Changes in chemical and isotopic signatures of plant materials during degradation: Implication for assessing various organic inputs in estuarine systems

Abstract

[1] To evaluate applicability of the end-member mixing model in assessment of input and transport of organic carbon in estuarine systems, we incubated marine diatom, land grass, and salt marsh plant in Altamaha estuarine water for two months. Chemical and isotopic parameters (bulk organic carbon/nitrogen contents, lipid compositions, stable C/N isotopes, and lipid stable carbon isotopic ratios) were analyzed for fresh and degraded materials. The results showed that although the C/N and d 15 N ratios of three materials varied similarly during degradation, the bulk d 13 C, lipid compositions, and lipid stable carbon isotopic compositions varied differently from material to material and from compound to compound, implying that applications of the end-member model should consider the diagenetic status of organic materials and the potential changes in chemical and isotopic signatures.

Distribution and lability of land-derived organic matter in the surface sediments of the Rhône prodelta and the adjacent shelf (Mediterranean Sea, France): a multi proxy study

“…14:0 and 16:0) are contributed by all organic matter sources and have distinct δ 13 C signatures from source to source (Canuel et al, 1997;Dai et al, 2005). The positive shift in δ 13 C of non-specific fatty acids along the transect reflects a variation in relative proportions of marine vs. terrestrial organic matter, and is consistent with those from our other molecular proxies.…”

“…Nonetheless, the isotopic signature of these fatty acids was in the range of values previously reported for LCFA of terrestrial origin (−35 ‰ to −30 ‰, Shi et al, 2001). Since they are abundant in terrestrial plants, the occurrence of 18:2ω6 and 18:3ω3 is often considered as another indicator of terrestrial OM in coastal environments (Dai et al, 2005). However, these compounds are rapidly lost as plant tissues are decomposed (Wannigama et al, 1981), resulting in low concentrations in sediments.…”

A laboratory study on biochemical degradation and microbial utilization of organic matter comprising a marine diatom, land grass, and salt marsh plant in estuarine ecosystems

“…The possible reason for larger shifts in molecular d 13 C in the earlier period of incubations is partly due to the fact that bacteria also produce 16:0 fatty acid during their growth by using different source materials with distinct isotopic compositions (Boschker et al 1999). In addition, some studies have observed significant isotopic fractionation of organic compounds during microbial degradation (Meckenstock et al 1999;Sun et al 2004;Dai et al 2005). In the sediment treated with mixed organic materials, the d 13 C values of 16:0 fatty acid gradually approached those of SMP over the course of incubations, implying that 16:0 fatty acid remained in the sediments is likely attributed to SMP.…”

Recent and Historic Drivers of Landscape Change in the Everglades Ridge, Slough, and Tree Island Mosaic

“…Wright et al, 2009). Although decomposition rates are expected to decrease nonlinearly over time as the labile fraction of the floc organic matter pool is preferentially removed (Dai et al, 2005;Wickland et al, 2007), metabolism of a significant fraction of the floc prior to its conversion to peat is likely. Using a mixing model based on δ 13 C signatures, Troxler and Richards (2009) estimated that in sloughs with low periphyton coverage, floc organic matter is 100% Utricularia spp.…”