Department of Earth and Environmental Sciences, KU Leuven, Belgium; Department of Soil Management, Ghent University, Belgium.
Department of Earth and Environmental Sciences, KU Leuven, Belgium; Research Foundation Flanders (FWO), Brussels, Belgium.
Sci Total Environ. 2015 Apr 1;511:756-66. doi: 10.1016/j.scitotenv.2014.12.048. Epub 2015 Jan 21.
During the past decades, land use change in the Lake Victoria basin has significantly increased the sediment fluxes to the lake. These sediments as well as their associated nutrients and pollutants affect the food and water security of millions of people in one of Africa's most densely populated regions. Adequate catchment management strategies, based on a thorough understanding of the factors controlling runoff and sediment discharge are therefore crucial. Nonetheless, studies on the magnitude and dynamics of runoff and sediment discharge are very scarce for the Lake Victoria basin and the African Rift region. We therefore conducted runoff discharge and sediment export measurements in the Upper Rwizi, a catchment in Southwest Uganda, which is representative for the Lake Victoria basin. Land use in this catchment is characterized by grazing area on the high plateaus, banana cropping on the slopes and Cyperus papyrus L. wetlands in the valley bottoms. Due to an increasing population pressure, these papyrus wetlands are currently encroached and transformed into pasture and cropland. Seven subcatchments (358 km2-2120 km2), with different degrees of wetland encroachment, were monitored during the hydrological year June 2009-May 2010. Our results indicate that, due to their strong buffering capacity, papyrus wetlands have a first-order control on runoff and sediment discharge. Subcatchments with intact wetlands have a slower rainfall-runoff response, smaller peak runoff discharges, lower rainfall-runoff ratios and significantly smaller suspended sediment concentrations. This is also reflected in the measured annual area-specific suspended sediment yields (SYs): subcatchments with encroached papyrus swamps have SY values that are about three times larger compared to catchments with intact papyrus vegetation (respectively 106-137 ton km(-2) y(-1) versus 34-37 ton km(-2) y(-1)). We therefore argue that protecting and (where possible) rehabilitating these papyrus wetlands should be a corner stone of catchment management strategies in the Lake Victoria basin.
在过去的几十年里，维多利亚湖流域的土地利用变化显著增加了流入湖泊的泥沙通量。这些泥沙及其相关的养分和污染物影响了非洲人口最密集地区之一的数百万人的粮食和水安全。因此，基于对控制径流量和泥沙排放的因素的透彻理解，采取适当的集水区管理策略至关重要。尽管如此，对于维多利亚湖流域和非洲大裂谷地区，关于径流量和泥沙排放的规模和动态的研究非常匮乏。因此，我们在乌干达西南部的上鲁齐流域进行了径流量和泥沙出口测量，该流域是维多利亚湖流域的代表。该流域的土地利用特点是高原上的放牧区、山坡上的香蕉种植区和谷底的香蒲湿地。由于人口压力不断增加，这些香蒲湿地目前正在被侵占并转化为牧场和农田。在 2009 年 6 月至 2010 年 5 月的水文年内，监测了七个不同湿地侵占程度的子流域（358 平方公里-2120 平方公里）。我们的研究结果表明，由于香蒲湿地具有很强的缓冲能力，因此对径流量和泥沙排放具有一级控制作用。湿地完整的子流域具有较慢的降雨-径流响应、较小的峰值径流量、较低的降雨-径流比和显著较小的悬浮泥沙浓度。这也反映在测量的年特定面积悬浮泥沙产量（SY）中：湿地被侵占的子流域的 SY 值大约是湿地完整的子流域的三倍（分别为 106-137 吨公里（-2）y（-1）与 34-37 吨公里（-2）y（-1））。因此，我们认为保护和（在可能的情况下）恢复这些香蒲湿地应该是维多利亚湖流域集水区管理策略的基石。
