Today we met in the Hotel Baluarte restaurant for breakfast again to strategize for our field trip to Isla Arenas. Our same team will make this trek, except for Otto, who needed to stay back and attend to academic affairs. We will also have a representative from the Biosphere Reserve going along with us.
The target area for today is the large mangrove swamp that extends over 100 miles to the north of Campeche, Campeche, all the way to Celestun, Yucatan. It is an amazingly large swamp that is fed by springs to give the brackish salinity gradient necessary. There are no surface rivers in the northern part of the Yucatan Peninsula, but there are many underground rivers that come to the surface in this area via springs both on the land and on the adjacent continental shelf.
This area is such a special natural area that it has been declared a biosphere reserve, the Reserva de la Biosfera de la Ria de Celestun, in the northern portion.
It is about a two hour drive from Campeche to Isla Arenas, first on the Campeche to Merida highway and then on a road that gets decreasingly smaller as you head from Calkini to Isla Arenas towards the coast. It is only one lane for the last 15 or so miles that go through the swamp.
My reason for wanting to visit this area, one that I have never been to before, because the road was only built less than ten years ago (after the time I lived here in the mid 1980s), are multifold. First, I have always been curious about the area and its vastness and the lack of study there, and I was almost certain that Ixtoc oil had gone in there 30 years ago. Julio Sanchez had confirmed this a few weeks ago when I talked to him and he went to the area and confirmed it with fishermen at Isla Arenas. The fishermen related that the mangrove oysters that were common before the spill had never come back, so that was very interesting and curious also. Lastly, the area is the tropical equivalent to the Mississippi Delta salt marshes that are now being impacted by the big BP spill, so a visit here might give us some information about the future for them.
The last mile or so to Isla Arenas is across a bridge into the little fishing village with no paved streets, only sand. After buying some expensive gasoline for a "charter panga" we climbed on board and headed southward for the extensive shoreline mangroves. The first stop did not reveal anything, and a trip up a side channel into the swamp was uneventful also. However, on our third stop..."bingo", we found tar. It was not heavy, and it was very degraded, so we cannot be certain that it was Ixtoc until analysis is completed, but we did find some. Large red mangroves with their distinctive prop roots line the outer margin of the swamp facing the Gulf of Mexico. Behind the red mangroves, which live in the subtidal fringe (edge of the water), are black mangroves with their distinctive pneumataphores. These are air roots that extend upwards in the intertidal zone where they live, instead of down into the mud where the sediment is anoxic.
The first evidence was what appeared to be dark brown pieces of humus on the sediment ridge just behind the black mangroves. Later we found a thin layer of what appeared to be tar, but it too looked like humus. Then at the edge between the red and black mangrove at low tide we found a layer of tar about 3/4 inch thick that still had a slight sheen when broken open and a slight smell of petroleum.
Without considerable sampling, I cannot say for sure, but it appears to me that this outer band of red and black mangroves were impacted by Ixtoc, or another spill sometime years ago, and that the remnant tar is almost completely degraded or weathered away today. There are some mangroves that appear dense in growth and normal, but there are some areas where the vegetative cover of mangroves is not as dense as it should be. This could be from effects of the tar. The small amount that we found was thin and had mangrove roots growing below and adjacent to it. A rough estimate on this short visit looks to me like about 80% recovery from the impact. Analysis by Gerardo Gold at CINVESTAV will later determine the true origin.
We did not find any mangrove oysters growing in the three areas that we visited, and the fishermen confirmed that they still do not see any. An old fisherman we spoke to said that he knew where some were, but he was not telling anyone. They tasted fine when you ate them, but then after digestion started, he got an oily tasting burp?
After our boat trip, we had some fish tacos in an open air beach restaurant facing the Gulf. I headed back to Merida, Julio went back to Campeche, and the writing team hung around for more stories with the fishermen regarding Ixtoc. Tomorrow, I will check out the Celestun area west of Merida, if the developing tropical system doesn't hinder our field trip.
No comments:
Post a Comment