Under climatic warming and increased melting, glaciers and ice caps are becoming secondary sources of contaminants deposited decades ago. Cryoconite, an organic-rich material found on the surface of many glaciers, is particularly efficient at accumulating airborne contaminants due to biogeochemical exchanges with the organic matter within cryoconite. Atmospherically derived radioactive isotopes, commonly referred to as fallout radionuclides, have now been found to accumulate in cryoconite globally. However, data from the polar regions, especially ice sheets and ice caps, is scarce. This study helps to address this regional gap in understanding fallout radionuclide accumulation in glacial settings. We present the first radioactivity dataset from cryoconite on a Greenlandic ice cap and assess the role of cryoconite in the distribution of radioactive species in the High Arctic. Forty-six cryoconite samples were collected from the Flade Isblink ice cap (NE Greenland) in August 2022. These samples were analysed via alpha and gamma spectrometry for atmospheric radionuclides, including 137Cs, 241Am, 210Pbexc., 207Bi, 7Be, and several plutonium isotopes. The results of this study confirm cryoconite's exceptional ability to accumulate fallout radionuclides, even in remote and relatively pristine regions such as Northern Greenland. The activities of radionuclides in cryoconite from Flade Isblink are among the highest reported across the High Arctic and the highest ever reported from Greenland. Flade Isblink's radioactivity source is compatible with the stratospheric reservoir established during atmospheric nuclear tests and with weapon-grade fissile fuel, likely originating from Novaya Zemlya. Our findings emphasise the necessity for continued research efforts on the release of legacy contaminants from glaciers, particularly given accelerated global warming and consequent glacier retreat.

Excess fine sediment supply and its associated contaminants can have detrimental effects on water quality and river ecology with sediment deposition on, and subsequent infiltration in, streambeds impacting riverine habitats. Fallout radionuclides (FRNs) are used as tracers in aquatic systems, and the 7Be/210Pbex ratio is a useful indicator for sediment residence/storage time. Suspended and submerged mid-channel bar sediments were collected during five surveys within a 5 km reach of a typical temperate lowland agricultural river system. Solids were analysed by gamma (7Be and 210Pbex) and inductively coupled plasma (ICP, trace metals and phosphorus) spectrometry, and analysed for total nitrogen and organic carbon, to assess sediment dynamics and associated contaminant and nutrient storage. Significant spatial and temporal variation in 7Be/210Pbex activity ratios was observed, indicating changes in sediment sources closely related to contaminant inputs from legacy mining and agriculture. Storage times and the proportion of recently deposited sediment (RDS) varied between sampling sites and seasons in response to local channel characteristics and floods, which also influenced particulate contaminant distributions. This study demonstrates that FRN technology offers improved understanding of fine sediment and contaminant storage and turnover in river channel systems, which is vital to aid sediment management, river restoration and to tackle the global challenge of siltation and associated pollution in riverine habitats.

The aims of this research were to assess the sources of variability of particulate FRNs (7Be, 210Pbex and 137Cs) in river channels, the influence of sediment properties such as particle size distribution (PSD) and organic matter (OM) on FRN distributions, and to discuss the implications for sediment tracing in rivers. Suspended and channel bed sediment samples were collected in the River Avon (Devon, UK) during five strategic surveys involving a wide variation of river flows, including flood conditions. Particulate matter was analysed for 7Be, 210Pbex and 137Cs by gamma spectrometry, PSD by laser diffraction, and organic constituents, total organic carbon (TOC) and total nitrogen (TN) by elemental analysis. FRNs activity concentrations vary significantly both spatially, characterised by changes in activity concentrations within and between locations, and temporally, with changes during the storm hydrograph and between seasons. Variability was attributed to changes in sediment sources and, on some occasions, to significant correlation of activity concentrations with sediment properties. The results also highlighted the influence of changes in channel characteristics and the magnitude and frequency of floods on FRN distributions. In the context of sediment tracing, attention should be given to seasonal changes in riverine conditions that have the potential to affect 7Be and 137Cs conservativeness. Application of FRNs in sediment fingerprinting studies should be accompanied by appropriate temporal characterisation of potential sediment sources. Finally, potential contribution of 7Be-depleted sediment from channel resuspension to the suspended load should also be considered.

The concentrations of Cd, Cu and Zn have been determined in the tissues and the cytosolic fraction of the common cockle, Cerastoderma edule, collected from sediments in the Tamar, Plym and Avon estuaries (South West, England). Metal concentrations in the tissues of C. edule from the Avon were lower than those from the Tamar and Plym, except for Cu in the digestive gland. Significant statistical relationships were only obtained between the total sedimentary metal concentrations and Cd in the body of C. edule and Cu in the digestive gland. The cytosolic fraction was extracted from each of the tissues and separated for protein analysis thereby allowing determination of the metal contents in high molecular weight (HMW) compounds, metallothionein-like proteins (MTLP) and very low molecular weight (VLMW) compounds. The digestive glands of C. edule from the Avon had relatively low concentrations of MTLP, whereas MTLP concentrations in the digestive gland of cockles from the Tamar and Plym were higher. The cytosolic fraction of C. edule had relatively low total Cd and Cu concentrations associated with MTLP, whereas Zn was preferentially associated with the HMW and the VLMW components. The results are relevant to metal distributions in C. edule and the role of cytosols in the management of metals by C. edule and other invertebrates.

Siltation and the loss of hydropower reservoir capacity is a global challenge with a predicted 26 % loss of storage at the global scale by 2050. Like in many other Latin American contexts, soil erosion constitutes one of the most significant water pollution problems in Chile with serious siltation consequences downstream. Identifying the sources and drivers affecting hydropower siltation and water pollution is a critical need to inform adaptation and mitigation strategies especially in the context of changing climate regimes e.g. rainfall patterns. We investigated, at basin scale, the main sources of sediments delivered to one of the largest hydropower reservoirs in South America using a spatio-temporal geochemical fingerprinting approach. Mining activities contributed equivalent to 9 % of total recent sediment deposited in the hydropower lake with notable concentrations of sediment-associated pollutants e.g. Cu and Mo in bed sediment between the mine tributary and the reservoir sediment column. Agricultural sources represented ca. 60 % of sediment input wherein livestock production and agriculture promoted the input of phosphorus to the lake. Evaluation of the lake sediment column against the tributary network showed that the tributary associated with both dominant anthropogenic activities (mining and agriculture) contributed substantially more sediment, but sources varied through time: mining activities have reduced in proportional contribution since dam construction and proportional inputs from agriculture have increased in recent years, mainly promoted by recent conversion of steep lands from native vegetation to agriculture. Siltation of major hydropower basins presents a global challenge exemplified by the Rapel basin. The specific challenges faced here highlight the urgent need for co-design of evidence-led, context-specific solutions that address the interplay of drivers both within and without the basin and its communities, enhancing the social acceptability of sediment management strategies to support the sustainability of clean, hydropower energy production.

Under climatic warming, glaciers are becoming a secondary source of atmospheric contaminants originally released into the environment decades ago. This phenomenon has been well-documented for glaciers near emission sources. However, less is known about polar ice sheets and ice caps. Radionuclides are one of the contaminants that can be remobilised through ice melting and accumulate in cryoconite material on the surface of glaciers. To understand the cycling of radionuclides in polar glacial contexts, we evaluate the radioactivity of cryoconite samples from Flade Isblink, a High Arctic ice cap in northeast Greenland. The measured radioactivity is among the highest reported across the High Arctic and the highest from Greenland. The high variability observed among the samples is explained by considering the different macroscopic features of single cryoconite deposits. The radioactivity source is compatible with the stratospheric reservoir established during atmospheric nuclear tests and with weapons-grade fissile fuel, likely originating from Novaya Zemlya proving grounds. This study shows that the ability of cryoconite to accumulate radioactivity in remote areas is undisputed, highlighting the need for a deeper understanding of the remobilisation of radioactive species in polar glacial contexts.

AbstractThis chapter provides an overview of nuclear tools used in sediment source apportionment studies, summarising essential information about the use of fallout radionuclides, elemental geochemistry, and compound-specific stable isotopes. Exemplar studies are described to show how the method can inform decision making at farm and basin scales to control diffuse water pollution by agriculture.

Cryoconite has been demonstrated to be an efficient accumulator of some classes of contaminants on glaciers in both mountain and polar environments, however the accumulation of contaminants in cryoconite in Iceland has received very little attention to date. To understand the spatial variability of natural and anthropogenic fallout radionuclides and metals on glaciers in Iceland, we present the first study of this region including both cryoconite from three glaciers: Virkisjökull; Skaftafellsjökull; and Falljökull, together with moss balls (‘glacier mice’) from Falljökull. The cryoconite samples and glacier mice were analysed using XRF spectrometry to assess their elemental composition and gamma spectrometry to identify, and quantify, fallout radionuclides, primarily 7Be, 137Cs, 241Am, excess 210Pb, and 40K. The results revealed that the cryoconite samples had similar compositions, influenced by local geology and natural sources of volcanic ash and dust. Higher concentrations of radionuclides and heavy metals were found in both cryoconite and glacier mice compared to control samples comprising nearby proglacial sediments. In comparison to other glaciers in the Northern Hemisphere, however, cryoconite from Icelandic glaciers contains some of the lowest activity concentrations of key radionuclides. Consequently, cryoconite deposits that are released and diluted during the melt and retreat of Icelandic glaciers are unlikely to be of environmental concern following transport to proglacial areas.

Industrialised rivers contain legacy contaminants stored in their sediments and floodplain soils which may inhibit attainment of environmental quality criteria. The River Fal catchment, SW England, is impacted by inputs from uranium mining and clay production and serves as an exemplar for understanding the consequences of medium-term process dynamics in contaminated basins. Radionuclides were determined, by gamma spectros-copy, in six cores from the river floodplain with the aim of quantifying the activities of 238U, and its decay products, and the bomb fallout radionuclides137Cs and 241Am. Activity concentrations of 238U implied inputs from mining, accentuated by flood events and historic industrial accidents, whereas 210Pb activities included a significant input of unsupported 210Pb linked to processed mine spoil. The radionuclide inventories did not decrease systematically downstream revealing evidence of attenuation of particulate radionuclides within the river floodplain sediment column. Storage of legacy contaminants in fluvial systems, at levels in excess of contemporary environmental quality guidelines, emphasises the challenges posed by changing climatic condi-tions. This scenario raises significant consequences for the management of uranium-contaminated, fertile riverine floodplains within Europe.

Atmospheric deposition on glaciers is a major source of legacy fallout radionuclides (FRNs) accumulating in cryoconite, a dark granular material with surface properties that efficiently bind FRN contaminants (specifically 137Cs; 210Pb; 241Am). Cryoconite-bound FRNs in glaciers can be released when they interact with and are transported by glacial meltwater, resulting in the discharge of amassed particulate contaminants into aquatic and terrestrial environments downstream. The environmental consequences of FRN release from the cryosphere are poorly understood, including impacts of cryoconite-sourced FRNs for alpine food chains. Consequently, there is limited understanding of potential health risks to humans and animals associated with the consumption of radiologically-contaminated meltwater. To assess the chemical availability of cryoconite-adsorbed FRNs we used a three-stage sequential chemical extraction method, applied to cryoconite samples from glaciers in Sweden and Iceland, with original FRN activity concentrations up to 3300 Bq kg-1 for 137Cs, 10,950 Bq kg-1 for unsupported 210Pb (210Pbun) and 24.1 Bq kg-1 for 241Am, and orders of magnitude above regional backgrounds. Our results demonstrate that FRNs attached to cryoconite are solubilized to different degrees, resulting in a stage-wise release of 210Pbun involving significant stepwise solubilization, while 137Cs and 241Am tend to be retained more in the particulate phase. This work provides an insight into the vulnerability of pristine glacial environments to the mobilization of FRN-contaminated particles released during glacier melting, and their potential impact on glacial-dependent ecology.

Cryoconite is a specific type of material found on the surface of glaciers and icesheets. Samples of cryoconite were collected from the Orwell Glacier and its moraines, together with suspended sediment from the proglacial stream on Signy Island, part of the South Orkney Islands, Antarctica. The activity concentrations of certain fallout radionuclides were determined in the cryoconite, moraine and suspended sediment, in addition to particle size composition and %C and %N. For cryoconite samples (n = 5), mean activity concentrations (& PLUSMN;1SD) of 137Cs, 210Pbun and 241Am were 13.2 & PLUSMN; 20.9, 66.1 & PLUSMN; 94.0 and 0.32 & PLUSMN; 0.64 Bq kg- 1, respectively. Equivalent values for the moraine samples (n = 7) were 2.56 & PLUSMN; 2.75, 14.78 & PLUSMN; 12.44 and <1.0 Bq kg- 1, respectively. For the composite suspended sediment sample, collected over 3 weeks in the ablation season, the values (& PLUSMN; counting uncertainty) for 137Cs, 210Pbun and 241Am were 2.64 & PLUSMN; 0.88, 49.2 & PLUSMN; 11.9 and <1.0 Bq kg- 1, respectively. Thus, fallout radionuclide activity concentrations were elevated in cryoconite relative to moraine and suspended sediment. In the case of 40K, the highest value was for the suspended sediment (1423 & PLUSMN; 166 Bq kg- 1). The fallout radionuclides in cryoconite were 1-2 orders of magnitude greater than values in soils collected from other locations in Antarctica. This work further demonstrates that cryoconite likely scavenges fallout radionuclides (dissolved and particulate) in glacial meltwater. In the case of 40K, the greater value in suspended sediment implies a subglacial source. These results are amongst the relatively few that demonstrate the presence of fallout radionuclides in cryoconites at remote locations in the Southern Hemisphere. This work adds to the growing contention that elevated activities of fallout radionuclides, and other contaminants, in cryoconites are a global phenomenon and may be a risk to downstream terrestrial and aquatic ecosystems.

&lt;p&gt;Fine sediment plays an important role in the healthy functioning of river ecosystems providing nutrients and contributing to habitat functioning. However, excessive sediment supply into rivers has several detrimental impacts on water quality and it causes sedimentation in river channels, reservoirs and estuaries. In addition, silts and clays are geochemically active and consequently are responsible for the transport of contaminants, including trace metals, phosphorus, pesticides and radionuclides among others which have high sorptive affinity for fine-grained particles. Hence, quantifying the timescales of sediment transfer throughout a river system is critical for understanding river basin sediment dynamics and the fate of their associated pollutants.&lt;/p&gt;&lt;p&gt;Fallout radionuclides (&lt;sup&gt;7&lt;/sup&gt;Be, &lt;sup&gt;210&lt;/sup&gt;Pb&lt;sub&gt;ex&lt;/sub&gt; and &lt;sup&gt;137&lt;/sup&gt;Cs) have been used to assess sediment travel distances, sediment age and sediment residence times in a variety of landscapes. An advantage of using these radionuclides as sediment chronometers is their half-lives which can be used to model sediment residence time from days to decades in different catchment compartments.&lt;/p&gt;&lt;p&gt;The River Avon (Devon, UK) is a 40 km long gravel-bed river, draining rough moorland and with a catchment area of 110 km&lt;sup&gt;2&lt;/sup&gt;. The mean annual flow is 3.7 m&lt;sup&gt;3&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt; and is moderated by managed discharges from a reservoir upstream. Suspended and channel bed sediments were sampled in a 5 km section of the river during four seasonal surveys (January, March, July and November 2022) and suspended sediments during a stormflow event were also sampled.&lt;/p&gt;&lt;p&gt;Radionuclide activity concentrations of channel deposited sediments varied substantially within and between river bars and seasonally. Suspended sediment activity concentrations varied within the stormflow hydrograph and seasonally. Relationships between radionuclide activity concentrations and sediment storage, particle size, total organic carbon and C:N ratios were also evaluated. Channel sediment residence times obtained using &lt;sup&gt;7&lt;/sup&gt;Be/&lt;sup&gt;210&lt;/sup&gt;Pb&lt;sub&gt;ex&lt;/sub&gt; activity ratios ranged between 0 to 110 days, reproducing the high variability found in activity concentrations. Future research will assess the influence of sediment sources on &lt;sup&gt;7&lt;/sup&gt;Be/&lt;sup&gt;210&lt;/sup&gt;Pb&lt;sub&gt;ex&lt;/sub&gt; ratios and the relationship between sediment storage dynamics and sediment-bound contaminants. Sediment residence time modelling will allow an improved understanding of sediment dynamics in gravel-bed rivers which is essential to inform management decisions and prediction of the timescales of transfer and fate of associated contaminants.&lt;/p&gt;

Pristine tropical river systems are coming under increasing pressure from the development of economic resources such as forestry and mining for valuable elements. The Lebir catchment, north eastern Malaysia, is now under development as a result of unregulated tree felling and mining for essential and rare metals. Two sediment cores, one in the upstream reaches and the other from the downstream reaches, were taken from flood prone area of the Lebir River, Malaysia, and analysed for their elemental composition by XRF, specifically Al, Si, Fe, Ca, K, Mg, Mn, V, Cu, Ni, Pb, Cr, Zn, As, Th and U. Activities of fallout radionuclides, 137Cs and 210Pb were also determined to from a geochronological context. The elemental concentrations in the soils were assessed in terms of their enrichment factor and Si, Ca, K, Mg, Mn, V, Cu, Ni and Zn were found not to be enriched, whereas As, Th and U had elevated enrichment factors. The Th and U were particularly enriched in the downstream core indicating inputs from a tributary that drains a catchment with known deposits of Th and possibly U. The results suggest that the growth in economic development is fostering the transport of contaminants by the major rivers which, in turn, is contaminating the riverine floodplains. This points to the need for a more integrated and holistic approach to river basin management to maintain the environmental quality of these fragile aquatic systems.

Riverine sediments play an important role in the healthy functioning of river ecosystems as they provide nutrients and a connectivity signal throughout the catchment sediment cascade. However, excess sediment supply to rivers can have several detrimental impacts on water quality, availability and ecology. The application of catchment management practices requires a comprehensive understanding of both spatial and temporal sediment dynamics to tackle point and diffuse river pollution. While the sources, pathways and fate of eroded sediment in river systems have been widely studied, temporal dynamics have received less attention, mainly due to the complexity of the processes and the lack of methods available to assess these dynamics. This contribution reviews the application of Fallout Radionuclides (FRNs) as sediment residence time tracers. We explore their suitability as sediment chronometers in rivers, the relevance of sediment residence time to sediment budgeting, and discuss the current models that have been employed to determine sediment residence time in river systems. Our review also identifies the challenges, opportunities and the future research needs for a comprehensive application of FRNs to evaluate sediment residence time. In evaluating approaches to sediment residence time, we have summarised several pitfalls requiring consideration and identified avenues for further research. For instance, attention should be given to sorption behaviour when using 7Be and 137Cs as residence time tracers in rivers under changing environmental conditions; particle size effects; activity concentration dilution by mixing of newly tagged 7Be sediment with 7Be-poor sediment from older or different sources; source controls on 7Be delivery to rivers; and the influence of direct fallout into stream channels. Finally, further research is needed to assess the influence of environmental and anthropogenic factors on sediment residence time such as land use, topography, flow regimes, soil type, soil erosion measures and climate change, all of which have important implications from a catchment management perspective.

Soil resources in parts of Tanzania are rapidly being depleted by increased rates of soil erosion and downstream sediment transport, threatening ecosystem health, water and livelihood security in the region. However, incomplete understanding to what effect the dynamics of soil erosion and sediment transport are responding to land-use changes and climatic variability are hindering the actions needed to future-proof Tanzanian land-use practices. Complementary environmental diagnostic tools were applied to reconstruct the rates and sources of sedimentation over time in three Tanzanian river systems that have experienced changing land use and climatic conditions. Detailed historical analysis of sediment deposits revealed drastic changes in sediment yield and source contributions. Quantitative sedimentation reconstruction using radionuclide dating showed a 20-fold increase in sediment yield over the past 120 years. The observed dramatic increase in sediment yield is most likely driven by increasing land-use pressures. Deforestation, cropland expansion and increasing grazing pressures resulted into accelerating rates of sheet erosion. A regime shift after years of progressive soil degradation and convergence of surface flows resulted into a highly incised landscape, where high amounts of eroded soil from throughout the catchment are rapidly transported downstream by strongly connected ephemeral drainage networks. By integrating complementary spatial and temporal evidence bases, this study demonstrated links between land-use change, increased soil erosion and downstream sedimentation. Such evidence can guide stakeholders and policy makers in the design of targeted management interventions to safeguard future soil health and water quality.

The release of legacy contaminants such as fallout radionuclides (FRNs) in response to glacier retreat is a process that has received relatively little attention to date, yet may have consequences as a source of secondary contamination as glaciers melt and down-waste in response to a warming climate. The presence of FRNs in glacier-fed catchments is poorly understood in comparison to other contaminants, yet there is now emerging evidence from multiple regions of the global cryosphere for substantially augmented FRN activities in cryoconite. Here we report concentrated FRNs in both cryoconite and proglacial sediments from the Isfallsglaciären catchment in Arctic Sweden. Activities of some FRNs in cryoconite are 2 orders of magnitude above those found elsewhere in the catchment, and above the activities found in other environmental matrices outside of nuclear exclusion zones. We also describe the presence of the short-lived cosmogenic radionuclide 7Be in cryoconite samples, highlighting the importance of meltwater–sediment interactions in radionuclide accumulation in the ice surface environment. It is currently unknown whether high accumulations of fallout radionuclides in glaciers have the potential to impact local environmental quality through down-wasting and downstream transport of contaminants to the proglacial environment through interaction with sediments and meltwater. We thus recommend that future research in this field focusses on processes of accumulation of FRNs and other environmental contaminants in cryoconite and whether these contaminants are present in quantities harmful for downstream ecosystems.

Evaluation of the spatial and temporal composition of floodplain sediments and soils is critical in the creation of soil management strategies for impacted riverine catchments. The objective of this study was to determine the distribution, and to identify the sources, of particulate trace elements and fallout radionuclides in the catchment of the River Avon (SW England), where sedimentary processes had been altered by reservoir construction in the 1950s. The catchment was compartmentalized into its main functional units namely, cultivated land, pasture, woodland, wet moorland, and channel bank. Surface soils were collected in each unit, along with four strategically-placed cores, all of which were analyzed for particle size, fallout radionuclides and elemental concentrations. Sediment particle sizes and sediment accumulation rates were affected by the construction of the reservoir, specifically the distributions of silt and clay. The concentrations of fertilizer constituent Cr and P were highly correlated in the mid-catchment but were unrelated downstream due to elevated concentrations of Cr from geological deposits. Copper, As, Pb and Sn had variable down-core distributions, with pulses in concentrations due to mining inputs. The contributions of the end-member sources of particulate elements in the sedimentary mixtures were evaluated, quantitatively, using a Bayesian Mixing Model and the cultivated land was identified as a significant contributor to the mixtures, independent of space and time. The results contribute to advances in soil quality and conservation measures as components of a catchment management plan for the Avon, an approach maybe applicable to other small catchments in the UK and internationally.

Saltmarshes, wetlands, inter-tidal mudflats are highly productive natural ecosystems with significant ecological value. 210Pb and 137Cs have been used for establishing chronologies at a centennial scale in these sediments. They are relevant for assessing how saltmarshes are vulnerable to climate change, natural hazards and contamination from human inputs. This paper aims to review and adapt existing methods for the 210Pb-based radiometric dating of these sediments where the subterranean production and decay of OM are sources of achronicity. This limits the use of the basic assumption of considering the sediment as a continuous medium. From the available evidence, 210Pb fluxes onto sediments may be mediated by the activities bound to the mass flows, suggesting that models assuming a constant flux should be handled with care. The activity concentrations of excess 210Pb required by CF-CS, CIC and TERESA radiometric models must be those of the sediment mineral fraction, while CRS and PLUM can work with the composite sediment matrix. A review of these issues and application of the models is illustrated with new data from two recent saltmarsh sediment cores. The effects of non-ideal boundary conditions in radiometric dating and the system time-average of 137Cs fluxes are discussed. Although specific to vegetated saltmarshes, this topic and the present results have generic applications for other vegetated coastal sediments.

Temporal and spatial sediment dynamics in an East-African Rift Lake (Lake Manyara, Tanzania), and its river inputs, have been evaluated via a combination of sediment tracing and radioactive dating. Changes in sedimentation rate were assessed using radioactive dating of sediment cores in combination with geochemical profile analysis of allogenic and autogenic elements. Geochemical fingerprinting of riverine and lake sediment was integrated within a Bayesian mixing model framework, including spatial factors, to establish which tributary sources were the main contributors to recent lake sedimentation. The novel application of Bayesian source attribution on sediment cores and subsequent integration with sedimentation data permitted the coupling of changes in the rate of lake sedimentation with variations in sediment delivery from the tributaries. These complimentary evidence bases demonstrated that Lake Manyara has experienced an overall upward trajectory in sedimentation rates over the last 120 years with distinct maxima in the 1960s and in 2010. Sedimentation rates are largely a result of a complex interaction between increased upstream sediment delivery following changes in land cover and natural rainfall fluctuations. Modelling results identified two specific tributaries as responsible for elevated sedimentation rates, contributing 58% and 38% of the recently deposited lake sediment. However, the effects of sedimentation were shown to be spatially distinct given the domination of different tributaries in various areas of Lake Manyara. The application of source-tracing techniques constrained sedimentation problems in Lake Manyara to specific tributary sources and established a link between upstream land degradation and downstream ecosystem health. This novel application provides a solid foundation for targeted land and water management strategies to safeguard water security and environmental health in Lake Manyara and has potential application to fill knowledge gaps on sediment dynamics in other East-African Rift Lakes.

A recreational impoundment was constructed in the mid-nineteenth century on the mudflats reclaimed from the Plym Estuary (SW England) following salt marsh removal and infilling with waste soils from local catchments. Restoration of the salt marsh was attempted about 25 years ago when a regulated tidal exchange system was installed in the embankment separating the impoundment from the estuary. Currently, the embankment is disintegrating with the potential loss of the impounded soils, of unknown composition, to the estuary. Cores were obtained from the impoundment and the adjoining estuary, sectioned, dried and analysed. The geochronology of the soils, and estuarine sediments, was established using gamma-ray spectroscopy to determine the activities of fallout radionuclides, 137Cs and 210Pb. The concentrations of As, Co, Cr Cu, Fe, Mn, Ni, Pb, Rb, Sn, W and Zn in the core sections were determined by quantitative X-ray fluorescence spectrometry. Below a shallow surface layer (> 5 cm and post-1963), metal concentrations were high with several exceeding soil quality indices, and enrichment factors (EFs) were elevated, in the sequence Sn > W≈As > Cu > Pb. Estimates of the total masses of particulate Sn, Pb, As and Cu available for down-estuary migration were significant. Given the ecotoxicological implications resulting from a loss of metal-contaminated soils into the estuary, a strategy for the future management of the impoundment is required. The conditions at this site are compared with ageing estuarine impoundments at other locations, where polluted sediments, or soils, could be vulnerable to release.