Origin Of Particulate Organic Matter Research Articles

Amino acid carbon isotope profiles provide insight into lability and origins of particulate organic matter

AbstractIdentifying the phytoplankton origin of particulate organic matter (POM) in the deep ocean is challenging due to the changing phytoplankton composition and varied extent of decomposition by heterotrophic bacteria and zooplankton. Here, we report vertical distributions of amino acid stable carbon isotope values (δ13C) measured in particles in the South China Sea. Carbon‐weighted amino acid δ13C values generally parallel bulk POM δ13C profiles with a positive offset from 2.4‰ in the surface water to 6.0‰ in deep. Accordingly, a lability model is introduced to describe the relative distribution and isotopic linkage of labile and refractory particulate organic carbon. Temporal changes of amino acid δ13C were observed during the microbial decomposition of two phytoplankton strains, the prokaryote cyanobacterium Synechococcus and the eukaryote diatom Thalassiosira weissflogii. Principal component analysis of individual amino acid δ13C values from the decomposing cells separate samples into two components, reflecting the influence of microbial decomposition and taxonomic differences, respectively. These two components were further applied to particles. A major contribution from decomposing phytoplankton to particles below the euphotic zone was observed, with more prokaryote organic matter in the basin and a larger contribution from eukaryotes at stations near the productive northern shelf. Our findings show the applicability of amino acid δ13C values in tracing the lability and phytoplankton origins of POM in samples with varied extents of decomposition in marine environments.

Sources of particulate organic matter in the Chukchi and Siberian shelves: clues from carbon and nitrogen isotopes

The stable isotopic composition (δ13C and δ15N) and carbon/nitrogen ratio (C/N) of particulate organic matter (POM) in the Chukchi and East Siberian shelves from July to September, 2016 were measured to evaluate the spatial variability and origin of POM. The δ13CPOC values were in the range of −29.5‰to −17.5‰ with an average of −25.9‰±2.09‰, and the δ15NPN values ranged from 3.9‰ to 13.1‰ with an average of 8.0‰±1.6‰. The C/N ratios in the East Siberian shelf were generally higher than those in the Chukchi shelf, while the δ13C and δ15N values were just the opposite. Abnormally low C/N ratios ( 10‰) values were observed in the Wrangel Island polynya, which was attributed to the early bloom of small phytoplankton. The contributions of terrestrial POM, bloom-produced POM and non-bloom marine POM were estimated using a three end-member mixing model. The spatial distribution of terrestrial POM showed a high fraction in the East Siberian shelf and decreased eastward, indicating the influence of Russian rivers. The distribution of non-bloom marine POM showed a high fraction in the Chukchi shelf with the highest fraction occurring in the Bering Strait and decreased westward, suggesting the stimulation of biological production by the Pacific inflow in the Chukchi shelf. The fractions of bloom-produced POM were highest in the winter polynya and gradually decreased toward the periphery. A negative relationship between the bloom-produced POM and the sea ice meltwater inventory was observed, indicating that the net sea ice loss promotes early bloom in the polynya. Given the high fraction of bloom-produced POM, the early bloom of phytoplankton in the polynyas may play an important role on marine production and POM export in the Arctic shelves.

Stable Carbon Isotope Signature of Particulate Organic Matter in the Southwestern Sumatran Waters of the Eastern Indian Ocean

The Southwestern Sumatran Waters of the Eastern Indian Ocean are known to be affected by the South Java Current and the South Equatorial Counter Current. Many studies have been carried out in relation to upwelling and the Indonesian Through Flow. However, there has been no systematic study into the properties of the particulate organic matter in the Southwestern Sumatran Waters. Therefore, the organic matter in these waters in terms of its origin is unknown. As part of the Widya Nusantara Expedition 2015 research cruise, this study aimed to examine the stable isotope ?13C signature of particulate organic matter (POM), especially with regards to the origins of the organic matter. The stable isotope ?13C is complemented by other variables such as chlorophyll-a, particulate organic carbon (POC), and nutrients (phosphate, silicate, ammonium and nitrate). The POC tends to be depth-dependent. The values of ?13C are ?23.56, ?24.30 and ?24.06‰ for 5, 100 and 300 m depths, respectively. We found that POM tended to be isotopically lighter with increasing POC and chl-a, especially in the surface water, potentially due to the preferential lighter carbon isotope for metabolism by the primary producer. The origin of POM in the Southwestern Sumatran waters is marine end-member in the surface (up to 100 m depth) and mixed compositions at the surface of twilight zone (100–300 m depth). The next layer, i.e. twilight zone (more than 300 m depth), is terrigenous end-member. The surface POM of SSW, as shown in 5 m depth, is not freshly produced and tends to be either autochthonous or allochthonous.

Origin of particulate organic matter in a river with remarkable water pollution in Shikoku Island, Japan

This study on the origin of particulate organic matter (POM) in a river under efficient water use for irrigation in a basin was carried out on the Shin River in Kagawa Prefecture, Japan. The organic pollution in the basin where water resources are scarce was studied. The level of POM in the Shin River was significantly influenced by the natural and artificial hydrological environment in the river basin. The degree of organic pollution in the Shin River was high, and most of the organic matter was algae. The δ18O of water of the middle and lower reaches of the Shin River was high, and water subjected to evaporation for a lengthy time period in the basin flows into the river. The concentration of organic matter in the Shin increases along with the increase in δ18O. Algae also increases in the stay waters in the basin of the middle–lower reaches and flows into the Shin. It was thought that the irrigation ponds in the basin were the main sources of water and organic matter for the river. This tendency was notable during the nonirrigation season in that the volume of water in the basin decreased. On the other hand, the proportion of algae in organic matter in the river decreased when there was considerable precipitation.

Tiny is mighty: seagrass beds have a large role in the export of organic material in the tropical coastal zone.

Ecosystems in the tropical coastal zone exchange particulate organic matter (POM) with adjacent systems, but differences in this function among ecosystems remain poorly quantified. Seagrass beds are often a relatively small section of this coastal zone, but have a potentially much larger ecological influence than suggested by their surface area. Using stable isotopes as tracers of oceanic, terrestrial, mangrove and seagrass sources, we investigated the origin of particulate organic matter in nine mangrove bays around the island of Phuket (Thailand). We used a linear mixing model based on bulk organic carbon, total nitrogen and δ13C and δ15N and found that oceanic sources dominated suspended particulate organic matter samples along the mangrove-seagrass-ocean gradient. Sediment trap samples showed contributions from four sources oceanic, mangrove forest/terrestrial and seagrass beds where oceanic had the strongest contribution and seagrass beds the smallest. Based on ecosystem area, however, the contribution of suspended particulate organic matter derived from seagrass beds was disproportionally high, relative to the entire area occupied by mangrove forests, the catchment area (terrestrial) and seagrass beds. The contribution from mangrove forests was approximately equal to their surface area, whereas terrestrial contributions to suspended organic matter under contributed compared to their relative catchment area. Interestingly, mangrove forest contribution at 0 m on the transects showed a positive relationship with the exposed frontal width of the mangrove, indicating that mangrove forest exposure to hydrodynamic energy may be a controlling factor in mangrove outwelling. However we found no relationship between seagrass bed contribution and any physical factors, which we measured. Our results indicate that although seagrass beds occupy a relatively small area of the coastal zone, their role in the export of organic matter is disproportional and should be considered in coastal management especially with respect to their importance as a nutrient source for other ecosystems and organisms.

Tracing carbon sources in small urbanising streams: catchment‐scale stormwater drainage overwhelms the effects of reach‐scale riparian vegetation

Summary Organic matter provides energy and nutrients to aquatic systems. Alterations to its sources and processing have repercussions for water quality and food‐web stability and structure. Despite worldwide recognition of the impacts of urbanisation, there is limited understanding of the relative importance of catchment‐scale urban stormwater drainage connection and reach‐scale riparian vegetation on organic matter sources. We investigated the effects of catchment‐scale urban stormwater drainage connection and reach‐scale riparian vegetation cover on organic matter sources in small streams. Using stable isotopes and elemental ratios (i.e. δ13C, δ15N and C : N), we traced the origin of microbially respired carbon and standing stocks of dissolved organic carbon (DOC), suspended particulate organic matter (POM) and benthic coarse particulate organic matter (CPOM). Catchment‐scale urban stormwater drainage connection significantly increased the contribution of labile organic matter to POM and DOC standing stocks. Greater POM lability was a product of increased inputs of autochthonous organic matter in more heavily urbanised streams, although the origin of labile DOC was less clear. While reach‐scale riparian vegetation was the most likely source of the terrestrially dominated CPOM observed across most sites, increasing cover had no significant effect on the origin of POM or DOC standing stocks. We conclude that catchment‐scale stormwater drainage impacts overwhelm the effects of reach‐scale riparian vegetation on the sources and lability of POM and DOC in small streams. Our results suggest that the protection or restoration of riparian vegetation, in the absence of modifications to catchment‐scale stormwater drainage connection, is insufficient to mitigate the effects of urbanisation on organic matter sources, lability and processing in these small streams.

Molecular and isotopic characterization of the particulate organic matter from an eutrophic coastal bay in SE Brazil

Abstract The present work aimed at studying the origin of particulate organic matter in Guanabara Bay and in some rivers of the Guanabara basin by using elemental composition, isotopic ratios (δ 13 C and δ 15 N) and molecular markers (sterols) in samples collected in two periods (winter and summer). Elemental and isotopic compositions were determined by dry combustion and mass spectrometry, respectively, while sterols were investigated by GC–FID and GC–MS. Higher sterol concentrations were present in the north-western part of the bay in winter (5.10–23.5 μg L –1 ). The high abundance of algal sterols (26–57% of total sterols), the elemental composition (C/N=6–8) and the isotopic signatures (δ 13 C=−21.3‰ to −15.1‰ and δ 15 N=+7.3‰ to +11.1‰) suggested the predominance of autochthonous organic matter, as expected for an eutrophic bay, although seasonal variation in phytoplankton activity was observed. Coprostanol concentration (fecal sterol) was at least one order of magnitude higher in the particulate material from fluvial samples (4.65–55.98 μg L –1 ) than in the bay waters ( –1 ). This could be ascribed to a combination of factors including efficient particle removal to sediments in the estuarine transition zone, dilution with bay water and bacterial degradation during particle transport in the water column.

The origin of particulate organic matter and the diet of tilapia from an estuarine ecosystem subjected to domestic wastewater discharge: fatty acid analysis approach

The fatty acid composition of suspended particulate organic matter (POM) and tilapia (Oreochromis mossambicus) and potential sources of organic material in the Manko Estuary, Okinawa Island, Japan, were investigated to elucidate the origin of organic matter in suspended particulate matter and the contribution of these inputs to the diet of tilapia. Fatty acid fingerprints of POM revealed that diatoms, bacteria, and possible material input originating from domestic waste discharges contributed a major proportion of the organic matter pool in the estuary. The diet of tilapia is likely influenced by domestic waste-derived organic matter through a POM link. Because of their highly plastic feeding habits, tilapia may develop a feeding strategy of utilizing the most favorable food resources in the ecosystem. Tilapia likely does not prefer mangrove detritus as a food source as indicated by the absence of even-number long-chain fatty acids (LCFAs) in their tissues. Instead of mangrove detritus, tilapia preferentially utilized more palatable organic food sources in the water column, such as phytoplankton and its detrital matter. In addition to phytoplankton and bacterioplankton, the other dietary sources that contributed a minor fraction were possible green macroalgal materials and zooplankton.

Interannual variation in stable carbon and nitrogen isotope biogeochemistry of the Mattaponi River, Virginia

Seasonal and interannual variation of the stable carbon (C) and nitrogen (N) isotope composition of suspended particulate organic matter (POM) was measured in the brackish and tidal freshwater regions of the Mattaponi River, a tributary of the York River, Virginia, and a pristine end member on a continuum of anthropogenic modification within Chesapeake Bay. A principal components analysis indicated that seasonal variation was related to physical mixing and river discharge. Freshwater POM had high C : N (.12), depleted particulate organic carbon isotopic composition (d13CPOC, 226% to 230%), and depleted particulate nitrogen isotopic composition (d15NPN, 2–10%) compared to brackish water POM, which had lower C : N and enriched d13CPOC (224% to 227%) and d15NPN (7–15%). During high discharge events, the d13CPOC was enriched, the d15NPN depleted, and the C : N high relative to low discharge periods, indicating a large contribution from terrestrial-derived material. Within tidal freshwater, POM was comprised of humic-rich sediment, vascular plant matter, and phytoplankton produced in situ. Nonconservative mixing behavior was observed. Endogenously produced phytoplankton increased POC concentrations in tidal freshwater and oligohaline portions during base flows. Where estuarine and riverine POM mixed, the isotopic composition of the POM was homogenized, blurring source-specific characters observed upriver and thereby emphasizing the need to characterize the freshwater end member of estuaries carefully in order to identify POM sources. In estuaries, identifying the origin of particulate organic matter (POM) is difficult because POM is received from multiple sources, including riparian vegetation, adjacent marsh vegetation, submerged and emergent aquatic vegetation and associated epiphytes, and phytoplankton produced in situ. Early research using the stable isotope composition of estuarine POM to identify its dominant origins and fates led investigators to conclude that estuarine phytoplankton and terrestrial material were the major contributors to estuarine organic matter (OM; dissolved and particulate fractions) and that these sources

Temporal variations in 13C and 14C concentrations in particulate organic matter from the southern North Sea

As a new approach for the characterization and determination of the origin of particulate organic matter (POM) in coastal waters, we measured the 14C activity and 13C/12C isotope ratios and applied molecular analysis by means of AMS, IRMS and pyrolysis-GCMS for both bulk samples and isolated fractions of POM from the North Sea off the Dutch coast. The fractions were obtained by a sequence of chemical treatments separating polysaccharides, proteins, lipids and non-hydrolysable resistant compounds. The 13C/12C and 14C/12C isotope ratios, the 14C activities and the polysaccharide/protein contents were high in the spring and summer samples and significantly lower in the autumn and winter samples. This is explained by the high amount of marine phytoplankton in summer and spring, and the presence of detrital material in autumn and winter. It was noted that phytoplankton as found in the spring and summer samples was ca. 20% enriched in 14C with respect to natural values, very likely caused by 14C contamination of the water from the English Channel by the nuclear fuel reprocessing plant at La Hague, Normandy, France. The 13C/12C isotope ratios and 14C activity data show that the winter sample was not a simple mixture of relatively recent marine phytoplankton and POM from the rivers Rhine and Meuse. The main source of both terrestrial and marine organic matter in POM in winter is resuspended organic matter derived from eroded sea floor deposits with relatively low contributions of polysaccharides and proteins.

Seasonal Variations in Suspended Particulate Matter in the Marennes-Oléron Bay, France, using Lipids as Biomarkers

In the most important oyster-producing area in France, an investigation was conducted to determine the origin of particulate organic matter (POM) of the size, <100 μm, available to oysters. Suspended particulate matter (SPM) was sampled monthly over 1 year at one estuarine station in the Bay, Fort Boyard, and at one river station in the Charente at St. Savinien. Lipid-class and fatty-acid profiles were determined in the SPM. At Fort Boyard, variations in amounts of SPM and its ratio of both POC:Chlorophyll aand C:N were associated with changes in river discharge rates, local resuspension and phytoplankton proliferation. High concentrations of mineral and detrital particles were observed in winter, and low levels during the rest of the year, when phytoplankton blooms occur frequently. Lipid-class and fatty-acid profiles varied in relation to seasonal changes in both weather and hydrology. The terrestrial contribution to SPM was highest in winter, when river outflow and resuspension in the Bay were also maximal. High bacterial biomass occurred in association not only with river detritus, but also with early-spring blooms. Microalgal fatty acids were predominant from spring to autumn and, by using compounds shown to be of taxonomic significance, the presence of diatoms could be discerned from that of other microalgae. In winter, the estuarine and freshwater stations showed similar lipid compositions, with dominance by terrestrial and bacterial biomarkers. In summer, however, fatty-acid profiles were very different at the two sites, showing clear temporal variations, which suggest that the Bay and the River then function as separate systems and follow different biological patterns.

Molecular and isotopic tracers used to examine sources of organic matter and its incorporation into the food webs of San Francisco Bay

Multiple indicators (Chl a, C: N ratios, [δ13C]POC, and two classes of lipid biomarker compounds—sterols and phospholipid ester‐linked fatty acids) were used to evaluate spatial and temporal variations in the origin of particulate organic matter (POM) in the San Francisco Bay (SFB) estuary. Comparisons were made between the northern and southern subestuaries of SFB, as well as along the salinity gradient of northern SFB. Two sample types were collected—seston, which was used to characterize the bulk POM, and tissues of the suspension‐feeding bivalve Potamocorbula amurensis—in order to evaluate the assimilable portion of the POM. Samples were collected around biological and physical events (phytoplankton blooms and freshwater inflow) thought to be the primary mechanisms controlling temporal variability in organic matter sources. Seston samples indicate that phytoplankton sources of POM are important throughout the entire SFB system, with additional inputs of organic matter from bacterial and terrestrial vascular plant sources delivered to the northern region. Analysis of biomarker compounds in P. amurensis tissues indicates that phytoplankton supply a large fraction of the assimilable carbon to clams throughout SFB, although isotopic analysis of clam tissues suggests that the origin of this reactive carbon varies spatially and that freshwater algae are an important source of reactive organic matter to clams living in northern SFB.