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The measurement of isotopic abundances and ratio variations of plutonium can provide important information about the sources and behaviours of radiogenic isotopes in the environment. The detection of ultra-trace isotopes of plutonium is increasing interest in the scientific literature for the determination of soil erosion rates due to their long retention times in the environment. The characteristics of plutonium within the environment make it an ideal tracer for the determination of soil redistribution rates and its robustness presents the opportunity to replace more commonly used radioisotopes such as 137Cesium and 210Lead. However, ultra-trace analysis of plutonium (fg g−1) presents analytical challenges which must be overcome in a variety of soil types. Inductively Coupled Plasma Mass Spectrometry has proven valuable for detection of plutonium in a range of environmental samples. However, severe polyatomic interferences from uranium isotopes significantly limits its application. Due to the improvements in detection sensitivity and reaction cell technology, inductively coupled plasma tandem mass spectrometry, which is also commonly referred to as triple quadrupole inductively coupled plasma tandem mass spectrometry (ICP-MS/MS), has emerged as an exceptional tool for ultra-trace elemental analysis of plutonium isotopes in environmental samples overcoming the limitations of standard quadrupole ICP-MS such as limited sensitivity and cost of analysis. In this review, common methods reported in the literature for the separation and subsequent detection of plutonium isotopes are compared to recent advances in analysis using ICP-MS/MS technology. Graphical Abstract

Water bodies in Tanzania are experiencing increased siltation, which is threatening water quality, ecosystem health, and livelihood security in the region. This phenomenon is caused by increasing rates of upstream soil erosion and downstream sediment transport. However, a lack of knowledge on the contributions from different catchment zones, land-use types, and dominant erosion processes, to the transported sediment is undermining the mitigation of soil degradation at the source of the problem. In this context, complementary sediment source tracing techniques were applied in three Tanzanian river systems to further the understanding of the complex dynamics of soil erosion and sediment transport in the region. Analysis of the geochemical and biochemical fingerprints revealed a highly complex and variable soil system that could be grouped in distinct classes. These soil classes were unmixed against riverine sediment fingerprints using the Bayesian MixSIAR model, yielding proportionate source contributions for each catchment. This sediment source tracing indicated that hillslope erosion on the open rangelands and maize croplands in the mid-zone contributed over 75% of the transported sediment load in all three river systems during the sampling time-period. By integrating geochemical and biochemical fingerprints in sediment source tracing techniques, this study demonstrated links between land use, soil erosion and downstream sediment transport in Tanzania. This evidence can guide land managers in designing targeted interventions that safeguard both soil health and water quality.

Wildfires can have major impacts on water scarcity and water quality linked to off-site transfer of polluting ash and nutrients. Understanding sediment sources in burnt landscapes can help to develop mitigation strategies, especially in catchments planted with introduced species that are prone to fire. We investigated sediment sources activated by post-fire rainfall in a small-forested catchment that was impacted by a severe wildfire. The aim was to use environmental radionuclides and elemental geochemistry as tracers to apportion sediment sources within burnt plantation systems. Surficial (0–2 cm) topsoil (n = 9), sub-surficial (2–4 cm) topsoil (i.e. below the burnt layer; n = 8) samples from burnt hillslopes and forest roads (n = 5) and stream banks (n = 5) soil samples were taken in the Quivolgo catchment, El Maule region, Chile. Sediment samples (n = 9) were collected from behind a v-notched weir on three dates after the fire: May 2017, July 2017 and October 2017. Soil and sediment samples were analysed by gamma spectrometry and wavelength-dispersive X-ray fluorescence (WD-XRF) used to obtain tracer properties. These were evaluated visually and statistically to identify potential non-conservative tracers. Sediment apportionment was undertaken using the MixSIAR mixing model. The tracer selection procedure resulted in ten tracers being used for sediment apportionment. Tracer suitability was based on (i) weak and non-significant linear relationship between tracer concentrations and specific surface area (SSA) and soil organic matter (SOM), and (ii) conservative behaviour supported by the inclusion of sediment samples within source convex hull. Sediments from sub-surface layer (2–4 cm) were the dominant source during the first two periods contributing 55 ± 11 and 78 ± 10% respectively, whereas road contribution was only important in the last period (71 ± 14%). Apportionment showed a shift in sediment source (i.e. from forest roads to hillslopes) compared to a previous study in the same catchment before wildfire. The main driver of erosion was attributed to overland flow convergence and consequent rill erosion across burnt hillslopes. The study demonstrated combined use of environmental radionuclides with elemental geochemistry for sediment apportionment within burnt forest plantations and highlighted a switch in predominant source (e.g. sub-surface burnt soil) activated by post-fire rainfall events. The findings in this research will help forest companies to develop strategies to reduce off-site impacts of sediment release after wildfire in forest plantations.

Soil erosion accelerated by poor agricultural practices, land degradation, deprived infrastructure development and other anthropogenic activities has important implications for nutrient cycling, land and lake productivity, loss of livelihoods and ecosystem services, as well as socioeconomic disruption. Enhanced knowledge of dynamic factors influencing soil erosion is critical for policymakers engaged in land use decision-making. This study presents the first spatio-temporal assessment of soil erosion risk modelling in the Winam Gulf, Kenya using the Revised Universal Soil Loss Equation (RUSLE) within a geospatial framework at a monthly resolution between January 2017 and June 2020. Dynamic rainfall erosivity and land cover management factors were derived from existing datasets to determine their effect on average monthly soil loss by water erosion. By assessing soil erosion rates with enhanced temporal resolution, it is possible to provide greater knowledge regarding months that are particularly susceptible to soil erosion and can better inform future strategies for targeted mitigation measures. Whilst the pseudo monthly average soil loss was calculated (0.80 t ha−1 month−1), the application of this value would lead to misrepresentation of monthly soil loss throughout the year. Our results indicate that the highest erosion rates occur between February and April (average 0.95 t ha−1 month−1). In contrast, between May and August, there is a significantly reduced risk (average 0.72 t ha−1 month−1) due to the low rainfall erosivity and increased vegetation cover as a result of the long rainy season. The mean annual gross soil loss by water erosion in the Winam Gulf catchment amounts to 10.71 Mt year−1, with a mean soil loss rate of 9.63 t ha−1 year−1. These findings highlight the need to consider dynamic factors within the RUSLE model and can prove vital for identifying areas of high erosion risk for future targeted investigation and conservation action.

The need for further research to investigate the possibility of using 7Be as a soil erosion tracer under a range of climatic conditions, specifically in arid and semi-arid agro-environments, has been emphasised in the literature. In this context, this paper reports research conducted in two semi-arid areas located in Western Iran and Southern Italy in order to assess the potential of using 7Be measurements for estimating soil erosion over short timescales. The two study sites differ in terms of land use. More specifically, the area in Western Iran, under cultivation, is cropped mostly under wheat, barley and pea rotation. The area in Southern Italy has never been cultivated, has few eucalyptus trees, resulting from re-afforestation conducted in 1966 and retains a sparse grass cover. Soil sampling required two field campaigns undertaken in April 2011 and April 2016 in Western Iran and Southern Italy, respectively. In Western Iran, the 7Be reference inventory was estimated at 326 ± 40 Bq m−2 and the corresponding value of the shape factor was equal to 3.57 kg m−2. The soil loss was calculated to be 6.8 Mg ha−1, resulting in a Sediment Delivery Ratio (SDR) of ca. 80%. In Southern Italy, the 7Be reference inventory was equal to 180 ± 20 Bq m−2, emphasising a lower penetration of 7Be into the soil that is documented by a lower value of the shape factor (2.45 kg m−2). The overall results provided a net soil loss of ca. 20.7 Mg ha−1. In this case, no deposition was documented and a SDR value of ca. 100% was calculated. The magnitude of soil erosion reflects, for both sites, the steep topography, the different management system and the heavy rainfall occurring during a period that coincides with the absence of vegetative cover. The results obtained in this study are in line with similar studies carried out in other countries and suggest that, in cultivated areas, care must be taken when traditional cultivation systems are applied; in re-afforested areas, the presence of a uniform vegetative cover is crucial in protecting soil from erosion. However, there still is a need for further work to assess the feasibility of using 7Be in different areas and under different land uses or vegetation covers. Also, further refining of the conversion model, which is based here on the simple exponential function, are still possible.

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.

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.

Quantitative assessment of soil erosion and deposition rates using fallout radionuclides (FRNs), including Beryllium-7 (

Soil erosion represents a critical socio-economic and environmental hazard for Mexico and the world. Given that soil erosion is a phenomenon influenced by human activities, it is essential to know the level of cultural perspectives on this matter. An instrument with eight scales was applied to 275 university students from a northwestern Mexican city, which measured the knowledge about soil erosion, self-efficacy in solving the problem, future perspectives, perceived consequences, obstacles to addressing soil erosion, and mitigation intentions and behaviors. To analyze the relationship between the scales and the intentions and behaviors of soil erosion mitigation, a model of structural equations was tested. In summary, the participants know the problem of soil erosion, its impacts, and recognize risks to human and environmental health. They also know their important role within soil conservation, however, they identified significant obstacles to action. This study determined that each indicator has a correlation with soil erosion mitigation intentions except for the obstacles. The indicators that had the greatest positive relationship in mitigation intentions were knowledge, self-efficacy, and the perspective of the future. The implications of these results open the landscape to the creation of efficient strategies to mitigate soil erosion in this region and Mexico.

This study aimed to reconstruct the sedimentation rates over time and identify the changing sources of sediment in a major hydropower reservoir in Tanzania, the Nyumba ya Mungu (NYM). Fallout 210Pb measurements were used to estimate age of sediment deposits and broad changes in sedimentation rates were reconstructed. Sedimentation peaks were cross referenced to geochemical profiles of allogenic and autogenic elemental constituents of the sediment column to confirm a causal link. Finally, geochemical fingerprinting of the sediment cores and potential sources were compared using a Bayesian mixing model (MixSIAR) to attribute the dominant riverine and land use sources to the reservoir together with changes through recent decades. Reservoir sedimentation generally increased from 0.1 g cm−2 yr−1 in the lower sediment column to 1.7 g cm−2 yr−1 in the most recent deposits. These results correlated to changes in allogenic and autogenic tracers. The model output pointed to one of two major tributaries, the Kikuletwa River with 60.3%, as the dominant source of sediment to the entire reservoir, while the other tributary, Ruvu River, contributed approximately 39.7%. However, downcore unmixing results indicated that the latest increases in sedimentation seem to be mainly driven by an increased contribution from the Ruvu River. Cultivated land (CU) was shown to be the main land use source of riverine sediment, accounting for 38.4% and 44.6% in Kikuletwa and Ruvu rivers respectively. This study explicitly demonstrated that the integration of sediment tracing and dating tools can be used for quantifying the dominant source of sediment infilling in East African hydropower reservoirs. The results underscore the necessity for catchment-wide management plans that target the reduction of both hillslope erosion reduction and the sediment connectivity from hillslope source areas to rivers and reservoirs, which will help to maintain and enhance food, water and energy security in Eastern Africa.

The build-up of heavy metals (HM) in agricultural soils accelerates the HM uptake by plants, which could potentially affect food quality and food safety. Here we studied the status and bioaccumulation of HM from soils to plant parts (roots, stem, and grains) in Usangu agro-ecosystem-Tanzania. In total 68 soil samples and 42 rice plant samples from six irrigation schemes were studied. The concentrations of cadmium-Cd, chromium-Cr, copper-Cu, lead-Pb, zinc-Zn, nickel-Ni, and iron-Fe were determined to estimate accumulation, distribution, bioconcentration. Total soil HM concentration in soil and plant samples was determined by acid digestion. The concentration of HM in soils samples (in mg/kg) were Cr (4.58–42.76), Co (1.486–6.12), Fe (3513.56–12593.99), Zn (7.89–29.17), Cd (0.008–0.073), Cu (0.84–9.25), Ni (0.92–7.98), and Pb (1.82–18.86). The total HM concentration in plant samples were (in mg/kg) were Cu (5.18–33.56), Zn (57.03–120.88), Fe (963.51–27918.95), Mn (613.15–2280.98), Cd (4.3–17.46), Pb (0.01–28.25), Cr (12.88–57.34) and Ni (9.65–103.33). The concentration of HM in soil and plant parts was observed to vary among locations where high concentrations of HM were detected in stems and roots compared to grains. The ratio HM in plants and soil samples (bioconcentration) was higher than one for some sites indicating higher HM uptakes by plants leading to possible health risk to soil invertebrates, animals, and humans. The bioconcentration factor varied among schemes, with the highest values at Igalako and Mahongole, which could be caused by artisanal gold mining and mining quarry existed in the area. Therefore, steps are needed to reverse the situation to balance the HM in agricultural soils and plant tissues to be within acceptable limits., Heavy metal; Paddy farming; Bioconcentration factor; Health risk; Agro-ecosystem.

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident released the most significant quantity of radiocesium into the environment since Chernobyl, and detailed measurements over the initial 5 years provide new insights into fluvial redistribution of radiocesium. We found that the high initial activity concentration of 137Cs-bearing suspended sediment in rivers was followed by a steep exponential decline (λ1) which extended to approximately 1 year after the accident, while the rate of initial decline in radiocesium activity concentration in water was an order of magnitude higher than rates measured after Chernobyl. Fluvial transport of 137Cs to the ocean from the Abukuma river totaled 12 TBq between June 2011 and August 2015 and almost all this radiocesium (96.5%) was transported in the particulate form. The primary sources of 137Cs were paddy fields, farmland, and urban areas [plaque-forming unit (PFU)], discharging 85% of the exported 137Cs from 38% of the watershed area. After 1 year, activity concentrations were lower and exhibited a more gradual secondary decline (λ2) which was associated with reduced radiocesium losses from PFU areas, while forest areas continue to represent more stable contaminant stores.

International audience; Note: Several figures follow the manuscript text towards the end of the word file

Sediment fingerprinting approaches help improve our understanding of the on- and off-site impacts of soil erosion in the critical zone, including upstream and downstream ecosystem services and the wider implications for food, water and energy security. This study evaluates the impact of intensive agricultural land management practices on overland flow generation with attention to process controls on sediment production and delivery from both hillslope and in channel sources. This study applied a sediment fingerprinting approach in the Merriott Stream catchment in rural Somerset, UK. Major and minor element geochemistry were determined for sources under cultivated (n = 12) and grazing (n = 12) land management regimes plus channel bank erosion (n = 10) for a notably incised downstream drainage network. These were compared to both suspended sediment (n = 3) and channel bed sediment (n = 4) sampled along the stream network. Sediment sources were apportioned with the MixSIAR mixing model. The dominant contributor to suspended sediment captured in transit was cultivated land (ca. 60–90%). The dominant contributor to channel bed sediment in the lower catchment was channel bank erosion (ca. 50–75%). The former was linked to enhanced overland flow and increased erodibility of cultivated soils. The latter was linked to contemporary incision of the stream network driven by a more erosive hydrological regime (i.e. increased magnitude and frequency of runoff events) which was causing localized erosion and bank failure. These in-channel processes of incision and bank failure were exacerbated by a lack of vegetation on the banks due to winter die-back of the invasive weed Himalayan Balsam. This exposes the bank surface to direct fluvial scour under winter high flows and prevents the establishment of a perennial root structure from native plants that typically plays an important role in bank stability. This study has demonstrated the need to consider a holistic catchment-based approach to understanding and managing bank erosion and, in particular, it highlights the need for integrated upstream and downstream thinking where distal runoff processes lead to increased potential for downstream channel instability.

Accurate Holocene relative sea-level curves are vital for modelling future sea-level changes, particularly in regions where relative sea-level changes are dominated by isostatically induced vertical land movements. In North Wales, various glacial isostatic adjustment (GIA) models predict a mid-Holocene relative sea-level highstand between 4 and 6 ka, which is unsubstantiated by any geological sea-level data but affects the ability of geophysical models to model accurately past and future sea levels. Here, we use a newly developed foraminifera-based sea-level transfer function to produce a 3300-year-long late-Holocene relative sea-level reconstruction from a salt marsh in the Malltraeth estuary on the south Anglesey coast in North Wales. This is the longest continuous late-Holocene relative sea-level reconstruction in Northwest Europe. We combine this record with two new late-Holocene sea-level index points (SLIPs) obtained from a freshwater marsh at Rhoscolyn, Anglesey, and with previously published regional SLIPs, to produce a relative sea-level record for North Wales that spans from ca. 13,000 BP to the present. This record leaves no room for a mid-Holocene relative sea-level highstand in the region. We conclude that GIA models that include a mid-Holocene sea-level highstand for North Wales need revision before they are used in the modelling of past and future relative sea-level changes around the British Isles.

New paleoclimatic data from the Casa Branca salt marsh, in the southwest coast of Portugal, are compared with records previously published on the northwest coast (Caminha salt marsh) to offer a more comprehensive overview of the environmental evolution of the west Iberian margin over the last six centuries. These reconstructions are based on the foraminiferal records of two dated sediment cores retrieved from the high marsh settings and supported by geochemical-sedimentological data. Both marshes were originally formed in the AD 1300s, between the Medieval Climatic Anomaly (MCA) and the Little Ice Age (LIA), highlighting a major episode of increased sediment supply in lower estuaries linked to climate-driven changes in continental runoff. Afterwards, the two marshes evolved under different climatic regimes as reflected by their foraminiferal assemblages. The environmental conditions are characterized by higher salinity in Casa Branca (southwest), with Jadammina macrescens and Trochammina inflata as dominant species, than in Caminha (northwest), where Haplophragmoides spp. dominates. We suggest that a long-term trend of a net gain in evapotranspiration at Casa Branca inducing a higher marsh salinity baseline may explain this microfaunal contrast. Trochammina inflata seems to be a good indicator of drier periods in the studied area, connected to key events of aeolian large-dust input to the southwest coast of Portugal. The influence of the most important climate drivers was assessed, namely external (solar) and internal (North Atlantic Oscillation – NAO) forcings. Spectral and wavelet transform coherence analyses were used to detect solar footprints on foraminiferal and climate-related time series. A main significant quasi-periodicity was identified within the range of the secular Gleissberg cycle of solar activity modulating the annual NAO and regional spring-summer (simulated) temperatures after AD 1700. This stronger solar-climate coupling may be related to the known upward secular trend in the total solar irradiance after the Maunder Minimum.

40 Pags.- 6 Figs.- 6 Tabls. The definitive version is available at: https://www.sciencedirect.com/science/journal/00167061, Sediment source fingerprinting is increasingly used to provide insight into the dynamics of catchment sediment transfer processes, yet relatively few studies seek to validate source apportionments obtained from unmixing models. Our work focuses on simulating natural processes to test the accuracy of source apportionments obtained using a multivariate unmixing model called FingerPro. A relevant laboratory experiment is proposed to test the sensitivity of the model, using as experimental sediments 14 artificial mixtures composed of different proportions and numbers of sources selected from five soils as experimental sources. Twelve artificial mixtures were created by mixing a known proportion of source soils sieved to, Financial support from project (CGL2014-52986-R) is gratefully acknowledged.

Soil fertility determines crop growth, productivity and consequently determines land productivity and sustainability. Continuous crop production exploits plant nutrients from soils leading to plant nutrient imbalance, thus affecting soil productivity. This study was conducted to monitor soil fertility status in soils of Usangu agro-ecosystem to establish management strategies. To assess soil fertility status in Usangu agro-ecosystem in Southern Highland Tanzania; 0–30 cm depth soil samples were taken for organic carbon, soil pH, N, P, Ca, K, Mg, S, Al, and micronutrients such as Zn, Mn, Cu, Fe, and Cr analyses by various established standard analytical methods. The results indicated most micronutrients were available in the deficient amount in many studied sites except for Fe and Mn, which were observed to be above optimum requirement. Based on critical levels established in other areas, 90 % of the soils were ranked as N, P, K, and Mg deficient. The micronutrients (Cu, Fe, and Zn) were inadequate in all soils resulting in limited crop growth and productivity. A high concentration of trace metals was detected in agricultural soils, this might affect plant nutrients availability and leading to environmental contamination affecting land productivity and sustainability. The study found that Usangu agro-ecosystem has deprived of soil fertility leading to poor crop growth and productivity. The authors recommend the addition of supplemental materials rich in plant nutrients such as inorganic fertilizer, manure, crop residues, and treated wastes to improve soil fertility for improved productivity and land sustainability., Plant nutrients; Paddy wetlands; Trace metals; Soil fertility; Land sustainability.

Hydropower reservoirs are essential for the climate-neutral development of East Africa. Hydropower production, however, is threatened by human activities that lead to a decrease in water storage capacity of reservoirs. Land use/land cover and climatic changes are driving accelerated soil erosion in semi-arid East Africa, which ultimately increases reservoir sedimentation and decreases energy production. Sediment delivery dynamics at the catchment scale are complex, involving the interaction of multiple factors and processes on different spatial and temporal scales. A lack of understanding of these processes and their interactions may impede the efficiency of sediment mitigation and control strategies. A deep understanding of the processes of erosion and connectivity of the land to river channel, as well as storage of eroded material within hillslopes and floodplains, and sediment accumulation in the reservoirs supports selection of future dam locations and sustainable management of reservoirs. The sediment budget approach can provide such a holistic perspective by accounting for the various sediment sources, transport, sinks, and redistribution when the sediment is routed through that catchment. Constructing sediment budgets is challenging, but the potential for integrating a number of different techniques offers new opportunities to collect the required information. In East Africa, the spatial planning of dams is mainly dominated by political and financial motives, and impacts of land use and climate on the sediment transport dynamics are not adequately considered. Production of sediment budgets under different scenarios of land use and climate change should be an essential step when deciding the location and management strategies for dams. Selection of new hydroelectric reservoir sites must consider long-term scientific data on climate change, and the sediment budget components for sustainable land management planning, hydropower sustainability.

The release of legacy fallout radionuclides (FRNs) in response to glacier retreat is a process that has received relatively little attention to date, yet may have important consequences as a source of secondary contamination as glaciers melt and down-waste in response to a warming climate. The prevalence 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 two 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. The presence of fallout radionuclides in glaciers may have the potential to impact local environmental quality through both isolated hotspots of radioactivity caused by glacier 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 both local and downstream ecosystems.

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

The combination of a changing climate and growing population poses a contemporary challenge for the water-food-energy security nexus in mountain regions, especially in glacier-fed catchments such as the Rio Santa in the Peruvian Andes. Soil erosion due to both natural processes and anthropogenic activities can exacerbate this challenge, with increased levels of sediment in river systems endangering crucial river functions, such as crop irrigation, drinking water, and hydroelectricity. Furthermore, sediment can act as a transport pathway for contaminants, in addition to being a source of contamination itself. Previous studies have suggested that soil erosion related to human activity vastly exceeds the rate of natural soil production in many Andean catchments, where research to date has primarily focused on larger eastern catchments. Smaller western catchments, however, are important for many major Andean cities reliant upon upstream water supplies. It is thus, important to identify sediment sources and better understand sediment dynamics to manage the threats to water supply.Sediment fingerprinting approaches are one technique that can contribute to improved understanding of sediment sources and dynamics and the impact of soil erosion in a catchment, and thus contribute to water resource management at the catchment level. Taking a distributed approach along the Rio Santa, this study aims to improve understanding of natural and anthropogenic contributions to sediment production in this Andean system. Key sediment sources explored are glacial sediment potentially enhanced by retreat, agricultural land, forestry operations, land under natural vegetation, and mining. The distributed approach permits quantification of their dynamics throughout the catchment. All source and mixture samples were analysed using Wavelength Dispersive X-ray Fluorescence (WD XRF) to develop geochemical fingerprints and the MixSIAR mixing model was used to apportion sediment sources. While sediment sampling presents a number of challenges when working in remote, mountainous regions such as the Rio Santa catchment, sediment fingerprinting has the potential to help reduce environmental degradation when used to guide local resource management decisions.

This paper explores the potential for using multiple particle size fractions in a hierarchical geochemical sediment fingerprinting approach to the assessment of changes in sediment sources through time within a small Mediterranean peri-urban catchment. Conventional sediment fingerprinting has focussed on the This study explores this approach using 2), on the outskirts of Coimbra in central Portugal. The climate is humid Mediterranean. Catchment geology is 56% sandstone (in the east), 41 % marly limestone (in the west) and 3 % alluvium. Current land-use is 56% woodland, 4 % agricultural and 40% urban (mainly residential, but also including a recently constructed enterprise park (5%) and major highway (1%)). Recent urbanization has largely occupied former agricultural land. The study adopts a multi-proxy sediment fingerprinting approach to assessment of changes in sediment sources, based on geochemical (elemental) characterization of the four different size fractions of fluvial bed-sediment and soil samples, using a Niton x-ray fluorescence (XRF) elemental analyser. Sampling of fluvial sediment was carried out at 33 sites within the stream network (including all significant tributaries, downstream sites and the catchment outlet). Samples were collected in July 2018 and November 2018 following contrasting ‘late-wet-season’ and ‘end-of-dry-season’ events. In July 2018, samples of potential sediment sources were collected including: (i) soil surface (0-2cm) samples at 64 locations, (ii) 17 samples from eroding channel margin sites, and (iii) 15 samples of road sediment. All fluvial and soil samples were sieved to obtain the four target size fractions. The elemental geochemistry of each sample fraction at all fluvial and source sites was derived using the XRF analyser. (These results were added to similar datasets previously obtained on three occasions in 2012-15 in a period of enhanced urban constructional disturbance). Differences (and similarities) in geochemical signatures between the different size fractions at each survey date at and between each tributary and potential source site were assessed using a range of statistical techniques. Messages arising are discussed. For each size fraction and survey date, Bayesian unmixing models were used in a hierarchical (confluence-based) fashion to assess the contributions of sub-catchments to downstream sites and the catchment outlet. Modelling results for the two 2018 events were validated by comparing them with suspended sediment records collected at five tributary locations and at the catchment outlet. Although overall, the modelling was successful in indicating and quantifying significant changes in sediment sources through time within the catchment, uncertainties in interpretation of the multiple fractions are identified and discussed.

East African farming communities face complex challenges regarding food and feed productivity. Primary production systems are under stress, nutritional choices are changing and the relationship between development and agriculture is undergoing profound transformation. In the face of severe threat of soil erosion, East African agro-pastoral systems are now at a tipping point and there has never been a greater urgency for evidence-led sustainable land management interventions to reverse degradation of natural resources that support food and water security. A key barrier, however, is a lack of high spatial resolution soil health data wherein collecting such information is beyond conventional research means. This research tests whether bridging this data gap can be achieved through a coordinated citizen science programme. Accessible and portable technology is currently available in the form of hand-held soil scanners that can enable farmers to become citizen scientists empowered to collect data to establish research data bases that support critical landscape decisions. The aim of the work was to test the potential for using soil scanners as a tool for mapping whole community soil health characteristics, using soil organic matter as an indicator, down to farm-scale; a resolution that is beyond that achievable in conventional research, with the ultimate objective to deliver information that empowers stakeholders to create a sustainable community landscape plan.Key outcomes included:(1) A training document for the usage of the soil scanner that includes a list of potential problems and their solutions. Moreover, a training session was organised in the Tanzanian partner institution to build capacity for the continuation of the project, wherein local researchers were trained in the application of the ‘Agrocares’ soil scanner to support continuing community engagement.(2) Local farmers being provided an opportunity to circumvent traditional power and knowledge inequities. During the introductory meeting and field measurements, we noticed the development of locally-embedded scientific interests and skills that foster stronger community ownership and engagement in action research.(3) A high resolution soil organic matter and nutrient status dataset in small-catchment and community setting. The citizen science data contributes to soil process and hydrological understanding of East African landscapes, which besides direct contribution to the scientific understanding, also supports co-design of effective management solutions to the soil erosion and land degradation challenges.The inclusion of ‘big data’ digital data training and sharing platforms and has the potential to create more robust and better informed collective decision-making, as well as identifying key data gaps. Further it can expand the utility and applicability of existing techniques and data sets beyond the reach of conventional research. Challenges and opportunities for wider use of soil scanning technology by community groups are evaluated.

Peak water is a concept that is increasingly used to describe a tipping point in time for glaciated drainage basins, where annual discharge reaches a maximum and thereafter is in continual decline. Millions of people across the globe depend on glacial meltwater, especially in regions such as the Himalayas and the Andes, and therefore current and future changes in meltwater generated flow and downstream water availability are important for society and ecosystem services. Due to the long-term negative consequence of glacier retreat on freshwater resources, peak water in glaciated basins has received more attention in recent years. Using an example case study from the Peruvian Andes, we highlight crucial considerations around scale, process, and terminology when measuring, modelling, and communicating peak water in glaciated basins. Through the application of commonly used peak water calculation methods, we explore the influence of these considerations on the estimation of peak water timing. One such consideration is the processes affecting discharge aside from direct glacial melt, such as catchment storage (aquifers, wetlands, lakes), precipitation, and human activities. In our example case study of the Rio Santa basin in Peru, we find that these factors may all play a much larger role than originally assumed. Subsequently, some peak water estimates may not isolate glacial melt peak water, but instead represent “basin peak water”. Depending on the basin of interest, these aspects can play a significant role in water availability, and thus in peak water estimates. We believe that these nuisances are important for ensuring that the peak water concept is appropriately communicated to end-users, and to inform suitable water management. As a scientific community, we now have an opportunity to assess and find ways to move forward with a unified approach to the terminology and communication of peak water.

Glacier retreat provides clear, visual evidence of environmental change in response to warming temperatures around the world. In the tropical Andes of Peru, glaciers act as critical buffers to water supply essential to water, food, and energy security downstream, especially during the dry season. The direct and indirect impacts of glacier change are an important part of the global sustainability challenge within the context of both climate change and increased pressures on resources. Public understanding around glacier-fed water supplies, and subsequent threats to this for millions of people due to climate change, is an important component of climate literacy.In this context, we have developed a web-based interdisciplinary citizen science glacier mapping tool (GlacierMap) to help to raise awareness of these issues, particularly amongst UK high school pupils, and to contribute to increased public support for mitigating and adapting to the impacts of climate change. Users of GlacierMap undertake an interactive learning experience by mapping a glacier from two different periods (1984 and 2018) from freely available Landsat data, resulting in a visual demonstration of glacier retreat within Peru’s Cordillera Blanca, while learning more about the impacts of this retreat from information provided by the project. During the first four months of data collection we integrated pre- and post-mapping questionnaires into the GlacierMap app to evaluate the extent to which participation in mapping impacted understanding of glacier change and concern regarding the associated impacts. We also assessed the value of ‘crowd-sourcing’ glacier mapping for the purposes of glacier monitoring and data generation through comparison of mapping conducted by the general public and that of a control group with previous education and/or work experience in glaciology. In doing so, we have identified a number of challenges and opportunities with regards to the use of a citizen science-based educational activity for climate learning. Challenges relate to recruitment of participants, evaluation, and ethics (particularly when working with children and young people), while opportunities were identified in terms of increasing public awareness, the provision of alternative forms of learning, and global reach.

The Rapel Basin (ca 14,000 km2), Chile, provides a wide range of ecosystem services from mining activities and water supply from its Central Andean headwaters to mixed agricultural food production and hydropower generation in the Central Valley. The breadth of ecosystem service provision, range of land use and wider anthropogenic pressures makes the Rapel system an ideal natural laboratory in which to evaluate tools to support soil erosion mitigation in the context of enhancing food, water and energy security.Taking a distributed approach to encompass geological variability plus superimposed land management and natural process variability, replicate tributary sediment samples (n = 10± per tributary, total number of sediment samples= 313) were collected from across the system to characterise sediment inputs from the major potential sediment sources : (a) natural sediment production in steep Andean headwaters driven by (i) glacial retreat and (ii) seasonal snow melt, (b) sediment inputs from major copper mining operations in the Andes, (d) soil erosion on agricultural land in the Central valley basin area and (e) soil erosion on agricultural land in the Coastal Mountain Belt bordering the hydropower reservoir, Lake Rapel. Samples of river bed sediment from two main sub-catchments (north: Cachapoal River, South: Tinguiririca River) were collected at the outlet to the upper Andean catchment, below the central valley agricultural zone and downstream of a major tributary confluence above the reservoir. In addition, 12 surficial sediment samples were collected from the main arm of the reservoir. All materials were analysed for major and minor element geochemistry by Wave-length Dispersive X-Ray Fluorescence (44 elements).Mixtures were compared in terms of their source material groups in a series of nested MixSIAR mixing model runs after selection of appropriate tracer groups following established procedures. In the northern tributary to the reservoir, mining effluent dominated the sediment supply in upper reaches (78%) with the reminder from natural landscape denudation plus a small proportion of glacial-derived sediments (5%). The influence of the mine was diluted by significant inputs of sediment from agricultural sources (fruit orchards and grain production) in the central basin (agriculture 53%, mining 25%) but given the scale of the system, mining remained a major contributor to the reservoir sediment column, with high Cu concentrations (ca 450 mg kg-1) observed in reservoir sediment. In the southern tributary, in the absence of mining, natural erosion upstream was dominated by snow melt processes (70%) compared to glacial melt (30%). In the lower reaches downstream of agricultural land, agricultural inputs dominated (53%) with natural erosion in mountain headwaters still contributing (45% overall). Evaluation of reservoir sediment against main geological, natural and anthropogenic tributary-based classification demonstrated significant inputs of sediment from Coastal Mountain agriculture (41%) where steep hillslopes are being actively converted from natural vegetation to plantations (olives, avocados etc). Moreover, sediment contribution coming from mining activities were still considerable (31%).Future land-management decisions require quantification of soil erosion hotspots for targeted mitigation measures. Natural science results are discussed in the context of parallel participatory approaches to developing stakeholder consensus on future actions.

Glaciers are temporary repositories for radionuclides and other airborne contaminants (eg. heavy metals). Retreat of glaciers results in the release of these contaminants to downstream ecosystems where they can be accumulated by biota, with further consequences along the trophic chain. Fallout radionuclides, and especially Pu released from nuclear weapons testing and nuclear accidents, concentrates on glacier surfaces in cryoconite granules. These aggregates of mineral and organic components are associated with biological consortia composed of archaea, algae, cyanobacteria, fungi and heterotrophic bacteria (Cook et al., 2016). Cryoconite is also responsible for local decrease ice albedo and is responsible for formation of water-filled holes. Contaminants are effectively trapped in cryoconite granules for long periods (up to decades) due to the “sticky” nature of the material. Cryoconite can thus be useful in monitoring of radionuclide deposition on glaciers (Łokas et al., 2019; Giovanni et al., 2020).Our collective research reveals widespread incidence of Pu isotopes in cryoconite across multiple sites on both hemispheres, including Svalbard, Sweden, Norway, Iceland, Greenland, British Columbia, Alaska, the European Alps, the Caucasus, Siberia, Tien Shan, Altai, South America and Antarctica. The levels of plutonium isotopes (238,239,240Pu) found in cryoconite at these sites are orders of magnitude higher than those detected in non-glaciated environments, raising important questions around the role of glaciers, and specifically cryoconite, in concentrating levels of Pu isotopes above those found in the surrounding environment. The activity ratios of 238Pu/239+240Pu show that the plutonium-related radioactivity of cryoconite from the Northern hemisphere is compatible with the worldwide signal from the global radioactive fallout (0.025) but in some samples from Svalbard higher activity ratios are associated with an additional source of pure 238Pu, pointing to an influence of the SNAP-9A satellite burn up in the atmosphere occurred in 1964. Also activity ratios from South America and Antarctica are consistent with the global radioactive fallout ratio (including SNAP 9 re-entry) in the southern hemisphere (0.14), with an exception concerning cryoconite from the Exploradores Glacier (Chilean Patagonia, ratio 0.35). There are no known nuclear test sites near this glacier which could explain this anomalous value. However, there is also no information about the atmospheric re-entry of the automatic Interplanetary Station “Mars’96” which was launched on 16 November 1996. It fell off the coast of Chile near the border with Bolivia and was not found so far. There were considerable quantities of 238Pu on board of the station, with a total activity of 174 TBq (IAEA, 2001). We hypothesize that this event could explain the anomaly observed at Exploradores Glacier, confirming the unmatched potential of cryoconite to study environmental radioactivity in glacial contexts.AcknowledgementsThis study was supported by the National Science Center grant no. NCN 2018/31/B/ST10/03057.ReferencesCook et al., 2016. Progress in Physical Geography, 40(1), 66-111.Giovanni et al., 2020. CATENA, 191, 104577.IAEA, 2001. International Atomic Energy Agency IAEA, Vienna).Łokas et al., 2019. The Cryosphere, 13(7), 2075-2086.

The dramatic increase in world population underpins current escalating food demand, which requires increased productivity in the available arable land through agricultural intensification. Agricultural intensification involves increased agrochemicals use to increase land productivity. Increased uses of agrochemicals pose environmental and ecological risks such as contamination and water eutrophication. Consequently, toxic metals accumulate in plant products, thus entering the food chain leading to health concerns. To achieve this study, secondary data from peer-reviewed papers, universities, and government authorities were collected from a public database using Tanzania as a case study. Data from Science Direct, Web of Science, and other internet sources were gathered using specific keywords such as nutrient saturation and losses, water eutrophication, potentially toxic metal (PTEs), and impact of toxic metals on soils, water, and food safety. The reported toxic metal concentrations in agro-ecosystem worldwide are linked to agricultural intensification, mining, and urbanization. Statistical analysis of secondary data collected from East African agro-ecosystem had wide range of toxic metals concentration such as; mercury (0.001–11.0 mg Hg/kg), copper (0.14–312 mg Cu/kg), cadmium (0.02–13.8 mg Cd/kg), zinc (0.27–19.30 mg Zn/kg), lead (0.75–51.7 mg Pb/kg) and chromium (19.14–34.9 mg Cr/kg). In some cases, metal concentrations were above the FAO/WHO maximum permissible limits for soil health. To achieve high agricultural productivity and environmental safety, key research-informed policy needs are proposed: (i) development of regulatory guidelines for agrochemicals uses, (ii) establishment of agro-environmental quality indicators for soils and water assessment to monitor agro-ecosystem quality changes, and (iii) adoption of best farming practices such as split fertilization, cover cropping, reduced tillage, drip irrigation to ensure crop productivity and agro-ecosystem sustainability. Therefore, robust and representative evaluation of current soil contamination status, sources, and processes leading to pollution are paramount. To achieve safe and sustainable food production, management of potential toxic metal in agro-ecosystems is vital.

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.

Radiocesium released from the Fukushima Daiichi nuclear power plant (FDNPP) and deposited in the terrestrial environment has been transported to the sea through rivers. To study the long-term effect of riverine transport on the remediation process near the FDNPP, a monitoring project was initiated by the University of Tsukuba. It was commissioned by the Ministry of Education, Culture, Sports, Science, and Technology, and the Nuclear Regulatory Commission in June 2011, and was taken over by the Fukushima Prefectural Centre for Environmental Creation from April 2015. The activity concentration and monthly flux of radiocesium in a suspended form were measured in the project. This provides valuable measurement data to evaluate the impact of the accidentally released radiocesium on residents and the marine environment. It can also be used as verification data in the development and testing of numerical models to predict future impacts., Measurement(s) Cesium-137 Gamma Radiation • Cesium-134 Gamma Radiation • Latitude • Longitude • grain size • radiocesium flux • radioactivity concentration Technology Type(s) gamma-ray spectroscopy • GPS navigation system • laser diffraction particle size analyzer • Calculation Factor Type(s) geographic location Sample Characteristic - Environment suspended sediment Sample Characteristic - Location Abukuma River • Fukushima Prefecture • Miyagi Prefecture Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.13055315

Eutrophication is a significant threat to surface water biodiversity worldwide, with excessive phosphorus concentrations being among the most common causes. Wetland ditches under these conditions shift from primarily submerged aquatic vegetation to algae or duckweed dominance, leading to excessive shading and anoxic conditions. Phosphorus, from both point (e.g. wastewater treatment works) and diffuse (largely agricultural runoff) sources, is currently the central reason for failure in the majority of surface water bodies in England to meet required water quality guidelines. This study assesses phosphorus storage in the ditch systems at West Sedgemoor, a designated site of special scientific interest. Elevated phosphorus concentrations in sediment was observed across the Moor up to 4220 mg Kg−1, almost 10 times that which may be expected from background levels. The highest concentrations were generally observed at the more intensively farmed sites in the north of the moor, near key inlets and the outlet. Based upon their chemical and physical properties, clear distinction was observed between sites outside and within the Royal Society of the Protection of Birds nature reserve, using principal component analysis.

Within a catchment context, statistical models are widely used to predict the load of pollutants (i.e. fine sediments, chemicals compounds) from potential sources around it, into a main channel (mixture). MixSIAR is a Bayesian mixing model framework that has been used in many environmental studies. As with other models, it presents some assumptions that might be assessed before its use. In this study, a set of artificial mixtures (from real sources) were created using four different catchment sediment sources (Channel Bank; Cultivated land; Pasture and Road Material). The material collected from each source was sieved (10%). The most precise and reliable results based on convergence were those using the “Residual error” structure, where the value of each mixture was closer to the real and model convergence was achieved more easily. On the other hand, “Multiplicative error” structure led to longer model run times (due to its complexity) and in most cases the model did not converge as for the “Residual error” structure when using the full set of tracers. To mitigate this problem, a posterior tracer selection based on diagnostic information was devised which made it possible to increase dramatically the convergence of the predicted parameters without a significant difference in the result. Although the “Residual error” structure showed to be the most convenient for further analysis, the technique applied for “Multiplicative error” structure can be used as a potential solution to achieve model convergence while reducing model runtime.

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.

An ability to identify and quantify changes in sediment sources and erosion within catchments would be of great use for landscape managers and planners. This is particularly the case in peri-urban catchments, which are characterized by complex and dynamically changing land-use mosaics – and where today’s planning decisions may be crucial as regards avoiding or exacerbating erosional, water quality and flooding problems. This study explores the potential for a sediment fingerprinting approach to provide a cost-effective way of assessing changes in sediment sources within a small peri-urban catchment. The study focuses on the Ribeira dos Covões catchment (6.2 km2), on the outskirts of Coimbra in central Portugal. The climate is humid Mediterranean and the geology is 56% sandstone, 41% marly limestone and 3% alluvium. Current land-use is 56% woodland, 4% agricultural and 40% urban (mainly residential, but also a recently constructed enterprise park (5%) and major highway (1%)). Recent urbanization has largely occupied former agricultural land. The study adopts a multi-proxy sediment fingerprinting approach, based on geochemical (elemental) characterization of fluvial fine bed-sediment and soil samples, using a Niton x-ray fluorescence elemental analyser. Sampling of fluvial sediment was carried out at 33 sites within the stream network (including all significant tributaries, downstream sites and the catchment outlet). Samples were collected in July 2018 and November 2018 following contrasting ‘late wet season’ and ‘end of dry season’ events. In addition, in July 2018 composite samples of potential sediment sources were collected, including (i) soil surface (0-2cm) samples at 64 representative locations, (ii) 17 samples from eroding channel margin sites, and (iii) 15 samples of road sediment. All samples were sieved to obtain

Soil erosion by water is critical for soil, lake and reservoir degradation in the mid-hills of Nepal. Identification of the nature and relative contribution of sediment sources in rivers is important to mitigate water erosion within catchments and siltation problems in lakes and reservoirs. We estimated the relative contribution of land uses (i.e. sources) to suspended and streambed sediments in the Chitlang catchment using stable carbon isotope signature (δ13C) of long-chain fatty acids as a tracer input for MixSIAR, a Bayesian mixing model used to apportion sediment sources. Our findings reveal that the relative contribution of land uses varied between suspended and streambed sediment, but did not change over the monsoon period. Significant over- or under-prediction of source contributions could occur due to overlapping source tracer values, if source groups are classified on a catchment-wide basis. Therefore, we applied a novel deconvolutional framework of MixSIAR (D-MixSIAR) to improve source apportionment of suspended sediment collected at tributary confluences (i.e. sub-catchment level) and at the outlet of the entire catchment. The results indicated that the mixed forest was the dominant (41 ± 13%) contributor of sediment followed by broadleaf forest (15 ± 8%) at the catchment outlet during the pre-wet season, suggesting that forest disturbance as well as high rainfall and steep slopes interact for high sediment generation within the study catchment. Unpaved rural road tracks located on flat and steep slopes (11 ± 8 and 9 ± 7% respectively) almost equally contributed to the sediment. Importantly, agricultural terraces (upland and lowland) had minimal contribution (each

Lack of long-term scientific land cover and erosional data impedes the development of sustainable land management plans to tackle land degradation and soil erosion problems in Tanzania. Using Landsat imagery, almost three decades of land cover change in the Lake Manyara catchment (1988–2016) was reconstructed. Data highlight that the major land cover types are highly dynamic and that there is a net conversion of natural or semi-natural land cover towards agricultural uses. Specifically, the biggest net declining cover types were found to be ‘bushland’, ‘seasonal grassland’ and ‘permanent savanna’, which have reduced by 8.7, 6.1 and 3.5% respectively. In this context an erosion risk model, based on the ‘Revised Universal Soil Loss Equation’, was applied to evaluate how changing land cover has affected risk of surface soil erosion by water. Model outputs indicate that a lot of land conversion has occurred in areas that are naturally vulnerable due to topography, soil type and rainfall patterns, seriously increasing the soil erosion risk. The resulting output maps can be particularly useful in pinpointing potential areas of increased erosion risk underpinning targeted investigation and management action to support soil conservation for improved food and water security.

Recent European Common Agricultural Policy (CAP) forces Flemish farmers in the Belgian loess belt to combat soil erosion on high erosion sensitive parcels. A possible measure against erosion is the application of reduced tillage operations. To evaluate the efficiency of reduced tillage practices, erosion rates of a maize field under conventional tillage, non-inversion tillage and strip-till were compared, all with and without wheel track compaction. To assess erosion rates, 20 min rainfall simulations in combination with fallout radionuclide (FRN) 7Be measurements were used. At the small plot scale (5 m²), runoff coefficient, suspended sediment concentration and soil loss were measured directly during rainfall simulation in order to compare the effect of the different tillage treatments and the effect of wheel track compaction. After the rainfall simulations soil samples were taken for 7Be analysis to explore spatial patterns in soil redistribution within the different plots. Furthermore, a total soil redistribution budget was obtained based on the 7Be measurements and validated with the direct erosion measurements during the rainfall simulations. Direct measurements showed a significant decrease in runoff coefficient, suspended sediment concentration and total soil loss in the non-inversion and strip-till treatments compared to the conventional tillage treatment. No difference was observed between the non-inversion and strip-till treatment. For all treatments, wheel track compaction increased runoff coefficients and soil loss. The 7Be measurements confirmed overall trends observed during the rainfall simulations, with high soil losses in the conventional treatment (5.96 ± 1.37 kg–6.23 ± 2.36 kg) and a decrease in soil loss with the non-inversion (1.50 ± 0.34 kg–1.95 ± 0.54 kg) and the strip-till treatment (−0.19 ± 0.60 kg–0.10 ± 2.50 kg). However, 7Be-derived net erosion estimates overestimated total soil loss per plot compared to the direct measurements. The appropriateness of correction factors, like particle size correction and variations in relaxation mass depth, to improve the tracer based assessment of absolute soil loss values was evaluated. Spatial patterns in soil redistribution clearly reflected the sediment and runoff buffering capacity of the inter-row area in the strip-till treatment, while higher erosion rates were observed in the plant rows. Yet, sample representativeness to construct the soil erosion budget is a key consideration in light of discrepancies between tracer and rainfall simulation results. The different rainfall simulations support the preference of non-inversion tillage and strip-till over conventional tillage in order to reduce soil loss in the Belgian loess belt. The increased soil loss due to wheel track compaction implies the need to till favorable soil moisture conditions to avoid soil compaction.