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Trapping of Suspended Sediment by Submerged Aquatic Vegetation in a Tidal Freshwater Region: Field Observations and Long-Term Trends
Estuaries and Coasts ( IF 2.7 ) Pub Date : 2020-07-14 , DOI: 10.1007/s12237-020-00799-w
Paul A. Work , Maureen Downing-Kunz , Judith Z. Drexler

Widespread invasion by non-native, submerged aquatic vegetation (SAV) may modify the sediment budget of an estuary, reducing the availability of inorganic sediment required by marshes to maintain their position in the tidal frame. The instantaneous trapping rate of suspended sediment in SAV patches in an estuary has not previously been quantified via field observations. In this study, flows of water and suspended sediment through patches of invasive SAV were measured at three tidally forced, freshwater sites, all located within the Sacramento-San Joaquin Delta in California. An acoustic Doppler current profiler deployed from a roving vessel provided velocity and backscatter data used to quantify fluxes of both water and suspended sediment. Sediment trapping efficiency, defined as instantaneous net trapped flux divided by incident flux, was positive in 24 of 29 cases, averaging + 5%. Coupled with 3 years of measured sediment flux data at one site, this suggests that trapping averages 3.7 kg m−2 year−1. This estimate compares favorably with the mean mass accumulation rate of 3.8 kg m−2 year−1 estimated from dated sediment cores collected at the study sites. Long-term measurements made upstream reveal a strong negative trend (− 1.8% year−1) in suspended sediment concentration, and intra-annual changes in both suspended sediment concentration and percent fines. The large footprint and high spatial density of invasive SAV coupled with declining sediment supply are diminishing downstream suspended sediment concentrations, potentially reducing the resiliency of marshes in the Delta and lower estuary to future sea-level rise.



中文翻译:

潮汐淡水地区淹没的水生植物对悬浮泥沙的捕集:实地观察和长期趋势

非原生的水下水生植物(SAV)的广泛入侵可能会改变河口的沉积物预算,从而降低沼泽维持其在潮汐框架中所需的无机沉积物的可用性。先前尚未通过野外观测来量化河口SAV斑块中悬浮泥沙的瞬时捕集率。在这项研究中,通过三个潮汐强迫淡水站点(位于加利福尼亚州萨克拉门托-圣华金三角洲)测量了水和悬浮沉积物通过侵入性SAV斑块的流量。从流动船上部署的声学多普勒电流剖面仪提供了速度和反向散射数据,用于量化水和悬浮沉积物的通量。沉积物捕获效率,定义为瞬时净捕获通量除以入射通量,29例中有24例呈阳性,平均为5%。结合在一个地点进行的3年实测沉积物通量数据,这表明平均捕集量为3.7 kg m-2 年-1。该估计值与根据研究地点收集的陈旧沉积岩心估计的3.8 kg m -2  year -1的平均质量累积速率相比具有优势。上游进行的长期测量显示,悬浮沉积物浓度以及悬浮沉积物浓度和细粉百分率年内变化均很大(-1.8%− 1年)。侵入性SAV的巨大足迹和高空间密度,以及沉积物供应量的减少,正在减少下游悬浮沉积物的浓度,从而可能降低三角洲沼泽地的复原力,并降低河口对未来海平面上升的抵抗力。

更新日期:2020-07-14
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