Ecosystem recovery at hypersaline salt marsh remediation projects impacted by the Gulf War Oil Spill

ABSTRACT #1141405 The 1990 Gulf War Oil Spill was the largest marine oil spill in history, spilling an estimated 6–11 million barrels of crude oil into the Arabian Gulf and impacting approximately 800 km of shoreline in Saudi Arabia between the border with Kuwait and Abu Ali Island near Jubail. Many intertidal areas were heavily oiled, severely damaging salt marsh ecosystems and facilitating the growth of thick algal mats, which, in turn, created a physical barrier that restricted tidal exchange and prevented recolonization of marsh flora and fauna at these sites. Remediation projects have been ongoing since early 2010 at 19 project areas throughout the area of impact. Remediation activities are focused on refreshing existing or creating new tidal channels to restore hydrology and tilling the substrate to expose moderately oiled sediment and enhance the degradation of oil and break up laminate algal mats. Additional activities include removal of heavily oiled sediments, re-use of excavated unoiled and lightly oiled sediments to create additional topography in restored marshes, and vegetation planting in selected areas. Monitoring plots for long-term study were established at remediation sites, impacted but untreated sites (set-asides), and nearby reference (comparison) sites. Initial monitoring data were collected before and after remediation activities, which were primarily undertaken between 2010 and 2013. Biannual (spring and fall) monitoring was resumed in fall 2018 and will continue through spring 2022 to characterize ecosystem recovery at these sites. Based on results from fall 2018 and spring 2019, most remediation sites show some level of recovery, indicated by the return of annual vegetation and resident marsh invertebrates in lower elevation plots, and thinner algal mat types and insect burrowing activity at the upper elevations. While the lower portions of untreated sites are beginning to show recruitment of annual vegetation and invertebrates (e.g. crabs), thick, laminated algal mat cover occurs in the middle-upper elevations at untreated sites. Multimetric indices (MMIs) summarizing ecosystem health and stressors were developed to summarize recovery of these projects and evaluate progress at remediation sites relative to set-aside and comparison sites. MMI results indicate that remediation work was effective at reducing stressors in remediation sites compared to set-asides; however, the level of ecosystem recovery is variable across sites, in part depending on the time since restoration.