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Reconstructing past responses of coastal wetlands to climate change contextualizes ongoing and future developments in these globally important ecosystems. The molecular distributions and stable isotope ratios (δ2H and δ13C) of sedimentary plant wax n-alkanes are frequently used to infer past vegetation and hydroclimate changes in wetland systems. However, there is limited modern information available about these compounds in subtropical wetlands. Here we analyzed mature leaves from 30 typical plant species and roots from 6 plant species collected in the Florida Everglades, including tree island plants, freshwater wetland plants, mangroves, and seagrass. The n-alkane abundance (2 to 884 µg/g dry weight), percent of aquatic plants ratio (Paq, 0 to 1), average chain length (ACL23-33, 24.0–30.7), concentration weighted average (CWA) δ2H (−231 to −78‰) and δ13C values (−38.9 to −14.4‰) spanned wide ranges with plant growth habit. Significant differences in n-alkane abundances, Paq, ACL23-33, CWA δ2H and δ13C values were found to exist between the leaves and roots of some emergent aquatic plants. Simple mass balance calculations of wetland aquatic plants suggest that long chain n-alkanes (e.g., C29 n-alkanes) are predominantly derived from leaves rather than roots in wetland surface sediments/soils. However, the contribution from mid-chain n-alkanes (e.g., C23 n-alkane) from roots may be equal to or greater than those from leaves. This implies that the differences in the isotopic compositions between root and leaf derived material need to be taken into account when interpreting down core changes in mid-chain n-alkane δ2H and δ13C values, which may be derived from variable contributions from leaves and roots rather than a change in hydroclimate or vegetation. Considering the large variation in both n-alkane distribution proxies and isotopic composition, no single molecular index or stable isotope ratio can capture multivariate changes of wetland ecosystems in the past. Nevertheless, principal component analysis shows promising potential to resolve different plant functional types. Paleo-reconstruction of subtropical aquatic ecosystems using n-alkanes will be most useful if the full molecular and isotopic distribution information of plant waxes are used.

Leaves from three mangrove species, and surface and deeper soils along salinity gradients in the Shark River estuary, USA, were analyzed to determine numerous diagenetic degradation products and pathways for mangrove derived triterpenoids. The dehydration of pentacyclic triterpenols was observed in mangrove leaves, leading to pentacyclic triterpadienes with Δ2,12 and Δ2,14 unsaturations. Surprisingly, various mono-unsaturated triterpenes (with Δ12 and Δ14), nor-, bisnor- (24,25-bisnortaraxer-14-ene), trisnor-triterpenes (1,2,3-trisnortaraxera-5(10),14-diene and 1,2,3-trisnortaraxer-14-ene) and tetrakisnor- and pentakisnor-triterpenes were detected in Rhizophora mangle leaves, suggesting that reduction and later demethylation of triterpadienes can occur prior to mangrove leaf abscission or senescence/death. Most of the unsaturated and nortriterpenes were also found in mangrove stand soils (>100 years old), suggesting their relative stability. In addition, a high diversity of aliphatic and aromatic des-A-triterpenes from the taraxerane, oleanane, ursane, and lupane precursors were present in the surface and deeper soils of mangrove stands, suggesting that isomerization, rapid diagenetic loss of ring-A and further aromatization of triterpenoids occurred early during litter decay. The overall diagenetic transformations could be caused by a combination of photodegradation, microbial alteration (bacteria/fungi), anaerobic alteration (reduction), oxidation and secondary processes. Possible mechanisms of the early diagenesis of triterpenoids were proposed using taraxerol, a triterpenol, highly enriched in R. mangle, as an example. These results, coupled with the detection of various intermediate compounds, provide a better understanding of the diagenetic fate of mangrove derived triterpenoids.

Human land use has led to significant changes in the character of dissolved organic matter (DOM) in lotic ecosystems. These changes are expected to have important environmental and ecological consequences. However, high spatiotemporal variability has been reported in previous studies, and the underlying mechanisms remain inadequately understood. This study assessed variation in the properties of stream water DOM within watersheds across a gradient of agricultural land use with grazing pasture lands as the dominant agricultural type in the southeastern United States. We collected water samples under baseflow conditions five times over eight months from a regional group of first- to fourth-order streams. Samples were analyzed for dissolved organic carbon (DOC) concentration, DOM quality based on absorbance and fluorescence properties, as well as DOM biodegradability. We found that air temperature and antecedent hydrological conditions (indicated by antecedent precipitation index and stream water sodium concentrations) positively influenced stream water DOC concentration, DOM fluorescence index, and the proportion of soil-derived, microbial humic fluorescence. This observation suggests that elevated production and release of microbial DOM in soils facilitated by high temperature, in conjunction with strong soil-stream hydrological connectivity, were important drivers for changes in the concentration and composition of stream water DOM. By comparison, watersheds with a high percentage of agricultural land use showed higher DOC concentration, larger proportion of soil-derived, humic-like DOM compounds, and higher DOC biodegradability. These observations reflect preferential mobilization of humic DOM compounds from shallow organic matter-rich soils in agricultural watersheds, likely due to enhanced soil erosion, organic matter oxidation and relatively shallow soil-to-stream flow paths.

This study investigates the effect of photodissolution on the production of dissolved black carbon (DBC) from particulate charcoal and a fire-impacted soil. A soil sample and a char sample were collected within the burn vicinity of the 2012 Cache La Poudre River wildfire and irradiated in deionized water with artificial sunlight. Photoexposure of the suspended char and soil significantly enhanced production of DBC after 7 days continuous exposure to the simulated sunlight. The increase was coupled with an increase in the DBC polycondensed character. In agreement with this, characterization using Fourier transform-ion cyclotron resonance-mass spectrometry (FT-ICR-MS) showed an increase in the number of BC molecular formulae detected and in their average molecular weight, suggesting that increasing photoexposure is required for dissolution of larger, more polycondenced DBC compounds. An increase in molecular signatures with lower H/C ratio and higher O/C ratio after 7 days photoexposure suggested increasing functionality of newly produced DBC with irradiation time, and therefore photooxidation as a potential mechanism for the photodissolution of BC. The photoproduced DBC was also strongly coupled with the photoproduced bulk dissolved organic carbon (DOC). The results suggest that photodissolution may be a significant and previously unrecognized mechanism of DBC translocation to aquatic systems.

The effect of salinity on hydrogen isotope fractionation during the production of leaf wax n-alkanes was assessed for Laguncularia racemosa (white mangrove), Rhizophora mangle (red mangrove), and Avicennia germinans (black mangrove) along a 31 ppt (parts per thousand) salinity gradient in the Shark River estuary, Florida, USA. Significant variation in hydrogen isotope ratios was observed among these three Atlantic-East Pacific (AEP) species, with increasing leaf wax n-alkane 2H/1H fractionation with increasing salinity. Net 2H/1H fractionation for hentriacontane (n-C31) increased by 0.8, 1.4 and 1.8‰/ppt in R. mangle, A. germinans and L. racemosa, respectively. The observations are consistent with published δ2HnC31 data from 5 species of Indo-West Pacific (IWP) mangroves, which increased with salinity by 0.7–1.5‰/ppt. Although all measured species from both the AEP and IWP regions have more 2H/1H fractionation at high salinity, differences in slope and intercepts of these relationships are observed among genera. The differences may result from variation in the composition of compatible solutes, reliance on storage carbohydrates, and/or physiological response to salt. However, no statistically significant difference in the sensitivity of δ2HnC31 to salinity was observed in four Rhizophora species from both Indo-West Pacific and Americas-East Atlantic regions, which makes sedimentary Rhizophora lipids a promising target for paleohydroclimatic reconstruction.

Mangrove ecotypes are distinct monospecific or mix-species assemblages and used as classification criteria to evaluate coastal biogeochemical cycles at the local, regional, and global scales. However, it is not clear how plant nitrogen and carbon content, including bulk δ13C and δ15N and n-alkane δ13C values, vary across species and within species when plants are exposed to the interaction between nutrient (nitrogen-N, phosphorus-P) availability and stressors (i.e., salinity). Here we present significant differences in green leaves wax n-alkane δ13C (δ13Cn-alkane) values and brown-senescent leaves C:N atomic ratios and total phosphorus (TP) concentrations of three mangrove species (Rhizophora mangle, Laguncularia racemosa, and Avicennia germinans) that reflect ecophysiological adaptations to nutrient availability and salinity along the Shark River estuary (SRE), South Florida, USA. Linear models between leaf wax δ13Cn-alkane values and species location along TP fertility and salinity gradients showed distinct differences, particularly between the species A. germinans and R. mangle. Our analyses showed that leaf wax δ13Cn-alkane properly represented major differences in ecophysiological responses by each mangrove species. We also found that both R. mangle and L. racemosa showed different isotopic footprints among the SRE upper, middle and lower estuarine salinity regions. Further, the green leaves bulk δ13C values in R. mangle (−32.3‰ to −27.6‰) were positively correlated with distance from the mouth of the estuary. In contrast, L. racemosa showed a negative relationship with distance and a narrower bulk δ13C range (−29.8‰ to −28.1‰) in comparison to the other two species. A. germinans, a species found only in the brackish (salinity: 18.8 ± 1.2) and saline (30.3 ± 0.53) estuarine regions, also showed a positive bulk δ13C relationship with distance. Because of the well-defined species-specific leaf wax n-alkane δ13C values along both water column/soil pore water salinity and TP gradients, we propose these values as a potential salinity proxy for paleoclimate reconstruction.

Human activities can alter dissolved organic matter (DOM) in lakes through both direct (i.e., exporting DOM of anthropogenic sources) and indirect effects (i.e., enhancing the autochthonous production of DOM via nutrient loading). Distinguishing between the direct and indirect effects is important to better understand human impacts on aquatic systems, but it remains highly challenging due to the interdependence of associated environmental variables. Here, we demonstrated that disentangling the direct and indirect effects can be achieved through combining large-scale environmental monitoring with the Partial Least Squares Path Modeling (PLS-PM). We presented DOM data from 61 lakes within the floodplain of the Yangtze River (Lakes-YR), China, a region that has been subjected to intense anthropogenic disturbances. We analyzed the amount and composition of DOM through dissolved organic carbon (DOC), chromophoric DOM (CDOM), and fluorescent DOM (FDOM). Four fluorescence components were identified, including one tyrosine-like component, one tryptophan-like component, and two humic-like components. Most of the lakes were dominated by freshly produced DOM with small molecular weights and low humification. Results from the PLS-PM models showed that the autochthonous production was more important than anthropogenic inputs in mediating DOC and CDOM. In contrast, FDOM parameters in lakes were more sensitive to the direct, anthropogenic sources, including treated domestic, industrial wastewater, and the effluents of aquaculture. These sources can be identified by elevated FDOM content per DOC (FDOM: DOC ratio) relative to autochthonous DOM, suggesting the potential of using FDOM as a tracer to identify and monitor the contribution of anthropogenic organic matter to inland waters.

Urban and agricultural development of the South Florida peninsula has disrupted historic freshwater flow in the Everglades, a hydrologically connected ecosystem stretching from central Florida to the Gulf of Mexico, USA. Current system-scale restoration efforts aim to restore natural hydrologic regimes to reestablish pre-drainage ecosystem functioning through increased water availability, quality and timing. Aquatic transport of carbon in this ecosystem, primarily as dissolved organic carbon (DOC), plays a critical role in biogeochemical cycling and food-web dynamics, and will be affected both by water management policies and climate change. To better understand DOC dynamics in South Florida estuaries and how hydrology, climate and water management may affect them, 14 years of monthly data collected in the Shark River estuary were used to examine DOC flux dynamics in a broader environmental context. Multivariate statistical methods were applied to long-term datasets for hydrology, water quality and climate to untangle the interconnected environmental drivers that control DOC export at monthly and annual scales. DOC fluxes were determined to be primarily controlled by hydrology but also by seasonality and long-term climate patterns and episodic weather events. A four-component model (salinity, rainfall, inflow, Atlantic Multidecadal Oscillation) capable of predicting DOC fluxes (R 2 = 0.84, p

This study aimed to assess the molecular properties of dissolved organic matter (DOM) and dissolved black carbon (DBC) using analytical pyrolysis (Py-GC-MS). The sample set was comprised of ultrafiltered DOM (UDOM) from North American headwater streams associated with Long Term Ecological Research network sites. Pyrolysis products for each UDOM sample were categorized as being sourced from non-pyrogenic sources and DBC. Major non-pyrogenic components of the headwater stream UDOM were comprised of phenolic compounds derived from lignin and chitin markers from microbial biomass, and their relative contributions indicated differences in organic matter dynamics of these ecosystems. The DBC pyrolyzates included benzene, PAHs and benzonitriles, which accounted for 12.5 ± 4.5% of total quantified peak area (TPQA), and decreased in the order Alaskan boreal forest (19%), Alaskan tundra (17%), Appalachian deciduous forest (11%), Colorado alpine tundra (9%), Puerto Rican mountainous tropical rainforest (9%) and Kansas tallgrass prairie (7%). Pyrolysis products were compared to DBC content as determined by the benzenepolycarboxylic acid (BPCA) method. Although Py-GC-MS has quantitative limitations, this technique can detect weakly condensed and other DBC structures which fall outside of the BPCA analytical window., This study was in part funded by NSF through the Florida Coastal Everglades long Term Ecological Research program (DEB-1237517). R.J. acknowledges additional funding through the George Barley Endowment.

Eight C25 highly branched isoprenoid (HBI) alkenes were detected in the freshwater wetland of the Florida Everglades and tentatively assigned as a C25 diene, three C25 trienes, two C25 tetraenes and two C25 pentaenes based on their mass spectra, retention index and literature reports. One diene and one triene were observed more frequently than the others. The HBIs were present in varying amount of up to 1000, 19,000, 780 and 150 ng/g dry weight in the periphyton, floc, surface soils and deeper soils (ca. 1900 AD), respectively. Compound specific carbon isotope analysis of the two most dominant HBIs (one diene and one triene) showed them to be highly depleted in 13C (δ13C −40.0‰ to −38.5‰) in freshwater floc, suggesting recycled CO2 produced from the decomposition of organic matter as an important C source in the biosynthesis of these compounds. HBIs were present across this freshwater wetland in greater diversity and abundance at locations with higher surface water N concentration and longer hydroperiod (inundation). Historical variation in the occurrence of the HBIs in soil cores from multiple slough and ridge environments was assessed. Their increased abundance after ca. 1960 AD in almost all cores suggests proliferation of their precursor biota (freshwater diatoms) over the past five decades.

Free radicals are produced in aquatic environments through photochemical reactions. They can affect the concentration and composition of organic matter and have negative effects on aquatic organisms. Free radical scavengers (antioxidants) can remove these highly reactive species from the media. Some dissolved organic matter (DOM) constituents are widely known to present antioxidant properties (e.g. phenols and hydroquinones). However, little is known about the free radical scavenger capacity of DOM. Here we applied two simple, analytical assays (ABST and DPPH) to assess the antioxidant capacity of aquatic DOM, after their validation against a more complex electrochemical technique. These assays were applied to DOM from various environmental settings, including freshwater marshes, fringe mangrove estuaries and a coastal bay in Everglades National Park, Florida. All the samples presented different degrees of antioxidant activity depending on their origin and thus DOM quality. Samples associated with mangrove areas presented the highest antioxidant activity, possibly due to the presence of tannins, which are known to be powerful antioxidants. The free radical scavenging capacity or antioxidant properties of DOM may have important implications in aquatic photochemistry as well as in microbial processes.

Several long-chain n-alkyl coumarates and ferulates were identified in cattails (Typha domingensis and Typha latifolia) from the Florida Everglades. Characterization of these compounds was achieved based on the interpretation of mass spectra obtained by GCMS as their trimethylsilyl ether derivatives, comparison with published mass spectra and available standards. Both n-alkyl p-coumarates and n-alkyl ferulates were identified in roots and leaves of both Typha species, featuring unique distribution patterns and differences between leaf and root biomass. For both Typha species, roots have higher concentrations and a much greater diversity of n-alkyl p-coumarates and ferulates but with different side chain carbon numbers ranging from C14 to C28. Typha domingensis leaves only contained n-alkyl ferulates with traces of n-alkyl p-coumarates, while both types of compounds were present in Typha latifolia leaf material. These chemicals were not found in the other dominant wetland vegetation, which suggests their potential for application as phytochemical tracers of fresh cattail-derived organic matter in the Everglades ecosystem.

The effects of photodegradation on the molecular size distribution and composition of dissolved black carbon (DBC) were explored using a surface water dissolved organic matter (DOM) sample from a terrigenous-influenced, fire-impacted Everglades area canal. The original and photodegraded DOM samples were fractionated using size exclusion chromatography and DBC was quantified via benzene polycarboxylic acid (BPCA) analysis. Size fractionation revealed that DBC was unequally distributed along the DOM molecular weight (MW) continuum and was preferentially associated with high MW (HMW) fractions. The photo-decomposition of HMW DBC generated less condensed DBC photo-products that preferentially re-associated with, and became enriched in, low MW (LMW) DOM size fractions. DBC composition in whole and size-fractionated DOM, as determined from relative BPCA distributions, was not considerably altered with short term photodegradation. This indicated that the size of the conjugated aromatic ring structure may drive the association of DBC compounds with different DOM MW fractions. HMW DBC was also more photo-labile than LMW DBC, which suggests that DBC associated with DOM over a range of size fractions may not exhibit the same degree of photo-reactivity, thereby resulting in different environmental fates for pyrogenic OM.

Annually, rivers and inland water systems deliver a significant amount of terrestrial organic matter (OM) to the adjacent coastal ocean in both particulate and dissolved forms; however, the metabolic and biogeochemical transformations of OM during its seaward transport remains one of the least understood components of the global carbon cycle. This transfer of terrestrial carbon to marine ecosystems is crucial in maintaining trophic dynamics in coastal areas and critical in global carbon cycling. Although coastal regions have been proposed as important sinks for exported terrestrial materials, most of the global carbon cycling data, have not included fjords in their budgets. Here we present distributional patterns on the quantity and quality of dissolved OM in Fiordland National Park, New Zealand. Specifically, we describe carbon dynamics under diverse environmental settings based on dissolved organic carbon (DOC) depth profiles, oxygen concentrations, optical properties (fluorescence) and stable carbon isotopes. We illustrate a distinct change in the character of DOC in deep waters compared to surface and mid-depth waters. Our results suggest that, both, microbial reworking of terrestrially derived plant detritus and subsequent desorption of DOC from its particulate counterpart (as verified in a desorption experiment) are the main sources of the humic-like enriched DOC in the deep basins of the studied fjords. While it has been suggested that short transit times and protection of OM by mineral sorption may ultimately result in significant terrestrial carbon burial and preservation in fjords, our data suggests the existence of an additional source of terrestrial OM in the form of DOC generated in deep, fjord water.

The aerobic respiration of flocculent detrital organic material (floc) from Everglades National Park was found to be dependent on phosphorus limitation and carbon quality and is likely influenced by substrate age, hydrology, and local biomass productivity. Floc was collected at four sites along the Shark River and Taylor Sloughs of Everglades National Park and incubated for up to one week at room temperature in the dark. Floc respiration was determined by measuring the total amount of CO2 evolved and CO2 generation rates. To investigate the effect of hydrological conditions, samples were collected in a typical dry (April) and wet (October) season and from short- and long-hydroperiod sites. Floc from the short-hydroperiod freshwater site generated more CO2 compared to the long-hydroperiod site due to the labile nature of the periphyton-derived organic matter at the former and the presence of more degraded and aged material at the latter. The tidally-influenced Shark River Slough mangrove site generated more CO2 compared to the Taylor Slough mangrove site, likely as a result of phosphorus inputs from the adjacent Gulf of Mexico at the former and reduced phosphorus inputs and prolonged inundation at the latter. Generally, more CO2 was generated during the dry season. Floc respiration rates were faster in the wet season, suggesting that fresh vegetation inputs to the floc can influence this process. Phosphorus and glucose additions enhanced CO2 generation suggesting that phosphorus limitation and carbon quality are important factors regulating floc decomposition.

Combustion produces a complex mixture of polycondensed aromatic compounds known as black carbon (BC). Such products can become remobilized from char and soil in the form of dissolved BC (DBC). Ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (ESI–FT-ICRMS) analysis of a variety of soil and char leachates showed that a significant proportion of DBC compounds contained one or more nitrogen atoms. While the presence of black nitrogen (DBN) in dissolved organic matter (DOM) has been reported, its molecular features were uncharacterized. Here we present results of FT-ICRMS characterization of DBN, where assigned formulae were validated on the basis on their 13C isotope signatures and fragmentation patterns obtained via collision induced dissociation. Possible chemical structures were assigned for several DBN formulae and suggest that nitrogen was incorporated into the core ring system as a pyrrole-type moiety. Most DBN compounds existed as part of homologous series where homologs differed by a mass corresponding to CO2, suggesting that they were polysubstituted with carboxylic acid groups. The environmental contribution of such novel, aromatic, combustion-derived nitrogen compounds with respect to global nitrogen cycling remains elusive. The biogeochemical implications of the input of such fire-derived products to aquatic ecosystems as part of climate change therefore need to be assessed.

The dynamics of dissolved organic matter (DOM) in subtropical coastal bays are complex. For example, variations in DOM characteristics and sources in Florida Bay are believed to be mainly driven by both hydrology and associated runoff of terrestrial DOM, and by primary productivity mostly from seagrass sources. However, confirmation and quantification of different DOM sources are still incomplete and needed for carbon budget assessments. Optical parameters based on excitation emission matrix fluorescence coupled with parallel factor analysis (EEM–PARAFAC) that had previously been tentatively assigned to both terrestrial and seasgrass sources. These correlated linearly with determined δ13C values, confirming an allochthonous, hydrologically-driven terrestrial source for the humic-like fluorescent components, while autochthonous DOM reflected by the protein-like fluorescence is mainly derived through primary productivity of seagrass communities. This study demonstrated the feasibility of combining optical signatures and stable isotopes in advancing the understanding of DOM dynamics in estuarine systems. Using stable carbon isotopic signatures of DOM, and applying a simple two end-member mixing model, the relative contributions of these two sources to the DOM pool in the bay were estimated. Results indicate that the highest proportion of DOM (ca. 72%) during the dry season was seagrass-derived, but clear variations were observed on both spatial and temporal scales. Limitations to the application of optical properties for the quantitative estimation of DOM sources in such coastal systems are discussed.

Assessing the sources and quantifying the contributions of particulate organic matter (POM) in estuaries is a challenge. Here we apply source-specific biomarkers to assess POM sources in an estuary receiving suspended material from freshwater wetlands, fringe mangroves and coastal environments. A three end-member mixing model, including terrestrial, estuarine and marine end-member contributions was developed and successfully validated to assess general OM dynamics and hydrologic processes that control POM distributions within the Shark River estuary in South Florida. Low tide and wet season conditions coincided with an enhanced signal of the freshwater end-member biomarker abundance, while high tide and dry season conditions resulted in enhanced POM input of marine origin. Incoming tide was observed to be an important factor in the re-suspension and tidal pumping of mangrove-derived POM, which seems to be the dominant source of particulate organic carbon (POC) in the estuary. The three end-member conceptual model was tested to obtain a rough estimate of POC source strength, with the ultimate goal of constraining carbon budgets in this sub-tropical estuary. Mangrove-derived POC flux of ca. 5.3 × 105 to 1.0 × 106 kg/yr POC from the Shark River to the Gulf of Mexico were estimated, but end-member values used in the assessment need to be better constrained to reduce the degree of variability.

As basic information for assessing reactivity and functionality of wetland-associated dissolved organic matter (DOM) based on their composition and structural properties, chemical characteristics of N in ultrafiltered DOM (UDON; > 1 kD) isolated from wetland-associated rivers in three climates (cool-temperate, Hokkaido, Japan; sub-tropical, Florida, USA; tropical, Sarawak, Malaysia) were investigated. The UDON was isolated during dry and wet seasons, or during spring, summer, and autumn. The proportion of UDON present as humic substances, which was estimated as the DAX-8 adsorbed fraction, ranged from 47 to 91%, with larger values in the Sarawak than at the other sites. The yield of hydrolyzable amino acid N ranged 1.24 to 7.01mg g − 1 , which correlated positively to the total N content of UDOM and tended to be larger in the order of Florida > Hokkaido > Sarawak samples. X-ray photoelectron N1s spectra of UDON showed a strong negative correlation between the relative abundances of amide/peptide N and primary amine N. The relative abundances of amide/peptide N and primary amine N in the Sarawak samples were smaller (70–76%) and larger (20–23%) respectively compared to those (80–88% and 4–9%) in the Florida and Hokkaido samples. Assuming terminal amino groups and amide N of peptides as major constituents of primary amine N and amide/peptide N, respectively, the average molecular weight of peptides was smaller in the Sarawak samples than that in the Florida and Hokkaido samples. Seasonal variations in UDON composition were scarce in the Sarawak and Florida samples, whereas the distribution of humic substance-N and nonhumic substance-N and compositions of amino acids and N functional groups showed a clear seasonality in the Hokkaido samples. While aromatic N increased from spring to autumn, contributions from fresh proteinaceous materials were also enhanced during autumn, resulting in the highest N content of UDOM for this season.

Dissolved organic carbon (DOC) measurements and optical properties were applied to assess the photo- and bio-reactivity of dissolved organic matter (DOM) from different sources, including biomass leaching, soil leaching and surface waters in a subtropical wetland ecosystem. Samples were exposed to light and/or dark incubated through controlled laboratory experiments. Changes in DOC, ultraviolet (UV-Vis) visible absorbance, and excitation-emission matrix (EEM) fluorescence combined with parallel factor analysis (PARAFAC) were performed to assess sample degradation. Degradation experiments showed that while significant amounts of DOC were consumed during bio-incubation for biomass leachates, a higher degree of bio-recalcitrance for soil leachate and particularly surface waters was displayed. Photo- and bio-humification transformations were suggested for sawgrass, mangrove, and seagrass leachates, as compared to substantial photo-degradation and very little to almost no change after bio-incubation for the other samples. During photo-degradation in most cases the EEM-PARAFAC components displayed photo-decay as compared to a few cases which featured photo-production. In contrast during bio-incubation most EEM-PARAFAC components proved to be mostly bio-refractory although some increases and decreases in abundance were also observed. Furthermore, the sequential photo- followed by bio-degradation showed, with some exceptions, a "priming effect" of light exposure on the bio-degradation of DOM, and the combination of these two processes resulted in a DOM composition more similar to that of the natural surface water for the different sub-environments. In addition, for leachate samples there was a general enrichment of one of the EEM-PARAFAC humic-like component (Ex/Em

Wetlands are key components in the global carbon cycle and export significant amounts of terrestrial carbon to the coastal oceans in the form of dissolved organic carbon (DOC). Conservative behavior along the salinity gradient of DOC and chromophoric dissolved organic matter (CDOM) has often been observed in estuaries from their freshwater end-member (salinity = 0) to the ocean (salinity = 35). While the oligo/meso-haline (salinity A 254 ) and excitation–emission matrix (EEM) fluorescence coupled with parallel factor analysis (PARAFAC) along the lower salinity range (salinity A 254 was observed, while these parameters showed similar conservative behavior for the third. Three distinct EEM-PARAFAC models established for each of the rivers provided similar spectroscopic characteristics except for some unique fluorescence features observed for the Judan River. The distribution patterns of PARAFAC components suggested that the inputs from plankton and/or submerged aquatic vegetation can be important in the Bekanbeushi River. Further, DOM photo-products formed in the estuarine lake were also found to be transported upstream. In the Harney River, whereas upriver-derived terrestrial humic-like components were mostly distributed conservatively, some of these components were also derived from mangrove inputs in the oligo/meso-haline zone. Interestingly, fluorescence intensities of some terrestrial humic-like components increased with salinity for the Judan River possibly due to changes in the dissociation state of acidic functional groups and/or increase in the fluorescence quantum yield along the salinity gradient. The protein-like and microbial humic-like components were distributed differently between three wetland rivers, implying that interplay between loss to microbial degradation and inputs from diverse sources are different for the three wetland-influenced rivers. The results presented here indicate that upper estuarine oligo/meso-haline regions of coastal wetland rivers are highly dynamic with regard to the biogeochemical behavior of DOM.

Biomass burning results in the formation and accumulation of pyrogenic products such as black carbon (BC) and black nitrogen (BN) in soils. The ubiquitous presence of pyrogenic products in natural dissolved organic matter (DOM) and potential implications in global carbon cycling have recently been reported. However, little is known about the environmental dynamics or the importance in the global N cycle of dissolved BN (DBN; or heteroaromatic N). Here we report the coupling between DBN and dissolved BC (DBC) in ultrafiltered DOM from six headwater streams across a climatic region of North America, suggesting similar combustion sources, and that DOC may play an important role in the translocation of soil BN to the dissolved phase. The export of potentially recalcitrant riverine DBN to the ocean may affect the biogeochemical cycling of N and possibly the microbial community structure in aquatic environments.

Herein, lipid biomarker analysis is applied to surface sediments from the southeastern Niger Delta region for the quantitative determination of aliphatic lipids, steroids and triterpenoids in order to differentiate between natural (autochthonous vs. allochthonous) and anthropogenic organic matter (OM) inputs to this deltaic environment. This ecosystem, composed of the Cross, Great Kwa and Calabar Rivers, is receiving new attention due to increased human and industrial development activities and the potential effects of these activities impacting its environmental health. While the presence of low molecular weight n -alkanes ( 22 ) and the fossil biomarkers pristane and phytane in all samples, are indicative of a minor petroleum related input, the total extractable organic component of the surface sediments of these rivers remains predominantly of a natural origin as characterized by the variety and predominance of lipid classes that are mainly derived from the epicuticular waxes of vascular plants and include n -alkanes, n -alkanols, n -alkan-2-ones, n -alkanoic acids, steroids and triterpenoids. In addition, recent OM inputs from microorganisms are indicated by the presence of lower molecular weight n -alkanoic acids (C max = 16), while the major triterpenoids of the sediments, taraxerol and friedelin, and the major sterol, sitosterol, indicate recent OM inputs from vascular plants. Plankton-derived sterols, such as fucosterol and dinosterol, are also found in sediments from the Cross and Great Kwa Rivers and likely originate from autochthonous primary productivity. Furthermore, the coprosterols coprostanol and 24-ethylcoprostanol are present in most samples and indicate measurable anthropogenic contributions from domestic untreated sewage inputs and agricultural run-off, respectively. Of the three rivers studied, the Cross River system was excessively influenced by human and industrial development activities, including drivers such as urbanization and population center growth, land-use change to support agricultural production and animal husbandry, and petroleum exploration and production. These influences were found to be regionally specific as controlled by point sources of pollution based on the relative distributions measured and on the fact that the molecular characteristics of sedimentary OM were not distributed smoothly along a gradient.

While the existence of black carbon as part of dissolved organic matter (DOM) has been confirmed, quantitative determinations of dissolved black carbon (DBC) in freshwater ecosystem and information on factors controlling its concentration are scarce. In this study, stream surface water samples from a series of watersheds subject to different burn frequencies in Konza Prairie (Kansas, USA) were collected in order to determine if recent fire history has a noticeable effect on DBC concentration. The DBC levels detected ranged from 0.04 to 0.11 mg L(-1), accounting for ca. 3.32±0.51% of dissolved organic carbon (DOC). No correlation was found between DBC concentration and neither fire frequency nor time since last burn. We suggest that limited DBC flux is related to high burning efficiency, possibly greater export during periods of high discharge and/or the continuous export of DBC over long time scales. A linear correlation between DOC and DBC concentrations was observed, suggesting the export mechanisms determining DOC and DBC concentrations are likely coupled. The potential influence of fire history was less than the influence of other factors controlling the DOC and DBC dynamics in this ecosystem. Assuming similar conditions and processes apply in grasslands elsewhere, extrapolation to a global scale would suggest a global grasslands flux of DBC on the order of 0.14 Mt carbon year(-1).

Dissolved organic matter (DOM) represents the largest organic matter pool in freshwater systems, but much of it remains molecularly uncharacterized. Although freshwater systems cover only a small area of the earth’s surface, inland waters are an important component of the global carbon cycle. The traditional idea that rivers are simply conduits for refractory carbon delivery to coastal areas is inconsistent with carbon flux estimates, and streams have been shown to serve as reactors for DOM cycling. The overall quality of DOM, and its associated reactivity, can be related to its chemical composition and molecular structure. However, the variability of DOM composition in freshwater ecosystems, particularly in headwater streams, is poorly characterized. Detailed molecular studies of DOM from small streams across climatic regions, which could provide critical information regarding carbon dynamics on a more global scale, have not been performed. To address these issues, this study applies a multi-method analytical approach in an attempt to assess molecular characteristics of DOM and ultrafiltered DOM (UDOM) in headwater streams from different climatic regions in North America. In general terms the chemical and molecular characteristics of UDOM from six different biomes were determined in unsurpassed detail to feature some clear general similarities but also specific differences. While the degree of similarity is remarkable, and suggests similar source strengths, such as soil-derived organic matter and/or similar diagenetic degradation processes for DOM from vastly different environments, each sample was clearly unique in its overall composition, featuring some distinct molecular patterns for at least one or more of the analytical determinations. Molecular and compositional differences of DOM from headwater streams should result from variations in DOM sources and localized environmental conditions, and consequently feature different photo- and bio-reactivity and associated re-mineralization potentials during fluvial transport. Such knowledge could assist in predicting the consequences of global change and its relationship to global carbon cycling.

The environmental dynamics of dissolved organic matter (DOM) were characterized for a shallow, subtropical, seagrass-dominated estuarine bay, namely Florida Bay, USA. Large spatial and seasonal variations in DOM quantity and quality were assessed using dissolved organic C (DOC) measurements and spectrophotometric properties including excitation emission matrix (EEM) fluorescence with parallel factor analysis (PARAFAC). Surface water samples were collected monthly for 2 years across the bay. DOM characteristics were statistically different across the bay, and the bay was spatially characterized into four basins based on chemical characteristics of DOM as determined by EEM-PARAFAC. Differences between zones were explained based on hydrology, geomorphology, and primary productivity of the local seagrass community. In addition, potential disturbance effects from a very active hurricane season were identified. Although the overall seasonal patterns of DOM variations were not significantly affected on a bay-wide scale by this disturbance, enhanced freshwater delivery and associated P and DOM inputs (both quantity and quality) were suggested as potential drivers for the appearance of algal blooms in high impact areas. The application of EEM-PARAFAC proved to be ideally suited for studies requiring high sample throughput methods to assess spatial and temporal ecological drivers and to determine disturbance-induced impacts in aquatic ecosystems.

This study shows that light exposure of flocculent material (floc) from the Florida Coastal Everglades (FCE) results in significant dissolved organic matter (DOM) generation through photo-dissolution processes. Floc was collected at two sites along the Shark River Slough (SRS) and irradiated with artificial sunlight. The DOM generated was characterized using elemental analysis and excitation emission matrix fluorescence coupled with parallel factor analysis. To investigate the seasonal variations of DOM photo-generation from floc, this experiment was performed in typical dry (April) and wet (October) seasons for the FCE. Our results show that the dissolved organic carbon (DOC) for samples incubated under dark conditions displayed a relatively small increase, suggesting that microbial processes and/or leaching might be minor processes in comparison to photo-dissolution for the generation of DOM from floc. On the other hand, DOC increased substantially (as much as 259 mgC gC(-1)) for samples exposed to artificial sunlight, indicating the release of DOM through photo-induced alterations of floc. The fluorescence intensity of both humic-like and protein-like components also increased with light exposure. Terrestrial humic-like components were found to be the main contributors (up to 70%) to the chromophoric DOM (CDOM) pool, while protein-like components comprised a relatively small percentage (up to 16%) of the total CDOM. Simultaneously to the generation of DOC, both total dissolved nitrogen and soluble reactive phosphorus also increased substantially during the photo-incubation period. Thus, the photo-dissolution of floc can be an important source of DOM to the FCE environment, with the potential to influence nutrient dynamics in this system.

Dissolved organic matter (DOM) in groundwater and surface water samples from the Florida coastal Everglades were studied using excitation–emission matrix fluorescence modeled through parallel factor analysis (EEM-PARAFAC). DOM in both surface and groundwater from the eastern Everglades S332 basin reflected a terrestrial-derived fingerprint through dominantly higher abundances of humic-like PARAFAC components. In contrast, surface water DOM from northeastern Florida Bay featured a microbial-derived DOM signature based on the higher abundance of microbial humic-like and protein-like components consistent with its marine source. Surprisingly, groundwater DOM from northeastern Florida Bay reflected a terrestrial-derived source except for samples from central Florida Bay well, which mirrored a combination of terrestrial and marine end-member origin. Furthermore, surface water and groundwater displayed effects of different degradation pathways such as photodegradation and biodegradation as exemplified by two PARAFAC components seemingly indicative of such degradation processes. Finally, Principal Component Analysis of the EEM-PARAFAC data was able to distinguish and classify most of the samples according to DOM origins and degradation processes experienced, except for a small overlap of S332 surface water and groundwater, implying rather active surface-to-ground water interaction in some sites particularly during the rainy season. This study highlights that EEM-PARAFAC could be used successfully to trace and differentiate DOM from diverse sources across both horizontal and vertical flow profiles, and as such could be a convenient and useful tool for the better understanding of hydrological interactions and carbon biogeochemical cycling.

Ester bound, long chain fatty acids (e-LFAs), hydroxy fatty acids (FAs) and di-acids are key components of the hydrolysable aliphatic lipids in soil organic matter (SOM). Cutin and suberin are important sources of these SOM components, which may contribute to the recalcitrant soil carbon pool. However, their carbon isotopic composition and turnover rates are largely unknown. This study represents the first compound specific isotopic analysis (CSIA) of major hydrolysable lipids in the surface mineral soil horizons from the Duke Forest, North Carolina, USA. The investigated lipids include hydroxy FAs and di-acids that only originate from cutin and suberin (i.e., cutin- and suberin-derived compounds) and e-LFAs that originate from plant waxes as well as cutin and suberin. These compounds were 2–7‰ more depleted in 13 C as compared to the bulk organic matter in plant tissues as well as in soils. Furthermore, they were more depleted in

A stable carbon isotope approach was taken to identify potential organic matter sources incorporated into biomass by the heterotrophic bacterial community of Florida Bay, a subtropical estuary with a recent history of seagrass loss and phytoplankton blooms. To gain a more complete understanding of bacterial carbon cycling in seagrass estuaries, this study focused on the importance of seagrass-derived organic matter to pelagic, seagrass epiphytic, and sediment surface bacteria. Particulate organic matter (POM), seagrass epiphytic, seagrass (Thalassia testudinum) leaf, and sediment surface samples were collected from four Florida Bay locations with historically different organic matter inputs, macrophyte densities, and primary productivities. Bulk (observed and those reported previously) and compound-specific bacterial fatty acid d 13 C values were used to determine important carbon sources to the estuary and benthic and pelagic heterotrophic bacteria. The d 13 C values of T. testudinum green leaves with epiphytes removed ranged from � 9.9 to � 6.9&. Thalassia testudinum d 13 C values were significant more enriched in 13 C than POM, epiphytic, and sediment samples, which ranged from � 16.4 to � 13.5, � 16.2 to � 9.6, and � 16.7 to � 11.0 &, respectively. Bacterial fatty acid d 13 C values (measured for br14:0, 15:0, i15:0, a15:0, br17:0, and 17:0) ranged from � 25.5 to � 8.2&. Assuming a � 3& carbon source fractionation from fatty acid to whole bacteria, pelagic, epiphytic, and sediment bacterial d 13 C values were generally more depleted in 13 C than T. testudinum d 13 C values, more enriched in 13 C than reported d 13 C values for mangroves, and similar to reported d 13 C values for algae. IsoSource mixing model results indicated that

Bulk geochemical parameters and organic matter biomarkers in a short, high resolution gravity core (Lake Valencia, Venezuela) were examined to reconstruct anthropogenic impacts on the lake’s conditions. During the period of ca. 1840–1990, sedimentary organic matter was characterized by high contents of total organic C (TOC) and total N (TN), low TOC/TN values as well as relatively enriched δ13C and δ15N signals, suggesting a primary autochthonous (algae and macrophytes) organic matter origin. The occurrence of large amounts of C23 and C25 relative to C29 and C31 n-alkanes indicated substantial inputs from submerged/floating macrophytes. The variations of C32 15-keto-ol, tetrahymanol, diploptene, C32 bishomohopanol, 2-methylhopane, dinosterol and isoarborinol concentrations over the investigated period record changes in the planktonic community structure, including Botryococcus braunii, bacteriavore ciliates, cyanobacteria, Eustigmatophytes and dinoflagellates. A principal shift occurred in the 1910s when cyanobacteria and dinoflagellates became more abundant at the expense and decline of B. braunii and Eustigmatophytes, likely related to increasing anthropogenic activity around the lake. A second shift (less obvious) occurred in the 1960s when cyanobacteria became the sole predominant planktonic class, coinciding with further deterioration of lake conditions.

The reactivity of higher plant derived 3-oxy-triterpenoids to sunlight was investigated using a series of pure reference standards both under simulated and real solar exposure. The majority of the exposed compounds showed reactivity to light, particularly to simulated sunlight and among others generated seco-derivatives. While photochemical processes have been suggested for the formation of such compounds, their abundances in some sediments have often been assumed to be the result of diagenetic reworking of parent triterpenoids. Analyses of mangrove leaf waxes, an important known source of taraxerol in coastal ecosystems, showed the presence of the 3,4-seco-derivative dihydrolacunosic acid, which could represent an important biotic source for des-A-triterpenoid precursors to such sediments, and is unrelated to aquatic organic matter diagenesis.

Three novel 3-oxygenated CD spiro -triterpenoids were tentatively identified as 13,15- spiro -arbor-9(11)-en-3-one, 3β-methoxy-13,15- spiro -arbor-9(11)-ene and 13,15- spiro -arbor-9(11)-en-3β-ol in solvent extracts of sediments from Lake Valencia. Their proposed origin from higher plants is based on structural precursor/product relationships and characteristics of the age distributions since the latest Pleistocene.

The extractable lipid compositions in four Florida Bay cores were determined in order to understand environmental changes over the last 160 years. The most significant environmental change was recorded by oscillations in the amplitude and frequency of biomarkers during the 20th century. Two seagrass molecular proxies ( Paq and the C 25 /C 27 n -alkan-2-one ratio) reached a maximum post 1900, suggesting that abundant seagrass communities existed during the 20th century. A sharp drop in the Paq value from 0.65 to 0.48 in the central Bay at about 1987 seems to reflect seagrass die-off. The concentrations of microbial biomarkers (C 20 HBIs, C 25 HBIs and dinosterol) substantially increased after 1950 in the TC, BA and NB cores, reflecting an increase in algal (planktonic organism) primary productivity. However, the RB core presented the highest abundance of C 25 HBIs and dinosterol during the period of 1880–1940, suggesting historically large inputs from diatoms and dinoflagellates. A substantial rise in abundance of taraxerol (a specific biomarker of mangroves) from 20 μg/g TOC in the 1830s to 279 μg/g TOC in the l980s is likely a result of increased mangrove primary productivity along the shore of the NE Bay. These changes are most likely the result of hydrological alterations in South Florida.

Long-chain mid-chain diols and keto-ols have been reported mainly in marine environments but only rarely in lacustrine sediments. In this work, exceptionally high abundances and diversity of keto-ols, diols and structurally related long-chain n -alkenols and secondary alkanols were detected in sediments from a hypereutrophic, freshwater lake (Lake Valencia, Venezuela). The maximum concentrations are 241 μg/g TOC for n -alkenols, 75 μg/g TOC for diols, 367 μg/g TOC for keto-ols, and 8.7 μg/g TOC for secondary alkanols. Eleven keto-ol isomers were identified, which is the highest diversity yet reported for sediments. The presence of five keto-ol isomers, namely 1,12-C 30 keto-ol, 1,14-C 31 keto-ol, 1,15-C 33 keto-ol, 1,16-C 33 keto-ol and 1,18-C 35 keto-ol is reported for the first time. The mass spectra for osmium tetroxide derivatives from long chain n -alkenols confirmed the double bond location at carbons 13, 14 or 15. The carbon isotope compositions were substantially enriched in 13 C for n -alkenols, diols and keto-ols ( δ 13 C = −22.0 ± 2.2‰) relative to the corresponding long-chain n -alkanols (−29.6 ± 0.8‰), suggesting an autochthonous aquatic microbial origin rather than from a terrestrial (i.e., fern) source. Although a strong predominance of cyanobacteria was reported for in the lake’s plankton community (>90%) and relatively low abundance of sedimentary sterols suggests cyanobacteria as a potential source, eustigmatophytes, a major reported producer of diols and keto-ols, cannot be excluded because eustigmatophytes are easily confused with other microalgae and may have been overlooked in previous studies. n -Alkenols and keto-ols displayed similar historical patterns over the past 10,000+ years, but there were distinct differences from the diol patterns. This result suggested that n -alkenols and keto-ols may be derived from the same sources, while diols either undergo different environmental diagenesis or have different sources. A keto-ol index coincides well with the hydrological changes of Lake Valencia over the last 10,000+ years, and corroborates its validity as a paleo-indicator.

16 pages, 4 figures, 6 tables., Water samples were collected from rivers and estuarine environments within the Florida Coastal Everglades (FCE) ecosystem, USA, and ultrafiltered dissolved organic matter (UDOM; 1 kDa) was isolated for characterization of its source, bioavailability and diagenetic state. A combination of techniques, including 15N cross-polarization magic angle spinning nuclear magnetic resonance (15N CPMAS NMR) and X-ray photoelectron spectroscopy (XPS), were used to analyze the N components of UDOM. The concentrations and compositions of total hydrolysable amino acids (HAAs) were analyzed to estimate UDOM bioavailability and diagenetic state. Optical properties (UV–visible and fluorescence) and the stable isotope ratios of C and N were measured to assess the source and dynamics of UDOM. Spectroscopic analyses consistently showed that the major N species of UDOM are in amide form, but significant contributions of aromatic-N were also observed. XPS showed a very high pyridinic-N concentration in the FCE–UDOM (21.7 ± 2.7%) compared with those in other environments. The sources of this aromatic-N are unclear, but could include soot and charred materials from wild fires. Relatively high total HAA concentrations (4 ± 2% UDOC or 27 ± 4% UDON) are indicative of bioavailable components, and HAA compositions suggest FCE–UDOM has not undergone extensive diagenetic processing. These observations can be attributed to the low microbial activity and a continuous supply of fresh UDOM in this oligotrophic ecosystem. Marsh plants appear to be the dominant source of UDOM in freshwater regions of the FCE, whereas seagrasses and algae are the dominant sources of UDOM in Florida Bay. This study demonstrates the utility of a multi-technique and multi-proxy approach to advance our understanding of DON biogeochemistry., This study was funded by the National Oceanographic and Atmospheric Administration (COP R.J.) and the National Science Foundation as part of the FCE-LTER program (DEB-9910514).

The sources and transformations of sedimentary organic matter along the Harney River, a representative subtropical river of the Florida Everglades, were assessed using a natural product biomarker approach. Sediment samples were collected from the headwaters to the Continental Shelf, with characteristic vegetation dominated by freshwater marsh species, mangrove (middle to lower estuary), and seagrass as the marine end-member. A peat sample was collected inland. All sample extracts were analyzed by GC-MS as underivatized and as silylated compounds. With these total extract analyses, major compound classes can be defined: n-alkanols, n-alkanoic acids, methyl alkanoates, methyl alpha- and omega-hydroxyalkanoates, triterpenoids, phytosterols and saccharides, with traces of hydrocarbons. In general, the peat sample extract has a different overall composition compared to the sediment extracts. The major differences include distinct carbon number maxima for the lipid series (e.g., C(max)=28 for n-alkanols) probably from sawgrass and periphyton biomass, and predominance of phytosterols (sitosterol and stigmasterol) from higher plant detritus. In contrast, river sediment extracts contain biomarkers predominantly from mangrove-derived organic matter, such as the triterpenoids taraxerol and myricadiol. Significant amounts of saccharides and omega-hydroxyalkanoates are also found. Generally, compound concentrations decrease downstream due to dilution, and alteration of organic compounds from plant waxes and coastal vegetation is obvious in both peat and sediment samples. This is confirmed by the significant low abundance of n-alkanes and n-alkenoic acids due to biodegradation, oxidation of alpha-tocopherol to homophytanic acid gamma-lactone, and presence of traces of dihydrolacunosic acid, a photochemical alteration product of taraxerol.

C25 highly branched isoprenoids (HBIs) are potentially valuable indicators of diatom-derived organic matter (OM) inputs to sediments and the C25 alkane has been used previously as a biomarker in paleoenvironmental studies. In this work, a suite of C25 HBI monoenes and dienes was detected in a sediment core from Russell Key, central Florida Bay, USA. Hydrogenation proved all these compounds to be acyclic alkenes with the parent structure of the C25 HBI alkane 2,6,10,14-tetramethyl-7-(3′-methylpentyl)pentadecane. The tentative double bond positions and geometry of three monoenes and one diene were also established on the basis of comparison of retention indices (RI) and mass spectra with those published for synthetic or isolated compounds. The abundance of individual alkenes showed significantly different depth profiles. The concentrations of dienes decreased rapidly with increasing depth, but this trend was not observed for the monoenes. The highest concentration of total C25 HBIs was observed at mid depth in the core, suggesting strong historical inputs of diatom-derived sedimentary OM during that period. In fact, the depth profile of C25 HBIs reflected quite well historical variations in diatom abundance and variations in diatom species composition in central Florida Bay, based on the results of fossil diatom species analysis using microscopy. This study provides further evidence that, with care, some C25 HBIs can be applied as biomarkers for diatom inputs in paleoenvironmental studies although our data did not allow the identification of one specific diatom group as the main HBI contributor.

A geochemical assessment was performed on Lake Leopoldo, a tropical lake located on the Guayana Shield, Venezuela. The lake water was characterized (Ca2+, Mg2+, Na+, K+, Cl−, NO 3 - , NO 2 - , SO 4 2 - , NH 4 + , Fe, and P), lacustrine setting the origin, transport and fate of sedimentary material in this highly unusual lacustrine setting. Lake sediments were analyzed for textural, mineralogical and chemical composition, including the rare earth element (REE) contents. In addition to %TOC, δ13C, δ15N and elemental C/N ratios, the molecular distributions of several biomarker compounds were determined and used to assess organic matter source and transport to the lake. Lake Leopoldo developed on a sequence of quartz arenites of the Precambrian Roraima Group. The area conforms to the definition of pseudo-karst morphology. The results show that the lake is oligotrophic where primary production seems to be limited by nutrients. In the sediments, organic matter shows an overwhelming higher plant-derived origin. Certain elements (K, V, Cu, Th, Ba, Hg, and LREE) displayed enrichments with organic matter, while others (Zr, Hf, Si, Sn, Pb, and Ta) displayed an association with the mineral fraction. The results obtained in this study suggest that the lake water characteristics and the affinities of trace elements for sediment organic fractions are controlled by biogeochemical processes within the surrounding forest soil environment, prior to the transport of the terrestrially-derived organic matter to the lake. The most significant geochemical finding is that organic matter can play an important role in the distribution of trace metals in such highly oligotrophic terrains of humid, tropical environments.

There is increasing evidence that certain microbially-derived compounds may account for part of the aquatic dissolved organic nitrogen (DON) pool. Enantiomeric ratios of amino acids were used to assess the microbial input to the DON pool in the Florida Everglades, USA. Elevated levels of d -alanine, d -aspartic acid, d -glutamic acid and d -serine indicated the presence of peptidoglycan in the samples. The estimated peptidoglycan contribution to amino acid nitrogen ranged from 2.8 ± 0.1% to 6.4 ± 0.9%, increasing with salinity from freshwater to coastal waters. The distribution of individual d -amino acids in the samples suggests additional inputs to DON, possibly from archaea or from abiotic racemization of l -amino acids.

The assessment of organic matter (OM) sources in sediments and soils is a key to better understand the biogeochemical cycling of carbon in aquatic environments. While traditional molecular marker-based methods have provided such information for typical two end member (allochthonous/terrestrial vs. autochthonous/microbial)-dominated systems, more detailed, biomass-specific assessments are needed for ecosystems with complex OM inputs such as tropical and sub-tropical wetlands and estuaries where aquatic macrophytes and macroalgae may play an important role as OM sources. The aim of this study was to assess the utility of a combined approach using compound specific stable carbon isotope analysis and an n-alkane based proxy (Paq) to differentiate submerged and emergent/terrestrial vegetation OM inputs to soils/sediments from a sub-tropical wetland and estuarine system, the Florida Coastal Everglades. Results show that Paq values (0.13–0.51) for the emergent/terrestrial plants were generally lower than those for freshwater/marine submerged vegetation (0.45–1.00) and that compound specific δ13C values for the n-alkanes (C23 to C31) were distinctively different for terrestrial/emergent and freshwater/marine submerged plants. While crossplots of the Paq and n-alkane stable isotope values for the C23 n-alkane suggest that OM inputs are controlled by vegetation changes along the freshwater to marine transect, further resolution regarding OM input changes along this landscape was obtained through principal component analysis (PCA), successfully grouping the study sites according to the OM source strengths. The data show the potential for this n-alkane based multi-proxy approach as a means of assessing OM inputs to complex ecosystems.

Dissolved organic nitrogen (DON) represents the least understood part of the nitrogen cycle. Due to recent methodological developments, proteins now represent a potentially characterisable fraction of DON at the macromolecular level. We have applied polyacrylamide gel electrophoresis to characterise proteins in samples from a range of aquatic environments in the Everglades National Park, Florida, USA. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) showed that each sample has a complex and characteristic protein distribution. Some proteins appeared to be common to more than one site, and these might derive from dominant higher plant vegetation. Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) provided better resolution; however, strong background hindered interpretation. Our results suggest that the two techniques can be used in parallel as a tool for protein characterisation: SDS-PAGE to provide a sample-specific fingerprint and 2D-PAGE to focus on the characterisation of individual protein molecules.

Measurements of dissolved organic carbon (DOC), UV–visible, fixed wavelength fluorescence, and synchronous fluorescence were performed in an effort to characterize spatial and temporal variability in concentration and source of dissolved organic matter (DOM) in surface waters of the southwest coast of Florida. Concentrations of DOC in the surface water ranged from 318 to 2043 μM and decreased from the upper estuary to the coastal areas, and were not only influenced by source strength but also by the hydrology and geomorphology of the mangrove-dominated southwest Florida estuarine area of Everglades National Park. Mangroves provided a significant input of DOM to the estuarine region. This terrestrially derived DOM underwent conservative mixing in these estuaries, but at salinities ≥30 a clear switch from terrestrial to marine DOM was observed indicating a change in the nature and origin of the dominant DOM. The results show that the dynamics of DOM in these subtropical estuaries are complex and that geomorphologically compartmentalized estuarine subregions can be distinguished based on the optical characteristics of their DOM.

In this study, the molecular composition of dissolved organic matter (DOM), collected from wetlands of the Southern Everglades, was examined using a variety of analytical techniques in order to characterize its sources and transformation in the environment. The methods applied for the characterization of DOM included fluorescence spectroscopy, solid state 13C CPMAS NMR spectroscopy, and pyrolysis-GC/MS. The relative abundance of protein-like components and carbohydrates increased from the canal site to more remote freshwater marsh sites suggesting that significant amounts of non-humic DOM are autochthonously produced within the freshwater marshes, and are not exclusively introduced through canal inputs. Such in situ DOM production is important when considering how DOM from canals is processed and transported to downstream estuaries of Florida Bay.

Two sub-tropical estuaries of south Florida, USA, were studied to determine the origin and transport of organic matter between the freshwater and marine end-members of these systems. Sediments, as well as main biomass components (vegetation) were analyzed for lipid composition and content. The molecular distribution of several biomarker compounds, organism-specific biomarkers and bulk sediment characteristics such as %OM, C/N and δ13C were used to assess differences in OM source and transport between a strongly tidally-influenced estuary (Harney River) and one that is only seasonally influenced by estuarine waters (Taylor River). The data show mixing of combined terrestrial and autochthonous freshwater-derived OM, with marine planktonic and seagrass-derived OM in the middle to lower estuary of the Harney River. In contrast, such mixing did not occur to a measurable degree at the Taylor River, where low water discharge and exchange does not allow for any significant mixing of OM from end-member sources. Differences in hydrological conditions and benthic plant biomass and productivity between the two systems results in different OM inputs, which are reflected in the quality and degree of diagenesis of the sedimentary OM. Specific applications and potential limitations of traditional biomarker compounds for OM source assessment are discussed.

n-Alkane-2-ones are lipids commonly found in sediments and soils. This group of compounds, frequently reported in the literature, usually occurs in the form of a homologous series ranging from about C19 to C33 characterized by a strong odd over even carbon number predominance. In this paper we report a different molecular distribution, centered about the C25 homologue as the dominant ketone. The relative abundance of the C25 compared to the C27 homologue in a sediment transect increased from the upper to the lower end of a South Florida estuary, and was found to correlate with surface water salinity in extracts from suspended solids. Analyses of different varieties of seagrasses showed these to be the most likely source of the C25 n-alkane-2-ones, while the C27+ homologues were mainly derived from mangroves and freshwater marsh vegetation. Compound-specific stable isotope measurements and statistical analyses support this finding, suggesting that molecular distributions of n-alkane-2-ones can be used to identify seagrass-derived organic matter in coastal environments.

Several hyphenated analytical techniques, including gas chromatography (GC) coupled with atomic fluorescence spectrometry (AFS), microwave-induced plasma atomic emission spectrometry (AES), and mass spectrometry (MS), have been evaluated for methylmercury and ethylmercury analysis following aqueous derivatization with both sodium tetraethylborate and sodium tetraphenylborate. Both GC-AFS and GC-AES were shown to be excellent techniques with detection limits in the range of sub-picogram levels (0.02-0.04 pg as Hg). Both techniques have wide linear ranges, although setting of the AFS sensitivity has to be selected manually based on the concentration of mercury in the sample. Phenylation seems to be more favorable in this study because of its capability of distinguishing between ethylmercury and inorganic mercury, and low cost compared to ethylation. Although sensitivity of GC-MS is poor with detection limits ranging from 30 to 50 pg as Hg, it is an essential technique for confirmation of the derivatization products.

Stepwise high temperature supercritical fluid extraction (HT–SFE) has been suggested as a tool to study the speciation of hydrocarbons in geological samples. Hydrocarbons extracted at the lower temperatures (e.g., 50°C) are presumed to be part of the freely extractable fraction, while those recovered at the high temperatures (e.g., 300 and 350°C) are those `trapped' within the macromolecular organic matrix and are therefore, resistant to desorption. The latter are released from the matrix after this undergoes thermally induced structural rearrangements. However, the question still remains if and to what extend, pyrolysis of the organic matrix can contribute to this fraction. This study shows, based on the characteristics of the sample matrix of two different shale samples subject to HT–SFE, that pyrolytic contributions at elevated extraction temperatures are only minor under the experimental conditions used, and that thermally induced structural changes in the macromolecular organic matrix are only partially irreversible.