Abstract

Analysis of a 195-cm core extracted from Polecat Bay (PB) in southern Alabama revealed that dramatic changes in diatom abundance/composition and sediment type took place sometime in the past. Examination of historical records and interviews with witnesses to industrial activity suggest that the changes were largely anthropogenically driven and caused by; (1) construction of the Mobile Bay Causeway, (2) spillage of bauxite dross from settling ponds, and (3) discharge of river dredge material directly into the bay. Analysis of the core showed increased clay content in its upper levels followed by an increase in motile benthic diatoms that tolerate turbid water, both likely the result of restricted circulation following construction of the Causeway. Energy-dispersive X-ray spectroscopy results coupled with archival evidence confirmed that between 1938 and 1983, bauxite dross was pumped into settling basins operated by ALCOA on Blakeney Island adjacent to PB, and that it periodically overflowed into the bay. Additional photographic evidence and interviews confirmed that in the late 1950s or early 1960s, the U.S. Army Corps of Engineers began filling ∼70% of PB with dredge material as part of a project to widen and deepen the Mobile River channel. This accelerated the rate of sedimentation and led to additional changes in diatom populations including a decline in non-motile diatoms in the most recent years. Our study demonstrates that impact(s) of human activities on sensitive Gulf Coast environments like PB can be detected through the combination of diatom reconstruction analysis, sedimentology, forensic-style examination of historical reports and witness interviews.

摘要

对从阿拉巴马州南部的北极猫湾（PB）提取的195厘米岩心的分析表明，过去某个时候硅藻的丰度/组成和沉积物类型发生了巨大变化。对历史记录的检查以及对工业活动见证人的采访表明，这些变化很大程度上是人为驱动的，并且是由人为驱动的；（1）建造移动湾堤道，（2）铝土矿渣从沉淀池中溢出，（3）河道疏material物直接排入海湾。对岩心的分析表明，其较高水平的粘土含量增加，随后能容纳混浊水的运动性底栖硅藻增加，这两者都可能是堤道建造后循环受限的结果。能量色散X射线光谱学结果以及档案证据证实，在1938年至1983年之间，铝土矿渣被泵送到ALCOA在靠近PB的布莱克尼岛上的沉降池中，并定期溢出到海湾中。额外的摄影证据和采访证实，在1950年代末或1960年代初，美国陆军工程兵团开始使用疏edge材料填充PB的约70％，作为拓宽和加深Mobile River河道项目的一部分。这加快了沉积速度，并导致硅藻种群的其他变化，包括近年来非活动硅藻的减少。我们的研究表明，通过硅藻重建分析的结合，可以检测出人类活动对敏感的墨西哥湾沿岸环境（如PB）的影响，