School of Geography, Earth and Environmental sciences, University of Plymouth, PL4 8AA, Portland Square, Drake Circus, Plymouth, UK.
School of Life Sciences and Bioengineering, Nelson Mandela African Institute of Science and Technology, P.O. BOX 447, Arusha, Tanzania.
Sci Total Environ. 2020 May 15;717:137266. doi: 10.1016/j.scitotenv.2020.137266. Epub 2020 Feb 12.
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.
东非裂谷湖（坦桑尼亚的马尼亚拉湖）及其河流输入物的时空泥沙动态已通过泥沙示踪和放射性测年的组合进行了评估。利用放射性测年对沉积岩芯进行评估，并结合异质和自生源元素的地球化学剖面分析，评估了沉积速率的变化。河流和湖泊沉积物的地球化学指纹信息已整合到贝叶斯混合模型框架中，包括空间因素，以确定哪些支流是最近湖相沉积的主要来源。在对沉积岩芯进行贝叶斯源归属的新应用，并随后与沉积数据进行整合，使湖相沉积速率的变化与支流的泥沙输送变化相耦合。这些互补的证据基础表明，在过去的 120 年中，马尼亚拉湖的沉积速率总体呈上升趋势，在 20 世纪 60 年代和 2010 年，沉积速率分别达到 0.80 到 0.85g/cm/yr 和 0.84 到 1.81g/cm/yr 的明显最大值。沉积速率的增加主要是由于土地覆被变化和自然降雨波动导致上游泥沙输送增加的复杂相互作用所致。建模结果确定了两条特定的支流是造成高沉积速率的原因，它们贡献了最近沉积的湖泊泥沙的 58%和 38%。然而，鉴于不同支流在马尼亚拉湖不同区域的主导地位，沉积的影响在空间上是不同的。示踪技术的应用将马尼亚拉湖的泥沙问题约束在特定的支流源上，并建立了上游土地退化与下游生态系统健康之间的联系。这项新的应用为有针对性的土地和水资源管理策略提供了坚实的基础，以保障马尼亚拉湖的水安全和环境健康，并有可能填补其他东非裂谷湖泥沙动力学知识空白。
