Browsing by Author "Boeckx, Pascal"

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A deconvolutional Bayesian mixing model approach for river basin sediment source apportionment
(Scientific Reports, 2018-08-30) Blake, William; Boeckx, Pascal; Stock, Brian; Smith, Hugh; Bodé, Samuel; Upadhayay, Hari; Gaspar, Leticia; Goddard, Rupert; Lennard, Amy; Lizaga, Ivan; Lobb, David; Owens, Philip; Petticrew, Ellen; Kuzyk, Zou; Gari, Bayu; Munishi, Linus; Mtei, Kelvin; Nebiyu, Amsalu; Mabit, Lionel; Navas, Ana; Semmens, Brice
Increasing complexity in human-environment interactions at multiple watershed scales presents major challenges to sediment source apportionment data acquisition and analysis. Herein, we present a step-change in the application of Bayesian mixing models: Deconvolutional-MixSIAR (D-MIXSIAR) to underpin sustainable management of soil and sediment. This new mixing model approach allows users to directly account for the ‘structural hierarchy’ of a river basin in terms of sub-watershed distribution. It works by deconvoluting apportionment data derived for multiple nodes along the stream-river network where sources are stratified by sub-watershed. Source and mixture samples were collected from two watersheds that represented (i) a longitudinal mixed agricultural watershed in the south west of England which had a distinct upper and lower zone related to topography and (ii) a distributed mixed agricultural and forested watershed in the mid-hills of Nepal with two distinct sub-watersheds. In the former, geochemical fingerprints were based upon weathering profiles and anthropogenic soil amendments. In the latter compound-specific stable isotope markers based on soil vegetation cover were applied. Mixing model posterior distributions of proportional sediment source contributions differed when sources were pooled across the watersheds (pooled-MixSIAR) compared to those where source terms were stratified by sub-watershed and the outputs deconvoluted (D-MixSIAR). In the first example, the stratified source data and the deconvolutional approach provided greater distinction between pasture and cultivated topsoil source signatures resulting in a different posterior distribution to non-deconvolutional model (conventional approaches over-estimated the contribution of cultivated land to downstream sediment by 2 to 5 times). In the second example, the deconvolutional model elucidated a large input of sediment delivered from a small tributary resulting in differences in the reported contribution of a discrete mixed forest source. Overall D-MixSIAR model posterior distributions had lower (by ca 25–50%) uncertainty and quicker model run times. In both cases, the structured, deconvoluted output cohered more closely with field observations and local knowledge underpinning the need for closer attention to hierarchy in source and mixture terms in river basin source apportionment. Soil erosion and siltation challenge the energy-food-water-environment nexus. This new tool for source apportionment offers wider application across complex environmental systems affected by natural and human-induced change and the lessons learned are relevant to source apportionment applications in other disciplines.
DeltaSense: Africa's remote sensing guardian of landscape degradation
(Copernicus Meetings, 2025-03-14) Lizaga, Ivan; Latorre, Borja; Bagalwa, Montfort; Cizungu, Landry; Musana, Bernard; Bizimana, Eric; Okello, Joseph; Munishi, Linus; Van Oost, Kristof; Blake, William; Navas, Ana; Boeckx, Pascal
Land degradation in East Africa poses significant challenges to ecosystem resilience and human wellbeing. While traditional monitoring approaches focus on direct land-use changes, we present DeltaSense, an innovative remote sensing tool that utilises inland lake deltas as sensitive indicators of regional landscape degradation. This newly funded project aims to expand the tool's coverage across the Democratic Republic of the Congo, Uganda, Rwanda, Burundi, Tanzania, and Mozambique, building upon a pilot study in the Lake Kivu region. Ourapproachcombinessatellite time series analysis with ground-truth data to detect and monitor environmental changes across multiple spatial and temporal scales. Through collaboration with key regional institutions, including the Observatoire Volcanologique de Goma (OVG), Université catholique de Bukavu (UCB), Rwanda Water Resources Board (RWB), Mountains of the Moon University (MMU), and the Nelson Mandela-African Institute of Science and Technology (NM-AIST), the project will establish a comprehensive monitoring network throughout the Great Lakes region. This multi-institutional approach ensures robust local expertise and sustainable implementation across the target countries. By analysing delta dynamics over 40 years, DeltaSense provides insights into the spatiotemporal patterns of land degradation. The tool integrates multiple satellite data sources with field measurements, including UAV imagery and bathymetric surveys, to validate and calibrate degradation assessments. This methodology enables the identification of degradation hotspots and evaluation of remediation practices. Initial results from the Lake Kivu region demonstrate the tool's capability to detect various degradation drivers, including deforestation, agricultural expansion, violent conflicts and mining activities. The open-source platform facilitates collaboration between researchers, government agencies, and local communities, promoting evidence-based environmental management decisions. This research represents a significant advancement in environmental monitoring by providing near real-time, actionable data for sustainable resource management. The approach's scalability and adaptability make it particularly valuable for regions facing similar environmental challenges globally, with potential applications extending beyond East Africa.
Determining tributary sources of increased sedimentation in East-African Rift Lakes.
(Elsevier B.V., 2020-05-15) Wynants, Maarten; Millward, Geoffrey; Patrick, Aloyce; Taylor, Alex; Brendonck, Luc; Gilvear, David; Boeckx, Pascal; Blake, William; Munishi, Linus; Mtei, Kelvin; Ndakidemi, Patrick
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 rates 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 between 0.80 and 0.85 g cm yr in the 1960s and between 0.84 and 1.81 g cm yr in 2010. Increased 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.
Drivers of increased soil erosion in East Africa’s agro-pastoral systems: changing interactions between the social, economic and natural domains
(Springer, 2019-06-08) Wynants, Maarten; Kelly, Claire; Mtei, Kelvin; Munishi, Linus; Patrick, Aloyce; Rabinovich, Anna; Nasseri, Mona; Gilvear, David; Roberts, Neil; Boeckx, Pascal; Wilson, Geoff; Blake, William; Ndakidemi, Patrick
Increased soil erosion is one of the main drivers of land degradation in East Africa’s agricultural and pastoral landscapes. This wicked problem is rooted in historic disruptions to co-adapted agro-pastoral systems. Introduction of agricultural growth policies by centralised governance resulted in temporal and spatial scale mismatches with the complex and dynamic East African environment, which subsequently contributed to soil exhaustion, declining fertility and increased soil erosion. Coercive policies of land use, privatisation, sedentarisation, exclusion and marginalisation led to a gradual erosion of the indigenous social and economic structures. Combined with the inability of the new nation-states to provide many of the services necessary for (re)developing the social and economic domains, many communities are lacking key components enabling sustainable adaptation to changing internal and external shocks and pressures. Exemplary is the absence of growth in agricultural productivity and livelihood options outside of agriculture, which prohibits the absorption of an increasing population and pushes communities towards overexploitation of natural resources. This further increases social and economic pressures on ecosystems, locking agro-pastoral systems in a downward spiral of degradation. For the development and implementation of sustainable land management plans to be sustainable, authorities need to take the complex drivers of increased soil erosion into consideration. Examples from sustainable intensification responses to the demands of population increase, demonstrate that the integrity of locally adapted systems needs to be protected, but not isolated, from external pressures. Communities have to increase productivity and diversify their economy by building upon, not abandoning, existing linkages between the social, economic and natural domains. Locally adapted management practices need to be integrated in regional, national and supra-national institutions. A nested political and economic framework, wherein local communities are able to access agricultural technologies and state services, is a key prerequisite towards regional development of sustainable agro-pastoral systems that safeguard soil health, food and livelihood security.
Drivers of increased soil erosion in East Africa’s agro-pastoral systems: changing interactions between the social, economic and natural domains
(Springer Berlin Heidelberg, 19-06-18) Wynants, Maarten; Kelly, Claire; Mtei, Kelvin; Munishi, Linus; Patrick, Aloyce; Rabinovich, Anna; Nasseri, Mona; Gilvear, David; Roberts, Neil; Boeckx, Pascal; Wilson, Geoff; Blake, William; Ndakidemi, Patrick
Increased soil erosion is one of the main drivers of land degradation in East Africa’s agricultural and pastoral landscapes. This wicked problem is rooted in historic disruptions to co-adapted agro-pastoral systems. Introduction of agricultural growth policies by centralised governance resulted in temporal and spatial scale mismatches with the complex and dynamic East African environment, which subsequently contributed to soil exhaustion, declining fertility and increased soil erosion. Coercive policies of land use, privatisation, sedentarisation, exclusion and marginalisation led to a gradual erosion of the indigenous social and economic structures. Combined with the inability of the new nation-states to provide many of the services necessary for (re)developing the social and economic domains, many communities are lacking key components enabling sustainable adaptation to changing internal and external shocks and pressures. Exemplary is the absence of growth in agricultural productivity and livelihood options outside of agriculture, which prohibits the absorption of an increasing population and pushes communities towards overexploitation of natural resources. This further increases social and economic pressures on ecosystems, locking agro-pastoral systems in a downward spiral of degradation. For the development and implementation of sustainable land management plans to be sustainable, authorities need to take the complex drivers of increased soil erosion into consideration. Examples from sustainable intensification responses to the demands of population increase, demonstrate that the integrity of locally adapted systems needs to be protected, but not isolated, from external pressures. Communities have to increase productivity and diversify their economy by building upon, not abandoning, existing linkages between the social, economic and natural domains. Locally adapted management practices need to be integrated in regional, national and supra-national institutions. A nested political and economic framework, wherein local communities are able to access agricultural technologies and state services, is a key prerequisite towards regional development of sustainable agro-pastoral systems that safeguard soil health, food and livelihood security.
Soil erosion and sediment transport in Tanzania: Part I – sediment source tracing in three neighbouring river catchments
(Earth Surface Processes and Landforms, 2021-12) Wynants, Maarten; Munishi, Linus; Mtei, Kelvin; Bodé, Samuel; Patrick, Aloyce; Taylor, Alex; Gilvear, David; Ndakidemi, Patrick; Blake, William; Boeckx, Pascal
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
Soil erosion in East Africa: an interdisciplinary approach to realising pastoral land management change
(IOP Publishing Ltd, 2018-12-03) Blake, William; Rabinovich, Anna; Wynants, Maarten; Kelly, Claire; Nasseri, Mona; Ngondya, Issakwisa; Patrick, Aloyce; Mtei, Kelvin; Munishi, Linus; Boeckx, Pascal; Navas, Ana; Smith, Hugh; Gilvear, David; Wilson, Geoff; Roberts, Neil; Ndakidemi, Patrick
Implementation of socially acceptable and environmentally desirable solutions to soil erosion challenges is often limited by (1) fundamental gaps between the evidence bases of different disciplines and (2) an implementation gap between science-based recommendations, policy makers and practitioners.Wepresent an integrated, interdisciplinary approach to support co-design of land management policy tailored to the needs of specific communities and places in degraded pastoral land in the East African Rift System. In a northern Tanzanian case study site, hydrological and sedimentary evidence shows that, over the past two decades, severe drought and increased livestock have reduced grass cover, leading to surface crusting, loss of soil aggregate stability, and lower infiltration capacity. Infiltration excess overland flow has driven (a) sheet wash erosion, (b) incision along convergence pathways and livestock tracks, and (c) gully development, leading to increased hydrological connectivity. Stakeholder interviews in associated sedenterising Maasai communities identified significant barriers to adoption of soil conservation measures, despite local awareness of problems. Barriers were rooted in specific pathways of vulnerability, such as a strong cattle-based cultural identity, weak governance structures, and a lack of resources and motivation for community action to protect shared land. At the same time, opportunities for overcoming such barriers exist, through openness to change and appetite for education and participatory decision-making. Guided by specialist knowledge from natural and social sciences, we used a participatory approach that enabled practitioners to start co-designing potential solutions, increasing their sense of efficacy and willingness to change practice. This approach, tested in East Africa, provides a valuable conceptual model around which other soil erosion challenges in the Global South might be addressed.
Tackling soil degradation and environmental changes in Lake Manyara Basin, Tanzania to support sustainable landscape/ecosystem management.
(EGU General Assembly Conference Abstracts, 2017-04) Munishi, Linus; Mtei, Kelvin; Bode, Samuel; Dume, Bayu; Navas, Ana; Nebiyu, Amsalu; Semmens, Brice; Smith, Hugh; Stock, Brian; Boeckx, Pascal; Blake, Will
The Lake Manyara Basin (LMB), which encompasses Lake Manyara National Park a world ranking World Biosphere Reserve, is of great ecological and socio-economic value because it hosts a small-holder rain fed and extensive irrigation agriculture, grazing grounds for pastoralists, terrestrial and aquatic habitat for wildlife and tourism business contributing to poverty alleviation. Despite these multiple ecosystem services that support the local communities, the LMB is threatened by; (a) siltation from eroded soil fed from the wider catchment and rift escarpment of the basin and (b) declining water levels due to water capture by agriculture and possibly climate change. These threats to the ecosystem and its services are augmented by increasing human population, pollution by agricultural pesticides, poaching, human encroachment and infrastructure development, and illegal fisheries. Despite these challenges, here is a dearth of information on erosion hotspots and to date soil erosion and siltation problems in LMB have been interpreted largely in qualitative terms, and no coherent interpretative framework of these records exists. Despite concerns that modern sediment fluxes to the Lake may exceed long-term fluxes, little is known about erosion sources, how erosion rates and processes vary across the landscape and how erosion rates are influenced by the strong climate gradients in the basin. This contribution describes a soil erosion and sediment management project that aims to deliver a demonstration dataset generated from inter-disciplinary sediment-source tracing technologies and approaches to assess erosion hotspots, processes and spatial patterns of erosion in the area. The work focuses on a sub basin, the Monduli Sub catchment, located within the greater LMB. This is part of efforts to establish an understanding of soil erosion and landscape degradation in the basin as a pathway for generating and developing knowledge, building capacity to assist conservationists, farmers and pastoralists, agro-entrepreneurs, and their support agents to address the problems while feeding the information into the national development policies in Tanzania and the entire East African region.