Degradation and resilience in Louisiana salt marshes after the BP–Deepwater Horizonoil spill

Abstract

More than 2 y have passed since the BP-Deepwater Horizon oil spill in the Gulf of Mexico, yet we still have little understanding of its ecological impacts. Examining effects of this oil spill will generate much-needed insight into how shoreline habitats and the valuable ecological services they provide (e.g., shoreline protection) are affected by and recover from large-scale disturbance. Here we report on not only rapid salt-marsh recovery (high resilience) but also permanent marsh area loss after the BP-Deepwater Horizon oil spill. Field observations, experimental manipulations, and wave-propagation modeling reveal that (i) oil coverage was primarily concentrated on the seaward edge of marshes; (ii) there were thresholds of oil coverage that were associated with severity of salt-marsh damage, with heavy oiling leading to plant mortality; (iii) oil-driven plant death on the edges of these marshes more than doubled rates of shoreline erosion, further driving marsh platform loss that is likely to be permanent; and (iv) after 18 mo, marsh grasses have largely recovered into previously oiled, noneroded areas, and the elevated shoreline retreat rates observed at oiled sites have decreased to levels at reference marsh sites. This paper highlights that heavy oil coverage on the shorelines of Louisiana marshes, already experiencing elevated retreat because of intense human activities, induced a geomorphic feedback that amplified this erosion and thereby set limits to the recovery of otherwise resilient vegetation. It thus warns of the enhanced vulnerability of already degraded marshes to heavy oil coverage and provides a clear example of how multiple human-induced stressors can interact to hasten ecosystem decline.geomorphology | multiple stressor | wetland | human impacts

Facilitation shifts paradigms and can amplify coastal restoration efforts

“…When plants are in close proximity to one another, there is a shared group benefit as oxygen "leaks" from shallow roots into sediments that then becomes available to neighboring plants (41,42). Secondly, grasses planted closely together can mitigate erosion stress generated by waves or high currents (43,44). This facilitative interaction occurs because belowground plant material on the edge of marsh culms or established marshes absorbs most of the wave and/or current stress and thus reduces erosion around more interior marsh plants (43,44).…”

“…Secondly, grasses planted closely together can mitigate erosion stress generated by waves or high currents (43,44). This facilitative interaction occurs because belowground plant material on the edge of marsh culms or established marshes absorbs most of the wave and/or current stress and thus reduces erosion around more interior marsh plants (43,44).…”

Marsh Loss Due to Cumulative Impacts of Hurricane Isaac and the Deepwater Horizon Oil Spill in Louisiana

“…In addition, hydrologic changes in the MDP in recent decades reduced sediment supply because of damming of the Mississippi River [9]. Freshwater wetlands experienced high rates of mortality due to saltwater intrusion after construction of deep navigational channels into the delta, and coastal wetlands have experienced direct loss due to dredging for pipelines [8,[10][11][12], oil extraction and spills [13,14]. Moreover, the MDP is in the path of many hurricanes, further reducing coastal wetland persistence.…”

“…Hurricane impact on plant ecosystems has also been frequently mapped using remote sensing [33]. The Deepwater Horizon (DWH) oil spill in the Gulf of Mexico, the biggest coastal oil spill in U.S. history [34], severely impacted wetland vegetation, especially along the contaminated shoreline [13,31,32,[35][36][37]. Vegetation die-off and an increase in plant stress were observed in the intertidal marshes up to 43 m inland from the shore [30,31,38,39].…”

Community response of deep-sea soft-sediment metazoan meiofauna to the Deepwater Horizon blowout and oil spill

“…These estuarine and shallow-water coastal investigations have documented impacts to salt marshes and associated communities (McCall & Pennings 2012, Silliman et al 2012, and benthic microbial and eukaryote communities (Kostka et al 2011, Bik et al 2012, Lu et al 2012, Mason et al 2012, and there has been extensive reporting of water-column microbial response to the DWH-derived hydrocarbons (Kessler et al 2011, Valentine et al 2014. However, few studies to date have documented deep-sea benthic impacts of the DWH oil spill (White et al 2012, Montagna et al 2013, Fisher et al 2014.…”