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Intermittent hydrologic perturbations control solute cycling and export in the Okavango Delta
Journal of Hydrology ( IF 6.4 ) Pub Date : 2021-01-12 , DOI: 10.1016/j.jhydrol.2021.125968
Goabaone J. Ramatlapeng , Eliot A. Atekwana , Loago Molwalefhe , Kopo V. Oromeng

We measured the concentrations of the total dissolved ions (TDI), dissolved silica, major cations and the δD and δ18O at sub-weekly intervals for one year in the Okavango River at the outlet of the Okavango Delta (Delta). Our objectives were to (1) document the temporal variations in the concentrations of solutes in the Okavango River, (2) determine the processes controlling the transfer of solutes to the river and (3) assess the temporal solute load and outflux from the Delta. We found that the TDI and major cation concentrations in the river were anomalously high during the rainy season and before the arrival of the annual flood pulse. The anomalous increases in the solute concentrations are due to dissolution and mobilization of precipitated salts stored in the floodplains and on hundreds of thousands of islands scattered across the Delta wetlands, as well as from ‘flushing’ of remnant evaporated flood water of higher salinity trapped in isolated wetland pools. Overland flow generated by local rains and flooding connect the river to the solute stores in the watershed. The temporally activated hydrologic flow pathways transfer solutes to the river that flushes them out of the Delta. The solute load in the river was higher during the rainy season and during pulse flooding, and mimicked the discharge hydrograph. We estimate that 17,838 Mg/y of dissolved solutes was flushed out of the Delta, with 67% removed during pulse flooding (6 months) and 30% during the rainy season (4 months). The transfer of solutes from the watershed to the river during pulse flooding and the rainy season, and solute export from the Delta is an important mechanism that keeps the Delta’s surface water resources fresh, which is critical for supporting a freshwater wetland ecosystem. Our results highlight the importance of intermittent activation of hydrologic flow pathways in controlling solute cycling in this and other arid watersheds.



中文翻译:

间歇性水文扰动控制了奥卡万戈三角洲的溶质循环和出口

我们测得的总溶解的离子(TDI),溶解的二氧化硅,主要阳离子和δD和δ的浓度18O在Okavango三角洲(Delta)出口处的Okavango河中以每隔一周的时间间隔O,为期一年。我们的目标是(1)记录奥卡万戈河中溶质浓度的时间变化,(2)确定控制溶质向河水迁移的过程,以及(3)评估瞬时溶质负荷和来自三角洲的涌出量。我们发现,在雨季和年度洪水脉冲到来之前,河流中的TDI和主要阳离子浓度异常高。溶质浓度异常增加是由于洪泛区和遍布三角洲湿地的数十万个岛上储存的沉淀盐的溶解和动员所致,以及“冲洗”残留在孤立的湿地池中的更高盐度的残留蒸发洪水。局部降雨和洪水造成的陆上径流将河流连接到流域中的溶质库。时间激活的水文流动路径将溶质转移至河流,从而将其冲刷出三角洲。在雨季和脉冲洪水期间,河流中的溶质负荷较高,并且模拟了排放水位图。我们估计有17838 Mg / y的溶解性溶质被冲出三角洲,其中脉冲洪水(6个月)中去除了67%,雨季(4个月)中去除了30%。在脉冲洪水和雨季期间,溶质从流域转移到河流,三角洲的溶质出口是保持三角洲地表水资源新鲜的重要机制,这对于支持淡水湿地生态系统至关重要。我们的结果强调了间歇性激活水文流动路径在控制该干旱流域和其他干旱流域中溶质循环中的重要性。

更新日期:2021-01-21
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