Composition Of POM Research Articles

Organic matter processing by the shrimp Palaemonetes sp .: Isotopic and elemental effects

Aquatic crustaceans often play a major role in organic matter (OM) transformation and recycling through their feeding and excretory activities. In this study, we measured the isotopic and elemental composition of organic matter fed to Palaemonetes sp. shrimp and the fecal pellets they produced. Nitrogen (N) content of the food (8.2 ± 0.2%, mean ± SD) was significantly higher than the fecal pellets (2.0 ± 0.9%), a pattern that also applied to the carbon (C) content of food (46.7 ± 1.0%) and fecal pellets (14.3 ± 6.8%). We also found a significant decrease in the N content of undigested, macerated food (6.1 ± 0.9 %) relative to food that had been soaked in artificial seawater (ASW) and artificial seawater that had previously contained shrimp (CASW) in the absence of feeding shrimp. We found no significant difference in N or C isotopic composition between the dry food, ASW- and CASW-soaked control food, and fecal pellets. We did, however, observe a significant increase in δ 15N of the undigested, macerated food ( δ 15N = 6.3 ± 0.6‰) relative to both the dry flake food ( δ 15N = 5.6 ± 0.2‰) and controls incubated in the absence of shrimp in either ASW ( δ 15N = 5.6 ±0.3‰) or CASW ( δ 15N = 5.8 ± 0.1‰). Our results differ from previous findings of isotopic alteration of OM during processing by crustaceans (copepods), suggesting that isotopic changes related to feeding might be either taxon- or food-specific. This study also provides information on the influence of grazers/shredders on both the elemental and isotopic composition of POM, suggesting that larger aquatic shredders can influence the chemical composition of particles by either physical manipulation of the POM (release of DOM) or by facilitating microbial colonization of the POM.

Mechanical and tribological properties of polyoxymethylene modified with nanoparticles and solid lubricants

AbstractPolyoxymethylene (POM) composites modified with nanoparticles, polytetrafluoroethylene (PTFE) and MoS2 were prepared by a twin‐screw extruder. The effect of nanoparticles and solid lubricant PTFE/MoS2 on mechanical and tribological properties of the composites were studied. Tribological tests were conducted on an Amsler friction and wear tester using a block‐on‐ring arrangement under dry sliding and oil lubricated conditions, respectively. The results showed that generally speaking POM nanocomposites had better stiffness and tribological properties than corresponding POM composites attributed to the high surface energy of nanoparticles, except that the tensile strength of three composites and dry‐sliding tribological properties of POM/3%Al2O3 nanocomposite decreased due to the agglomeration of nanoparticles. Tribological properties differed under dry sliding and oil lubricated conditions. The friction coefficient and wear volume of POM nanocomposites under oil lubricated condition decreased significantly. The increased deformation resistance supported the increased wear resistance of POM nanocomposites. POM/PTFE/MoS2/3%Al2O3 nanocomposite had the best mechanical and tribological properties of all three composites, which was attributed to the synergistic effect of nanoparticles and PTFE/MoS2. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Green and self‐lubricating polyoxymethylene composites filled with low‐density polyethylene and rice husk flour

AbstractPolyoxymethylene (POM) composites filled with low‐density polyethylene (LDPE) and rice husk flour (RHF) were prepared by injection molding. The POM/5 wt % LDPE/7.5 wt % RHF composite exhibited the lowest wear rate, whereas the coefficient of friction remained low, and the POM/5 wt % LDPE/5 wt % RHF composite had the best mechanical properties. X‐ray diffraction analysis was carried out, and the worn surfaces were examined with scanning electron microscopy. The results showed that the addition of the filler reduced the crystallinity degree of the POM composites. The main wear mechanism for unfilled POM was adhesion, whereas for the POM composites, wear seemed to occur mainly by fatigue and abrasion. It was experimentally confirmed that the POM composite filled with LDPE and RHF, which is well‐performing, low‐cost, and environmentally friendly, could be a potential material for tribological applications. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Growth variability and feeding of scallop Patinopecten yessoensis on different bottom sediments: Evidence from fatty acid analysis

Growth and feeding of the Japanese scallop, Patinopecten (= Mizuhopecten) yessoensis, from two populations inhabiting neighboring sites with similar water temperature, salinity, and hydrodynamic regimes but with different bottom sediment types were investigated. Fatty acid biomarkers were used to investigate the diets of scallops and to evaluate the food availability at the sites with different bottom sediments. Fatty acid composition of digestive gland and soft tissues of scallops from two populations were examined and compared to those of plankton, particular organic matter of near-bottom water and bottom sediments as its potential food sources. The high level of 20:5( n − 3) coupled with the high ratio of 16:1( n − 7) to 16:0 in the digestive gland of scallop indicated an important contribution of diatoms to scallop nutrition. The relatively high proportions of 18:2( n − 6), 20:4( n − 6), and 22:6( n − 3) suggested that heterotrophic flagellates, ciliates, and invertebrate larvae were also an important source of nutrition for the scallop. Trace amounts of branched and odd fatty acids were indicative of an insignificant contribution of detritus to scallop diet. Lipid and fatty acid compositions of scallops from two sites were characterized by pronounced differences pointing to the different food availability in near-bottom water at the muddy and sandy sites. Higher food availability at the muddy site resulted in an increase in the total lipid content in scallop's digestive gland due to increased proportion of triacylglycerols. Increased contents of diatom biomarkers indicated that scallops inhabiting muddy bottom were more reliant on diatom food sources. Scallops from the sandy site showed higher proportions of biomarkers derived from flagellates, ciliates, and invertebrate larvae, compared to scallops from the muddy site. This is consistent with the distribution of the fatty acids in near-bottom water POM at the study sites. In spite of the high microbial biomass in muddy bottom sediments and elevated proportion of bacterial fatty acids in near-bottom water POM, bacterial input in scallop diet increased slightly. Thus, the distribution of marker fatty acids in scallops collected at the two sites indicated spatial variability primarily due to the composition and abundance of near-bottom POM, suggesting that scallop feeding is dependent on food availability. Comparison of linear and weight parameters of scallops showed that, in spite of the best food potential at the muddy site, scallops grew significantly slower at the muddy site than at the sandy site. Thus, food potential was not the only factor regulating growth of scallops inhabiting different bottom sediments. It was found, that oxygen concentration in near-bottom water and bottom sediment resuspension depended on the grain-size composition of the sediments. Most probably, low oxygen concentration in the near-bottom water and high resuspension of inorganic fine-grained particles enriched with inedible dead organic matter are the main reasons of the reduction in growth of scallop inhabiting the muddy site.

A comparative study on the abundance and elemental composition of POM in three interconnected basins: the Black, the Marmara and the Mediterranean Seas

The abundance and elemental composition of suspended particulate organic matter in the upper layers of the interconnected Mediterranean, Marmara and Black Seas having different ecosystems were determined in 1990-1998. The aim was principally to compare the C:N:P ratio of seston and understand factors controlling the seston composition in near- and off-shore waters of these seas. In the Marmara Sea, euphotic zone average particulate concentrations varied regionally and seasonally between 10-35 ìM for POC, 0.4-4.5 ìM for PON and 0.05-0.45 ìM for PP. These concentrations are mostly above the off-shore Black Sea values but much greater than those measured in the open waters of the north-eastern Mediterranean whose near-shore data are comparable with the seston content of the deep Black Sea. Comparison of C:N:P ratios of seston reveals that atmospheric and land-based phosphorus input influences the C:P and N:P ratios in the near-shore waters. Apparent nutrient deficiencies observed in the water column were not as remarkable in the elemental composition of seston. Unexpectedly, in the NE Mediterranean, N:P ratios from regression analyses of particulate data are very low (7-9) in the coastal region but slightly increase to levels of 10-15 in the open sea. In the Sea of Marmara, the N:P ratios (7-12) of seston are as low as in the Mediterranean, being consistent with the particulate ratios of the Black Sea inflow and NO3:PO4 ratios of the Marmara sub-halocline water. The Black Sea seston is relatively rich in carbonaceous compounds with N:P ratio ranging merely between 15-17 in the open sea but 9-27 in coastal waters where riverine discharges markedly influence the stoichiometry of seston.

Ecophysiological model of growth and reproduction of the black pearl oyster, Pinctada margaritifera: potential applications for pearl farming in French Polynesia

A model of bioenergetics of the black pearl oyster ( Pinctada margaritifera) was built to simulate growth, reproduction and spawning in suspended culture at field sites in Takapoto lagoon (French Polynesia). This model was based on allometric scaling of physiological functions and scope for growth (SFG) calculations. The input functions were clearance rate (CR, l day −1), retention efficiency (RE, %) for each kind of particle encountered in suspended matter, pseudofaeces and faeces productions (PF and F, mg C day −1), excretion and respiration rate (U and R, mg C day −1). The assimilated carbon (i.e., SFG, mg C day −1) was partitioned to the three internal state variables (somatic tissue, shell and gonad) according to the asymptotic increase of the reproductive effort (ER, %) with the age. Given organic and mineral particulate matter in suspension in lagoon water (POM and PIM, mg L −1) and assuming that the taxonomic composition of POM was fairly constant throughout the year, the model predicted annual evolution of total tissue weight ( W Tissue, g dry weight), shell weight ( W Shell, g DW) and gonad weight ( W Gonad, g DW) of pearl oysters at various ages. Data on tissue and shell growth, but also on gonad development of cultivated pearl oysters, acquired in 1997–1998 in Takapoto lagoon, were used to validate the model outputs. Results of the simulations indicated that the P. margaritifera growth model provided realistic growth trajectories for shell, somatic tissue and gonad, for pearl oysters aged from 1 to 4 years. For scientists, this validated model is very useful to understand more extensively feeding processes and reproduction features of P. margaritifera in Polynesian lagoons. It provides also valuable information for pearl farmers and for management of cultured populations, especially concerning the time to produce a pearl, spat collection, density in system culture, choice of farming site and carrying capacity of the whole lagoon. In this respect, the model demonstrates that local overdensity must be avoided especially when water current is low (<1 cm s −1) and that global consumption of the cultivated pearl oyster stocks plays a insignificant role in comparison with the consumption of all the natural bivalves occurring in the lagoon. Nevertheless, this first growth model developed for P. margaritifera was only validated for a Takapoto atoll and presents several limitations concerning especially the temperature effect and the range of food concentration. Consequently, some improvements will be necessary to apply this work to other pearl farming sites in French Polynesia.

Seasonal variation in the stable carbon and nitrogen isotope biogeochemistry of a coastal cold ocean environment

The carbon and nitrogen isotopic composition of seston, sinking POM, and inorganic nitrogen was determined on a seasonal basis in a coastal cold-ocean embayment, Conception Bay, Newfoundland. Isotopic variation in particulate organic matter and nitrate as a function of depth and season was large and reflected the dynamic nature of carbon and nitrogen cycling in continental shelf environments. Seston and sinking POM were most similar in δ 13C and δ 15N during a spring bloom in March and April when diatom productivity dominated both of these particle fractions. Following the spring bloom, differences in the isotopic composition of seston and sinking POM were related to distinctions in residence times or phytoplankton species contributing to these materials. Shifts in the δ 15N and δ 13C of sinking POM toward those of seston in late summer were indicative of an increase in zooplankton grazing and fecal pellet production. Evidence for the control of phytoplankton δ 13C by pC0 2 during the spring bloom was illustrated by a maximum in the δ 13C of seston concomitant with reductions in the concentration of DIC and high chlorophyll fluorescence from March through mid-April. Following the spring bloom, seston δ 13C values were decreased in association with increases in DIC concentration and a change in phytoplankton species composition. The δ 15N of nitrate in Conception Bay averaged 0.2%o, a value that is markedly lower than those of other oceanic environments and most likely reflects isotopic discrimination associated with mineralization and nitrification in the cold, well oxygenated waters of this system. Seston was considerably more enriched in 15N than nitrate at all times, which clearly indicated that in contrast to other environments, an isotope effect during nutrient uptake was not the predominant control on the isotopic character of seston in this bay. The exact processes contributing to enrichments in 15N in seston are not clear, but most likely include regenerative processes such as losses of dissolved organic nitrogen and ammonium, microzooplankton grazing, protein hydrolysis, and microbial degradation. In addition, losses of 15N depleted material as sinking POM may have contributed to the high δ 15N values for seston in Conception Bay. In that marked enrichments in the '5N content of seston were most pronounced at the base of the chlorophyll fluorescence maximum in spring, the magnitude of isotopic fractionation during these processes may be controlled by the availability of phytoplankton-produced substrates. Seston δ 15N also increased at the end of the spring bloom and may therefore reflect a change in the nutrient source supporting productivity from nitrate, with a low δ 15N, to regenerated nitrogen. In this manner, the δ 15N of seston may be a sensitive indicator of the transition from productivity based on nitrate to one based on regenerated ammonium. The large distinction in δ 15N between seston and nitrate in Conception Bay may be related to a greater supply of nitrate via destratification and coastal upwelling, which initiates primary production and regenerative processes, than is typical of more oligotrophic environments.

Changes in the δ13C of surface water particulate organic matter across the subtropical convergence in the SW Indian Ocean

We have measured the carbon isotopic composition of particulate organic matter suspended in surface waters (POM) between 59°S and 30°S in the SW Indian Ocean during the austral summer. In an attempt to further document the pattern and causes of covariance between POC‐δ13C and [CO2aq], we concurrently measured surface water pCO2, temperature, salinity, nitrate concentration, POM concentration, chlorophyll a and the δ13C of total dissolved inorganic carbon. While we found the previously reported general negative correlation between POC‐δ13C and [CO2aq], we also observed a prominent maximum in POC‐δ13C in the region immediately north of the Subtropical Convergence, coinciding with a maximum in [POM] and chlorophyll a, and with a minimum in pCO2. The increase in POC‐δ13C between 59°S and the Subtropical Convergence is consistent with the trend expected if [CO2aq] were the main factor controlling the isotopic composition of POM. In contrast, data from the region north of the Subtropical Convergence clearly illustrate that POC‐δ13C can also vary independently of [CO2aq] as a 5 per mil decrease in POC‐δ13C was found in a region characterized by nearly constant [CO2aq]. We review several physiological factors which may account for these observations and discuss their implications for paleoceanographic reconstruction of [CO2aq] from the carbon isotopic composition of sedimentary organic matter.