Strong latitudinal patterns in the elemental ratios of marine plankton and organic matter

The biochemical composition and spatial distribution of particulate organic matter (POM) were studied in the Ross Sea (Antarctica) in summer 1989 to assess the quantitative role of organic carbon fractions in the cycling of organic matter in the water column. Large differences in chemical composition were observed between surface and deep layers. The results indicated that, despite large geographical differences, POM was quite homogeneous, of phytoplankton origin and mostly detrital. Different ratios were used to investigate the changes in biochemical composition of particulate organic matter in relation to the ice-melting: C∶N (organic carbon∶organic nitrogen ratio) and C-POM∶POC (sum of carbohydrate, protein and lipid carbon∶total organic carbon ratio) were used to analyse the percentage of refractory organic material. PPRT∶PCHO (protein∶carbohydrate ratio) were used to establish POM “age” and RNA∶DNA ratios as a relative measure of particulate activity; POC∶Chl a and N-PPRT∶Chl a ratios were used to estimate the autotrophic contribution to the suspended particulate organic matter. Despite its low caloric value (5.3 Kcal g POM−1), an high caloric content in the photic layer (1.6 Kcal m−3 of POM and 2.5 Kcal m−3 of POC) was found thus indicating that a large amount of food was available to higher trophic levels.

The stable carbon isotope composition (δ 13 C) of particulate organic matter (POM) has been used to infer sources of organic matter and major biogeochemical processes in lakes. However, very few studies have compared the δ 13 C POM among lakes of different limnological properties. Here, we report such an analysis to understand the patterns and controls of stable isotopes of POM from 96 lakes in Florida, USA. Results indicated that δ 13 C POM increased significantly with the increases in lake area, pH and trophic state, but decreased with the increase in CO 2 concentration and water color content. δ 13 C POM in a small set of these lakes showed a positive relationship with δ 13 C of dissolved inorganic carbon (DIC). There was a widespread 13 C depletion of POM in the study lakes, especially in lakes with high water color, suggesting allochthonous subsidy of phytoplankton production. Multiple regression models pointed to the importance of trophic state, color and pH. This study demonstrated that the δ 13 C POM is indicative of carbon source, trophic state and ecosystem metabolism in lakes.

Weekly water samples were taken to measure stable isotope composition (δ13C and δ15N) of particulate organic matter (POM) in Lake Wauberg, Florida, from June 1994 to May 1995. The average δ13C of POM was ‐19.3%, consistent with an autochthonous origin from phytoplankton production, and exhibited a seasonal pattern that coincided with changes in water temperature, pH, CO2 concentration, and phytoplankton biomass in the surface water. The 13C enrichment in POM was attributed to reduced isotope fractionation due to carbon (C) limitation and the use of an isotopically heavy dissolved inorganic carbon pool supported mainly by atmospheric invasion and anaerobic respiration. Intermittent declines in δ13C of POM were related to the frequent collapses of phytoplankton blooms and increases in CO2 concentration resulting from both increased community respiration and terrestrial loading. Average δ15N of POM was 1.3% and varied within a narrow range (20.1% to 2.5%). No significant correlation between phytoplankton biovolume and the δ15N of POM was found. The low δ15N is indicative of strong N2 fixation, which is in line with the low concentration of dissolved inorganic nitrogen and the presence of high biovolume of N2‐fixing cyanobacteria in the surface water. This study suggests that stable C isotopes are good proxies for surface water CO2 concentration and primary production, while stable N isotopes can be used to indicate N2 fixation.

Water samples and particulate materials settling under the pack ice were collected in an ice-covered area near the Terra Nova Bay Italian Station during late summer 1995, in order to study short-term changes in the biochemical composition of particulate organic matter. At the end of the study period the phytoplankton biomass increase (up to >3.0 μg chlorophyll-a l−1) was probably related to the intrusion under the pack ice of chlorophylls-enriched surface waters coming from the near ice-free area. Such increase was associated also with a notable increase in particulate organic matter concentrations, as well as in particulate organic matter vertical fluxes (up to >100 mg C m−2 day−1). Proteins were the most abundant biochemical class of particulate organic matter (on average about 49%), followed by lipids (29%) and carbohydrates (22%). By contrast, organic matter collected in the sediment trap was characterized by the dominance of lipids (about 55% of the total biopolymeric carbon flux) over carbohydrates (28%) and proteins (17%). The hydrolizable particulate biopolymeric carbon accounted for about 23% of total biopolymeric carbon. This value was about one-half of that found in ice-free waters, suggesting that the suspended particulate organic material under the pack ice was less digestible than in ice-free waters or was already partially digested. Despite this, and the decay of labile organic compounds in the sediment trap during the deployment, material settling towards the sea bottom under the pack ice in Terra Nova Bay, owing to its high lipid content, might represent an important high-quality food source for benthic consumers. Finally, assuming as possible the intrusion under sea ice of primary organic matter-enriched waters, we hypothesize the occurrence of a “fertilization” effect deriving from ice-melting areas towards under-ice waters, supplying the latter with an additional rate of primary organic matter.

Effects of river inputs on particulate organic matter composition and distributions in surface waters and sediments of the Mersin Bay, Northeastern Mediterranean Sea

Characterizing fluvial impact on the biochemical composition of particulate organic matter in the Laptev Sea and Western East Siberian Sea during the late summer of 2018

The chemical composition of Black Sea suspended particulate organic matter: pyrolysis-GC/MS as a complementary tool to traditional oceanographic analyses

Assuming the paradigm that catchment vegetation is the main source of particulate organic matter (POM) to rivers, the main objective of this study was to determine what the proportion of original C3 carbon from the forest had already been replaced by C4 carbon from sugar cane and pasture in the rivers of the Piracicaba Basin. In order to achieve this objective, we first produced a detailed landcover map using Landsat5‐TM images, and then we measured the carbon stable isotopic composition of the particulate riverine organic matter (δ13C‐POM) in seven sites along the major rivers and in two sites along a small creek. Sugar cane and pasture (C4 plants) covered almost 60% of the basin area, while silviculture, mostly of other crops, citrus, and forest that are C3 plants, covered 35%. Isotopic studies conducted in large pristine tropical rivers of South America and of Africa have shown that catchment vegetation is the main source of carbon in suspended POM. Our study demonstrates that relatively recent changes (70–80 yr ago) in landcover in the Piracicaba River Basin have already affected the composition of the riverine POM. Therefore, as in natural ecosystems, the vegetation (allochthonous source) plays an important role in the composition of the riverine POM in agricultural systems such as the Piracicaba River Basin. This control can be supported by the good correlation between cumulative area of the basin covered with C4 plants and the δ13C of the riverine POM. However, our study, differently from others, also shows that, during the low water period, in situ processes, such as primary production, may be an important source of carbon to the riverine POM.

Organic matter–mediated root rot suppression is unpredictable in field soils. This study was conducted to determine whether particulate organic matter (POM) composition and content were related to Pythium damping‐off (DO) incidence in a sand amended with sawdust‐bedded dairy manure compost (15% compost:85% sand, v/v) incubated in pots for 506 d. Suppressive and conducive POM composition was then related to literature values for agricultural and forest soil POM fractions. The suppressive potential of the substrate was determined with a Cucumis sativus L. (cucumber)/ Pythium ultimum DO bioassay. Particulate organic matter composition was determined spectroscopically. The compost‐amended sand supported suppression of DO for a period of ∼1 yr. Suppression was sustained by the degradation of the less decomposed coarse and mid‐sized POM fractions. After these fractions stabilized in mass, suppression was lost. Plant constituents were highly degraded during composting before amendment to sand. Compost‐derived POM composition changed little as suppression was supported for 1 yr. In contrast, aromatic and aliphatic contents and alkyl‐ and O‐alkyl C declined as suppression was lost. Suppressive POM was similar in composition to forest soil organic horizons and soil unprotected light fraction (ULF), suggesting that the least‐decomposed soil physical fractions may be the only fractions compositionally capable of supporting suppression of DO in field soils.

Chemical and Isotopic Composition of the Organic Matter Sources in the Gulf of Gdansk (Southern Baltic Sea)

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 29:63-72 (2002) - doi:10.3354/ame029063 Combined effects of nutrients and small-scale turbulence in a microcosm experiment. II. Dynamics of organic matter and phosphorus Marie Maar1,*, Laura Arin2, Rafel Simó2, Maria-Montserrat Sala2, Francesc Peters2, Cèlia Marrasé2 1National Environmental Research Institute, Frederiksborgvej 399, 4000 Roskilde, Denmark 2Institut de Ciències del Mar (CMIMA-CSIC), Passeig Marítim de la Barceloneta 37-49, 08003 Barcelona, Spain *E-mail: mam@dmu.dk ABSTRACT: In the oligotrophic sea, phytoplankton and bacteria compete for nutrients. Turbulence changes the outcome of this competition by means of an increase in the nutrient flux to cells by the shear fields, which is cell-size dependent. This effect is insignificant for small cells such as natural bacteria. The hypothesis is that turbulence will increase the phytoplankton competition-capability for nutrients and reduce the organic matter utilisation by bacteria. Consequently, the composition of particulate organic matter should change. To test this hypothesis, we studied the response of natural plankton communities to turbulence enclosed in 15 l microcosms. We evaluated the response in terms of the ratio of heterotrophic:total biomass and the stoichiometry of particulate organic matter. Results under turbulent and still conditions were compared in 3 nutrient-induced conditions: nitrogen surplus (N, with initial addition of an excess of nitrogen, N:P ratio = 160), nitrogen:phosphorus ratio balanced (NP, with initial addition of nitrogen and phosphorus as Redfield ratio, N:P ratio = 16) and control (C, no nutrient addition). In N and NP conditions, turbulence decreased the heterotrophic:total biomass ratio up to 2-fold, and induced changes in the stoichiometry of the particulate organic matter. We found higher values of carbon:phosphorus and nitrogen:phosphorus ratios in turbulent than in still treatments. The magnitude of these responses to turbulence depended on the induced nutrient conditions. In the control microcosms, we found the maximum differences of carbon:phosphorus ratio between turbulence and still treatments. In terms of biomass, the response to turbulence was clear in the enriched conditions and insignificant in the control microcosms. KEY WORDS: Small-scale turbulence · Phosphorus · Particulate organic matter stoichiometry · Microcosms Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 29, No. 1. Online publication date: September 03, 2002 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2002 Inter-Research.

To investigate the sources of particulate organic matter (POM) and the impact of Three Gorges Dam (TGD), two large lakes and erosion processes on determining the composition and flux of POM in low water discharge periods along the middle and lower Changjiang, suspended particulate samples were collected along the middle and lower reaches of the Changjiang (Yangtze River) in January 2008. Organic geochemistry of bulk sediment (particulate organic carbon, organic carbon to nitrogen molar ratio (C/N), stable carbon isotope (δ13C) and grain size) and biomarker of bulk sediment (lignin phenols) were measured to trace the sources of POM. The range of C/N ratios (6.4–8.9), δ13C (−24.3‰ – −26.2‰) and lignin phenols concentration Λ8 (0.45 mg/100 mg OC-2.00 mg/100 mg OC) of POM suggested that POM originated from the mixture of soil, plant tissue and autochthonous organic matter (OM) during the dry season. POM from lakes contained a higher portion of terrestrial OM than the mainstream, which was related to sand mining and hydropower erosion processes. A three end-member model based on δ13C and Λ8 was performed. The results indicated that soil contributed approximately 50% of OM to the POM, which is the dominant OM source in most stations. POM composition was affected by total suspended matter (TSM) and grain size composition, and the direct OM input from two lakes and channel erosion induced OM. The lower TSM concentration in January 2008 was mainly caused by seasonal variations; the impact from the TGD in the dry season was relatively small. A box model indicated that more than 90% of the terrestrial OM transported by the Changjiang in January 2008 was from the middle and lower drainage basins. Channel erosion induced OM, and contributions from Poyang Lake were the major terrestrial OM sources in the dry season. Copyright © 2012 John Wiley & Sons, Ltd.

Marginal seas influenced by large rivers are characterized by complex hydrodynamic and organic matter cycling processes. However, the impacts of hydrodynamics on the composition and reactivity of particulate organic matter (POM) remain unclear. Here we conducted a comprehensive study on the bulk, molecular and biological properties of suspended POM in the Changjiang Estuary and adjacent area subjected to strong currents, eddies as well as typhoons during spring and autumn. D/L‐enantiomers of particulate amino acids (PAA) were analyzed to evaluate the bioreactivity of POM and quantify bacterial‐derived organic carbon. We found that POM bioavailability as indicated by carbon‐normalized yields of PAA (PAA‐C%) reflected the ecosystem productivity. Relatively high PAA‐C% values (20−35%) were observed in productive areas influenced by Changjiang River plume, cyclonic eddies and typhoons, likely related to the enhanced nutrient availability arising from hydrodynamic processes. In contrast, the oligotrophic Taiwan Warm Current‐influenced regions featured relatively low POM bioavailability (PAA‐C% < 10%) despite typhoons facilitating water mixing. The PAA‐C% values showed a significant positive correlation with extracellular enzyme activity, indicating that bioavailable POM can rapidly stimulate heterotrophic transformation. Hot spots of elevated bioavailable POM showed high contributions of bacterial organic carbon. A large portion (∼2/3) of bacterial organic carbon was present in the form of bacterial detritus, suggesting that patches of these biological hot spots represent important sites of carbon sequestration. Together, our findings indicate that fresh POM production is largely controlled by nutrient supply driven by hydrodynamic processes, with important implications for carbon sequestration in the dynamic ocean margins.

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

Relations between river flow, primary production and fatty acid composition of particulate organic matter in San Francisco and Chesapeake Bays: a multivariate approach