Tracking rates of ecotone migration due to salt-water encroachment using fossil mollusks in coastal South Florida
Tracking rates of ecotone migration due to salt-water encroachment using fossil mollusks in coastal South Florida
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DOI：
10.1007/s10750-006-0135-y
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发表时间：
2006-10-01
期刊：
影响因子：
2.6
通讯作者：
Ross, Michael S.
中科院分区：
文献类型：
--
作者：
Gaiser, Evelyn E.;Zafiris, Angelikie;Ross, Michael S.
我们通过对佛罗里达东南部沿海湿地5.5 km（2）带中垂直于海岸的沿着36个沉积物柱状样中软体动物的古生态学分析，确定了沿海植被带对盐水侵蚀的迁移速率。植被带分为淡水沼泽林、淡水沼泽林、矮林、过渡林和边缘红树林。植被组成，土壤深度和有机质含量，孔隙水盐度和当代软体动物群落确定在226个站点，以建立软体动物区系的盐度偏好。校准模型允许精确推断的盐度和植被类型的化石软体动物组合按年代校准的沉积物。大多数沉积物是浅（20-130厘米）允许粗尺度的时间推断为三个区域：上部泥炭层（区1）代表过去30-70年，混合泥炭泥灰岩层（区2）代表以前的CA。150-250年和基底部分（区3）的范围从3 10至2990 YBP。现代泥炭的增长率平均为3.1毫米/年（-1），而地下泥灰岩的增长速度更慢，为0.8毫米/年（-1）。盐度和植被类型区I显示了一个陡峭的梯度与淡水社区被限制在1960年建成的南北排水渠西部。对2区（排水前）的推断表明，淡水沼泽和相关的森林单位覆盖了90%的面积，红树林只存在于沿着外围海岸线。在整个排水前的历史中，整个地区的盐度平均保持在2 ppt以下，只有小块红树林存在;目前，盐度平均为13.2 ppt，红树林占湿地的95%。由于盐水的侵蚀，该盆地已经失去了超过3平方公里的淡水湿地植被类型。根据过去70年淡水植被的软体动物推断迁移率3.1/yr-1估算（相比之下，排水前时期为0.14 m/yr（-1））。这种快速的侵蚀速度是由海平面上升和淡水分流驱动的。用淡水补充这些盆地水分的计划将需要大量的重新导流，以抵消当地海平面上升的高速度。
We determined the rate of migration of coastal vegetation zones in response to salt-water encroachment through paleoecological analysis of mollusks in 36 sediment cores taken along transects perpendicular to the coast in a 5.5 km(2) band of coastal wetlands in southeast Florida. Five vegetation zones, separated by distinct ecotones, included freshwater swamp forest, freshwater marsh, and dwarf, transitional and fringing mangrove forest. Vegetation composition, soil depth and organic matter content, porewater salinity and the contemporary mollusk community were determined at 226 sites to establish the salinity preferences of the mollusk fauna. Calibration models allowed accurate inference of salinity and vegetation type from fossil mollusk assemblages in chronologically calibrated sediments. Most sediments were shallow (20-130 cm) permitting coarse-scale temporal inferences for three zones: an upper peat layer (zone 1) representing the last 30-70 years, a mixed peat-marl layer (zone 2) representing the previous ca. 150-250 years and a basal section (zone 3) of ranging from 3 10 to 2990 YBP. Modern peat accretion rates averaged 3.1 mm yr(-1) while subsurface marl accreted more slowly at 0.8 mm yr(-1). Salinity and vegetation type for zone I show a steep gradient with freshwater communities being confined west of a north-south drainage canal constructed in 1960. Inferences for zone 2 (pre-drainage) suggest that freshwater marshes and associated forest units covered 90% of the area, with mangrove forests only present along the peripheral coastline. During the entire pre-drainage history, salinity in the entire area was maintained below a mean of 2 ppt and only small pockets of mangroves were present; currently, salinity averages 13.2 ppt and mangroves occupy 95% of the wetland. Over 3 km(2) of freshwater wetland vegetation type have been lost from this basin due to salt-water encroachment. estimated from the mollusk-inferred migration rate of freshwater vegetation of 3.1 in yr-1 for the last 70 years (compared to 0.14 m yr(-1) for the pre-drainage period). This rapid rate of encroachment is driven by sea-level rise and freshwater diversion. Plans for rehydrating these basins with freshwater will require high-magnitude re-diversion to counteract locally high rates of sea-level rise.