How Anthropogenic Activities Impacted Polecat Bay Near Mobile, Alabama, Usa: A Paleoecological Study And Forensic Investigation

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 similar to 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.