of stable isotopes (δ¹⁸O_H2O, δ²H_H2O, δ¹⁸O_NO3, δ¹⁵N_NO3, δ¹⁸O_SO4, δ³⁴S_SO4, δ¹¹B) suggest impact of paleo-groundwater in the abstractions of the wells nearest to the coast. Nitrate isotopes indicate farming activities sources that can be masked due to the contribution from the nitrate-poor paleo-groundwater. Nitrate reduction processes are expected near to the recharge front. Sulphate and boron isotopes further suggest that influence of ancient evaporite dissolution in salinization. Management efforts should be focused on the diffuse sources of quality mitigations that can be vital in fingerprinting local and regional (transboundary) effects.

Holocene monsoon dynamics at Kunlun Pass on the northeastern Qinghai-Tibet Plateau

Various proxy records have been used for the understanding of environmental and climate variations during the Holocene. Here, for the first time, we use meteoric ¹⁰Be isotope measurements performed on sediments from a drill core collected at the Kunlun Pass (KP) on the northeastern Qinghai-Tibet Plateau (NETP) to investigate hydroclimate changes during the Holocene. The ¹⁰Be flux suggests relative low levels in the Early Holocene, followed by a sharp increase to high values at around 4 ka BP (4 ka BP = 4000 years before present). Afterwards, the ¹⁰Be flux remains on a high level during the Late Holocene, but decreases slightly towards today. These ¹⁰Be deposition patterns are compared to moisture changes in regions dominated by the Indian Summer Monsoon (ISM), East Asian Summer Monsoon (EASM), and the Westerlies. Different from the gradual changes in monsoon patterns, the ¹⁰Be data reveal low levels during the Early Holocene until ~4 ka BP when an obvious increase is indicated and a relative high level continues to this day, which is relatively more in agreement with patterns of the Westerlies. This finding provides a new evidence for a shift in the dominant pattern of atmospheric circulation at the KP region from a more monsoonal one to one dominated by the Westerlies. Our results improve the understanding of non-stationary interactions and spatial relevance of the EASM, the ISM and the Westerlies on the Qinghai-Tibet Plateau.

Solar and meteorological influences on seasonal atmospheric 7Be in Europe for 1975 to 2018

Assessing the transport of natural radionuclides in the atmosphere provides a powerful tool to study air mass circulation. Here, we investigated the seasonal atmospheric distribution of the naturally produced ⁷Be in surface air over Europe between 40° N and 68° N during the period 1975-2018. The results suggest that the inter-annual variability of ⁷Be reflects production rates of the radionuclide induced by solar modulation of cosmic rays. Further analysis of the meteorological influences indicates that the meteorological influences on ⁷Be concentrations are geographically and seasonally dependent. We found that, in general, the tropopause pressure plays an important factor influencing ⁷Be activity for winter and spring seasons while the sea level pressure and temperature are more dominant during summer and autumn seasons. The combination of tropospheric production rates and meteorological parameters explains 24%-79% variances of the seasonal ⁷Be activity. We further applied a three-box model to study the influence of stratosphere-troposphere exchanges on ⁷Be concentrations. The simulation supports that the seasonal cycle of ⁷Be in Europe is controlled by two main factors: the changing height of the troposphere (seasonality of the tropopause height) and seasonal variations of the stratosphere-troposphere exchanges.

Circulation of Circumpolar Deep Water and marine environment traced by 127I and 129I speciation in the Amundsen Sea Polynya, Antarctica

The long-lived anthropogenic ¹²⁹I released from human nuclear activities has been widely employed as an effective oceanographic tracer to investigate circulation of water masses in marine environment. Depth profiles of seawater collected from the Amundsen Sea Polynya, Antarctica were analyzed for total ¹²⁹I and ¹²⁷I, as well as their species of iodide and iodate. The measured ¹²⁹I concentrations ((1.15-3.43) × 10⁶ atoms/L) and ¹²⁹I/¹²⁷I atomic ratios ((0.53-1.19) × 10^-11) indicate that anthropogenic ¹²⁹I has not only reached the Antarctic surface marine environment but also the deep water due to a strong vertical mixing of water masses. The Circumpolar Deep Water (CDW) flowed southward along continental shelf towards the ice shelf zone (74.25°S) at a depth of 1025 m and then migrated upward and northward to the polynya and finally to the sea ice zone (71.95°S). The maximum upwelling depth of the CDW was around 200 m in the polynya. The source of ¹²⁹I^- in the polynya is predominantly the intrusion of source waters rather than the in-situ reduction of iodate by phytoplankton, implying a considerably slow reduction process of iodate to iodide in this region.

Use of 10Be isotope to predict landscape development in the source area of the Yellow River (SAYR), northeastern Qinghai-Tibet Plateau

The magnitude of soil and sediment erosion and accumulation processes can profoundly affect landscape development and hamper efficient management of natural resources. Consequently, estimating the rates and causes of these processes is essential, particularly in remote regions, for prediction of changes in landform and river evolution and protection of local ecosystem. We here present the results of a soil and sediment erosion investigation in the Source Area of the Yellow River (SAYR), northeast Qinghai-Tibet Plateau based on a combined analysis of ¹⁰Be cosmogenic isotope and Soil and Water Assessment Tool (SWAT) simulation modelling. The data reveal variable soil erosion trends that range between 103 and 830 t km^-2 a^-1. The low values occur in the western part of the basin that are associated with low sediment yield, while the high values appear in the dominant sediment export part of the basin along the main stream of the Yellow River in the east. Generally, soil and sediment accumulation is characterized by high ¹⁰Be concentration in the western part and the northwest of Ngöring Lake. The style of landform development by the erosion/accumulation processes is closely linked to the distribution and degradation extent of the permafrost in the study region. Soil surface erosion increases with more permafrost degradation from the western to the eastern part of the basin, and surface soil particles are dominantly removed from the surface rather than deeper layers.

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.

Iodine isotopes (129I and 127I) in the hydrosphere of Qinghai-Tibet region and South China Sea

The radioactive isotope ¹²⁹I, with a half-life of 1.57 × 10⁷ years, is widely used as a tracer to assess nuclear safety, to track environmental and geological events and to figure out the details of the stable iodine geochemical cycle. This work investigated the ¹²⁹I and ¹²⁷I distribution in water samples collected from the terrestrial (rivers, lakes and springs) and marine water systems (estuary and sea) in China. The measured ¹²⁹I concentrations of (1-51) × 10⁶ atoms/L and ¹²⁹I/¹²⁷I ratios of (0.03-21) × 10^-10 shows the variability of ¹²⁹I level in the water systems. The local permafrost and seasonal frozen environment play a key role in groundwater recharge in the Qinghai-Tibet region, which is reflected in the ¹²⁹I distribution in surface water. The depth distribution of ¹²⁹I in the water column of the South China Sea reflects the effluence of different currents. The results also indicate that the hydrosphere of China contains one to three orders of magnitude less ¹²⁹I compared to those reported in Europe. Despite the large distance, the European nuclear fuel reprocessing facilities represent the major source of ¹²⁹I in the hydrosphere of China through atmospheric transport. The contribution of the Fukushima nuclear accident to ¹²⁹I levels in the hydrosphere of China was negligible.

Assessment of groundwater quality and 222Rn distribution in the Xuzhou region, China

Evaluation of groundwater quality represents significant input for the development and utilization of water resources. Increasing exploitation of groundwater and man-made pollution has seriously affected the groundwater quality of the North China Plain, such as in the Xuzhou region which is the target of this investigation. The assessment of the groundwater quality and sources in the region was based on analyses of water chemistry and ²²²Rn activity in samples collected from wells penetrating unconfined and confined aquifers. The results indicate that most of the untreated groundwater in the region is not suitable for the long-term drinking based on permissible limits of the Chinese Environmental Agency and the World Health Organization. However, the groundwater can be used as healthy source of drinking water when they can pass the biological test and softening water treatment. Most of the groundwater is suitable for irrigation. Excessive amounts of SO₄^2- and NO₃^- are attributed to mainly influence of wastewater, irrigation, and dissolution of sulfate minerals in local coal strata. The major source of the groundwater is meteoric recharge with addition from irrigation and wastewater discharges. Variability of the water quality seems to be also reflecting the type of aquifers where the highest concentration of HCO₃^- occurs in water of the carbonate fractured aquifer, while the highest Cl^- concentration in the unconfined aquifer. Source of ²²²Rn activity is mainly related to the rock-water interaction with possible addition from the agricultural fertilizers. Protection of groundwater is vital to maintain sustainable drinking quality through reducing infiltration of irrigation water and wastewater.

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.

Quality assessment of groundwater from the south-eastern Arabian Peninsula

Assessment of groundwater quality plays a significant role in the utilization of the scarce water resources globally and especially in arid regions. The increasing abstraction together with man-made contamination and seawater intrusion have strongly affected groundwater quality in the Arabia Peninsula, exemplified by the investigation given here from the United Arab Emirates, where the groundwater is seldom reviewed and assessed. In the aim of assessing current groundwater quality, we here present a comparison of chemical data linked to aquifers types. The results reveal that most of the investigated groundwater is not suitable for drinking, household, and agricultural purposes following the WHO permissible limits. Aquifer composition and climate have vital control on the water quality, with the carbonate aquifers contain the least potable water compared to the ophiolites and Quaternary clastics. Seawater intrusion along coastal regions has deteriorated the water quality and the phenomenon may become more intensive with future warming climate and rising sea level.

Multiradionuclide evidence for the solar origin of the cosmic-ray events of ᴀᴅ 774/5 and 993/4

The origin of two large peaks in the atmospheric radiocarbon (¹⁴C) concentration at AD 774/5 and 993/4 is still debated. There is consensus, however, that these features can only be explained by an increase in the atmospheric ¹⁴C production rate due to an extraterrestrial event. Here we provide evidence that these peaks were most likely produced by extreme solar events, based on several new annually resolved ¹⁰Be measurements from both Arctic and Antarctic ice cores. Using ice core ³⁶Cl data in pair with ¹⁰Be, we further show that these solar events were characterized by a very hard energy spectrum with high fluxes of solar protons with energy above 100 MeV. These results imply that the larger of the two events (AD 774/5) was at least five times stronger than any instrumentally recorded solar event. Our findings highlight the importance of studying the possibility of severe solar energetic particle events.

Natural spikes in radiocarbon have been identified at ᴀᴅ 774/5 and 993/4 and attributed to exceptional cosmic-ray events, although the cause remains uncertain. Here, the authors analyse records recovered from ice cores and suggest these spikes originated from extreme solar particle events.

Iodine-129 in snow and seawater in the Antarctic: level and source

Anthropogenic (129)I has been released to the environment in different ways and chemical species by human nuclear activities since the 1940s. These sources provide ideal tools to trace the dispersion of volatile pollutants in the atmosphere. Snow and seawater samples collected in Bellingshausen, Amundsen, and Ross Seas in Antarctica in 2011 were analyzed for (129)I and (127)I, including organic forms; it was observed that (129)I/(127)I atomic ratios in the Antarctic surface seawater ((6.1-13) × 10(-12)) are about 2 orders of magnitude lower than those in the Antarctic snow ((6.8-9.5) × 10(-10)), but 4-6 times higher than the prenuclear level (1.5 × 10(-12)), indicating a predominantly anthropogenic source of (129)I in the Antarctic environment. The (129)I level in snow in Antarctica is 2-4 orders of magnitude lower than that in the Northern Hemisphere, but is not significantly higher than that observed in other sites in the Southern Hemisphere. This feature indicates that (129)I in Antarctic snow mainly originates from atmospheric nuclear weapons testing from 1945 to 1980; resuspension and re-emission of the fallout (129)I in the Southern Hemisphere maintains the (129)I level in the Antarctic atmosphere. (129)I directly released to the atmosphere and re-emitted marine discharged (129)I from reprocessing plants in Europe might not significantly disperse to Antarctica.

Natural radioactivity in groundwater from the south-eastern Arabian Peninsula and environmental implications

Groundwater is the most valuable resource in arid regions, and recognizing radiological criteria among other water quality parameters is essential for sustainable use. In the investigation presented here, gross-α and gross-β were measured in groundwater samples collected in the south-eastern Arabian Peninsula, 67 wells in Unite Arab Emirates (UAE), as well as two wells and one spring in Oman. The results show a wide gross-α and gross-β activities range in the groundwater samples that vary at 0.01∼19.5 Bq/l and 0.13∼6.6 Bq/l, respectively. The data show gross-β and gross-α values below the WHO permissible limits for drinking water in the majority of the investigated samples except those in region 4 (Jabel Hafit and surroundings). No correlation between groundwater pH and the gross-α and gross-β, while high temperatures probably enhance leaching of radionuclides from the aquifer body and thereby increase the radioactivity in the groundwater. This conclusion is also supported by the positive correlation between radioactivity and amount of total dissolved solid. Particular water purification technology and environmental impact assessments are essential for sustainable and secure use of the groundwater in regions that show radioactivity values far above the WHO permissible limit for drinking water.

10Be climate fingerprints during the Eemian in the NEEM ice core, Greenland

Several deep Greenland ice cores have been retrieved, however, capturing the Eemian period has been problematic due to stratigraphic disturbances in the ice. The new Greenland deep ice core from the NEEM site (77.45 °N, 51.06 °W, 2450 m.a.s.l) recovered a relatively complete Eemian record. Here we discuss the cosmogenic (10)Be isotope record from this core. The results show Eemian average (10)Be concentrations about 0.7 times lower than in the Holocene which suggests a warmer climate and approximately 65-90% higher precipitation in Northern Greenland compared to today. Effects of shorter solar variations on (10)Be concentration are smoothed out due to coarse time resolution, but occurrence of a solar maximum at 115.26-115.36 kyr BP is proposed. Relatively high (10)Be concentrations are found in the basal ice sections of the core which may originate from the glacial-interglacial transition and relate to a geomagnetic excursion about 200 kyr BP.

Temporal variation of iodine isotopes in the North Sea

Monitoring temporal variability of (129)I in the North Sea, a relatively large reservoir of radioactive discharges from the nuclear fuel reprocessing facilities, is vital for the environmental situation in the region. New information on concentration levels and distribution of (129)I and (127)I and their species forms (iodide and iodate) are gained here through sampling of surface water in 2010. The results show generally large spatial and temporal (compared to data from 2005) fluctuations of total (129)I and (127)I, and iodide and iodate. In samples south of 53°N, the level of (127)I(-) in 2010 was generally comparable or higher than in 2005. The results also show total (129)I concentrations comparable in the south, but 2-8 times lower in the north, to the analyses made in 2005. Different from total (129)I, the (129)I(-)/(129)IO3(-) values in the northern part were 2 times higher in 2010 than values observed in 2005. These variations in total (129)I and (127)I and their species are related to coastal water offshore propagation and surface currents that are linked to long-term and seasonal climatic changes over the North Atlantic and North Sea. Inventory estimation shows that >90% of (129)I resides in the Southern and German Bights, which also suggests negligible contribution from the Sellafield facility discharges when compared with that from the La Hague. Variability in discharge rate from La Hague may also affect the distribution patterns of (129)I in the North Sea on the monthly scale.

Iodine isotopes species fingerprinting environmental conditions in surface water along the northeastern Atlantic Ocean

Concentrations and species of iodine isotopes ((127)I and (129)I) provide vital information about iodine geochemistry, environmental conditions and water masses exchange in oceans. Despite extensive investigations of anthropogenic (129)I in the Arctic Ocean and the Nordic Seas, concentrations of the isotope in the Atlantic Ocean are, however, still unknown. We here present first data on (129)I and (127)I, and their species (iodide and iodate) in surface water transect along the northeastern Atlantic between 30° and 50°N. The results show iodate as the predominant species in the analyzed marine waters for both (127)I and (129)I. Despite the rather constant ratios of (127)I(-)/(127)IO3(-), the (129)I(-)/(129)IO3(-) values reveal variations that apparently response to sources, environmental conditions and residence time. These findings provide a new tracer approach that will strongly enhance the application of anthropogenic (129)I in ocean environments and impact on climate at the ocean boundary layer.

Model simulation of inflow water to the Baltic Sea based on ¹²⁹I

The semi-enclosed Baltic Sea represents a vital economic and recreational resource for more than 90 million people inhabiting its coasts. Extensive contamination of this sea by a variety of anthropogenic pollutants has raised the concern of the people in the region. Quantifying seawater inflow is crucial for estimating potential environmental risks as well as to find the best remedial strategy. We present here a model to estimate water inflow from the North Sea to the Baltic Sea by utilizing ¹²⁹I as a tracer. The results predicted inflow range of 230-450 km³/y with best fit value around 330 km³/y from the North Sea to the Baltic Sea during 1980-1999. Despite limited time series data on ¹²⁹I, the model presented here demonstrates a new management tool for the Baltic Sea to calculate inflow water compared to conventional methods (such as salinity, temperature and hydrographic models).

129I in the Baltic Proper and Bothnian Sea: application for estimation of water exchange and environmental impact

We report here new data and a mass balance model for (129)I in the Baltic Proper and the Bothnian Sea covering the period from November-December 2009. The results showed that the general (129)I concentrations in the Bothnian Sea were two-four folds lower than in the Baltic Proper for both surface and deep water. Water exchange between the two basins based on the (129)I mass balance model suggests fluxes from the Baltic Proper to the Bothnian Sea and vice versa at 980 km(3)/y (600-1400 km(3)/y) and 1180 km(3)/y (780-1600 km(3)/y) respectively. Water retention time (residence time) in the Bothnian Sea was estimated at up to 4 years. Applying the (129)I exchange model, an estimate of total phosphorus and nitrogen inflow from the Baltic Proper to the Bothnian Sea indicates values of 20 ± 7 × 10(3) tons/y and 300 ± 50 × 10(3) tons/y respectively. The values for the outflow from the Bothnian Sea to the Baltic Proper hold 12 ± 3 × 10(3) tons/y for total phosphorus and 283 ± 55 × 10(3) tons/y for total nitrogen. These data and application of (129)I as a tracer of water masses provide information on small scale salinity changes which are vital for accurate understanding of the Baltic Sea ecosystems evolution through time.

127I and 129I species and transformation in the Baltic proper, Kattegat, and Skagerrak basins

Occurrence of anthropogenic (129)I in seawater has provided invaluable information about water circulation and exchange rates, but results on (129)I species (iodide and iodate) are limited and only available for surface water. We here present the first extensive results on (129)I and (127)I species in samples of seawater depth profiles, which were collected in August 2006 and April 2007 in the Skagerrak, Kattegat, and Baltic Proper. The results expose ≤10% annual reduction of iodate as (129)I is transported from the English Channel along the Dutch coast and German Bight into the Skagerrak and Kattegat. The results also suggest strong variability between surface and bottom seawater with respect to the predominant iodine species. Distribution of iodide and iodate of both (127)I and (129)I in the Kattegat mainly reflects water mixing process rather than speciation transformation. In water of the Baltic Proper, high (127)I(-)/(127)IO(3)(-) and (129)I(-)/(129)IO(3)(-) values suggest effective reduction of iodate with a maximum rate of 8 × 10(-7) ((127)IO(3)(-)) and 6 × 10(-14) ((129)IO(3)(-)) (g/m(3).day). The reduction process of iodate seems to be related to decomposition of organic matter and photochemically induced reactions.

Speciation of ¹²⁹I in sea, lake and rain waters

Concentrations of the very long-lived fission product (129)I and stable iodine ((127)I) in the Baltic Sea and lake and rain waters from Finland, were measured as well as their occurrence as iodide (I(-)) and iodate (IO(3)(-)). The highest concentrations of both (127)I and (129)I occurred in sea water, on average 11.1 ± 4.3 μg/l and 3.9 ± 4.1 × 10(-9) at/l. In rain and lake waters the concentration of (129)I was more or less identical and almost one order of magnitude lower than in sea water. Based on these observations, and data from the literature, it is assumed that the source of (129)I in lakes is precipitation and the major source in the Baltic Sea is the inflow of sea water from the North Sea through the Danish Straits. The concentration of (129)I in the Baltic Sea has increased by a factor of six during ten years from 1999. In all studied water types the main chemical form of both iodine isotopes was iodide; in sea and lake waters by 92-96% and in rain water by 75-88%. Compared to (127)I the fraction of iodide was slightly higher in case of (129)I in all waters.

Iodide and iodate (129I and 127I) in surface water of the Baltic Sea, Kattegat and Skagerrak

Despite the common incorporation of iodine in the biological cycle and occurrence of huge contamination of the radioactive isotope (129)I in the Baltic Proper, Skagerrak and Kattegat, there is no data on chemical speciation of iodine in these waters. We here present first time data on iodine isotopes (129)I and (127)I species as iodide and iodate in surface seawater samples collected from 16 locations in August 2006 and 19 locations in April 2007 in the Baltic Proper, Skagerrak and Kattegat. After extensive separation methods, the isotopes concentrations were determined using accelerator mass spectrometry (AMS) technique for the (129)I and inductively coupled plasma mass spectroscopy (ICP-MS) for (127)I. High concentrations of both isotopes species were found in the Skagerrak-Kattegat basins, whereas the values in the Baltic Proper are low for both species. The ratios of (129)I(-)/(129)IO(3)(-) and (127)I(-)/(127)IO(3)(-) significantly increase from south to central Baltic Sea, and iodide (both isotopes) appears as the predominant inorganic iodine species along the Baltic Sea. The results show insignificant change in (129)I and (127)I speciation and suggest that reduction of iodate and oxidation of iodide in Skagerrak and Kattegat may be a slow process. Additionally, the positive correlation between salinity and iodide and iodate (both isotopes) may reflect effective control of Skagerrak water mass on iodine distribution in surface water of the Baltic Sea.

Partition of iodine (¹²⁹I and ¹²⁷I) isotopes in soils and marine sediments

Natural organic matter, such as humic and fulvic acids and humin, plays a key role in determining the fate and mobility of radioiodine in soil and sediments. The radioisotope ¹²⁹I is continuously produced and released from nuclear fuel reprocessing plants, and as a biophilic element, its environmental mobility is strongly linked to organic matter. Due to its long half-life (15.7 million years), ¹²⁹I builds up in the environment and can be traced since the beginning of the nuclear era in reservoirs such as soils and marine sediments. Nevertheless, partition of the isotope between the different types of organic matter in soil and sediment is rarely explored. Here we present a sequential extraction of ¹²⁹I and ¹²⁷I chemical forms encountered in a Danish soil, a soil reference material (IAEA-375), an anoxic marine sediment from Southern Norway and an oxic sediment from the Barents Sea. The different forms of iodine are related to water soluble, exchangeable, carbonates, oxides as well as iodine bound to humic acid, fulvic acid and to humin and minerals. This is the first study to identify ¹²⁹I in humic and fulvic acid and humin. The results show that 30-56% of the total ¹²⁷I and 42-60% of the total ¹²⁹I are associated with organic matter in soil and sediment samples. At a soil/sediment pH below 5.0-5.5, (¹²⁷I and ¹²⁹I in the organic fraction associate primarily with the humic acid while at soil/sediment pH > 6 ¹²⁹I was mostly found to be bound to fulvic acid. Anoxic conditions seem to increase the mobility and availability of iodine compared to oxic, while subaerial conditions (soils) reduces the availability of water soluble fraction compared to subaqueous (marine) conditions.

Iodine isotopes (129I and 127I) in the Baltic Proper, Kattegat, and Skagerrak basins

Radioactive anthropogenic pollution has raised concerns about the present and future environmental status of the semienclosed Baltic Sea. We here study the distribution and inventory of the anthropogenic radioactive (129)I in water depth profiles collected from 16 sites in August 2006 and 19 sites in April 2007 in the Baltic Proper and related Kattegat and Skagerrak basins. The results reveal considerable differences of (129)I concentration in terms of spatial and temporal variability and expose relatively high concentrations in the deep waters. Variability in the concentration of (127)I, stable natural isotope of iodine, seems to follow changes in the seawater salinity, but in oxygen-poor bottom waters sediment diagenetic release may contribute to the concentration of both isotopes in the water body. Inventory estimates show that (129)I in August 2006 (24.2 ± 15.4 kg) is higher than that in April 2007 (14.4 ± 8.3 kg) within the southern and central Baltic Proper whereas almost a constant load occurs in the Kattegat Basin. Calculated model inventory shows correspondence to empirical data and provides a guideline for future environmental assessment on the impact of (129)I load in the studied region.

Time series of 129I and 127I speciation in precipitation from Denmark

Environmental 129I mainly released from reprocessing plants at La Hague (France) and Sellafield (U.K.) provides a unique atmospheric and environmental tracer. This study deals with 129I and 127I speciation in precipitation collected in Denmarkduring 2001-2006 that indicates many newfindings. The concentrations of total 129I in precipitation vary from 0.28 to 5.63 x 10(9) atoms 129I L(-1) with an average of (2.34 +/- 1.43) x 10(9) atoms 129I L(-1), and the annual deposition flux of 129I is (1.25 +/- 0.30) x 10(12) atoms m(-2). Increased 129I levels in precipitation and 129I/ 127I ratio are attributed to the releases of 129I from the reprocessing plants at La Hague and Sellafield. Iodide is the major specie of 129I, which accounts for 50-99% of total 129I. The concentrations of total 127I vary from 0.78 to 2.70 microg iodine L(-1) with an average of 1.63 +/- 0.47 microg iodine L(-1), and annual deposition flux of 0.95 +/- 0.26 mg m(-2). Unlike 129I, iodate is the major specie of 127I, which accounts for 43-93% of total 127I. The 291I/ l27I atomic ratios for total iodine vary from 5.04 to 76.5 x 10(-8) with an average of (30.1 +/- 16.8) x 10(-8). These values are 10 times lower for iodate with an average of (2.95 +/- 3.13) x 10(-8). Seasonal variations of 129I/127 ml values and 129I concentrations are associated with highs in spring and lows in summer-autumn periods. Re-emission of 129 from the surface water of the English Channel, Irish Sea, North Sea, and Norwegian Sea, especially from the European continental coast areas, is evidently the major source of 129I in the precipitation, while stable 127I in the precipitation has multiple sources, i.e., marine, as well as terrestrial emission. This work shows that data on speciation of iodine isotopes can provide thorough indications about the sources and geochemical cycle despite the complicated atmospheric chemistry of iodine.

Modeling fallout of anthropogenic 129I

Despite the relatively well-recognized emission rates of the anthropogenic 129I, there is little knowledge about the temporal fallout patterns and magnitude of fluxes since the start of the atomic era atthe early 1940s. We here present measurements of annual 129I concentrations in sediment archives from Sweden and Finland covering the period 1942-2006. The results revealed impression of 129I emissions from the nuclear reprocessing facility at Sellafield and La Hague and a clear Chernobyl fallout enhancement during 1986. In order to estimate relative contributions from the different sources, a numerical model approach was used taking into accountthe emission rates/estimated fallout, transport pathways, and the sediment system. The model outcomes suggest a relatively dominating marine source of 129I to north Europe compared to direct gaseous releases. A transfer rate of 129I from sea to atmosphere is derived for pertinent sea areas (English Channel, Irish Sea, and North Sea), which is estimated at 0.04 to 0.21 y(-1).

Tracing anthropogenic nuclear activity with (129)I in lake sediment

This study reports the first data of (129)I fallout in Scandinavia, covering the last 80 years. The investigation is based on sediment sections from a lake in central Sweden. In addition to analysis of (129)I, a combination of several radionuclides ((210)Pb, (137)Cs and (14)C) was used to establish an accurate chronology of the sediment profile. The concentration of (129)I exhibits an increasing trend ( approximately 10(7) to approximately 10(9)atoms/g) during the last 40 years, suggesting a significant atmospheric input from the nuclear reprocessing facilities in Sellafield (UK) and La Hague (France). A peak corresponding to fallout from the Chernobyl accident (1986) is clearly distinguishable, whereas the impact of fallout from the nuclear weapons' tests since the early 1950s is not distinguished.

Speciation of 129I and 127I in seawater and implications for sources and transport pathways in the North Sea

Surface seawater samples collected from the North Sea and English Channel were analyzed for total 129I and 127I, as well as for iodide and iodate. Relatively high 129I concentrations (2-3 x 10(11) atoms/L) were observed in the northern part of the English Channel and in the southeastern North Sea. The atomic ratio of 129I/127I decreases from the eastern (1.0-1.9 x 10(-6)) to the western (4-6 x 10(-8)) parts of the North Sea and from the northeastern (1.5 x 10(-6)) to southwestern (1-5 x 10(-8)) parts of the English Channel. The ratios of iodide to iodate are 0.1-0.5 and 0.5-1.6 for 127I and 129I, respectively, in open seawaters, whereas these ratios range from 0.6 to 1.3 and 0.8 to 2.2, respectively, in coastal waters. The results suggest that (1) imprints of the La Hague facility dominates the 129I distribution in the surface water of the North Sea, (2) reduction of iodate to iodide is relatively fast during the transport to the European continental coast, (3) oxidation of newly produced 129I- to (129)IO3- is insignificant during water exchange between the coastal area and open sea, (4) reduction of iodate and oxidation of iodide in the open sea seems to be a slow process.

Trends in the spatial and temporal distribution of 129I and 99Tc in coastal waters surrounding Ireland using Fucus vesiculosus as a bio-indicator

Spatial and temporal trends in (129)I and (99)Tc concentrations around the Irish coastline have been evaluated using Fucus vesiculosus as a bio-indicator. (129)I concentrations in a recent set of seawater samples have also been recorded and reveal an identical spatial pattern. Concentrations of (129)I in Fucus from the northeast coast of Ireland proved to be at least two orders of magnitude higher than concentrations in Fucus from the west coast. The (129)I content of Fucus increased significantly between 1985 and 2003, in line with increases in discharges of (129)I from the Sellafield nuclear reprocessing plant. Similar trends were observed in the case of (99)Tc. (129)I/(99)Tc ratios in Irish seawater were deduced from the Fucus data, and compared to ratios in discharges from Sellafield and from the French reprocessing plant at Cap de la Hague. Levels of (129)I and (99)Tc in Fucus from the west coast were found to be enhanced with respect to levels in seaweeds from other regions in the Northern Hemisphere unaffected by discharges from nuclear installations such as those referred to.

Anthropogenic iodine-129 in the Arctic Ocean and Nordic Seas: numerical modeling and prognoses

A numerical model simulation has been used to predict extent and variability in the anthropogenic (129)I pollution in the Arctic Ocean and Nordic Seas region over a period of 100 years. The source function of (129)I used in the model is represented by a well-known history of discharges from the Sellafield and La Hague nuclear reprocessing facilities. The simulations suggest a fast transport and large inventory of the anthropogenic (129)I in the Arctic and North Atlantic Oceans. In a fictitious case of abrupt stop of the discharges, a rapid decline of inventories is observed in all compartments except the North Atlantic Ocean, the deep Nordic Seas and the deep Arctic Ocean. Within 15 years after the stop of releases, the model prediction indicates that near-equilibrium conditions are reached in all compartments.

Distribution and sources of (129)I in rivers of the Baltic region

The concentration of (129)I was measured in 54 river waters discharging into the Baltic Sea from Sweden, Finland, Estonia, Latvia, Lithuania, Poland and Germany. Sample collection was performed during a well-bracketed time interval (June-July 1999), thus allowing comparison of the rivers over a wide latitude range without the effect of long temporal spread. Although there is no direct input of anthropogenic (129)I in the watersheds, the concentration of the isotope is about two to three orders of magnitude higher than the expected pre-nuclear era natural values in the rivers of Finland and northern Sweden, and in the rivers of southern Sweden, Lithuania, Estonia, Latvia, Poland and Germany; the (129)I concentration may reach five orders of magnitude higher. Furthermore, there are significant correlations between the (129)I concentration and latitude and/or distance from the North Sea and between (129)I and Cl. These findings suggest seawater as a main source of (129)I to the rivers through atmospheric transport. Of the many chemical parameters investigated, the pH may account for some of the variability in (129)I concentrations of the rivers. The contribution from nuclear weapon tests and the Chernobyl accident to the riverine (129)I is insignificant compared to the releases from the nuclear fuel reprocessing facilities. The total flux of (129)I by rivers to the Baltic Sea and related basins represents minor amounts of the isotope pool in these marine waters. External radioactivity hazards from (129)I are considered to be negligible in the Baltic region. However, as the main (129)I intake to the human body is likely through water, due to the large amount of daily water consumption, more concern should be given to internal radioactivity hazard that may be associated with the isotope's localized elevated concentration in the human organs.

Retrospective search for evidence of the 1957 Windscale fire in NE Ireland using 129I and other long-lived nuclides

The accident at Windscale in October 1957 resulted in the release to the atmosphere of a large quantity of radioactivity. The presented work is a retrospective search for evidence of contamination from the accident in the northeastern region of Ireland. A lake yielding a high-resolution sedimentary record was identified near the northeast coast of Ireland. This site was used to reconstruct the history of radionuclide input to the region, based on the analysis of a set of cores extracted from the lake. A chronology for sediment accumulation within the lake was established using radioisotopic dating techniques (including 270Pb). High-resolution gamma and alpha spectrometry techniques were used to quantify concentrations of 137Cs, 239,240Pu and 241Am, all of which were released during the accident. The primary radioactive component of the release was 131I (T1/2 = 8 days), but this short-lived isotope has long since decayed. However, 129I (T1/2 = 1.57 x 10(7) years) was also released during the accident, and in a known ratio to 131I. Recent advances in accelerator mass spectrometry now make it feasible to measure 129I at ultra-trace level and thereby retrospectively reconstruct 131I deposition. Clearly resolved concentration profiles for 137Cs, 239,240Pu and 241Am in the lake cores reflect known historical fallout trends. The data suggest that any contamination from the Windscale fire that might have reached this catchment has been overwritten by input from the testing of nuclear weapons in the atmosphere. A time-series for 129I in lake sediment shows that concentrations in recent sediments are approximately 10 times greater than concentrations recorded in strata corresponding to the period of maximum fallout of other radionuclides from atmospheric testing of nuclear weapons (1964). These recent increases in 129I are attributed to increased emissions from the nuclear industry. The study yields no evidence of any enhancement in radioisotope concentrations, over and above global fallout, in strata dated to 1957, and we conclude that contamination from the Windscale fire had negligible impact on the northeastern region of Ireland.

Anthropogenic iodine-129 in seawater along a transect from the Norwegian coastal current to the North Pole

Variation in the concentrations of iodine-129 (129I, T1/2=15.7 Myr), a low-level radioactive component of nuclear fuel waste, is documented in surface waters and depth profiles collected during 2001 along a transect from the Norwegian Coastal Current to the North Pole. The surface waters near the Norwegian coast are found to have 20 times higher 129I concentration than the surface waters of the Arctic Ocean. The depth profiles of 129I taken in the Arctic Ocean reveal a sharp decline in the concentration to a depth of about 300-500 m followed by a weaker gradient extending down to the bottom. A twofold increase in the 129I concentration is observed in the upper 1000 m since 1996. Based on known estimates of marine transient time from the release sources (the nuclear reprocessing facilities at La Hague, France, and Sellafield, UK), a doubling in the 129I inventory of the top 1000 m of the Arctic Ocean is expected to occur between the years 2001 and 2006. As 129I of polar mixed layer and Atlantic layer of the Arctic Ocean is ventilated by the East Greenland Current into the Nordic Seas and North Atlantic Ocean, further dispersal and increase of the isotope concentration in these regions will be encountered in the near future.

129I in Swedish rivers: distribution and sources

We analyzed the concentration of 129I in the water of 26 rivers covering most of the runoff from Sweden, with the aim of assessing current contamination levels, distribution patterns and potential sources in freshwater systems of northern Europe. The results show relatively high values (up to 1.4 x 10(9) atoms l(-1)), steeply decreasing levels with increasing latitude and a positive correlation with Cl concentration and other chemical parameters. The 129I concentrations observed in south Sweden are probably the highest ever recorded in rivers without any direct discharge from a nuclear installation. The strong latitudinal dependence suggests a northward dilution and possibly depletion of the isotope and a transport from a source located to the south. The most plausible source of the 129I in the studied rivers is atmospheric fallout of 129I emitted either by atmospheric discharges from the nuclear reprocessing facilities at Sellafield (England) and La Hague (France) or by volatilization from seawater contaminated by the same sources. The question is now whether and at what rate the 129I concentration in Nordic watersheds will increase further if discharges from nuclear reprocessing continue.

129I in lakes of the Chernobyl fallout region and its environmental implications

We present seasonal results of 129I in fresh-water lakes located in central Sweden, an area over which the amount of fallout deposition from the Chernobyl accident varied significantly (2-120 kBq/m2 for 137Cs). 129I concentrations in the lakes ranged from 2.1 to 15.0 x 10(8) atoms per liter and did not show elevated concentration in lakes located in regions of high Chernobyl fallout. Apparently, the studied region is strongly influenced by 129I releases from the reprocessing facilities through precipitation. Desorption or resuspension of 129I from soils and sediments does not seem to be an active process to increase the concentration of 129I in the lakes.

129I from the nuclear reprocessing facilities traced in precipitation and runoff in northern Europe

A huge amount of radioactive 129I has been released into the environment from the nuclear energy industry, atomic weapon tests, and nuclear accidents. In this study, we present weekly and seasonal data on 129I measured in precipitation and runoff of northern Europe during 1998 and 1999. The 129I concentration is at 10(8)-10(9) atoms/L in precipitation and (2-5) x 10(8) atoms/L in runoff water, and it is 3-4 orders of magnitude higher than in the prenuclear era. Snow shows lower 129I concentration than rain, and there is apparently a positive correlation between surface air temperature and 129I. Precipitation chemistry, expressed as the content of Cl, SO4, and NO3 and atmospheric ozone, exhibits weak negative correlation with 129I values. Our 129I data on precipitation suggest significant influence of the northern European atmosphere by the discharges from the nuclear reprocessing facilities at Sellafield and La Hague.