Chris Ross wrote:
>
> Hi all,
>
> regarding my post about the light diesel, I didn't mean to imply it was
> harmless. I just wanted to point out that it was a hell of a lot less
> of a problem than heavy fuel oil which other posts had suggested was
> spilt, as it disperses and evaporates far more quickly, so it is a
> hazard to wildlife for less time. Once it disperses it is quickly
> consumed by naturally occurring bacteria. Heavy Fuel oil will coat
> every bird, rock, beach etc. that it touches with a thick sticky goo.
> Wildlife would not like swimming through a slick of either product.
Following on the subject of the impact of diesel, some BOzzers may recall a New
Scientist Item 6 weeks ago, which looked at the impact of a spill in the
Galapagos Islands ...
http://www.newscientist.com/news/news.jsp?id=ns99992372
Galapagos oil spill devastated marine iguanas
19:0005June02
Over 60 percent of the marine iguanas on a closely studied Galapagos Island were
killed within months of relatively small oil spill in 2001.
The tanker Jessica ran aground on San Cristobal Island on 17 January. But the
weather and ocean currents quickly dispersed most of the three million litres of
diesel and bunker oil, suggesting a limited impact on the islands' famous
wildlife.
Only a few marine animals died immediately after the spill but, by December, 62
per cent of the marine iguanas on nearby Santa Fe Island had perished. In a
normal year, only 2 to 7 percent mortality is expected.
The good news is that Galapagos marine iguanas are not endangered, Martin
Wikelski of Princeton University told New Scientist. But the bad news is that
"even very low levels of contamination can affect animals a lot". He warns that
the potential dangers of even small spills raises the risk of drilling in such
sensitive environments the Arctic National Wildlife Refuge in Alaska - currently
under consideration in the US.
Fermentation bacteria
Wikelski has studied Galapagos marine iguanas since 1987, tracing their life
history in an area little affected by humans. He saw no fatalities immediately
after the spill and the algae on which they feed appeared healthy.
However, he did find elevated levels of stress hormones just after the spill in
iguanas on Santa Fe Island, where about one litre of oil washed ashore per metre
of beach. The number of iguanas remained unchanged on the smaller Genovesa
island, which was unaffected by the spill.
The discovery of dead iguanas with stomachs full of algae shows food was
available and that the animals could eat. He believes the oil had killed
fermentation bacteria in their hindguts that normally break down algal cell
walls so iguanas can digest their food. Without the symbionts, Wikelski told New
Scientist, they "couldn't digest it so they couldn't get the nutrients out."
Legal action
The Galapagos spill was not severe by oil-industry standards. Diesel fuel
evaporates quickly and is far less toxic than the crude oil spilled in the Exxon
Valdez accident in Alaska. Contamination in the Galapagos was orders of
magnitude lower than on the worst oiled beaches in Prince William Sound.
Nonetheless, the spill took a heavy toll on the iguanas. It also interrupted
Wikelski's long-term research project, before the males he had marked in 1987
had become breeders with their own territories.
Dismayed at the loss, he has joined with the Galapagos National Park to sue the
tanker's owner, Petroecuador, for $600,000 in damages. Meanwhile, park
authorities are overhauling methods of oil delivery to the islands.
Journal reference: Nature (vol 417, p 607)
Jeff Hecht
***
An environmental scientist I know commented that to him the article highlighted
the myth that the lighter oil fractions were less toxic than the heavier
fractions [that persist visibly and cause bird fouling etc]. He noted that the
lighter fractions were more water soluble and that this dissolved petroleum is
bioavailable and hence poisons aquatic animals that come into contact with it.
Apparently, the new ANZECC Water Quality Guidelines make this point "in the
small print deep within the guideline documents". Similarly petroleum industry
publications dealing with the hazards associated with oil spills apparently
acknowledge that "as much as 50% of spilt oil actually dissolves in the water
column, and it is that portion which does the most damage."
The bottom line is that it can take a while for the impact of an oil spill to
become apparent.
Regards, Laurie.
Birding-Aus is on the Web at
www.shc.melb.catholic.edu.au/home/birding/index.html
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