Iron and nutrient content of wind-erodible sediment in the ephemeral river valleys of Namibia
Iron and nutrient content of wind-erodible sediment in the ephemeral river valleys of Namibia
复制标题
DOI：
10.1016/j.geomorph.2017.03.016
复制
发表时间：
2017-08
期刊：
影响因子：
3.9
通讯作者：
A. Dansie;G. Wiggs;D. G. Thomas
中科院分区：
文献类型：
--
作者：
A. Dansie;G. Wiggs;D. G. Thomas
关于风尘源全球分布的研究主要集中在盐土/粘土层和干湖排放区。在南部非洲，这种来源被确定为纳米比亚北部的埃托沙潘和博茨瓦纳北部的马克加迪加迪潘。然而，从短暂的河谷排放的尘埃在很大程度上被忽视了。河流是已知的营养物质运输途径，短暂河谷的洪水制度经常补充储存的细小沉积物，这些沉积物在干燥后可能会变得容易受到风沙侵蚀。这种悬浮在空气中的沉积物可能营养丰富，因此一旦沉积，对海洋水域的肥力具有重要意义。本文研究了纳米比亚三个短暂河谷的尘源沉积物的粒度分布及其生物有效氮、磷和铁的浓度。我们将这些来自短暂河谷的沉积物的营养含量与从埃托沙和马克加迪平底锅收集的沉积物进行比较，并考虑它们相对的海洋肥力潜力。我们的结果表明，短暂的河谷含有细粒沉积物，在物理特征上类似于埃托沙和马克加迪平底锅，但它们拥有高达43倍的生物有效铁浓度以及丰富的N和P常量营养素，这两种元素对海洋肥力都很重要。因此，纳米比亚已知的扬尘河谷对邻近海洋系统的肥沃作用可能比之前认为的、尚未调查的更大。鉴于这一发现，有必要重新评估短暂河谷在向其他旱地地区的风沙和海洋系统提供营养丰富的沉积物方面的潜在作用。
Research concerning the global distribution of aeolian dust sources has principally focussed on salt/clay pan and desiccated lacustrine emission areas. In southern Africa such sources are identified as Etosha Pan in northern Namibia and Makgadikgadi Pans in northern Botswana. Dust emitting from ephemeral river valleys, however, has been largely overlooked. Rivers are known nutrient transport pathways and the flooding regimes of ephemeral river valleys frequently replenish stores of fine sediment which, on drying, can become susceptible to aeolian erosion. Such airborne sediment may be nutrient rich and thus be significant for the fertilisation of marine waters once deposited. This study investigates the dust source sediments from three ephemeral river valleys in Namibia in terms of their particle size distribution and their concentrations of bioavailable N, P and Fe. We compare the nutrient content of these sediments from the ephemeral river valleys to those collected from Etosha and Makgadikgadi Pans and consider their relative ocean fertilising potential. Our results show that the ephemeral river valleys contain fine grained sediment similar in physical character to Etosha and Makgadikgadi Pans yet they have up to 43 times greater concentrations of bioavailable iron and enriched N and P macronutrients that are each important for ocean fertilisation. The known dust-emitting river valleys of Namibia may therefore be contributing a greater fertilisation role in the adjacent marine system than previously considered, and not-yet investigated. Given this finding a re-assessment of the potential role of ephemeral river valleys in providing nutrient-rich sediment into the aeolian and marine systems in other dryland areas is necessary.