Early diagenesis of plant‐derived dissolved organic matter along a wetland, mangrove,estuary ecotone

Abstract

We studied the role of photochemical and microbial processes in contributing to the transformation of dissolved organic matter (DOM) derived from various plants that dominate the Florida Everglades. Plant-derived DOM leachate samples were exposed to photochemical and microbial degradation and the optical, chemical, and molecular weight characteristics measured over time. Optical parameters such as the synchronous fluorescence intensity between 270 and 290 nm (Fnpeak I), a strong indicator of protein and/or polyphenol content, decreased exponentially in all plant leachate samples, with microbial decay constants ranging from Ϫ1.0 d Ϫ1 for seagrass to Ϫ0.11] ϭ 0.7-6.3 d). Similar decreases in polyphenol content and dissolved organic carbon (DOC) concentration also occurred but were generally an order of magnitude lower or did not change significantly over time. The initial molecular weight composition was reflected in the rate of Fnpeak I decay and suggests that plantderived DOM with a large proportion of high molecular weight structures, such as seagrass derived DOM, contain high concentrations of easily microbially degradable proteinaceous components. For samples exposed to extended simulated solar radiation, polyphenol and Fnpeak I photochemical decay constants were on average Ϫ0.7 d Ϫ1 (t 1/2 1.0 d). Our data suggest that polyphenol structures of plant-derived DOM are particularly sensitive to photolysis, whereas high molecular weight protein-like structures are degraded primarily through physical-chemical and microbial processes. Furthermore, microbial and physical processes initiated the formation of recalcitrant, highly colored high molecular weight polymeric structures in mangrove-derived DOM. Thus, partial, biogeochemical transformation of plant-derived DOM from coastal areas is rapid and is likely to influence carbon and nutrient cycling, especially in areas dominated by seagrass and mangrove forests.Dissolved organic matter (DOM) plays a pivotal role in the ecological structure of aquatic ecosystems (Hessen and Tranvik 1998;Findlay and Sinsabaugh 2003). The presence of DOM can influence microbial growth, light penetration, the complexation of metals, and the availability of nutrients

Saltmarshes as a source of chromophoric dissolved organic matter (CDOM) to Southern California coastal waters

“…8), with a significant blue shift in the T peak emission maximum for this species only (Table 2). This variability might be due to the rapid transformation of photochemically active polyphenols, as previously shown for mangrove plant leachates (Scully et al 2004); polyphenols have similar fluorescence characteristics to the T and B peaks. The marine (M) and Fig.…”

“…Senescent plant samples were washed with deionized water and placed in 2.0-liter glass flasks containing a 0.1% sodium azide (NaN 3 ) solution (Fisher Scientific) to kill bacteria. The addition of NaN 3 has been shown to initiate the formation of color and polymerization reactions (Scully et al 2004). We monitored the rate of fluorescence decay on specific EEM peaks from the initial solution, which should not be affected.…”

Tracing the production and degradation of autochthonous fractions of dissolved organic matter by fluorescence analysis

“…Because of the relatively simple design of the experiment, we cannot at present show exactly which processes are responsible. However, it is possible that reactions with products of primary photochemical processes and photoinduced flocculation are responsible (Scully et al 2004). This illustrates the potential that secondary reactions have to influence the DOM pool as a whole, not just the CDOM.…”

Atmospheric deposition as a source of carbon and nutrients to an alpine catchment of the Colorado Rocky Mountains

“…Molecular weight averages and polydispersity were calculated from the sample chromatograms between retention times of 14-25 min according to Maie et al (2004) using standards of polystyrene (MW = 1400, 4300, 6800, 13 000, 36 000 Da), blue dextran, and glycine. Average molecular weight values presented here serve as a guide along the MW continuum and are not actual values (e.g., Scully et al, 2004).…”