Chemical characteristics of dissolved organic matter in an oligotrophic subtropical wetland/estuarine ecosystem
Fluorescence properties of whole water samples and molecular characteristics of ultrafiltrated dissolved organic matter (UDOM 1,000 D) such as lignin phenol and neutral sugar compositions and 13 C nuclear magnetic resonance (NMR) spectra were determined along a freshwater to marine gradient in Everglades National Park. Furthermore, UDOM samples were categorized by hierarchical cluster analysis based on their pyrolysis gas chromatography/mass spectrometry products. Fluorescence properties suggest that autochthonous DOM leached/exuded from biomass is quantitatively important in this system. 13 C NMR spectra showed that UDOM from the oligotrophic Taylor Slough (TS) and Florida Bay (FB) ecosystems has low aromatic C (13% 3% for TS; 2% 2% for FB) and very high O-alkyl C (54% 4% for TS; 75% 4% for FB) concentrations. High O-alkyl C concentrations in FB suggest seagrass/phytoplankton communities as dominant sources of UDOM. The amount of neutral sugars was not appre-ciably different between the TS and FB sites (115 12 mg C g C 1 UDOM) but their concentrations suggest a low level of diagenesis and high production rates of this material in this oligotrophic environment. Total yield of lignin phenols (vanillyl syringyl phenols) in TS was low (0.20–0.39 mg 100 mg C 1 UDOM) compared with other riverine environments and even lower in FB (0.04–0.07 mg 100 mg C 1 UDOM) and could be a result of photodegradation and/or dilution by other autochthonous DOM. The high O-alkyl and low aromatic nature of this UDOM suggests significant biogenic inputs (as compared with soils) and limited bioavailability in this ecosystem. The Everglades, located in the southern part of the Florida Peninsula, is a unique oligotrophic ecosystem and is one of the largest subtropical wetlands in the world. The most cru-cial factor that makes the Southern Everglades (Everglades National Park; ENP) so unique is the limited source of nu-trients (particularly phosphorus), which depends mostly on dry and wet depositions, while most other wetland and es-tuarine systems depend on riverine nutrient inputs (Davis 1994). In addition, because the base rock of the Florida Pen-insula is calcareous, there is almost no supply of phospho-rous from its weathering products (Noe et al. 2001). As a result, microbial activities in ENP are controlled by the lim-ited availability of nutrients (Amador and Jones 1993; Four-qurean et al. 1993).