Specific Research Question 1: Does the [allochthonous and
autochthonous] supply of DOM and "floc" to the oligohaline ecotone vary
seasonally, and how do hydrological, ecological, and climatological
processes interact to control this supply?
Approach - The dynamics of "floc" and DOM will be investigated
along the SRS transect, where we expect freshwater flow rates to
increase during FCE II, and along the TS/Ph transect, where we expect
that water residence time plays a strong role in ecotone dynamics. We
will collect samples bimonthly at several sites along both transects,
emphasizing the ecotone regions. Bulk DOM, "floc", and SPOM will be
collected and analyzed using biomass-specific biomarkers and stable
isotope determinations (for SPOM = Hernandez et al. 2001; Mead 2003;
Mead et al. 2005) and optical and chemical properties (for DOM = Lu et
al. 2003; Jaffé et al. 2004; Scully et al. 2004; Maie et al. 2005,
2006c). We will estimate seasonal variation in the allochthonous OM
input to each ecotone from bimonthly samples collected at end-member
sites (SRS-2 and 6; TS/Ph-3 and 9) and from offshore of both estuaries.
This approach will allow the application of a three-end-member mixing
model (freshwater marsh-oligohaline ecotone-outer estuary/marine, as
per Jaffé et al. 2001) using biomass-specific biomarkers, namely C20
and C25 highly branched isoprenoids from periphyton and marine diatoms
respectively (Neto et al. 2005; Xu et al. 2006a; Hajje & Jaffé
2006; Saunders et al. 2006) and taraxerol for mangroves (Xu et al.
2006b; Rushdi et al. 2006). We will calibrate biomass-specific
molecular markers for quantitative assessment of the contribution of
each end-member source. We will also attempt to identify a molecular
marker specific for the oligohaline ecotone planktonic component
(possibly unsaturated C17 n-alkanes or pigments). We will continue to
characterize DOM seasonally using optical properties, primarily through
fluorescence-based excitation emission matrices (EEMs; Maie et al.
2006b,c) in conjunction with PARAFAC (Stedmon & Markager 2005),
while DOM quality will also be assessed through chemical analyses
(total hydrolysable amino acids and carbohydrates).
Specific Research Question 2: Are the chemical characteristics and
quality of DOM leaching from soils discernible from groundwater DOM
sources, and [if so] what is the relative contribution of each source to
surface water in the oligohaline ecotone?
Approach - We will characterize DOM from groundwater samples
collected seasonally along both FCE transects, with particular emphasis
on the ecotone regions. Samples will be analyzed as above (Specific
Research Question 5-1) and a subset of samples of the high molecular
weight components (UDOM, >1000 Dalton) will be run through more
advanced techniques including 13C-NMR (carbon composition; Maie et al.
2005; Fig. 2-23) and 14C dating (age) for their characterization. We
will also quantify and characterize DOM inputs via rainwater. In
addition, microcosm experiments will be set up during both wet and dry
seasons using Plexiglas enclosures placed around vegetation
characteristic of freshwater marsh and mangrove sites. Water within the
enclosures (24 hr. experiments) will be recycled through activated
carbon filters during several hours at night to remove as much existing
DOM as possible (we have used this method successfully in seagrass
beds). The DOM within the enclosures must come from one of 3 primary
sources: 1) exudation by the plants (=”new” DOM); 2) leaching from the
soils (=”old” DOM), or; 3) groundwater discharge. We will sample this
DOM throughout the day for bulk characterization, and at the beginning
and the end of the experiment for UDOM characterization (Maie et al.
2005) and DOM bioavailability (Boyer et al. 2006). We will continue to
calibrate and will use geochemical proxies of DOM characteristics to
distinguish plant derived DOM from DOM in groundwater inputs or from
soil leaching (Maie et al. 2006a; Maie et al. 2006c; Fig. 2-23). We
performed a number of biomass leaching experiments during FCE I (Davis
et al. 2003b; Davis & Childers in review; Davis et al. 2006; Maie
et al. 2006b), and will continue them, with particular emphasis on soil
leaching. We will also continue to study the photo-degradation of
Everglades DOM (Scully et al. 2004; Maie et al. 2006b). Our continued
molecular characterization of soil and “floc” will include improvements
to our molecular methods for paleoenvironmental studies (Xu et al.
2006a; Saunders et al. 2006).
Specific Research Question 3: How are soil dynamics (nutrient and OM
content, peat accumulation, sedimentation) in the oligohaline ecotone
controlled by water source and hydrologic residence time?
Approach - In south Florida wetlands, the processing and
accumulation of soil organic matter is a function of many processes,
including soil P availability, the amount of reduced sulfur (S)
compounds, and the availability of reactive iron (as it influences both
P and S cycles in carbonate soils; Chambers et al. 2001). We will
continue to quantify the bulk properties of soils and sediments from
the 14 FCE II sites annually (organic matter, bulk density, and forms
of P, S, and iron; Chambers & Pederson 2006). We will also quantify
wetland soil responses to the long-term interaction of nutrients,
belowground production, storm deposition, and sea-level rise by
measuring changes in soil elevation at our ecotone and freshwater marsh
sites using SETs through continued collaborations with T.Smith (USGS;
SRS-4, 5, & 6; see Appendix 1) and C.Coronado-Molina (SFWMD;
TS/Ph-6 & 7; Childers et al. 1993b, Whelan et al. 2005) and using
soil elevation pins at our other wetland sites (Reed 1992). In
addition, molecular parameters such as biomass-specific lipid
biomarkers and other geochemical proxies will be applied in
paleoenvironmental assessments along the FCE transects.