Composition Of Particulate Organic Matter Research Articles

Particulate Organic Matter Affects Soil Nitrogen Mineralization under Two Crop Rotation Systems.

Changes in the quantity and/or quality of soil labile organic matter between and after different types of cultivation system could play a dominant role in soil nitrogen (N) mineralization. The quantity and quality of particulate organic matter (POM) and potentially mineralizable-N (PMN) contents were measured in soils from 16 paired rice-rapeseed (RR)/cotton-rapeseed (CR) rotations sites in Hubei province, central China. Then four paired soils encompassing low (10th percentile), intermediate (25th and 75th percentiles), and high (90th percentile) levels of soil PMN were selected to further study the effects of POM on soil N mineralization by quantifying the net N mineralization in original soils and soils from which POM was removed. Both soil POM carbon (POM-C) and N (POM-N) contents were 45.8% and 55.8% higher under the RR rotation compared to the CR rotation, respectively. The PMN contents were highly correlated with the POM contents. The PMN and microbial biomass N (MBN) contents concurrently and significantly decreased when POM was removed. The reduction rate of PMN was positively correlated with changes in MBN after the removal of POM. The reduction rates of PMN and MBN after POM removal are lower under RR rotations (38.0% and 16.3%, respectively) than CR rotations (45.6% and 19.5%, respectively). Furthermore, infrared spectroscopy indicated that compounds with low-bioavailability accumulated (e.g., aromatic recalcitrant materials) in the soil POM fraction under the RR rotation but not under the CR rotation. The results of the present study demonstrated that POM plays a vital role in soil N mineralization under different rotation systems. The discrepancy between POM content and composition resulting from different crop rotation systems caused differences in N mineralization in soils.

Biogeochemical interactions control a temporal succession in the elemental composition of marine communities

Author(s): Martiny, AC; Talarmin, A; Mouginot, C; Lee, JA; Huang, JS; Gellene, AG; Caron, DA | Abstract: Recent studies have revealed clear regional differences in the particulate organic matter composition and stoichiometry of plankton communities. In contrast, less is known about potential mechanisms and patterns of temporal changes in the elemental composition of marine systems. Here, we monitored weekly changes in environmental conditions, phytoplankton abundances, and particulate organic carbon, nitrogen, and phosphorus concentrations over a 3-yr period. We found that variation in the particulate organic matter (POM) concentrations and ratios were related to seasonal oscillations of environmental conditions and phytoplankton abundances. Periods with low temperature, high nutrient concentrations and a dominance of large phytoplankton corresponded to low C: N: P and vice-versa for warmer periods during the summer and fall. In addition to seasonal changes, we observed a multiyear increase in POM C: P and N: P that might be associated with the Pacific Decadal Oscillation. Finally, there was substantial short-term variability in all factors but similar linkages between environmental variability and elemental composition as observed on seasonal and interannual time-scales. Using a feed-forward neural network, we could explain a large part of the variation in POM concentrations and ratios based on changes in environmental conditions and phytoplankton abundances. The apparent links across all time-scales between changes in physics, chemistry, phytoplankton, and POM concentrations and ratios suggest we have identified key controls of the elemental composition of marine communities in this region.

Quantity and biochemical composition of particulate organic matter in a highly trawled area (Thermaikos Gulf, Eastern Mediterranean Sea)

Bottom trawling represents nowadays one of the most severe anthropogenic disturbances at sea, and determines large impacts on benthic communities and processes. Bottom trawling determines also local sediment resuspension and the effects of the injection of large amounts of surface sediments into the water column have been repeatedly investigated. Few studies have assessed the consequences of sediment resuspension caused by bottom trawling on the quantity, biochemical composition and bioavailability of suspended organic particles and how these eventually rival those exerted by natural storms. To provide insights on this poorly addressed issue, we investigated concentrations and biochemical composition of total and enzymatically digestible pools of particulate organic matter (POM) in the Thermaikos Gulf (Mediterranean Sea) under calm sea conditions, during intensive trawling activities, and after a severe storm. We show here that sediment resuspension caused by trawling can cause large effects on POM quantity, biochemical composition and bioavailability. Both during trawling and after the storm, the relative importance of the carbohydrate pools increased (in the upper water column) and the total lipid concentrations decreased (in the intermediate and bottom layers) when compared to values measured during calm conditions. These results would suggest that bottom trawling could inject in the upper water column POM pools more refractory in nature (<em>e.g</em>., carbohydrates) than those present in calm or after-storm conditions. By contrast, we show also that the bioavailable fraction of biopolymeric C increased significantly during trawling in the upper water column of the shallowest stations and in the bottom water column layer of the deepest ones. These results provide evidence that bottom trawling can influence the overall trophic status of coastal waters, exerting effects similar or stronger than those caused by natural storms, though of variable amplitude depending on the water depth. Since bottom trawling is carried out worldwide and natural storms at sea can be frequent and intense, we claim for the need of assessing new adapting management strategies of bottom trawling in order to mitigate the synergistic impacts of anthropogenic and natural sediment resuspension on coastal biogeochemical cycles.

Tide-Induced Variations in the Fatty Acid Composition of Estuarine Particulate Organic Matter

The particulate organic matter (POM) in hydrodynamically variable habitats such as the lower reaches of estuaries can change in its content and quality on very short time scales (example, hourly), and these changes can potentially influence higher-level consumers in river-estuary-marine systems. Estuarine water samples were collected hourly for 12 h downstream in a small river to evaluate the fatty acid composition of POM over a tidal cycle. Fatty acid constituents of POM collected during the flood tide were dominated by the saturated, higher plant and bacterial fatty acids, whereas unsaturated, polyunsaturated, essential, and diatom-associated fatty acids dominated the POM collected during the ebb tide. Elevated algal biomass (as indicated by high chlorophyll a concentrations), diatom, and freshness indices in the POM indicated enhanced fresh autochthonous-origin materials that dominated the mixed organic pool during the ebb tide compared to more degraded detritus during the flood tide. Tidal retention of organic matter and algal primary production were the most influential factors that differentiated the fatty acid composition of estuarine POM over the short time scale. The results of this study have important implications on the quality of POM at the time of sampling, especially in estuaries where mixed organic pools have multiple inputs and are strongly influenced by tidal cycles.

Temporal variability of particulate organic carbon in the lower Changjiang (Yangtze River) in the post‐Three Gorges Dam period: Links to anthropogenic and climate impacts

AbstractSuspended particles from the lower Changjiang were collected monthly from 2003 to 2011, which corresponds to the three construction periods of the Three Gorges Dam. Organic carbon (%OC), organic carbon to total nitrogen molar ratio, stable carbon isotope, and terrestrial biomarkers were examined. Rating curve studies were applied for the temporal trend analysis. The composition of particulate lignin phenols exhibited clear annual and periodic variations but only minor seasonal changes. Lignin phenol ratios (vanillyl/syringyl and cinnamyl/vanillyl) indicated that the terrigenous organic matter (OM) was primarily composed of woody and nonwoody tissue derived from angiosperm plants. The low‐lignin phenol yields (Λ8) in combination with higher acid to aldehyde ratios reflected a substantial contribution from soil OM to the particle samples or modifications during river transport. The temporal shift of the lignin phenol vegetation index with the sediment load during the flood seasons revealed particulate organic matter (POM) erosion from soils and the impact of hydrodynamic processes. The dam operations affected the seasonal variability of terrigenous OM fluxes, although the covariation of lignin and sediment loads with discharged water implies that unseasonal extreme conditions and climate change most likely had larger influences, because decreases in the sediment load and lignin flux alter the structure and composition of particulate OM (POM) on interannual time scales, indicating that they may be driven by climate variability. The modification of the composition and structure of POM will have significant impacts on regional carbon cycles and marine ecosystems.

Stable isotope ratios in bentho-demersal biota along a depth gradient in the Bay of Biscay: A multitrophic study

Although stable isotope ratios are increasingly used to investigate the trophic ecology of marine organisms, their spatial variations are still poorly understood in the coastal environment. In this study, we measured the stable isotope composition (δ13C, δ15N) of suspended particulate organic matter (SPOM) (primary producer), a suspension feeder, the great scallop Pecten maximus (primary consumer), megabenthic decapods and benthic fishes (secondary consumers) along a depth gradient (from 5 m to 155 m depth) across the continental shelf of the Bay of Biscay. Although the three trophic levels exhibited similar δ13C patterns along the gradient, the δ15N patterns varied between SPOM, scallops and carnivores. The δ15N difference between SPOM and scallops decreased with increasing depth, suggesting that non trophic factors may affect the stable isotope composition of scallops at deepest sampling stations. An opposed trend was found between scallops and carnivores, suggesting that the trophic level of these carnivores increased at higher depth, possibly as an adaptation to lower prey abundances. Although our results suggest that primary consumers are suitable to establish isotopic baselines in coastal environments, we stress the need for further studies aiming at characterizing the variability of stable isotopes in coastal biota, and the respective effects of baseline, trophic and metabolic factors in their isotopic composition.

Zooplankton trophic niches respond to different water types of the western Tasman Sea: A stable isotope analysis

The trophic relationships of 21 species from an oceanic zooplankton community were studied using stable isotopes of carbon and nitrogen. Zooplankton and suspended particulate organic matter (POM) were sampled in three different water types in the western Tasman Sea: inner shelf (IS), a cold core eddy (CCE) and a warm core eddy (WCE). δ15N values ranged from 3.9‰ for the parasitic copepod Sapphirina augusta to 10.2‰ for the euphausiid, Euphausia spinifera. δ13C varied from −22.6 to −19.4‰ as a result of the copepod Euchirella curticauda and E. spinifera. The isotopic composition of POM varied significantly among water types; as did the trophic enrichment of zooplankton over POM, with the lowest enrichment in the recently upwelled IS water type (0.5‰) compared to the warm core eddy (1.6‰) and cold core eddy (2.7‰). The WCE was an oligotrophic environment and was associated with an increased trophic level for omnivorous zooplankton (copepods and euphausiids) to a similar level as carnivorous zooplankton (chaetognaths). Therefore carnivory in zooplankton can increase in response to lower abundance and reduced diversity in their phytoplankton and protozoan prey. Trophic niche width comparisons across three zooplankton species: the salp Thalia democratica, the copepod Eucalanus elongatus and the euphausiid Thysanoessa gregaria, indicated that both niche partitioning and competition can occur within the zooplankton community. We have shown that trophic relationships among the zooplankton are dynamic and respond to different water types. The changes to the zooplankton isotopic niche, however, were still highly variable as result of oceanographic variation within water types.

Use of allochthonous resources by zooplankton in reservoirs

Aquatic food webs are supported by primary production from within the system (autochthony) as well as organic matter produced outside of and transported into the system (allochthony). Zooplankton use allochthonous resources, especially in systems with high terrestrial loading and moderate to low internal primary production. We hypothesized that due to high terrestrial loads and remnant submerged terrestrial material, allochthonous resource use by zooplankton would be significant in all reservoirs and would decline along an increasing reservoir age gradient. Using hydrogen stable isotopes and a Bayesian mixing model, we estimated the contribution of allochthonous sources to organic matter pools and crustaceous zooplankton biomass for ten reservoirs. Dissolved organic matter (DOM) in all systems was dominated by allochthonous sources (posterior distribution median >92% allochthonous), while particulate organic matter (POM) composition varied (2–68% allochthonous) and had a lower allochthonous fraction in older reservoirs. There was no relationship between zooplankton allochthony and reservoir age. Crustaceous zooplankton allochthony varied among systems from 26 to 94%, and Chaoborus allochthony, measured in four reservoirs, was similarly variable (33–94%). Consumer allochthony was higher than POM allochthony in some reservoirs, potentially due to terrestrial DOM pathways being important and/or algal resources being inedible (e.g., cyanobacteria). As with many lakes, in the reservoirs we studied, allochthonous inputs account for a significant fraction of the organic matter of basal consumers.

Seasonal changes in quantity and composition of suspended particulate organic matter in lagoons of the Alaskan Beaufort Sea

Seasonal changes in quantity and composition of suspended particulate organic matter in lagoons of the Alaskan Beaufort Sea

Differences in organic matter and bacterioplankton between sections of the largest Arctic river: Mosaic or continuum?

AbstractWe studied biogeochemical characteristics, including organic carbon and nitrogen contents, fatty acid (FA) composition, stable isotope ratios, and primary production in conjunction with species composition of bacterioplankton, using next generation sequencing, in the Yenisei River along a distance ∼1800 km. Basing on FA composition of particulate organic matter (POM) and on other indicators of sources of POM, the river was subdivided into four sections. The upper section 1, situated in mountain region, was the net source of high‐quality autochthonous organic matter, produced primarily by diatoms and partly consumed by specialized bacteria species. Section 2 in plain taiga was net sink of high quality allochthonous and autochthonous organic matter, produced by cyanobacteria and green algae. Section 3 was net sink of organic matter, primarily allochthonous, consumed by the specialized species of bacteria. The lowest section 4, situated in tundra, was primarily the conduit of recalcitrant terrestrial organic matter, but also the net source of autochthonous organic matter, produced by diatoms. Biogeochemical traits of sections of the Yenisei River evidently shaped dominant species composition of bacterioplankton of these sections. Regarding the biogeochemical and microbiological data, we concluded that the Yenisei River ecosystem complexly combines features of river mosaic, river continuum, and “neutral pipe.”

Seasonal survey of the composition and degradation state of particulate organic matter in the Rhône River using lipid tracers

Abstract. Lipid tracers including fatty acids, hydroxyacids, n-alkanols, sterols and triterpenoids were used to determine the origin and fate of suspended particulate organic matter (POM) collected in the Rhône River (France). This seasonal survey (April 2011 to May 2013) revealed a year-round strong terrestrial higher-plant contribution to the particulate organic matter (POM), with significant algal inputs observed in March and attributed to phytoplanktonic blooms likely dominated by diatoms. Major terrigenous contributors to our samples are gymnosperms, and more precisely their roots and stems, as evidenced by the presence of high proportions of ω-hydroxydocosanoic acid (a suberin biomarker). The high amounts of coprostanol detected clearly show that the Rhône River is significantly affected by sewage waters. Specific sterol degradation products were quantified and used to assess the part of biotic and abiotic degradation of POM within the river. Higher-plant-derived organic matter appears to be mainly affected by photo-oxidation and autoxidation (free radical oxidation), while organic matter of mammal or human origin, evidenced by the presence of coprostanol, is clearly more prone to bacterial degradation. Despite the involvement of an intense autoxidation-inducing homolytic cleavage of peroxy bonds, a significant proportion of hydroperoxides is still intact in higher plant debris. These compounds could affect the degradation of terrestrial material by inducing an intense autoxidation upon its arrival at sea.

Sources and export of particle-borne organic matter during a monsoon flood in a catchment of northern Laos

Abstract. The yields of the tropical rivers of Southeast Asia supply large quantities of carbon to the ocean. The origin and dynamics of particulate organic matter were studied in the Houay Xon River catchment located in northern Laos during the first erosive flood of the rainy season in May 2012. This cultivated catchment is equipped with three successive gauging stations draining areas ranging between 0.2 and 11.6 km2 on the main stem of the permanent stream, and two additional stations draining 0.6 ha hillslopes. In addition, the sequential monitoring of rainwater, overland flow and suspended organic matter compositions was conducted at the 1 m2 plot scale during a storm. The composition of particulate organic matter (total organic carbon and total nitrogen concentrations, δ13C and δ15N) was determined for suspended sediment, soil surface (top 2 cm) and soil subsurface (gullies and riverbanks) samples collected in the catchment (n = 57, 65 and 11, respectively). Hydrograph separation of event water was achieved using water electric conductivity and δ18O measurements for rainfall, overland flow and river water base flow (n = 9, 30 and 57, respectively). The composition of particulate organic matter indicates that upstream suspended sediments mainly originated from cultivated soils labelled by their C3 vegetation cover (upland rice, fallow vegetation and teak plantations). In contrast, channel banks characterized by C4 vegetation (Napier grass) supplied significant quantities of sediment to the river during the flood rising stage at the upstream station as well as in downstream river sections. The highest runoff coefficient (11.7%), sediment specific yield (433 kg ha−1), total organic carbon specific yield (8.3 kg C ha−1) and overland flow contribution (78–100%) were found downstream of reforested areas planted with teaks. Swamps located along the main stream acted as sediment filters and controlled the composition of suspended organic matter. Total organic carbon specific yields were particularly high because they occurred during the first erosive storm of the rainy season, just after the period of slash-and-burn operations in the catchment.

Source-age dynamics of estuarine particulate organic matter using fatty acid δ 13 C and Δ14 C composition

This study used a multiproxy approach to elucidate the source and age composition of estuarine particulate organic matter (POM) using bulk stable isotopes (δ13CPOC), fatty acid (FA) biomarkers, and compound specific isotopic analyses in surface waters along the Delaware River and Bay (Delaware Estuary, hereafter). δ13C values of FA (δ13CFA) ranged more widely (−30.9‰ to −21.8‰) than δ13CPOC (−27.5‰ to −23.5‰), providing greater insight about POM sources along the estuary. δ13C values of C16:0 phospholipid FA (primarily, aquatic sources) increased along the salinity gradient (−29.8‰ to −23.4‰), while δ13CFA values of long-chain neutral fatty acid (terrestrial sources) decreased (−28.6‰ to −30.9‰). δ13CFA values for C18's FA indicated the importance of marsh-derived organic matter within Delaware Estuary. Compound specific radiocarbon analysis showed the heterogeneous age structure of FA associated with POM (FAPOM). 14C ages of FA ranged from modern (postbomb) to 1790 BP; aged FA (120 BP to 1700 BP) derived primarily from the watershed, whereas modern FA were produced within Delaware Estuary. 14C ages of short-chain FA (aquatic sources) reflected differences in the age of dissolved inorganic carbon along the estuary and had older 14C ages at the river end-member. 14C ages of FA from terrigenous sources were older than water and sediment residence times indicating this source derived from the watershed. This study is the first to document the complex age distribution of FAPOM along the estuarine salinity gradient and shows that inorganic carbon sources, watershed inputs and autochthonous production contribute to variation in the ages of POM.

Organic PM Emissions from Vehicles: Composition, O/C Ratio, and Dependence on PM Concentration

A suite of real-time instruments was used to sample vehicle emissions at the California Air Resources Board Haagen-Smit facility. Eight on-road, spark-ignition gasoline and three alternative vehicles were tested on a chassis dynamometer and the emissions were diluted to atmospherically relevant concentrations (0.5–30 μg/m3). An Aerodyne high resolution time-of-flight aerosol mass spectrometer (HR-ToF-MS) characterized the real-time behavior of the nonrefractory organic and inorganic particulate matter (PM) in vehicle emissions. It was found that the emission of particulate organic matter (POM) was strongly affected by engine temperature and engine load and that the emission concentrations could vary significantly by vehicle. Despite the small sample size, consistent trends in chemical characteristics were observed. The composition of vehicle POM was found to be related to overall PM mass concentration where the oxygen-to-carbon (O/C) ratio tended to increase at lower concentration and had an average value...

Carbon and nitrogen isotopic composition of particulate organic matter and its biogeochemical implication in the Bering Sea

Stable carbon and nitrogen isotopic composition of particulate organic matter (POM) were measured for samples collected from the Bering Sea in 2010 summer. Particulate organic carbon (POC) and particulate nitrogen (PN) showed high concentrations in the shelf and slope regions and decreased with depth in the slope and basin, indicating that biological processes play an important role on POM distribution. The low C/N ratio and heavy isotopic composition of POM, compared to those from the Alaska River, suggested a predominant contribution of marine biogenic organic matter in the Bering Sea. The fact that δ13C and δ15N generally increased with depth in the Bering Sea basin demonstrated that organic components with light carbon or nitrogen were decomposed preferentially during their transport to deep water. However, the high δ13C and δ15N observed in shelf bottom water were mostly resulted from sediment resuspension.

Chemical and isotopic composition of estuarine organic matter: implications for the relative contribution and reactivity of anthropogenic sources of organic matter

The source and composition of suspended particulate organic matter in the Manko estuary, Okinawa Island, Japan, has been evaluated using fatty acid biomarkers and stable carbon and nitrogen isotopes. Fatty acid signature and stable isotope data have revealed that terrestrial organic matter (including terrestrial vascular plants), bacteria, phytoplankton produced within the estuary and coastal sea, green macroalgae and mixed planktonic-sources predominantly contributed to the organic matter pool in the estuary. The combined approach has also allowed for the prediction of the following mixing regime and distribution of organic matter sources along the estuarine salinity gradient; Allochthonous, both terrestrial and river-borne organic matter which dominate the riverine section of the estuary seem to be slightly diluted with autochthonous organic matter in the middle estuary (site M) and thereafter, in the lower reaches of the estuary (Site SW2) are measurably admixed with tidally introduced marine organic matter. However, the autochthonous primary production within the estuary seems to be highly dependent on the discharges of terrestrial organic matter and nutrients as depicted in fatty acid signatures and isotopic composition of residential and agricultural wastewater runoff. Isotopic composition of dissolved constituents (particularly, ammonia and nitrate) highly influences the composition of autochthonous primary producers. The linkage between suspended organic matter sources and the diet of tilapia (Oreochromis mossambicus [Peters]) is also discussed.

Animal regeneration and microbial retention of nitrogen along coastal rocky shores

Animal contributions to ecosystem productivity via nutrient regeneration are increasingly recognized as significant for ecosystem productivity. The paradigm in coastal upwelling systems, in contrast, remains centered around the idea that nutrient supply is extrinsic and sourced from deep water. Here we tested for both animal contributions to nitrogen regeneration and microbial retention of nitrogen along a gradient of animal abundance in Washington State, USA. Using inferences from the concentration and isotopic composition of nitrogen forms, as well as the stable nitrogen isotopic composition of particulate organic matter, and plant and animal tissue, we found increased ammonium as well as greater stable nitrogen isotope values in these organisms in areas of increased animal abundance. We further tested the effect of the nearshore biota by comparing it with an immediately adjacent offshore area, and found an enriched δ15N value for nitrate and particulate organic matter. Further, an analysis of the dual isotopes of δ15N and the δ18O of nitrate indicated increasing microbial processing in the nearshore. Isoscapes, or the spatial pattern of stable isotopes, revealed that animal and microbial processing of nitrogen leave a consistent signature and are thus a previously overlooked and essential component of nearshore productivity.

Carbon and nitrogen isotopic composition of suspended particulate organic matter in Zuari Estuary, west coast of India

The spatio-temporal variations of the δ13C and δ15N of suspended particulate organic matter (SPOM), along with ancillary chemical and hydrographic parameters, have been examined monthly for one year (October 2010 to September 2011) at a total of seven stations to refine the understanding of SPOM sources and biogeochemical pathways in the tropical Zuari Estuary, west coast of India. The dynamic nature of C and N cycling in estuaries is reflected in the isotopic variation of SPOM as a function of space and time. The results exhibit marked seasonality, with the autochthonous component and the terrestrial component being the major SPOM sources during periods of low and high river discharges, respectively. Spatially, enrichments of δ13C and δ15N from the head (δ13C=−29.6‰, δ15N=1.78‰, C/N=7.09) to the mouth (δ13C=−20.9‰, δ15N=5.77‰, C/N=6.12) of the estuary indicate downstream reduction of terrigenous influence. The mean C:N ratios varied between 4 and 9 over the study period with low values during the monsoon, in spite of large terrestrial input, which can be attributed to microbial modification of terrestrial SPOM. A significant positive correlation of δ13C with salinity suggests the reliability of δ13C as a biogeochemical tracer for organic matter provenance. Carbon:chlorophyll plots reveal suppressed autochthonous production during the southwest monsoon which may be attributed to the rapid flushing time, light-limitation due to cloud cover and high water-column turbidity.

Chemical and isotopic composition of estuarine organic matter: implications for the relative contribution and reactivity of anthropogenic sources of organic matter

The source and composition of suspended particulate organic matter in the Manko estuary, Okinawa Island, Japan, has been evaluated using fatty acid biomarkers and stable carbon and nitrogen isotopes. Fatty acid signature and stable isotope data have revealed that terrestrial organic matter (including terrestrial vascular plants), bacteria, phytoplankton produced within the estuary and coastal sea, green macroalgae and mixed planktonic-sources predominantly contributed to the organic matter pool in the estuary. The combined approach has also allowed for the prediction of the following mixing regime and distribution of organic matter sources along the estuarine salinity gradient; Allochthonous, both terrestrial and river-borne organic matter which dominate the riverine section of the estuary seem to be slightly diluted with autochthonous organic matter in the middle estuary (site M) and thereafter, in the lower reaches of the estuary (Site SW2) are measurably admixed with tidally introduced marine organic matter. However, the autochthonous primary production within the estuary seems to be highly dependent on the discharges of terrestrial organic matter and nutrients as depicted in fatty acid signatures and isotopic composition of residential and agricultural wastewater runoff. Isotopic composition of dissolved constituents (particularly, ammonia and nitrate) highly influences the composition of autochthonous primary producers. The linkage between suspended organic matter sources and the diet of tilapia (Oreochromis mossambicus [Peters]) is also discussed.

Broad sampling and diverse biomarkers allow characterization of nearshore particulate organic matter

Suspended particulate organic matter (POM) is a primary food source for benthic and pelagic consumers in aquatic and marine ecosystems. POM is potentially composed of many sources including phytoplankton, bacteria, zooplankton and macrophyte (seaweed and seagrass) and terrestrial detritus. The relative importance of these sources to POM consumers is debated, in large part due to differing interpretations of stable isotope and fatty acid biomarkers. We investigated POM composition in a nearshore marine ecosystem using multiple methods including visual quantification of living and detrital components, multiple stable isotope (MSI) and fatty acid (FA) analyses. Sampling was conducted at multiple temporal and spatial scales to 1) determine the range of variability in POM biomarkers, 2) quantitatively evaluate δ13C, δ15N, δ34S and FA biomarkers with proportional abundance of putative sources and 3) determine the availability of phytoplankton, macrophytes and terrestrial carbon in nearshore POM. Variation of total FA concentration and proportions, and δ13C and δ34S were strongly correlated to phytoplankton abundance, at tidal and seasonal timescales. Using multivariate multiple regressions, MSI and FA explained 59.6% and 89.7% of the variation in POM composition, respectively. As phytoplankton abundance increased, total FA concentration increased concurrent to δ13C and δ34S enrichment. In high detritus samples, bacterial FA and saturated FA were proportionally higher, corresponding to depletion of δ13C and δ34S and enrichment of δ15N. We identify MSI and FA biomarkers that are good predictors of diatom, dinoflagellate and detrital contributions to the POM. The results of this multi‐scale study show that POM composition is highly dynamic and largely driven by phytoplankton abundance, with minor contributions from terrestrial or macrophyte subsidies. This quantitative approach provides novel and critical empirical information linking POM compositional dynamics to specific biomarkers that are commonly used for tracking energy subsidies and biogeochemical cycling in aquatic ecosystems.