Terrestrially-derived Organic Matter Research Articles

Sediment organic matter predicts polycyclic aromatic hydrocarbon distribution in port sediments

We evaluated the influence of organic matter in polycyclic aromatic hydrocarbons (PAHs) in port sediments using multiple linear regression (MLR) and prediction models. Total sediment PAHs ranged between 45 and 3230 ng/g dw (average: 557 ± 962 ng/g dw), with PAHs primarily originating from river inputs, confined to areas near the estuaries. Coal/biomaterial combustion and petroleum mainly contribute to the presence of PAHs along estuaries, with medium-high to high ecological risks. MLR TPAHs prediction model included variables, namely, the marine-derived total organic carbon (TOCmar), terrestrial fraction of organic matter (Fterr), and carbon-to‑nitrogen ratio (CNR). Results indicate that mainly marine- followed by terrestrially-derived organic matter influenced sediment PAH distribution. Total organic nitrogen and CNR were variables in the toxic equivalent (TEQ) prediction model, demonstrating that terrestrial pollution sources primarily influenced TEQ. The study analyzes and predicts the impact of organic matter and its sources on the fate and transport of PAHs in port sediments.

Seasonal dynamics of airborne biomolecules influence the size distribution of Arctic aerosols

Organic matter is crucial in aerosol–climate interactions, yet the physicochemical properties and origins of organic aerosols remain poorly understood. Here we show the seasonal characteristics of submicron organic aerosols in Arctic Svalbard during spring and summer, emphasizing their connection to transport patterns and particle size distribution. Microbial-derived organic matter (MOM) and terrestrial-derived organic matter (TOM) accounted for over 90% of the total organic mass in Arctic aerosols during these seasons, comprising carbohydrate/protein-like and lignin/tannin-like compounds, respectively. In spring, aerosols showed high TOM and low MOM intensities due to biomass-burning influx in the central Arctic. In contrast, summer exhibited elevated MOM intensity, attributed to the shift in predominant atmospheric transport from the central Arctic to the biologically active Greenland Sea. MOM and TOM were associated with Aitken mode particles (<100 nm diameter) and accumulation mode particles (>100 nm diameter), respectively. This association is linked to the molecular size of biomolecules, impacting the number concentrations of corresponding aerosol classes. These findings highlight the importance of considering seasonal atmospheric transport patterns and organic source-dependent particle size distributions in assessing aerosol properties in the changing Arctic.

Carbonate Chemistry and the Potential for Acidification in Georgia Coastal Marshes and the South Atlantic Bight, USA

In coastal regions and marginal bodies of water, the increase in partial pressure of carbon dioxide (pCO2) in many instances is greater than that of the open ocean due to terrestrial (river, estuarine, and wetland) influences, decreasing buffering capacity and/or increasing water temperatures. Coastal oceans receive freshwater from rivers and groundwater as well as terrestrial-derived organic matter, both of which have a direct influence on coastal carbonate chemistry. The objective of this research is to determine if coastal marshes in Georgia, USA, may be “hot-spots” for acidification due to enhanced inorganic carbon sources and if there is terrestrial influence on offshore acidification in the South Atlantic Bight (SAB). The results of this study show that dissolved inorganic carbon (DIC) and total alkalinity (TA) are elevated in the marshes compared to predictions from conservative mixing of the freshwater and oceanic end-members, with accompanying pH around 7.2 to 7.6 within the marshes and aragonite saturation states (ΩAr) <1. In the marshes, there is a strong relationship between the terrestrial/estuarine-derived organic and inorganic carbon and acidification. Comparisons of pH, TA, and DIC to terrestrial organic material markers, however, show that there is little influence of terrestrial-derived organic matter on shelf acidification during this period in 2014. In addition, ΩAr increases rapidly offshore, especially in drier months (July). River stream flow during 2014 was anomalously low compared to climatological means; therefore, offshore influences from terrestrial carbon could also be decreased. The SAB shelf may not be strongly influenced by terrestrial inputs to acidification during drier than normal periods; conversely, shelf waters that are well-buffered against acidification may not play a significant role in mitigating acidification within the Georgia marshes.

Geochemistry of organic matter by multi-proxy analyses and temperature sensitivity of methanogenesis in clearwater Amazonian lake sediments

Despite the relevance of bottom sediments from clearwater floodplain lakes in organic matter preservation and degradation, there is a scarcity of data regarding the composition of molecular biomarkers and responses of benthic methanogenesis in Amazonian lakes in global warming scenarios. Here, surface sediments from a small clearwater floodplain lake (Jacundá Lake) in the Brazilian Amazon (Tapajós River) were assessed in a combined approach between molecular biomarker composition and the sensitivity of methanogenesis under two experimental temperatures: 25 °C as control vs. + 4 °C as an Intergovernmental Panel on Climate Change (IPCC) global warming scenario for 2081–2100. Lipid biomarker composition (n-alkanes, sterols) in a 12-cm sediment core revealed a strong predominance of terrestrial-derived organic matter over aquatic contributions, indicating more refractory preserved organic matter, while aquatic organic matter represents substrates to biological degradation. Moreover, alkanoic acids and microbial triterpenoids indicated an intense microbial contribution and elevated organic matter processing. Compound specific isotopic analysis confirmed the presence of methanotrophic microorganisms (diploptene δ13C = −53.5‰) and an uptake of depleted 13C in aquatic organic matter. Diagenetic transformation of biomarkers also indicated a highly anoxic depositional environment throughout the core. Methanogenesis in the upper 15-cm sediment layer under 25 °C (39.3 mg C–CH4 m−2 d−1) was similar to higher rates reported in Amazonian lakes and increased about 60% in the treatment when the temperature increased by 4 °C. Despite the predominant terrestrial sources and subsequent refractory composition of organic matter, our findings integrating biomarkers and metabolic processes support that biomass stocks in clearwater lake sediments of the Amazon basin may be sensitive to global warming.

Deciphering the Composition of Fulvic Acids from Recirculating Aquaculture Systems by Quadrupole Time-of-Flight Mass Spectrometry

The constant reuse of waters in recirculating aquaculture systems (RAS) together with the continuous addition of organic matter from fish degradation components, faeces and non-consumed feed promote the accumulation of dissolved organic matter (DOM), particularly of fulvic acids (FA), leading to the yellow discoloration of their waters. The accumulation of these acids in RAS can have potential effects on its water quality, and consequently fish health and welfare. Thus, the characterization of FA is paramount for improving water quality, and subsequently fish productivity in RAS. In this study, a non-targeted analysis by quadrupole time-of-flight mass spectrometry (QTOF-MS) was used to characterize the recirculating aquaculture systems fulvic acids (RASFA) and then compare their molecular fingerprints with actual reference standards of fulvic acids (FA) (Suwannee River; SRFA, Elliott soil; ESFA and Pahokee Peat; PPFA) purchased from the International Humic Substance Society (IHSS). The results of this study demonstrated the applicability of QTOF-MS as a rapid and comprehensive screening technique to characterize the FA fraction of DOM from RAS and to monitor differences in their molecular fingerprints when compared with other FA samples (SRFA, ESFA and PPFA). The QTOF-MS data from SRFA and ESFA standards matched the list of formulas obtained by 17 high-resolution mass spectrometry (HRMS) instruments with 90 and 76% accuracy, respectively, which guaranteed the power of QTOF-MS without the need for further coupling to liquid chromatography (LC). RASFA was found to be rich in low- and high-oxygen unsaturated classes of compounds (lowOC: 61.73% and highOC: 19.28%) and was similar in composition to SRFA. On the contrary, the ESFA and PPFA soil standards consisted mainly of aliphatic compounds (36.77 and 55.74%, respectively) and differed significantly in composition from the RASFA and SRFA water samples. RASFA matched with 66% of the elemental compositions obtained from the DOM of makeup waters analyzed in a previous experiment, indicating freshwater and seawater origins with a high fraction of terrestrial-derived organic matter (Tanimoto score: 0.53 between RASFA and SRFA). The unique information obtained from the molecular-level analysis of FA samples by QTOF-MS highlights the importance of this technique to characterize and compare FA from different origins rendering it possible to track the FA compositional changes along the water treatment processes of RAS. To our knowledge, this is the first study that characterizes the molecular fingerprints of the RASFA by QTOF-MS and compares them with the available FA reference standards from IHSS.

Lipid biomarkers, stable C and N isotope ratios coupled with multivariate statistics as sources indicators in coastal sediments of Brunei Bay, Southern South China Sea

The surface distribution of lipid biomarkers, elemental and isotopic compositions (δ13C and δ15N, C/N) were investigated from coastal sediments of Brunei Bay, in order to understand the sources and biogeochemical processes of the organic matter. Fatty acid biomarkers from terrestrial higher plants (e.g., long-chain fatty acids>20), phytoplankton (e.g., 20:5n-3 and 22:6n-3) and microbial activity (e.g., iso-, anteiso fatty acids, 10Me-16:0) were identified. The ratios of carbon and nitrogen isotopes (δ13C, δ15N) and C/N had values ranging from –30.62 to –27.43‰, 1.70 to 3.57‰, and 4.07 to 15.62 respectively, suggesting the prevailed inputs of terrestrially-derived organic matter sources with typical characterization of mangrove estuaries. Principal component analysis separated lipids of autochthonous aquatic production as the major source, followed by allochthonous terrestrial derived input. The presence of bacterial derived lipids and short chain lipids with low and C/N ratios suggest the preferential utilization and decomposition of organic matter by microbial activity. An enrichment of the δ15N ratios could be due to marine cage culture activities and surface runoff from cultivated areas via fluvial transport.

Fatty acids as indicators of sediment organic matter dynamics in a monsoon-influenced tropical estuary

Sedimentary organic matter (OM) composition serves as a biomarker and helps in hindcast analysis of the events in the habitat. The present study was carried out on a monthly basis to evaluate the contribution of different biological communities to the surface sediment in a monsoon-influenced tropical Zuari estuary, west coast of India, using source-specific fatty acid (FA) biomarkers and total organic carbon to nitrogen ratio (TOC/TN). Our observations revealed spatio-temporal variation in the OM composition in this estuary, which is influenced by in situ production, bacterial re-working, riverine inputs, and hydrodynamics. The content of TOC, TN, and total FAs in the sediment ranged from 0.13 to 4.27%, 0.01 to 0.31%, and 29 to 122 µg g−1 sediment dry weight, respectively. High content of TOC, TN, total FAs, terrestrial plants-specific FAs, and detrital derived FAs at the lower mid-estuarine (inner) stations when compared to the mouth of the estuary, points out lower mid-estuarine region as the major depositional site for the OM. Low amount of OM at the mouth of the estuary is attributed to high bacterial contribution, which seems to be maintained by repetitive cycles of resuspension-deposition of organic materials. Thus, it seems that the estuarine morphology influences the deposition of OM and plays an important role in the functioning of the estuarine ecosystem. The contribution of phytoplankton-specific FAs was high at the banks of the estuary, which form a suitable habitat for benthic organisms including artisanal fisheries. Diatom, dinoflagellate, and zooplankton-specific FAs were high during the post-monsoon season and decreased from the pre-monsoon to monsoon season. Terrestrial plants and bacteria-derived FAs were high during the monsoon suggesting the role of bacteria in the assimilation of terrestrial material. Elucidating the degradation pattern of in situ produced and terrestrial-derived organic matter through the laboratory designed microcosm experiments is a way forward.

Spatial and temporal variations in stable isotope values (δ13C and δ15N) of the primary and secondary consumers along the southern coastline of the Caspian Sea

Spatial and temporal variations in stable isotope values of the coastal communities in the Caspian Sea remain poorly understood. We followed carbon stable isotope ratios (δ13C) and nitrogen stable isotope ratios (δ15N) of primary (gammarids) and secondary (common carp) consumers at four sites with different organic matter loadings along the southern coastline of the Caspian Sea from May to November 2019. Consumers from the site receiving higher sewage effluent and aquaculture wastes were more enriched in δ15N whereas those from the site receiving lower terrestrial-derived organic matter had enriched δ13C values. Trophic position of consumers varied among sites as a function of organic matter inputs but was independent of month. The observed temporal and spatial variations in the stable isotope values and C:N ratios of the primary and secondary consumers with regards to organic matter loadings, suggesting a possible effect of anthropogenic disturbance on the Caspian Sea ecosystem function.

Dissolved organic matter in large lakes: a key but understudied component of the carbon cycle

The world’s largest five freshwater lakes include tropical meromictic, temperate weakly stratified, and temperate holomictic lakes ranging in age from twenty-five million to ~ 10,000 years old. They contain > 50% of Earth’s surface liquid freshwater and 15% of Earth’s lake-water dissolved organic carbon. Large lakes, however, are understudied in terms of carbon cycling, including the roles of dissolved organic matter (DOM) as dissolved organic carbon (DOC), as chromophoric dissolved organic matter (CDOM), and at the compound class or molecular level. Existing data show that the five largest lakes have lower DOC and CDOM concentrations and clearer water than the global lake median. In Baikal, Superior, and Michigan, however, CDOM is the main non-water absorber of visible light. DOM in these three lakes contain a large proportion of reworked, terrestrially-derived organic matter. Isotopic data for Lake Superior show that its DOM consists of carbon converted into organic matter in the previous decade, though it is difficult to resolve if this organic matter is terrestrial or autochthonous material. No DOC or CDOM characterization or reactivity data exist for the tropical large lakes. Large lakes seem to fall on a continuum with smaller lakes and ocean water, in which water residence time (WRT) and DOC age are linearly related and DOC concentration is negatively correlated with log(WRT). However, existing data are sparse and the mechanisms behind these trends remain to be determined.

Organic fouling assessment of novel PES/SPSf/Double layered hydroxide mixed matrix membrane for water treatment application

Fouling mitigation is of critical importance to warrant the widespread application of membrane filtration. Mixed matrix membranes (MMMs) have emerged as the attractive modified edition of traditional membrane due to their enhanced filtration performance, higher rejection and less fouling potential. This study examined the performance of MMMs by incorporating double layered hydroxide nanomaterials (DLH NMs) within the polyethersulfone/sulfonate polysulfone (PES/SPSf) blend matrix. The MMM with a loading rate of 0.5 wt.% DLH NMs showed an improved performance. The MMM exhibited enhanced antifouling ability than the pristine PES/SPSf membrane for terrestrial-derived organic matter. For sodium alginate (SA), the two membranes showed similar fouling potential, and the MMM even displayed worse irreversible fouling ascribed to higher roughness, reduced negative charge alongside the specific gel-box structure of SA-Ca2+. The fouling potential was further investigated by the thermodynamic analysis. The obtained results suggested that the specific free energies (ΔGho) should be used with the free energies as a function of distance (U) to prevent any fouling misinterpretation. The work clearly implied that the organic fouling behavior during water treatment is somewhat complex and DLH NMs could be promising materials for MMMs to address terrestrial organic matter dominated water resources.

Shrimp farming influence on carbon and nutrient accumulation within Peruvian mangroves sediments

In order to investigate the influence of shrimp farming activities on carbon and nutrient accumulation, sediment cores were collected from two areas at different distances from shrimp farms within a Peruvian mangrove ecosystem. In both areas two sediment cores were collected in a transect, one from a mangrove-covered site and one from a mudflat site. At both study sites, the isotopic values of carbon and nitrogen as well as the C:N molar ratios suggest that the highest carbon accumulation rates were linked to terrestrial-derived organic matter, with higher carbon stocks and fluxes within mangrove-covered zones. The historical records indicate that since the mid-1970′s, the areas nearest to the shrimp farming activity have been accumulating higher proportions of algal derived organic matter, which were likely triggered by the high nutrient influx derived from shrimp farming effluents. The carbon and nutrient fluxes were up to threefold higher within the area nearest to the shrimp farms, whereas the geochronologies showed that the carbon and nutrient stocks in this area increased by up to twofold. The results showed that mangrove-covered zones are more capable to keep pace with sea level rise (SLR) as compared to the mudflat zones, indicating the importance of mangrove vegetation in terms of the vulnerability of this region to SLR and an ongoing capacity to continue accumulating sediments. This study highlights the role that mangrove vegetation plays in mitigating the impact of shrimp farming activities, accumulating carbon and nutrients in pace with SLR.

PAES and PAHs in the surface sediments of the East China Sea: Occurrence, distribution and influence factors

A total of 29 sediment samples were collected from the East China Sea (ECS), with the Yangtze River estuary and the Zhejiang costal area. These sediment samples were analyzed for 6 phthalate esters (PAEs) and 16 polycyclic aromatic hydrocarbons (PAHs): the ΣPAEs and ΣPAHs concentrations ranged between 1649.5 and 8451.5 ng g−1 (mean = 3446.3 ng g−1) and 57.5–364.5 ng g−1 (mean = 166.2 ng g−1), respectively. Overall, the PAEs and PAHs concentrations gradually decreasing in the offshore and southward directions: their compositions and distributions suggest they could have mainly derived from the Yangtze River. In particular, their distribution was influenced by the sources’ proximity, hydrodynamics, and sediment geochemistry (i.e., TOC content and grain size). A classical two-end member model was utilized to estimate the fraction of terrestrial organic carbon in the sediments of the ECS. When the sediment was dominated by terrestrial-derived organic matter (OM), the concentrations of PAEs and PAHs were significantly correlated to the TOC content and gran size of the sediments. In contrast, the poor correlation of TOC content and grain size with PAEs in those sediments dominated by marine-derived OM, implied that the distribution of PAEs in the ECS was mainly related to land-based inputs, (especially to that of the Yangtze River). Regardless of the origin of most of the OM contained in the sediments, we observed positive correlations between the TOC content, and grain size of those containing PAHs. These results suggest that the distribution of PAHs in the ECS was not only related to the Yangtze River input, but also to the geochemical characteristics of the sediments.

Riparian vegetation subsidizes sea lamprey ammocoetes in a nursery area

Fluxes of organic matter (OM) from terrestrial ecosystems subsidize stream food webs, which support the production of ecologically and economically important species such as the sea lamprey Petromyzon marinus. Debris have been previously observed in the gut contents of sea lamprey ammocoetes, but their origin and/or the nutritional sources assimilated are still poorly known. We used carbon (δ13C: 13C/12C) and nitrogen (δ15N: 15N/14N) stable isotopes to identify the main OM sources supporting the production of ammocoetes in a tributary of the Minho River (NW-Iberian Peninsula). Ammocoetes δ13C and C:N values increased with length. Smaller individuals likely assimilated more 13C- depleted sources such as fresh or decaying plant material. The increase in the C:N values with length suggests that ammocoetes accumulate lipids to support their metamorphosis and recruitment into an adult animal. Ammocoetes smaller than 30 mm presented an unusual variability for both δ15N and δ13C values, with values varying between 3.2‰ and 17.8‰ for δ15N and between − 38‰ and − 25.5‰ for δ13C in the same sampling site. This suggests that factors such as organic pollution inputs or time to the first feeding may have contributed to the observed variability. Detritus from the adjacent riparian vegetation was identified as the main food source assimilated by sea lamprey ammocoetes. The stable isotope mixing model (95% CI) indicates that the relative contribution of decaying riparian plants detritus varied between 38–59% and 55–73% at the end of the summer decreasing towards the end of the winter (2–34%). The relative contribution of other terrestrial-derived OM (i.e. fresh riparian detritus and particulate OM with terrestrial origin) was only relevant (> 40%) at the end of the winter. This study shows that there is a strong connectivity between the stream food web and the adjacent riparian ecosystem, and that protection of both riparian and catchment forest cover are essential to preserve terrestrial-aquatic linkages which can support the development of sea lamprey ammocoetes.

Seasonal and spatial variability in the optical characteristics of DOM in a temperate shelf sea

The Celtic Sea is a productive temperate sea located on the Northwest European Shelf. It is an important pathway for the delivery of land-derived material to the North Atlantic Ocean, including dissolved organic matter (DOM). The aim of this study was to determine the seasonal and spatial variability in the magnitude, source and composition of DOM at three sites representing on shelf, central shelf and shelf edge regions in the Celtic Sea, using observations collected during the UK Shelf Sea Biogeochemistry (SSB) research programme (November 2014 – August 2015). The concentration of dissolved organic carbon (DOC) alongside DOM absorbance and fluorescence indices were measured and fluorescence Excitation and Emission Matrices (EEMs) combined with Parallel Factor Analysis (PARAFAC) were used to assess DOM composition and lability. The PARAFAC model identified four unique fluorescent components for autumn (November 2014), winter (March 2015), spring (April 2015) and summer (July 2015) consisting of two humic-like components attributed to terrestrial (C1) and marine sources (C2), and two protein components identified as tyrosine-like (C3) and tryptophan-like (C4) attributed to in situ production. DOC varied seasonally and there were strong cross shelf trends. The protein components (C3 and C4) exhibited large seasonal and within season variability particularly during productive periods. In contrast, there were persistent cross shelf gradients in the CDOM absorption coefficient at 305 nm (a305), the UV specific absorbance at 280 nm (SUVA280), the humification index (HIX), and the humic-like fluorescent components (C1 and C2), which were higher in the on shelf region and decreased towards the shelf edge. The humic-like components and the slope ratio (SR) were significantly correlated with salinity throughout all seasons, indicating a strong influence of terrestrially-derived organic matter in the Celtic Sea, with potentially up to 35% of DOC in the central shelf during winter originating from terrestrial inputs. Results from this study illustrate the importance of monitoring DOM quantitatively and qualitatively for a better understanding of the supply, production, cycling and export of this dynamic organic carbon pool in shelf seas.

Fractionation of Dissolved Organic Matter by Co-Precipitation with Iron: Effects of Composition

Interactions between dissolved organic matter (DOM) and different physical-chemical forms of iron (Fe) represent important biogeochemical processes in the organic carbon cycle. Due to the effect of climate change and anthropogenic activities such as land-use change, the loading of terrestrial DOM into aquatic systems is increasing, and thus, enhancing the organic matter-based acidity in aquatic ecosystems. While complexation of Fe with DOM and the sorption of DOM on iron oxides and (oxy)hydroxides have been reported, less is known about how co-precipitation processes might affect by DOM composition. Here the co-precipitation of two DOM standards, namely the Suwannee River Standard Humic Acid Standard II (SRHA) and Nordic Aquatic Fulvic Acid Reference (NAFA), with Fe was investigated in a pH range of 4.0–8.0. The DOM remaining after co-precipitating with Fe was systematically characterized by various analytical methods to reveal the molecular fractionation of DOM. The co-precipitation of SRHA or NAFA with Fe was enhanced by decreasing the pH, where at pH 4.0, about 70~80% DOC of SRHA or NAFA was removed at Fe(III)/C ratios higher than 0.12. The decrease in SUVA254 and the humification index (HIX) during the co-precipitation process suggests that DOM with high aromatic character was preferentially co-precipitated with Fe. DOM molecular weight influenced the selectivity to co-precipitation, with high molecular weight (HMW) DOM showing a stronger affinity. DOM co-precipitation with Fe was clearly dependent on DOM composition, showing an affinity order of terrestrial humic-like> ubiquitous humic-like> microbial humic-like components. The difference in the reactivity and the relative abundances of excitation emission matrix fluorescence combined with parallel factor analysis (EEM-PARAFAC) components explained the difference in DOC removal efficiency between SRHA and NAFA. This study provides direct insights into the effects of DOM composition on its fractionation specifically through co-precipitation with Fe, and suggests that for aquatic systems rich in iron-based (oxy)hydroxides, and for environmental redox interfaces, co-precipitation of DOM with iron might affect optical properties of the aqueous phase, and represent an important sink for terrestrially-derived organic matter.

Tracing of particulate organic C sources across the terrestrial-aquatic continuum, a case study at the catchment scale (Carminowe Creek, southwest England)

Soils deliver crucial ecosystem services, such as climate regulation through carbon (C) storage and food security, both of which are threatened by climate and land use change. While soils are important stores of terrestrial C, anthropogenic impact on the lateral fluxes of C from land to water remains poorly quantified and not well represented in Earth system models. In this study, we tested a novel framework for tracing and quantifying lateral C fluxes from the terrestrial to the aquatic environment at a catchment scale. The combined use of conservative plant-derived geochemical biomarkers n-alkanes and bulk stable δ13C and δ15N isotopes of soils and sediments allowed us to distinguish between particulate organic C sources from different land uses (i.e. arable and temporary grassland vs. permanent grassland vs. riparian woodland vs. river bed sediments) (p<0.001), showing an enhanced ability to distinguish between land use sources as compared to using just n-alkanes alone. The terrestrial-aquatic proxy (TAR) ratio derived from n-alkane signatures indicated an increased input of terrestrial-derived organic matter (OM) to lake sediments over the past 60years, with an increasing contribution of woody vegetation shown by the C27/C31 ratio. This may be related to agricultural intensification, leading to enhanced soil erosion, but also an increase in riparian woodland that may disconnect OM inputs from arable land uses in the upper parts of the study catchment. Spatial variability of geochemical proxies showed a close coupling between OM provenance and riparian land use, supporting the new conceptualization of river corridors (active river channel and riparian zone) as critical zones linking the terrestrial and aquatic C fluxes. Further testing of this novel tracing technique shows promise in terms of quantification of lateral C fluxes as well as targeting of effective land management measures to reduce soil erosion and promote OM conservation in river catchments.

Energy transfer in the Congo deep-sea fan: From terrestrially-derived organic matter to chemosynthetic food webs

Large amounts of recent terrestrial organic matter (OM) from the African continent are delivered to the abyssal plain by turbidity currents and accumulate in the Congo deep-sea fan. In the recent lobe complex, large clusters of vesicomyid bivalves are found all along the active channel in areas of reduced sediment. These soft-sediment communities resemble those fuelled by chemoautotrophy in cold-seep settings. The aim of this study was to elucidate feeding strategies in these macrofaunal assemblages as part of a greater effort to understand the link between the inputs of terrestrially-derived OM and the chemosynthetic habitats. The biochemical composition of the sedimentary OM was first analysed in order to evaluate how nutritious the available particulate OM is for the benthic macrofauna. The terrestrial OM is already degraded when it reaches the final depositional area. However, high biopolymeric carbon contents (proteins, carbohydrates and lipids) are found in the channel of the recent lobe complex. In addition, about one to two thirds of the nitrogen can be assigned to peptide-like material. Even if this soil-derived OM is poorly digestible, turbiditic deposits contain such high amounts of organic carbon that there is enough biopolymeric carbon and proteacinous nitrogen to support dense benthic communities that contrast with the usual depauperate abyssal plains.Stable carbon and nitrogen isotopes and fatty acid biomarkers were then used to shed light on the feeding strategies allowing the energy transfer from the terrestrial OM brought by the turbidity currents to the abyssal food web. In the non-reduced sediment, surface detritivorous holothurians and suspension-feeding poriferans rely on detritic OM, thereby depending directly on the turbiditic deposits. The sulphur-oxidising symbiont bearing vesicomyids closely depend on the reprocessing of OM with methane and sulphide as final products. Their carbon and nitrogen isotopic signatures vary greatly among sites and could reflect the intensity of the anaerobic oxidation of methane (AOM) in the sediments. Within the vesicomyid habitats, the heterotrophic fauna exhibits a distinctively light carbon isotopic signature in comparison to the background sediments, clearly indicating the utilisation of chemosynthetically-derived OM. Fatty acid biomarkers further confirm that dorvilleid polychaetes consume aggregates that perform AOM. Terrestrial OM reprocessing by microbial consortium thus ensures its transfer to the benthic food web in the Congo deep-sea fan.

Processes affecting the spatial distribution of seagrass meadow sedimentary material on Yao Yai Island, Thailand

Many islands throughout SE Asia are experiencing rapid development and land-cover conversion that potentially threaten sensitive coastal ecosystems, such as seagrasses, through increased loading of sediment and nutrients originating from disturbed catchments draining to the sea. To evaluate this threat for one such island in Southern Thailand (Yao Yai), we perform sediment source tracing via end-member mixing analysis using stable isotopes δ13C and δ15N in organic matter to explore sediment loading in a seagrass meadow. The analysis indicates that sedimentary material in the meadow originates mostly from ocean-associated sources (∼62% from seagrass detritus, seston, and ocean sediments). Terrestrial material comprises ∼19% of the organic material found in the seagrass meadow, with another 20% originating from an adjacent mangrove forest. Approximately one-fourth of the seagrass meadow material (24%) is detritus that has been (re)deposited internally. The high contribution of terrestrial-derived organic matter deposited near the river mouth demonstrates that substantial quantities of sediment are being transferred from upslope erosion sources into the seagrass meadow. However, only a small amount of this material is deposited throughout the entire bay because much of the terrestrial- and mangrove-derived sediment is transferred to the open ocean via channels that are periodically dredged to allow boat access to two small inland harbours. This positive affect of dredging has not received very much attention in existing literature. River water flowing to the channels during falling tide delivers sediment to these efficient pathways, where much of it bypasses the seagrass meadow at periods of time when sediment deposition would normally be the greatest. There is growing concern that ongoing land-cover changes and planned urbanization related to tourism and agriculture on the island may boost sediment/nutrients above a critical threshold, beyond that revealed in our baseline survey. Our tracer-based sediment source approach did not corroborate our observations of substantial erosion and land degradation in the upper catchment—but this could be a result of sediment flushing through the dredged channels. We encourage others to combine such methods with sediment budgeting approaches to triangulate results for consistency. Finally, from an ecological perspective, the high presence of seagrass detritus we found in bay sediments suggests seagrass is potentially a key source of nutrients for the meadow itself, as well as other connected ecosystems.

Distribution and sources of aliphatic hydrocarbons and fatty acids in surface sediments of a tropical estuary south west coast of India (Cochin estuary).

Surface sediments samples from the Cochin estuary were measured for elemental, stable isotopic and molecular biomarkers (aliphatic hydrocarbons and fatty acids) to study the sources and distribution of sedimentary organic matter. Concentrations of total organic carbon (TOC), total nitrogen (TN) and stable isotopic ratios of carbon (δ(13)C) ranged from 0.62 to 2.74%, 0.09 to 0.25% and -27.5 to 21.7 ‰, respectively. Sedimentary n-alkanes ranged from 6.03 to 43.23μgg(-1) with an average of 16.79μgg(-1), while total fatty acids varied from 22.55 to 440.69μgg(-1). The TOC/TN ratios and δ(13)C suggest a mixture of marine- and terrestrial-derived organic matter in the surface sediments with increasing contributions from marine-derived organic matter towards the seaward side. Long-chain n-alkanes derived from higher plants predominated the inner part of the estuary, while short-chain n-alkanes derived from planktonic sources predominated the bar mouth region. The even carbon preference of the C12-C22 n-alkanes may refer to the direct biogenic contribution from bacteria, fungi and yeast species and to the potential direct petroleum inputs. The presence of odd mid-chain n-alkanes in the sediments indicates the organic matter inputs from submerged and floating macrophytes (water hyacinth). Various molecular indices such as carbon preference index, terrestrial to aquatic ratio, average chain length and the ratios of mid-chain n-alkanes support the aforementioned inferences. The high contribution of odd and branched chain fatty acids along with very low contribution of polyunsaturated fatty acids, suggest the effective utilisation of algae-derived organic matter by bacteria and the effective recycling of labile organic matter in whole settling and deposition processes. The distributional variability of n-alkanes and fatty acids reveals the preferential utilisation of marine-derived organic matter and the selective preservation of terrestrial-derived organic matter in surface sediments of the Cochin estuary.

Contrasting patterns of allochthony among three major groups of crustacean zooplankton in boreal and temperate lakes.

The importance of terrestrial-derived organic matter for lake zooplankton communities remains debated, partly because little is known about the basic pathways by which allochthonous carbon is transferred to zooplankton, and whether these vary among the major taxonomic and functional groups. We quantified allochthony of three zooplankton groups (Cladocera, Calanoida, and Cyclopoida) across 18 lakes in Quebec, spanning broad gradients of dissolved organic matter (DOM) and lake trophy, using a multi-isotope (delta2H + delta13C), multi-source (terrestrial, phytoplanktonic, benthic) approach. All three zooplankton groups had significant levels of allochthony, but differed greatly in their respective patterns across lakes. Allochthony in Calanoida and Cyclopoida was linked to detrital food chains based on particulate organic matter (POM) and on DOM, respectively, whereas in Cladocera it appeared related to both pathways; not surprisingly this latter group had the highest mean allochthony (0.31; compared to 0.18 in Cyclopoida and 0.16 in Calanoida). This study highlights the complexity of the pathways of delivery and transfer of terrestrial organic matter in freshwaters, and underscores the role that microbial food webs play in this transfer.