On April 20, 2010, the Deepwater Horizon oil rig exploded, spewing the first of what would be an estimated 170 million gallons of oil into the Gulf of Mexico. Additionally, workers applied almost 2 million gallons of dispersants, both on the surface and injected into the oil plume, in an effort to make the cleanup activities easier. One year later, the ecological effects of oil and dispersants are still largely unknown.

British Petroleum (BP), owner of the oil rig, has stated, without supporting data, that the damage was less than expected and that Gulf ecosystems will fully recover by 2012. It also backed out of several restoration projects, including efforts to restore wetlands and oyster beds in Louisiana. The reality is that little scientific data is available on the spill's true impact or how well the Gulf area can recover — with or without help. Research is ongoing and will last for years.

The National Oceanic and Atmospheric Administration also continues to work with federal and state agencies to assess damage and determine appropriate restoration activities. It has even requested public comment and ideas.

The spill's effect on bacterial populations

A team of researchers led by Yuriy Fofanov of the University of Houston sampled water and beach soil in Gulfport, Miss., and Grand Isle, La., before and after the oil arrived. By sequencing the DNA in those samples, the the researchers were able to identify bacterial populations and note how they changed.

Populations of several pathogenic organisms, including Rickettsiales species and Vibrio cholera, spiked after oil arrived. Levels of Synechococus, a photosynthesizer important to the marine food web, dropped significantly. The bacterial distribution did not recover during the study period.

The work is preliminary, and no data exists regarding the current condition of the Gulf's microbial community, but according to Fofanov's team, "abrupt and severe changes in the microbial metabolism can produce long-term effects on the entire ecosystem."

The Gulf oil spill's effect on wildlife

A study published in Conservation Letters on March 30, 2011, suggests that the number of animal carcasses recovered after the spill does not provide an accurate estimate of the true death toll. The researchers argue that many animals will die away from shore and that their carcasses will never be found.

Scientists looked at cetacean (marine mammals, including whales and dolphins) populations and compared recent historical estimated annual mortality and carcass recovery rates. Their calculations suggest that the number of carcasses recovered may underestimate the number of deaths by as much as a factor of 50.

The National Wildlife Federation has published animated maps, using data from the National Oceanic and Atmospheric Administration and the U.S. Fish and Wildlife Service, showing where and when animals were dying as the oil spread. Animal deaths appear to correlate with the advance of the oil, and many of the animals collected showed visible signs of oil exposure.

The organization also suggests that egg and larval stages of some organisms could have been severely impacted or even completely destroyed. If true, this could have long-lasting effects on the food web in the Gulf.

The effects of dispersants used

Questions also remain about the environmental effects of injecting large quantities of dispersant into deep water, which was done for the first time during this spill. A team led by Elizabeth B. Kujawinski of Woods Hole Oceanographic Institution has attempted to find some answers.

In a report published in Environmental Science & Technology, she and her researchers describe how they analyzed the distribution of the injected dispersant. They focused on one ingredient, an anionic surfactant called dioctyl sodium sulfosuccinate (DOSS), and measured its levels both while oil was flowing and after the well had been plugged.

The material did appear to mix with the oil as intended, but it was not clear if it broke up the oil. In addition, the DOSS had not degraded two months after oil flow stopped. If the material persists in the environment, it raises still more questions about its long-term impacts.

One year after Gulf oil spill, scientists, the government and residents have more questions than answers. The Gulf has not recovered, and we don't know when it will or how it may have permanently changed. What we do know is that scientists will be working to answer these questions for many years to come.