Legal Issues and Scientific Constraints in the Environmental Assessment of the Deepwater Horizon Oil Spill in Mexico Exclusive Economic Zone (EEZ) in the Gulf of Mexico

Luis A Soto,Alfonso Vázquez-Botello

doi:10.4236/ijg.2013.45b007

Abstract

The largest accidental marine oil spill (4.9 million barrels) in the Gulf of Mexico (GoM) seabed (1600 m) caused by the sinking of the Deepwater Horizon oil rig in 2010, put to the test once again the resilient capacity of the pelagic and benthic realms of this Large Marine Ecosystem. Many are the ecological services provided by its waters (fisheries, tourism, aquaculture and fossil fuel reserves) to neighboring countries (US, Mexico and Cuba). However, the unprecedented volumes of hydrocarbons, gas and chemical dispersants (Corexit) introduced in the system, represent ecological stressors whose deleterious effects are still the subject of civil claims and scientific controversy. Presumably, the short scale effects were confined to the Gulf’s northeastern shallow waters, and the combined actions of weathering, biodegradation, and oil recovery left the system almost under pre-spill conditions. Unfortunately, surface and subsurface oil plumes were detected in the spill aftermath, and their dispersion trajectories threatened Mexico EEZ. Surface oil slicks were detected in the pristine waters of northern Yucatan, while subsurface oil plumes from the Macondo’s well blowout were dangerously advancing southwest towards key fishing grounds in the northwestern GoM. This disaster prompted the Mexican government to implement an ambitious ocean monitoring program adopting a bottom-up approach focused on building a base line for more than 42 physicochemical and biological variables for water, sediment and biota from the continental shelf-slope region of the NW GoM. Technological constraints have precluded systematic observations in the vast Mexican EEZ that could discriminate natural variability and oil seep emissions from antropic disturbances. Therefore, preliminary risk analyses relied on seasonal and historical records. Two years of field observations revealed subtle environmental changes in the studied area attributed to antropic disturbances. Waters maintained oligotrophic conditions and zooplankton and benthic infaunal biomass were also poor. Biomarkers in sediments and biota did not exceed EPA’s benchmarks, and sediment’s fingerprinting (δ13C) indicated marine carbon sources. Geomarkers revealed an active transport from the Mississippi towards the NW GoM of phyllosilicates bearing a weathered oil coating. Consequently, shelf and slope sediment toxicity begins to show an increasing trend in the region. The complexity of hydrocarbons bioaccumulation and biodegradation processes in deep waters of the GoM seems to indicate that meso-and large-scale observations may prove to be essential in understanding the capacity of the GoM to recover its ecological stability.

Highlights

The oil spill caused by the sinking of the Deepwater Horizon Platform (DWH) in the northern Gulf of Mexico (GoM) is unprecedented in the history of catastrophic events in the marine environment in both coastal and deep-waters
In the aftermath of the unfortunate Macondo’s blowout in which nearly 5 million barrels of crude oil were spilled both in deep and surface waters of the northern GoM, a heated debate emerged among experts on the fate and persistence of the hydrocarbons in coastal and deep environments
The severe disruption of the ecological balance absorbed by the GoM due to this massive spill tended to be officially underrated by the contention and emergency procedures implemented during the acute phase of the accident

Summary

Introduction

The oil spill caused by the sinking of the Deepwater Horizon Platform (DWH) in the northern Gulf of Mexico (GoM) is unprecedented in the history of catastrophic events in the marine environment in both coastal and deep-waters. In spite of this environmental emergency, that lasted for more than four months, there was a consensus among experts [5,6,7], that while the expected damage in the coastal zone was not as severe as anticipated, it was recognized that the Corexit dispersant injected near the base of the oil well, promoted the formation of subsurface hydrocarbon plumes, whose dispersion and degradation in the deep sea was enigmatic given our limited knowledge on deep water circulation of the GOM. The present study highlights the most relevant environmental issues related to the Macondo’s oil spill from a Mexican perspective

Background

Main Oceanographic Features in Mexico’s EEZ

Economic Damage Assessment

General Discussion

Conclusions