Organic Biogeochemistry of Detrital Flocculent Material (Floc) in a Subtropical, Coastal Wetland

Abstract

Flocculent materials (floc), in aquatic systems usually consist of a non-consolidated layer of biogenic, detrital material relatively rich in organic matter which represents an important foodweb component for invertebrates and fish. Thus, variations in its composition could impact food webs and change faunal structure. Transport, remineralization rates and deposition of floc may also be important factors in soil/sediment formation. In spite of its relevance and sensitivity to external factors, few chemical studies have been carried out on the biogeochemistry of floc material. In this study, we focused on the molecular characterization of the flocculent organic matter (OM), the assessment of its origin and its environmental fate at five stations along a freshwater to marine ecotone, namely the Taylor Slough, Everglades National Park (ENP), Florida. To tackle this issue, suspended, unconsolidated, detrital floc samples, soils/sediments and plants were analyzed for bulk properties, biomarkers and pigments. Both geochemical proxies and biomass-specific biomarkers were used to assess OM sources and transformations. Our results show that the detrital organic matter of the flocculent material is largely regulated by local vegetation inputs, ranging from periphyton, emergent and submerged plants and terrestrial plants such as mangroves, with molecular evidence of different degrees of diagenetic reworking, including fungal activity. Evidence is presented for both hydrodynamic transport of floc materials, and incorporation of floc OM into soils/sediments. However, some molecular parameters showed a decoupling between floc and underlying soil/sediment OM, suggesting that physical transport, incorporation and degradation/ remineralization of OM in floc may be controlled by a combination of a variety of complex biogeochemical variables including hydrodynamic transport, hydroperiod characteristics, primary productivity, nutrient availability, and OM quality among others. Further investigations are needed to better understand the ecological role of floc in freshwater and coastal wetlands.

Fatty acids and stable isotopes as indicators of early-life feeding and potential maternal resource dependency in the bull shark Carcharhinus leucas

“…Fatty acids in shark muscle tissue were not sufficient to distinguish between freshwater/estuarine versus seagrass-based food sources, as demonstrated by the similarity in fatty acid composition among group ii sharks, despite the substantial range of δ 13 C. Typical markers for terrestrial organic matter in freshwater/estuarine environments, such as longchain saturated fatty acids characteristic of vascular plant debris (Eglinton & Hamilton 1967) or 18:3ω3 indicative of cyanobacterial inputs to the abundant periphyton in the freshwater prairies of the Everglades (Neto et al 2006), were either absent or only present in trace levels in shark muscle tissue. Whether this absence reflects a lack of feeding on food sources that use vascular plant debris or periphyton as basal resources, or, alternatively, that inputs from these sources are not accumulating up the food chain to high trophic level consumers remains to be determined.…”

The feeding ecology of penaeid shrimp in tropical lagoon-estuarine systems

“…In the soft bottom estuarine sediments, where the input of organic matter is higher than the re-mineralization rate, benthic animals are stimulated by their activities and by the nutrient cycling decomposition of detritus via bacteria (Neto et al 2006). There are a few examples where specialized interactions exist between benthic animals and bacteria.…”

New perspectives on an iconic landscape from comparative international long‐term ecological research

“…Instead, detrital organic matter (DOM) generated by palatable algae and macrophytes appears to form the base of most Everglades food webs (Williams and Trexler 2006). For this reason, the abundance, movement and fate of dissolved and particulate organic matter (POM) has been an important area of investigation in coastal Everglades research (Neto et al 2006, Xu and Jaffé 2007, Chen et al 2013. Data on the optical properties of DOM in the FCE are now available at unusually large spatial and temporal scales , Chen et al 2013, which led to the development of DOM reactivity proxies to study the degradation of this important OM pool.…”