Drought-associated shifts in Spartina alterniflora and S. cynosuroides in the Altamaha River estuary
Drought-associated shifts in Spartina alterniflora and S. cynosuroides in the Altamaha River estuary
复制标题
阿尔塔马哈河口互花米草和狼牙草与干旱相关的变化
作者：
Susan N. White;M. Alber
在河口系统中，明智的水资源管理决策部分依赖于评估淡水流入和盐度的变化如何影响选定的管理目标（即栖息地或生物体变化）。这项研究调查了乔治亚州阿尔塔马哈河口沿岸的互花米草和S. cynosuriodes物种的分布与大范围干旱的关系，在此期间淡水流入量大幅减少，咸水侵入了以前的咸水地区。在干旱开始和结束时（2000年、2002年），以及2004年流量增加后，对河口沿岸植被进行了调查。此外，在干旱期间（2001-2002年）进行了一项移除实验，从自然混合群落中移除一种或另一种植物。在所有调查中，S. cynosuroides 密度在平均高潮盐度 > 14 psu 的位置下降，因此下游边界在 2000 年至 2002 年期间从距河口约 3 至 6 公里移动，然后在 2004 年又回到 3 公里。虽然互花 S. alterniflora 的峰值密度在 2000 年至 2002 年间也向上游移动，但上游密度2004年盐度较高，植物分布与盐度不对应。在去除实验中，所有处理（包括对照）中互花链霉菌的密度和相对覆盖百分比均有所增加，而除了有意去除的处理外，狼尾草的密度保持相对恒定。我们对这些结果的解释表明，互花链霉菌是一种强大的入侵者，可以在压力（盐度增加、流量低）条件下扩展到新的栖息地，并且一旦建立，它可以与狼链球菌共存。 S. cynosuroides 的更快响应（两年内发生变化）表明其下游限制是该系统流入条件变化的潜在指标。
In estuarine systems, informed water resource management decisions rely, in part, on evaluating how changes in freshwater inflow and salinity affect a selected management target (i.e., habitat or organismal changes). This study examined the distribution of Spartina alterniflora and S. cynosuriodes species along the Altamaha River estuary in Georgia in association with an extensive drought, during which time freshwater inflow decreased considerably and salty water encroached into previously brackish areas. Bankside vegetation was surveyed along the length of the estuary at the beginning and end of the drought (2000, 2002), and again in 2004 after flows had increased. In addition, a removal experiment, in which one or the other plant was removed from naturally mixed communities, was conducted during the drought (2001–2002). In all surveys, S. cynosuroides densities decreased at a location that corresponded to where average high tide salinities were > 14 psu, such that the downstream border shifted from approximately 3 to 6 km from the mouth of the river between 2000 and 2002 and then back to 3 km in 2004. Although the peak density of S. alterniflora also shifted upstream between 2000 and 2002, upstream densities were high in 2004 and plant distribution did not correspond with salinity. In the removal experiment, densities and relative % cover of S. alterniflora increased in all treatments (including controls), whereas densities of S. cynosuroides remained relatively constant except in treatments where it was purposely removed. We interpret these results to suggest that S. alterniflora is a strong invader that can expand into new habitat under stressful (increased salinity, low flow) conditions, and that once it is established it can co-exist with S. cynosuroides. The more rapid response of S. cynosuroides (shifts occurred within 2 years) suggests that its downstream limit is a potential indicator of changes in inflow conditions in this system.