The Gulf of Mexico is the dominant source of P to our SRS ecotone sites while the freshwater Everglades is the dominant source of N to both ecotone regions. Inputs of relatively high P groundwater may also be important to nutrient dynamics and belowground productivity, particularly during the dry season. Long water residence times during this period would enhance this importance. Our biogeochemical work will continue to focus on quantifying the content of surface waters influencing both ecotone regions. In FCE II, we will expand this focus to also quantify groundwater nutrient to each other and are controlled by autochthonous versus allochthonous nutrient sources.
One specific research question being asked is: What are the mechanisms by which P availability acts to regulate N cycling rates in marshes and mangroves of the southern Everglades? We are investigating this coupling by examining changes in potential rates of nitrification, denitrification, and N2 fixation following P additions to soils, "floc", and periphyton from key oligohaline ecotone sites. Specifically, we expect that nitrification and denitrification potentials will be highest in soils while N-fixation potential will be highest in periphyton. We also expect that higher P availability and high salinity will stimulate N cycling rates more in the dry season compared to the wet season.
The second research question being asked is: How is the soil bacterial community influenced by temporal changes in water source in the oligohaline ecotone, and how are these community shifts reflected in ecosystem processes, such as those of the N cycle? We are addressing this question by characterizing the bacterial communities present in the SRS and TS/Ph sites using a metagenomic approach. In addition, we are characterizing the microbial community of floc in an effort to determine its decomposition and contribution to nutrient cycling in the ecotone.