In Phase II of the FCE-LTER project, scientists are studying the accumulation of
organic matter in
the estuarine ecotones. Organic matter, which can occur in surface waters in the form of dissolved
organic matter (DOM) or in clumps known as floc, is an important component of ecosystems, providing
nutrients to microbial communities, plants and animals, thus increasing their productivity. In the
estuarine ecotones, organic matter can be produced locally, or it can be delivered by upstream
freshwater, through groundwater exchange, and from coastal sources through tidal action. Estimating
the contributions of each of these and their ecological effects is a big challenge during Phase ll.
In Phase I, researchers found that the balance of organic matter transport and internal production
appears to differ between the two ecotone regions. In Phase II, they are investigating whether these
differences are due to seasonal variations. They also expect to examine the effects of increased
freshwater flow resulting from restoration projects on patterns of organic matter. They believe that
organic matter will increase in concentration and its quality will change when freshwater inflow
increases, and that, combined with the elevated levels of phosphorus that occur in the ecotones,
will provide the necessary nutrients to promote productivity in the region.
The biogeochemistry of iron, sulfur and phosphorus is tied closely to the cycling and preservation
of organic matter in soils and sediments. In Phase I. researchers established a baseline context of
soil biogeochemical properties for spatial comparisons among FCE-LTER sites/transects, against which
"push-press" changes in the Everglades-mangrove-Florida Bay system can be documented during FCE-II.
Mangrove soils in the estuarine ecotones tend to have higher concentrations of organic matter,
extractable iron, total sulfur and total phosphorus than do soils from either the freshwater
(Everglades) or saltwater (Florida Bay) end-members along TS/Ph and SRS transects. This effect is
much more pronounced along the SRS transect and may be exacerbated with projected increases in
freshwater inflow.
Finally, researchers are investigating the importance of organic matter in groundwater, as this
water intrudes into surface water through crevices in the limestone bedrock. They want to know if
this organic matter is of sufficient quality, in terms of nutrient content, to promote productivity
in the region. They are comparing the quality of groundwater DOM with soil- and plant-derived DOM
and their relationship to the composition of surface water DOM.
How do these factors affect people in south Florida?
The distribution and amounts of historically low levels of phosphorus and other chemicals in
Everglades soils are changed not only by agricultural runoff and by water management decisions
(human activities), but also by factors like hurricanes and sea level rise. The long-term structure
of the Everglades Ecosystem and the services it provides as the largest freshwater wetland in the
U.S. help to maintain the environment and the economy of south Florida. FCE research details how the
Everglades ecosystem responds to factors that might alter its ability to continue providing those
services.
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Oliva collecting a water sample in Shark River
Randy Chambers taking a soil core
Soil cores
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