Michael J. Watts

Soil erosion is an increasing environmental problem in the Lake Victoria Basin (LVB), resulting in the transfer of sediment, nutrients and contaminants from terrestrial landscapes to aquatic ecosystems. These land-to-lake transfers have implications for soil fertility, water quality, ecosystem functioning and food security, yet the temporal evolution and catchment origins of sediment inputs remain poorly understood. This study combines Pb-210 geochronology, sediment geochemistry and geochemical source apportionment to reconstruct historical sediment delivery to the Winam Gulf of Lake Victoria from the Nyando, Sondu-Miriu, Awach, Luanda and Kisat river catchments. Sediment-core chronologies demonstrate a substantial acceleration in sediment accumulation from the 1960s, with the most rapid increases occurring after 2000. Sedimentation rates increased approximately seven-fold in the Nyando catchment and three-fold in the Sondu-Miriu catchment between the 1960s and 2021. Temporal changes in sediment geochemistry, including phosphorus, sulphur, calcium and organic matter, indicate increasing influence of agricultural expansion, forest clearance and urban development. Using a Frequentist sediment fingerprinting approach, historical sediment contributions were linked to specific sub-catchments, revealing that recent increases in sediment delivery were associated with shifts in sediment provenance driven by land-use change in key source areas. The integration of geochronology and source apportionment provides a multi-decadal reconstruction of land-lake connectivity and identifies priority locations for intervention. From an environmental geochemistry and health perspective, accelerated sediment transfer represents the mobilisation of nutrient-rich topsoil, organic carbon and associated contaminants into aquatic systems, with potential consequences for agricultural productivity, eutrophication, fisheries, water quality and human wellbeing. The approach offers a practical framework for targeting catchment restoration and improving ecosystem resilience across the Lake Victoria Basin and other rapidly changing tropical catchments.

Potassium (K) is an essential plant nutrient and is often in short supply in the highly weathered soils of East Africa. The development of effective and sustainable fertilisation strategies could be helped by developing rapid and relatively cheap methods that provide initial assessments of inherent nutrient stocks and soil K behaviour. Mid‐infrared (MIR) and near‐infrared (NIR) models are presented covering a range of soil K properties and K‐bearing mineralogy. Initially, 90 soils from Kenya, Tanzania and Uganda were analysed for total K, SrCl ₂ exchangeable K, K‐release rates ( β ) and quantitative X‐ray diffraction (XRD). Using MIR and NIR scans for each sample, as well as an additional 446 soil samples from the Winam Gulf (WG) in Kenya, key spectral components were identified using a ‘Single Mixture Modelling Resolution’ analysis, which were used to parameterise models using either stepwise or censored regression techniques for the measured soil K properties and K‐bearing minerals in the 90 samples analysed. Stepwise regression models were fitted for K _Total ( R ² = 0.90), SrCl ₂ extractable K ( R ² = 0.68), the release constant β ( R ² = 0.53), Kaolinite ( R ² = 0.79) and the Chemical Index of Alteration ( R ² = 0.93), with all models being highly significant ( p < 0.001). Censored regression models were fitted for the K‐containing minerals K‐feldspar, mica and illite, along with quartz. The logSigma parameter was highly significant for each ( p < 0.001). Models were applied to the WG soil samples, and estimates were plotted using different lithologies as variables. Potential exists for these models to act as a toolbox to assess inherent K stocks and likely K dynamics as an initial assessment in developing strategies to improve K sustainability and fertilisation practices. Models could be rerun to include newly generated MIR and NIR scans from soil surveys.

In Kenya, less than 10% of the land is arable, out of which 30% suffers severe soil degradation. This study investigates impact of various agricultural land use management practices (on the concentration and distribution of essential nutrients in different soil particle size fractions (SPSF) within Oroba Valley, Nandi County. Two agricultural plots were selected: Plot 1 (non-terraced) and Plot 2 (terraced cultivation), with topsoil (0–20 cm) sampled using a stratified method. Soil particles were separated by sieving (2000–500 µm, 500–100 µm, 100–50 µm, 50–25 µm) and sedimentation (25–10 µm and < 10 µm). Organic matter (OM), soil pH, and nutrient concentrations were quantified using loss on ignition (LOI), a pH meter in CaCl2, and ICP-QQQ analysis, respectively. Median soil pH was 5.6 for Plot 1 and 5.9 for Plot 2, with OM concentrated at 40% in smaller particles (< 25 µm) and 24% in larger particles (100–2000 µm). Nutrients such as I, Se, Zn, Mg, P, Al, Mn, Fe, Co, Mo, and Cu were concentrated in SPSF of < 10 µm, while Na, K, and Ca were concentrated in medium particle sizes (25 µm–100 µm). Terraced plot (Plot 2) experience greater nutrient loss down the slope compared to Plot 1, that showed nutrient accumulation at lower elevations. Principal component analysis (PCA) revealed that soil pH did not significantly influence element adsorption within SPSFs. Differences in land use management between plots directly impacted nutrient distribution. Optimising agricultural land management can improve soil health, contributing to attaining the United Nations sustainable development goals 1, 2, 6, and 8.

In artisanal small-scale gold mines (ASGM), mercury (Hg) is known to pollute nearby river waters and sediments where it can be methylated to the highly bioavailable methylmercury (MeHg). The assessment of Hg speciation in water samples has been challenging for many years, with recommended procedures often not adequately allowing for analysis of samples in a suitable timeframe. Using a novel solid-phase extraction (SPE) method for sampling and preservation of Hg species, representative speciation data can be safely and easily collected and retained for up to 4-weeks (MeHg = 115 ± 8% refrigerated and 109 ± 13% unrefrigerated storage; Hg²⁺ = 100 ± 14% refrigerated and 94 ± 12% unrefrigerated storage). Concentrations of MeHg in environmental water samples and drinking water were below detection limit across two ASGM sites in western Kenya and concentrations of Hg²⁺ were below drinking water guidelines; however, drinking water sources contribute 20–30% of the tolerable weekly intake of Hg, indicating a need to minimise exposure of Hg from dietary sources to prevent Hg poisoning. Sediments from receiving rivers at ASGM sites showed total Hg concentrations above guideline limits (0.08–1.84 mg kg⁻¹ total Hg) along the length of the river; however, MeHg concentrations fluctuated dependent on the stagnation of the river due to damns and ponds (5.9 ± 14.3 µg kg⁻¹ MeHg). The findings show that SPE can be used as a robust sample collection and preservation approach for Hg speciation, which can better inform mitigation measures, understand ecological and human health implications, and improve environmental monitoring.

Africa’s potential for scientific research is not yet being realized, for various reasons including a lack of researchers in many fields and insufficient funding. Strengthened research capacity through doctoral training programmes in higher education institutes (HEIs) in Africa, to include collaboration with national, regional and international research institutions, can facilitate self-reliant and sustainable research to support socio-economic development. In 2012, the Royal Society and the UK’s Department for International Development (now the Foreign, Commonwealth and Development Office) launched the Africa Capacity Building Initiative (ACBI) Doctoral Training Network which aimed to strengthen research capacity and training across sub-Saharan Africa. The ACBI supported 30 core PhD scholarships, all registered/supervised within African HEIs with advisory support from the UK-based institutes. Our ‘Soil geochemistry to inform agriculture and health policies’ consortium project, which was part of the ACBI doctoral training programme network, was implemented in Malawi, Zambia and Zimbabwe between 2014 and 2020. The aims of our consortium were to explore linkages between soil geochemistry, agriculture and public health for increased crop productivity, nutrition and safety of food systems and support wider training and research activities in soil science. Highlights from our consortium included: (i) the generation of new scientific evidence on linkages between soils, crops and human nutrition; (ii) securing new projects to translate science into policy and practice; and (iii) maintaining sustainable collaborative learning across the consortium. Our consortium delivered high-quality science outputs and secured new research and doctoral training funding from a variety of sources to ensure the continuation of research and training activities. For example, follow-on Global Challenges Research Funded Translation Award provided a strong evidence base on the prevalence of deficiencies in children under 5 years of age and women of reproductive age in Zimbabwe. This new evidence will contribute towards the design and implementation of a nationally representative micronutrient survey as an integral part of the Zimbabwe Demographic and Health Surveys conducted by the Ministry of Health and Child Care. The award also generated new evidence and a road map for creating quality innovative doctorates through a doctoral training landscape activity led by the Zimbabwe Council for Higher Education. Although our project and the wider ACBI has contributed to increasing the self-reliance and sustainability of research within the region, many challenges remain and ongoing investment is required.

Climate change poses an immediate threat to tropical soils with changes in rainfall patterns resulting in accelerated land degradation processes. To ensure the future sustainability of arable land, it is essential to improve our understanding of the factors that influence soil erosion processes. This work aimed to evaluate patterns of soil erosion using the activity of plutonium isotopes (Pu) at sites with different land use and clearance scale in the Winam Gulf catchment of Lake Victoria in Kenya. Erosion rates were modelled at potential erosive sites using the MODERN model to understand small-scale erosion processes and the effect of different management practices. The lowest soil redistribution rates for arable land were 0.10 Mg ha⁻¹ yr⁻¹ showing overall deposition, resulting from community-led bottom-up mitigation practices. In contrast erosion rates of 8.93 Mg ha⁻¹ yr⁻¹ were found in areas where steep terraces have been formed. This demonstrates the significance of community-led participation in effectively managing land degradation processes. Another key factor identified in the acceleration of soil erosion rates was the clearance of land with an increased rate of erosion over three years reported (0.45 to 0.82 Mg ha⁻¹ yr⁻¹) underlining the importance vegetation cover plays in limiting soil erosion processes. This novel application of fallout plutonium as a tracer, highlights its potential to inform the understanding of how soil erosion processes respond to land management, which will better support implementation of effective mitigation strategies. Graphical abstract Modelling of soil erosion and deposition patterns using the MODERN model to calculate the depth of soil loss/gain.

Emerging from the shadow of the COVID-19 pandemic, it is time to ground ourselves and retrospectively assess the recent achievements of SEGH over the past years. This editorial serves as a comprehensive report on the progress made in comparison to the aspirations and goals set by the society's board in 2019 (Watts et al., Environ Geochem Health 42:343–347, 2019) (Fig. 1) and reflects on the state of the SEGH community as it reached its 50th anniversary at the close of 2021 (Watts et al. Environ Geochem Health 45:1165–1171, 2023). The focus lies on how the SEGH community navigated through the extraordinary challenges posed by the COVID-19 pandemic since early 2020, and to what extent the 2023 targets have been met.