Centennial Changes of Salt Marsh Area in Coastal Georgia (USA) Related to Large-Scale Sediment Dynamics by River, Waves, and Tides

IF 2.3 3区 环境科学与生态学 Q3 ENVIRONMENTAL SCIENCES
G. Mariotti, G. Ceccherini, C. R. Alexander, A. C. Spivak
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引用次数: 0

Abstract

Marsh lateral expansion and retreat are often attributed to sediment availability, but a causal link is difficult to establish. To shed light on this problem, we analyzed changes in salt marsh area along the ~ 200-km-long Georgia coast (USA) from the 1850s to 2010s in relation to total suspended sediment (TSS) and to proxies for river sediment input and local sediment resuspension. Marsh area is characterized by large gains and losses (up to 200 m2/m/yr), but relatively small net change (-50 to 50 m2/m/yr or -0.1 to 0.1%/yr). This has resulted in a general loss of marsh area, except close to the mouths of major rivers, where there is net gain. Net expansion rates decreased in the Savannah Estuary but increased in the Altamaha Estuary from the 1850s–1930s period to the 1930s–2010s period, which are consistent with observed decreases and likely increases in sediment discharge in the two estuaries, respectively. To explain the spatial patterns in the 1930s–2010s marsh area change, we estimated TSS from satellite measurements (2003 to 2020). Along the northern part of the Georgia coast, net marsh gain is positively correlated to the average TSS within the estuarine region. However, this correlation breaks down in more southern areas (Cumberland Sound). Coast-wide, there is a better correlation between TSS associated with new input from the rivers, estimated as the TSS difference between high-discharge (Jan–Mar) and low-discharge (Sept–Nov) months. To identify the effect of wave resuspension in the nearshore, we consider the TSS difference between high-wave, low-discharge (Sept–Nov) and low-wave, low-discharge periods (Jun–Aug). Wave resuspension is relatively uniform along the coast and does not explain spatial patterns of marsh area change. Sediment input from the nearshore is likely contributing to the estuarine sediment budget in Georgia, but it is not sufficient to prevent marsh lateral retreat. To identify the role of tidal resuspension and advection, we consider differences in TSS between low and high tide. This differential is relatively constant along most of the coast, but it is much lower in the southern part of the coast, suggesting a lower tidal action in this region. Sediment resuspended by tides is likely originating from internal recycling (i.e., erosion) within the estuary, and thus does not contribute to marsh lateral expansion. The proposed approach to partition TSS is a general demonstration and could be applied to other coastal regions.

Abstract Image

美国佐治亚州沿海盐沼面积百年变化与河流、波浪和潮汐造成的大规模沉积物动力学有关
沼泽的横向扩展和后退通常归因于沉积物的可用性,但因果关系难以确定。为了揭示这个问题,我们分析了从 19 世纪 50 年代到 2010 年代美国佐治亚州约 200 公里长的海岸线上盐沼面积的变化与总悬浮沉积物(TSS)以及河流沉积物输入和当地沉积物再悬浮的代用指标的关系。沼泽面积的增减幅度较大(高达 200 平方米/平方米/年),但净变化相对较小(-50 至 50 平方米/平方米/年或-0.1 至 0.1%/年)。这导致沼泽面积普遍减少,只有靠近主要河流入海口的地方有净增加。从 1850-1930 年代到 1930-2010 年代,萨瓦纳河口的净扩展率下降,但阿尔塔玛哈河口的净扩展率上升,这与观测到的两个河口沉积物排放量分别减少和可能增加是一致的。为了解释 1930 年代至 2010 年代沼泽面积变化的空间模式,我们通过卫星测量(2003 年至 2020 年)估算了总悬浮固体。在佐治亚州海岸北部,沼泽净增加与河口区域内的平均总悬浮固体呈正相关。然而,这种相关性在南部地区(坎伯兰湾)有所减弱。在整个海岸范围内,与河流新输入有关的总悬浮固体物质之间的相关性较好,总悬浮固体物质是以高排水量月份(1 月至 3 月)和低排水量月份(9 月至 11 月)之间的总悬浮固体物质差值估算的。为了确定波浪再悬浮对近岸的影响,我们考虑了高波浪、低排水量(9-11 月)与低波浪、低排水量时段(6-8 月)之间的总悬浮固体含量差异。沿岸的波浪再悬浮相对均匀,不能解释沼泽面积变化的空间模式。来自近岸的沉积物输入可能对佐治亚州的河口沉积物预算有所贡献,但不足以防止沼泽横向后退。为了确定潮汐再悬浮和平流的作用,我们考虑了退潮和涨潮时总悬浮固体的差异。这一差异在海岸的大部分地区相对稳定,但在海岸的南部地区要低得多,这表明该地区的潮汐作用较弱。潮汐重新悬浮的沉积物可能来自河口的内部循环(即侵蚀),因此不会促进沼泽的横向扩展。拟议的总悬浮固体分区方法是一种通用的示范方法,可应用于其他沿海地区。
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来源期刊
Estuaries and Coasts
Estuaries and Coasts 环境科学-海洋与淡水生物学
CiteScore
5.60
自引率
11.10%
发文量
107
审稿时长
12-24 weeks
期刊介绍: Estuaries and Coasts is the journal of the Coastal and Estuarine Research Federation (CERF). Begun in 1977 as Chesapeake Science, the journal has gradually expanded its scope and circulation. Today, the journal publishes scholarly manuscripts on estuarine and near coastal ecosystems at the interface between the land and the sea where there are tidal fluctuations or sea water is diluted by fresh water. The interface is broadly defined to include estuaries and nearshore coastal waters including lagoons, wetlands, tidal fresh water, shores and beaches, but not the continental shelf. The journal covers research on physical, chemical, geological or biological processes, as well as applications to management of estuaries and coasts. The journal publishes original research findings, reviews and perspectives, techniques, comments, and management applications. Estuaries and Coasts will consider properly carried out studies that present inconclusive findings or document a failed replication of previously published work. Submissions that are primarily descriptive, strongly place-based, or only report on development of models or new methods without detailing their applications fall outside the scope of the journal.
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