Primary Production Of Organic Matter Research Articles

Extensive Turnover of Compatible Solutes in Cyanobacteria Revealed by Deuterium Oxide (D2O) Stable Isotope Probing.

Cyanobacteria are important primary producers of organic matter in diverse environments on a global scale. While mechanisms of CO2 fixation are well understood, the distribution of the flow of fixed organic carbon within individual cells and complex microbial communities is less well characterized. To obtain a general overview of metabolism, we describe the use of deuterium oxide (D2O) to measure deuterium incorporation into the intracellular metabolites of two physiologically diverse cyanobacteria: a terrestrial filamentous strain (Microcoleus vaginatus PCC 9802) and a euryhaline unicellular strain (Synechococcus sp. PCC 7002). D2O was added to the growth medium during different phases of the diel cycle. Incorporation of deuterium into metabolites at nonlabile positions, an indicator of metabolite turnover, was assessed using liquid chromatography mass spectrometry. Expectedly, large differences in turnover among metabolites were observed. Some metabolites, such as fatty acids, did not show significant turnover over 12-24 h time periods but did turn over during longer time periods. Unexpectedly, metabolites commonly regarded to act as compatible solutes, including glutamate, glucosylglycerol, and a dihexose, showed extensive turnover compared to most other metabolites already after 12 h, but only during the light phase in the cycle. The observed extensive turnover is surprising considering the conventional view on compatible solutes as biosynthetic end points given the relatively slow growth and constant osmotic conditions. This suggests the possibility of a metabolic sink for some compatible solutes (e.g., into glycogen) that allows for rapid modulation of intracellular osmolarity. To investigate this, uniformly 13C-labeled Synechococcus sp. PCC 7002 were exposed to 12C glucosylglycerol. Following metabolite extraction, amylase treatment of methanol-insoluble polymers revealed 12C labeling of glycogen. Overall, our work shows that D2O probing is a powerful method for analysis of cyanobacterial metabolism including discovery of novel metabolic processes.

Spring bloom onset in the Nordic Seas

Abstract. The North Atlantic spring bloom is a massive annual growth event of marine phytoplankton, tiny free-floating algae that form the base of the ocean's food web and generates a large fraction of the global primary production of organic matter. The conditions that trigger the onset of the spring bloom in the Nordic Seas, at the northern edge of the North Atlantic, are studied using in situ data from six bio-optical floats released north of the Arctic Circle. It is often assumed that spring blooms start as soon as phytoplankton cells daily irradiance is sufficiently abundant that division rates exceed losses. The bio-optical float data instead suggest the tantalizing hypothesis that Nordic Seas blooms start when the photoperiod, the number of daily light hours experienced by phytoplankton, exceeds a critical value, independently of division rates. The photoperiod trigger may have developed at high latitudes where photosynthesis is impossible during polar nights and phytoplankton enters into a dormant stage in winter. While the first accumulation of biomass recorded by the bio-optical floats is consistent with the photoperiod hypothesis, it is possible that some biomass accumulation started before the critical photoperiod but at levels too low to be detected by the fluorometers. More precise observations are needed to test the photoperiod hypothesis.

Water Quality Monitoring of Sur Sarovar (Keetham) Lake, Agra (Uttar Pradesh)

Water quality information in aquatic ecosystem is crucial in setting up guideline for resource management. The biota in the surface water is governed entirely by various environmental conditions that determine the selection of species as the physiological performance of the individual organisms. This study explores the water quality status and pollution sources in Sur Sarovar (Keetham) Lake, Agra (Uttar Pradesh), water quality parameters analyze of five sampling zone was done from water samples collected monthly from September 2014 to July 2015. The primary production of organic matter, in the form of phytoplankton and macrophytes is more intense in Sur Sarovar (Keetham) Lake. In contrast to the chemical quality of water bodies, which can be measured by suitable analytical methods, biological quality is a combination of both qualitative and quantitative characterization. The present piece of research work is initiated on pollution status at Sur Sarovar (Keetham) Lake by interference and increase in the population of phytoplankton and microbe. We were selected keys physico chemical parameters for analysis like, temperature 19.50 to 38.00 °C, pH 7.39±0.04 to 8.21±0.06, dissolve oxygen 5.90 ± 0.55 mg/L to 6.48 ± 0.87 mg/L, alkalinity 93.73 ± 5.09 mg/L to 124.27 ± 5.05 mg/L, hardness 119.33 ± 9.06 mg/L to 138.93 ± 8.07 mg/L, ammonia 0.52± 0.03 mg/L to 0.64 ± 0.032 mg/L, nitrate 0.71 ± 0.02 mg/L to 1.79 ± 0.02 mg/L, nitrite 0.21 ± 0.01 to 0.47 ± 0.02 mg/L, phosphate 0.22 ± 0.03 mg/L to 0.36 ± 0.05 mg/L and heavy metal concentration like Zn 0.023 ± 0.00 mg/L to 0.27 ± 0.00 mg/ L, Cr 0.022 ± 0.00 to 0.036 ± 0.00 mg/L , Cd 0.002 ± 0.00 mg/L to 0.010 ± 0.00 mg/L, Pb 0.013 ± 0.00 mg/L to 0.033 ± 0.00 mg/L, Hg 0.015 ± 0.00 to 0.02 ± 0.00 mg/L in the water were undertaken.

Practical Applicability and Preliminary Results of the Baltic Environmental Satellite Remote Sensing System (Satbałtyk)

Abstract The SatBałtyk (Satellite Monitoring of the Baltic Sea Environment) project is being realized in Poland by the SatBałtyk Scientific Consortium, specifically appointed for this purpose, which associates four scientific institutions: the Institute of Oceanology PAN in Sopot - coordinator of the project, the University of Gdańsk (Institute of Oceanography), the Pomeranian Academy in Słupsk (Institute of Physics) and the University of Szczecin (Institute of Marine Sciences). The project is aiming to prepare a technical infrastructure and set in motion operational procedures for the satellite monitoring of the Baltic Sea ecosystem. The main sources of input data for this system will be the results of systematic observations by metrological and environmental satellites such as TIROS N/NOAA, MSG (currently Meteosat 10), EOS/AQUA and Sentinel -1, 2, 3 (in the future). The system will deliver on a routine basis the variety of structural and functional properties of this sea, based on data provided by relevant satellites and supported by hydro-biological models. Among them: the solar radiation influx to the sea’s waters in various spectral intervals, energy balances of the short- and long-wave radiation at the Baltic Sea surface and in the upper layers of the atmosphere over the Baltic, sea surface temperature distribution, dynamic states of the water surface, concentrations of chlorophyll a and other phytoplankton pigments in the Baltic waters, spatial distributions of algal blooms, the occurrence of coastal upwelling events, and the characteristics of primary production of organic matter and photosynthetically released oxygen in the water and many others. The structure of the system and preliminary results will be presented.

Stable carbon isotope ratios of aliphatic biomarkers in Late Palaeozoic coals

Stable carbon isotope ratios for aliphatic biomarkers were measured on 34 Late Palaeozoic coals. Compound specific isotope analysis allowed the determination of δ13C values of individual organic compounds such as chlorophyll side-chain derived substances (pristane and phytane), leaf wax constituents (n-alkanes), or bacteria related compounds (hopanoids).Pristane and phytane can be regarded as excellent isotopic tracer molecules to ascertain isotope fractionation during primary production of organic matter by land plants in the Late Palaeozoic. Compared to the organic carbon isotope values for total terrestrial organic carbon, partly different isotope shifts and temporal trends are discernible for these isoprenoids. Such differences in carbon isotope ratios of total terrestrial organic matter and isoprenoids indicate that both isotope data sets record different bio-geochemical information. Since phytol-derived isoprenoids are directly linked to the primary production of organic matter, their carbon isotopic properties seem to be most appropriate for the reconstruction of ecological systems and climate in the Palaeozoic.Interestingly, isotopic values of isoprenoids and hopanoids were not significantly affected by maturity and maceral composition of the coals. However, differences between the isotopic composition of total organic matter and of phytane (Δδ13C values) and differences between the isotopic composition of total organic matter and of hopane seem to correlate with provenance of the samples, i.e. samples from different basins show different values. Hence, variations in different types of organic biomass might be successfully traced by the isotopic properties of characteristic molecular fossils in Palaeozoic coals. This might become an appropriate approach for future palaeoenvironmental, palaeoclimatic and palaeogeographical studies.In conclusion, the present study clearly demonstrates that molecular and carbon isotopic analyses of terrestrial organic matter, range in resolution from bulk to compound specific analyses, and it allows for the reconstruction of ecological and climatic conditions in the Late Palaeozoic.

IN VITRO ANTIOXIDANT ACTIVITIES OF THE FERMENTED MARINE MICROALGA PAVLOVA LUTHERI (HAPTOPHYTA) WITH THE YEAST HANSENULA POLYMORPHA(1).

Microalgae are major primary producers of organic matter in aquatic environments through their photosynthetic activities. Fermented microalga (Pavlova lutheri Butcher) preparation (FMP) is the product of yeast fermentation by Hansenula polymorpha. It was tested for the antioxidant activities including lipid peroxidation inhibitory activity, free-radical-scavenging activity, inhibition of reactive oxygen species (ROS) on mouse macrophages (RAW264.7 cell), and inhibited myeloperoxidase (MPO) activity in human myeloid cells (HL60). FMP exhibited the highest antioxidant activity on free-radical scavenging, inhibitory intracellular ROS, and inhibited MPO activity. MTT [3-(4,5-dimethyl-2-yl)-2,5-diphenyltetrazolium bromide] assay showed no cytotoxicity in mouse macrophages (RAW264.7 cell), human myeloid cells (HL60), and human fetal lung fibroblast cell line (MRC-5). Furthermore, the antioxidative mechanism of FMP was evaluated by protein expression levels of antioxidant enzyme (superoxide dismutase [SOD] and glutathione [GSH]) using Western blot. The results obtained in the present study indicated that FMP is a potential source of natural antioxidant.

PALEO OCEANOGRAPHIC AND GEOCHEMICAL SEDIMENTARY ENVIRONMENTS OF UPPER VENDIAN BLACK SHALE PHOSPHORITE-BEARING DEPOSITS OF THE SOUTH-WESTERN MARGIN EAST-EUROPEAN PLATFORM

On the base of analysis of materials on geological paleooceanography of the World Ocean and factual data on ancient sedimentogenesis of "early Paleo-Tethys" for the first time the depositional environments of black shale phosphorite-bearing formation of Vendian (Kalus beds) of the Volyno-Podilian monocline and adjacent regions were reconstructed. Process of phosphorogenesis of black shale deposits was genetically interrelated with sedimentation of primary producer of organic matter: plant detritus, phyto- and, possibly, zooplankton, caused by the influence of coastal upwelling, as a result of geochemical activity of biogenic triad P - С - N as a result of coastal upwellig. Deposition of these carbon-bearing deposits occurred in anoxic environment. The Late Vendian oceanic anoxic event has been indexed by the authors as "OAEV".

Complete genome sequence of the hyperthermophilic chemolithoautotroph Pyrolobus fumarii type strain (1A).

Pyrolobus fumarii Blöchl et al. 1997 is the type species of the genus Pyrolobus, which belongs to the crenarchaeal family Pyrodictiaceae. The species is a facultatively microaerophilic non-motile crenarchaeon. It is of interest because of its isolated phylogenetic location in the tree of life and because it is a hyperthermophilic chemolithoautotroph known as the primary producer of organic matter at deep-sea hydrothermal vents. P. fumarii exhibits currently the highest optimal growth temperature of all life forms on earth (106°C). This is the first completed genome sequence of a member of the genus Pyrolobus to be published and only the second genome sequence from a member of the family Pyrodictiaceae. Although Diversa Corporation announced the completion of sequencing of the P. fumarii genome on September 25, 2001, this sequence was never released to the public. The 1,843,267 bp long genome with its 1,986 protein-coding and 52 RNA genes is a part of the Genomic Encyclopedia of Bacteria and Archaea project.

Primary production of organic matter and phototrophic communities in the soda lakes of the Kulunda steppe (Altai krai)

The rates of photosynthesis and dark CO2 fixation were determined in 12 soda lakes of the Kulunda steppe. Characterization of the phototrophic communities was given, and the cell numbers of anoxygenic phototrophic bacteria (APB) were determined. The photosynthetic production in different lakes was substantially different, constituting from 0.01 to 1.32 g C m−2 day−1. The main part of carbon dioxide was assimilated in the process of oxygenic photosynthesis. Anoxygenic photosynthesis was recorded only in 5 of the 12 lakes studied. Its values varied between 0.06 and 0.42 g C m−2 day−1, constituting from 8 to 34% of the total photosynthetic activity. Anoxygenic photosynthesis was revealed in the lakes where the number of APB reached 107–109 CFU cm−3. Dark CO2 fixation constituted 0.01–0.15 g C m−2 day−1. Positive correlation was observed between the primary production value and water alkalinity. No relationship between productivity and water mineralization was revealed in the 30–200 g l−1 range, whereas an increase in salinity above 200 g l−1 suppressed the photosynthetic activity. The mechanisms of influence of the environmental factors on the rate of photosynthesis are discussed.

Application of 13C mineral carbon for assessment of the primary production of organic matter in aquatic environments

The possibility of measuring the rates of light and dark CO2 assimilation using 13C carbonate was demonstrated on Lake Kichier (Marii El). The application of methods utilizing the stable 13C and the radioactive 14C isotopes resulted in comparable values of the rates of light and dark CO2 fixation. Due to its absolute environmental safety, the method with 13C mineral carbon can be recommended as an alternative to radioisotope methods for qualitative measurements of CO2 fixation rates in aquatic ecosystems.

Carbonate factories: A conundrum in sedimentary geology

Describing, characterizing and interpreting the nearly infinite variety of carbonate rocks are conundrums – intricate and difficult problems having only conjectural answers – that have occupied geologists for more than two centuries. Depositional features including components, rock textures, lithofacies, platform types and architecture, all vary in space and time, as do the results of diagenetic processes on those primary features. Approaches to the study of carbonate rocks have become progressively more analytical. One focus has evolved from efforts to build reference models for specific Phanerozoic windows to scrutinize the effect of climate and long-term oscillations of the ocean–atmosphere system in influencing the mineralogy of carbonate components. This paper adds to the ongoing lively debates by attempting to understand changes in the predominant types of carbonate-producing organisms during the Mesozoic–Cenozoic, while striving to minimize the uniformitarian bias. Our approach integrates estimates of changes in Ca 2+ concentration in seawater and atmospheric CO 2, with biological evolution and ecological requirements of characteristic carbonate-producing marine communities. The underlying rationale for our approach is the fact that CO 2 is basic to both carbonates and organic matter, and that photosynthesis is a fundamental biological process responsible for both primary production of organic matter and providing chemical environments that promote calcification. Gross photosynthesis and hypercalcification are dependent largely upon sunlight, while net primary production and, e.g., subsequent burial of organic matter typically requires sources of new nutrients (N, P and trace elements). Our approach plausibly explains the changing character of carbonate production as an evolving response to changing environmental conditions driven by the geotectonic cycle, while identifying uncertainties that deserve further research. With metazoan consumer diversity reduced by the end-Permian extinctions, excess photosynthesis by phytoplankton and microbial assemblages in surface waters, induced by moderately high CO 2 and temperature during the Early Mesozoic, supported proliferation of non-tissular metazoans (e.g., sponges) and heterotrophic bacteria at the sea floor. Metabolic activity by those microbes, especially sulfate reduction, resulted in abundant biologically-induced geochemical carbonate precipitation on and within the sea floor. For example, with the opening of Tethyan seaways during the Triassic, massive sponge/microbe boundstones (the benthic automicrite factory) formed steep, massive and thick progradational slopes and, locally, mud-mounds. As tectonic processes created shallow epicontinental seas, photosynthesis drove lime-mud precipitation in the illuminated zone of the water column. The resulting neritic lime-mud component of the shallow-water carbonate factory became predominant during the Jurassic, paralleling the increase in atmospheric pCO 2, while the decreasing importance of the benthic automicrite factory parallels the diversification of calcifying metazoans, phytoplankton and zooplankton. With atmospheric pCO 2 declining through the Cretaceous, the potential habitats for neritic lime-mud precipitation declined. At the same time, peak oceanic Ca 2+ concentrations promoted biotically-controlled calcification by the skeletal factory. With changes produced by extinctions and turnovers at the Cretaceous–Tertiary boundary, adaptations to decreasing Ca 2+ and pCO 2, coupled with increasing global temperature gradients (i.e., high-latitude and deep-water cooling), and strategies that efficiently linked photosynthesis and calcification, promoted successive changes of the dominant skeletal factory through the Cenozoic: larger benthic foraminifers (protist–protist symbiosis) during the Paleogene, red algae during the Miocene and modern coral reefs (metazoan–protist symbiosis) since Late Miocene.

The light transmission and seiche depth of Izmir Bay, western Turkey

Izmir Bay is one of the most polluted estuaries in the whole Mediterranean Sea. The inner part of the Bay (Inner Bay) is heavily affected by domestic and industrial discharge. As a result of these loads, strong eutrophication occurs in the Inner Bay, which is temporally anaerobic. The ecologically sensitive approach of the local authorities during the last decade has given rise to a wide variety of monitoring and research studies on this bay. On the other hand, the municipality of Izmir started to operate wastewater treatment facilities since January 2000. The Institute of Marine Sciences and Technology — Izmir (IMST) with its research vessel R/V K Piri Reis has been conducting an intensive monitoring program since 1988 and especially during the recent few years. These investigations provide an opportunity for the evaluation of the performance of the wastewater treatment plant in terms of the change in the optical properties of Izmir Bay water in a positive manner. The turbidity values measured in these monitoring studies indicate that the values have changed drastically after January 2000. Their spatial variation indicates that the values decrease from the Inner Bay towards the Aegean Sea. The turbidity (light transmission) values are measured with an automatic CTD (conductivity, temperature and depth) system during each cruise. The seiche disc depth measurement is carried out only occasionally. The accuracy of the seiche disc depth is dependent on certain daylight conditions and depends on the operator. The seiche disc depth (D s) is an important parameter to estimate primary production of organic matter (hereafter called production). A relation between light transmission (turbidity) value and seiche disc depth (D s) is found with very good agreement. The correlations are very high (approximately 0.94) with slight seasonal variation.

Primary production of organic matter in the ocean and phosphate accumulation

Primary production of organic matter in the ocean and phosphate accumulation

On the Problem of Assessing the Resistance of Planktonic Community to Adverse Influences

An experimental-analytical method for assessing the vulnerability of aquatic ecosystems under conditions of anthropogenic pollution is considered. Such data are very important for estimating economic damage from accidental environmental pollution and determining the seasons in which industrial activities will be less hazardous in ecological terms. A feasible approach to this problem is based on the study of ecosystem behavior under critical conditions. Phytoplankton, being the main primary producer of organic matter in the aquatic ecosystem, is the key element providing for its stability.

Recent Sediments of Makirina Cove (Northern Dalmatia, Croatia): Their Origin Viewed Through a Multidisciplinary Approach

Makirina Cove was formed by the Holocene sea-level rise whichcaused a marine ingression into the depression formed within Albian–Cenomanian dolomites at approximately 4.5 ka B.P. At present, MakirinaCove represents an restricted, stressed, shallow-marine (<2 m)ecosystem characterized by varying seawater temperatures (0–35°C)as well as fluctuating salinities (up to 41‰) affected by seasonallyenhanced evaporation, continuous freshwater supply through on-shoreand submarine springs associated with the coastal karst area and surface run-off episodes. These environmental conditions have beenconducive to high primary production of organic matter resulting inthe formation of organic-rich deposits which contain up to 5 wt.% oforganic carbon. Up to the present times, 3.5 m of sediments have beendeposited indicating a relatively high sedimentation rate estimated at0.75 m/1.0 ka in the northern central part of the Cove.The sediments are being deposited mostly as poorly sortedclayey–sandy silts. The distribution and concentration of most of thechemical elements is dependant on the mineralogical composition andgranulometric features of the Makirina sediments, which show valuesmore or less similar to those from the Central Adriatic. Accordingly,there is a positive correlation with Al and K concentrations increasingoff-shore and with the depth being associated with increasing concentrations of clay minerals within the clay fraction. The same holdstrue for concentrations of some trace elements, especially Mo and Sewhich is consistent with the distribution pattern of sulphides.Selenium is preferentially enriched in authigenic pyrite and itis probably the major source of Se in the Makirina Cove sediments.The concentrations of Ca, Mg and Sr decrease off-shore and they arelinked to the composition of the surrounding carbonate rocks. Thesaturation indices show that the water is supersaturated with respectto carbonates enabling the precipitation of authigenic amorphous orcrystalline carbonate phases from the pore water in the upper segmentof the sediment column. According to the oxygen isotopic (δ18O) composition,molluscs precipitated their carbonate shells mostly duringwarmer periods (May to November) at or near isotopic equilibriumwith their ambient waters. The carbon isotopic δ13C composition ofmollusc carbonate shells is environmentally affected due to oxidationand decomposition of organic matter as well as influxes of fresh waterinto the Cove, indicating their formation out of the predicted isotopicequilibrium with atmospheric CO2. Palynological and organic carbonisotopic (δ13C) composition shows that the sedimentary organic matter(SOM) is 70–90% lipid- and hydrogen-rich and on average 2/3 marinederived (mainly phytoplankton, bacteria and marine macrophytes) and1/3 terrestrially derived (mainly woody tissue). The variations in composition of SOM have been noted as a function of the distance fromthe shore. The type and the preservation state of SOM and pyrite aswell as the measurements of Eh, pH, total alkalinity, dissolved inorganiccarbon (DIC) and the enrichment of redox-sensitive trace elements,indicate oxygen-depleted depositional conditions and that thesediment is highly reductive even in the uppermost segment at thesediment/water interface. According to the results obtained from theapplied methods, the features of Makirina sediments strongly reflectthe given depositional conditions within this restricted, stressed, shallow-marine environment where these organic-rich sediments originate,and may therefore serve as a calibration standard in further investigations

Theme 6: The early earth and planets

Microorganisms play a role both in primary production of organic matter and its decomposition that may vary through time and across different basinal environments. Compound-specific carbon isotope analysis has shown that bacterial and archaeal remains dominate organic carbon (OC) accumulations in many modern anoxic seafloor environments; however, only cyanobacteria and eukaryote biomarkers have been identified to date in Archaean strata. Nevertheless the very negative d13C values in Late Archaean (2.8-2.5 Ga) organic matter world-wide provide good evidence for marine ecosystems dominated by biological oxidation and assimilation of methane. Here we report the identification of well preserved encapsulated bacteria-like forms in a filamentous carbonaceous matrix in thermally immature organic-rich strata of the 2.5 Ga Mt McRae Shale, Hamersley Basin, Western Australia. The probable microfossils range from 1.5 to 5 microns in length, with an electron dense shell often encased in membraneous organic matter reminiscent of the structure of consortia of archaea and sulphate-reducing bacteria responsible for anaerobic oxidation of methane in modern cold seeps. Bulk d13C values vary between -29.1 and -43.3 per mil and are consistent with OC sourced from several different groups of microorganisms. The major contributors to OC in the Mt McRae Shale are interpreted to be indigenous archaea and sulphate-reducing bacteria. This supports the hypothesis that Late Archaean atmospheric oxygen levels were sufficiently low to allow a global methanogen-methylotroph cycle.

Differences in the biological carbon pump at three subtropical ocean sites

We report primary production of organic matter and organic carbon removal from three subtropical open ocean time‐series stations, two located in the Atlantic and one in the Pacific, to quantify the biological components of the oceanic carbon pump. We find that within subtropical gyres, export production varies considerably despite similar phytoplankton biomass and productivity. We provide evidence that the removal of organic carbon is linked to differences in nutrient input into the mixed layer, both from eddy induced mixing and dinitrogen fixation. These findings contribute to our knowledge of the spatial heterogeneity of the subtropical oceans, which make up more than 50% of all ocean area and are thought to spread in the course of CO2‐ induced global warming.

Depositional and Tectonic Setting of the Lower Silurian Hydrocarbon Source Rock Facies, Central Saudi Arabia

The Lower Silurian Qalibah Formation consists of two members, the (upper) Sharawra Member and the (lower) Qusaiba Member. The Qusaiba is the main hydrocarbon source rock for the known Paleozoic hydrocarbon accumulations in central Saudi Arabia. The Qusaiba Member is composed mostly of claystone and shale with interbeds of siltstone and sandstone. Depositionally, the Qusaiba Member is interpreted to represent the delta-toe clays, whereas the Sharawra Member was deposited as pro-delta sandstones of an immense fluviodeltaic system that dominated the Silurian-Carboniferous of Arabia. The Qalibah Formation accumulated syndepositionally in at least two rapidly subsiding depocenters. One depocenter was located in central and southern Arabia, and the other depocenter was located in northwestern Saudi Arabia. The former trough began subsiding during the Late Ordovician following the Taconic uplift. The latter trough began subsiding during the Early Silurian. At least 10,000 ft (3100 m) of Upper Ordovician- Lower Devonian strata accumulated in the trough located in central and southern Saudi Arabia. About 3300 ft (1000 m) of Lower Silurian sediments accumulated in the depocenter found in northwestern Saudi Arabia. The development of these troughs documents a period of crustal extension probably related to the rifting of the Lower Paleozoic continental margin of Saudi Arabia. The Qusaiba Member organic-rich facies occurs near the base of the unit and has up to 8% total organic carbon content. The development of favorable source rock facies in the Qusaiba is observed along the flanks of the depositional thicks associated with the lower Qusaiba Member. The basal Qusaiba Member organic-rich facies was produced during periods of elevated primary productivity of organic matter within the water column in an open-marine, nonsilled basin setting. Deposition of the basal organic-rich facies of the Qusaiba Member occurred as a condensed sequence along a sediment-starved continental margin. The basal Qusaiba Member organic-rich facies accumulated in normally to partly oxygenated bottom-water settings; however, the sediments below the sediment/water interface were probably preserved in an anoxic setting. Geochemical data also demonstrate that the organic-rich Qusaiba Member sediments found in the depositional thicks have characteristics consistent with a more oxidized sediment column. Geo chemical data also show that the basal Qusaiba Member organic-rich facies deposited more distally to these depocenters are more dysoxic to anoxic in their characteristics. The organic-rich facies of the basal Qusaiba Member found in depositional thicks was produced under conditions that either reworked the organic-rich sediments, thereby oxidizing them, or diluted the organic matter, resulting in less preservation of potential source rock.

Carbon in tropical wetlands

About half of the world's wetlands area is found in the tropics. The importance of wetlands to the global carbon cycle, water balance, wildlife, biodiversity and human food production is much greater than their proportional surface area on Earth (7%) would suggest. High net primary production of organic matter produced by retarded decomposition make natural tropical wetlands an important sink for carbon. About 250 Gt carbon are conserved in tropical wetlands. Tropical wetlands are also a significant source for atmospheric methane. Wetland rice agriculture alone contributes 5 to 20% to the global methane budget. Rice, the stable food for about half of mankind, is grown on tropical wetlands. Small differences in climate, water and nutrient regimes, and land use can drastically change the delicate balance of tropical wetlands.

Variations in primary production of northern Gulf of Mexico continental shelf waters linked to nutrient inputs from the Mississippi River

Increases in nutrient concentrations in the Mississippi River over the past 35 yr have led to speculation that primary production of organic carbon has been elevated as a result of increased nutrient fluxes that have occurred in the northern Gulf of Mexico coastal ecosystem. However, studies thus far have not provided direct demonstration of temporal relationships between measured primary production in continental shelf waters and nver-borne nutrient fluxes. This ~nvestlgation co~npared temporal variations in primary production with associated annual and interannual changes in riverborne nutrient inputs. Prlmary production In shelf waters near the river delta were found to be signlflcantly correlated with nitrate (NO1-) + nitrite (NO? ) concentrations and fluxes over a 6 yr period from 1988 to 1994. Although light limitation was probably an important factor during winter months, a positive correlation was demonstrated between river inputs of NO,-+NO; and primary production for data collected from other times of the year. Peak nutrient inputs generally occurred in the spring. The magnitude of the riverborne NO? +NO, inputs averaged 106% of estimated nitrogen requirements for phytoplankton in the river-impacted region, considerably greater than in Amazon shelf waters, which have been less subject to anthropogenic nutrient increases. The possibility exists that further Increases In anthropogenic nutrients in the ~ i s s i s s ~ p p i R ver could lead to h ~ g h e r and more widespread primary production, and this may intensify and extend the depletion of oxygen that has already been observed in the Louisiana shelf ecosystem. However, such a prediction is difficult because relationships between increasing nutnent inputs and pnmary production are unlikely to be linear, and a complete understanding of processes intermediate between primary production of organic matter and oxygen depletion in bottom waters on the Louisiana shelf is still lacking.