Florida Coastal Everglades Long Term Ecological Research
Untitled Document


Organic Matter Dynamics Working Group
(Phase II, 2007-2012)

Hypotheses and Proposed Work for FCE II (2006-2012)

General Question: How are organic matter dynamics (DOM, "floc", and soils) in the oligohaline ecotone controlled by local processes versus allochthonous freshwater, marine, and groundwater sources?

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.

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