John Cheeseman, Mat Wooller, Marilyn Twin Cayes |
Twin Cayes
were originally preserved for scientific research, but with time, local
fishermen built small enclaves with shacks, outhouses, and rickety docks on
several areas. In general, our field sites were kept safe from interference by
others, including tourists, but we were required to find remote areas of the
islands to set up more permanent experimental plots.
Feller and her colleagues had three
areas that they established in 1995 at The Dock, Boa Flats, and The Lair. At
each of these sites, a transect between mangrove trees growing at the fringe of
the island through a transition zone at higher tide level and ending in an
interior region was established. Trees at each zone (i.e, fringe, transition,
and interior) were marked with plastic flagging. The experimental design
included three treatments: control where nothing was done, nitrogen fertilization, and phosphorus
fertilization. Twice per year, Feller and colleagues traveled to Twin Cayes to
fertilize the trees, collected leaf samples for isotope analysis, and measured
the trees’ productivity and other biological parameters.
My first collecting expedition included
Matthew Wooller, postdoctoral fellow at Geophysical Laboratory. Wooller joined
my lab group after completing his Ph.D. at the University of Swansea in Wales.
Mat, a British citizen, has a devilish sense of humor. His language is peppered
with British slang and off-color phrases. We were joined by Myrna Jacobson and
her postdoc Barbara Smallwood. Myrna, now at the University of Southern
California, was a fountain of ideas, sometimes coming out in torrents of words
with a slightly quirky bent to them. Accustomed to field work, her expertise in
geochemistry provided a foil to our biogeochemistry. Babs Smallwood, also a
recent Ph.D. from Great Britain, was a novice in the field.
My task in this project was to collect
the leaves, stems, and roots from different species of mangroves, decaying
mangrove biomass (detritus), surface mud (sediment), seagrasses, particulate
organic matter (small bits of decaying leaves, some bacteria, and
phytoplankton), and any animals we could catch. In the lab in Washington, we
were to measure the stable isotope composition of carbon and nitrogen of each
of these organic matter groups, as well as the amount of carbon and nitrogen in
each type of sample. The data was to be used in a theoretical model crafted by
Bob Ulanowicz and Ursula Scharler of the Univ. of Maryland. The model was
designed using our data in order to connect the branches of possible food webs
and for determining nutrient flows in the fringe, transition, and dwarf
mangrove ecosystem zones. The model would also quantity how fertilization
affected the mangrove ecosytem. This seemed like a very straight-forward task.
Mangroves are trees using a type of carbon fixation in photosynthesis similar
to terrestrial trees. We expected them to show similar patterns in carbon
cycling as terrestrial plants. Twin Cayes were small islands. We figured there
would be very small variations in nitrogen cycling as well.
Wooller and
I planned to collect the above samples across the Cayes at locations laid out
on a grid--every 100 meters. We came armed with GPS coordinates, a couple older
GPS units, and a lot of sample bags and tubes. Jacobson, on the other hand,
shipped a portable gas chromatograph for measuring gases evolving from
sediments. The instrument was held up in customs so the USC team had to cool
their heals for several days. Also, the instrument required a clean source of
helium to operate; there was no helium of suitable purity in the entire
country--they were stuck. Because of they lacked the right equipment for their
work, Jacobson and Smallwood joined our efforts. We became a team.
Adventures awaited us at nearly every
“station” that we occupied. The locations of Feller’s experimental transects
were readily accessible, once you climbed over some serious mangrove roots and
waded maybe 10 meters onshore. Our grid stations provided greater challenges.
GPS units in 1999 were not as accurate as they are today. Under the mangrove
canopies, we often lost signals and had to approximate our location. Climbing
over mangrove roots is a learned skill. Wearing rubber dive booties and loaded
down with sampling gear, we balanced carefully on flat sections of roots, while
keeping our eyes out for tree crabs and boa constrictors.
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