The origin and biogeochemistry of organic matter in surface sediments of Lake Shihwa and Lake Hwaong

To understand the origin and biogeochemistry of the organic matter in surface sediments of Lake Shihwa and Lake Hwaong, organic nitrogen, inorganic nitrogen, labile organic carbon, and residual organic carbon contents as well as stable isotope ratios for carbon and nitrogen were determined by KOBr-KOH treatment. Ratios of organic carbon to organic nitrogen (C_org/N_org) (mean = 24) were much higher than ratios of organic carbon to total nitrogen (C_org/N_tot) (mean=12), indicating the presence of significant amounts of inorganic nitrogen in the surface sediments of both lakes. Stable isotope ratios for organic nitrogen were, on average, 5.2‰ heavier than ratios of inorganic nitrogen in Lake Shihwa, but those same ratios were comparable in Lake Hwaong. This might be due to differences in the origin or the degree of degradation of sedimentary organic matter between the two lakes. In addition, stable isotope ratios for labile organic carbon were, on average, 1.4‰ heavier than those for residual organic carbon, reflecting the preferential oxidation of¹³C-enriched organic matter. The present study demonstrates that KOBr-KOH treatment of sedimentary organic matter can provide valuable information for understanding the origin and degradation state of organic matter in marine and brackish sediments. This also suggests that the ratio of C_org/N_org and stable isotope ratios for organic nitrogen can be used as indexes of the degree of degradation of organic matter.     

Degradation and dissolution of zooplanktonic organic matter and lipids in early diagenesis

A degradation experiment with zooplankton was carried out to investigate the diagenesis of zooplanktonic organic matter, lipids, and lipid classes. In addition, reactivities and the quantitative relation between bulk organic carbon and waxes (which are the biomarkers of zooplankton) were compared during the experiment to evaluate the possibility of estimating the contributions of zooplanktonic organic matter in organic carbon pools, such as settling particles and surface sediments, from the wax concentration. Lipids were found to be more labile than the bulk organic carbon. Major parts of the organic carbon and lipids which remained on day 120 were found in the particulate fraction, and the accumulations of stable organic carbon and lipids in the dissolved fraction were limited. Although the lipids were more labile than the bulk organic carbon in the early phase of the experiment, the degradation rate of lipids obviously decreased in the subsequent degradation period, demonstrating the presence of stable lipids in zooplankton. Whereas triglycerides readily decreased, phospholipids persisted, making a major contribution to particulate lipids throughout the experiment. Waxes and other structural lipids such as glycolipids were also stably preserved in particulate lipids, suggesting that stable lipids in particulate matter are composed of structural lipids and waxes during early diagenesis. The degradation rate of waxes showed values comparable to that of bulk organic carbon after 11 days of degradation, resulting in constant ratios of waxes/bulk organic carbon (0.8 ± 0.2%, n = 7) during the later incubation period (after 11 days). This result suggests that the ratio could prove useful in evaluating the zooplanktonic organic carbon in organic carbon pools such as surface sediments and settling particulates.     

Geochemistry and organic petrology study of Kimmeridgian organic-rich shales in the Marib-Shabowah Basin,Yemen: Origin and implication for depositional environments and oil-generation potential

Kimmeridgian organic-rich shales of the Madbi Formation from the Marib-Shabowah Basin in western Yemen were analysed to evaluate the type of organic matter, origin and depositional environments as well as their oil-generation potential. Results of the current study establishes the organic geochemical characteristics of the Kimmeridgian organic-rich shales and identifies the kerogen type based on their organic petrographic characteristics as observed under reflected white light and blue light excitation. Kerogen microscopy shows that the Kimmeridgian organic-rich shales contain a large amount of organic matter, consisting predominantly of yellow fluorescing alginite and amorphous organic matter with marine-microfossils (e.g., dinoflagellate cysts and micro-foraminiferal linings). Terrigenous organic matters (e.g., vitrinite, spores and pollen) are also present in low quantities. The high contributions of marine organic matter with minor terrigenous organic matter are also confirmed by carbon isotopic values. The organic richness of the Kimmeridgian shales is mainly due to good preservation under suboxic to relatively anoxic conditions, as indicated by the percent of numerous pyritized fragments associated with the organic matter. The biomarker parameters obtained from mass spectrometer data on m/z 191 and m/z 217 also indicate that these organic-rich shales contain mixed organic matter that were deposited in a marine environment and preserved under suboxic to relatively anoxic conditions.The Kimmeridgian organic-rich shales thus have high oil and low gas-generation potential due to oil window maturities and the nature of the organic matter, with high content of hydrogen-rich Type II and mixed Type II-III kerogens with minor contributions of Type III kerogen.     

The use of soft X-ray spectromicroscopy to investigate the distribution and composition of organic matter in a diatom frustule and a biomimetic analog

Diatoms play a significant role in the global carbon cycle through their role in biogenic silica production and the transport of organic matter to the seafloor. Recent work has shown that silicified diatom frustules contain a significant amount of organic matter, and that the proportion of diatom-bound organic matter increases with depth in the water column and sediments. Here, we investigate the association between organic matter and the mineral phase. We used a combination of scanning transmission X-ray microscopy (STXM) and carbon X-ray absorption near-edge structure (XANES) spectroscopy to characterize the distribution and composition of organic matter in frustules of the diatom Cylindrotheca closterium and a biomimetic silica gel. To our knowledge, this study represents the first successful attempt to simultaneously image and obtain chemical information about the organic matter within a diatom frustule using X-ray spectromicroscopy near the carbon edge. Organic carbon, most likely protein, was distributed throughout the frustules and was not removed by harsh chemical treatment. The physical structure of the frustules appeared to be related to the chemical composition of this organic matter, with aromatic or unsaturated carbon being concentrated in the most intricately patterned regions of the frustule. A similar physical and chemical structure was observed in a biomimetic silica gel precipitated spontaneously with polylysine. These results are consistent with the theory that organic constituents of diatom frustules direct silica precipitation and become incorporated within the silica matrix as it forms. The relationship between organic matter composition and silica morphology, the failure of harsh chemical treatments to remove this organic matter, and the spontaneous nature of the co-precipitation of silica and organic matter indicate some chemical interaction between the siliceous and organic components of diatom frustules. Frustule-bound organic matter should therefore be protected from decomposition in the water column or diagenetic alteration in sediments unless the frustule dissolves.     

珠江口及近海表层沉积有机质的特征和来源

测定了珠江口及近海表层沉积物中总有机碳(TOC), 总氮(TN)及稳定碳同位素组成和几类主要有机化合物(水解氨基酸THAA、糖类TCHO、脂类lipid、酸不溶有机物AIOC), 并分析了沉积有机质及化合物的特征和来源。结果表明珠江口表层沉积有机质主要为陆源和水生混合来源, 而近海有机质主要为当地水生来源。大量的陆源高等植物(含有较多的木质素、纤维素等)输入珠江口, 使得珠江口个别站位沉积物中糖类物质含量大幅高于近海样品; 而珠江口与近海沉积物中水生来源有机质的含量相当。氨基酸和糖类占TOC的份额在浮游生物和悬浮颗粒物中分别为56%和48%, 在表层沉积物中为19%, 说明珠江口和近海的有机质从水柱到达沉积物-水界面的过程中经历了较充分的降解。珠江口样品中活性组分氨基酸和糖类占TOC的份额低于近海, 可能说明珠江口沉积有机质的降解程度高于近海。     

Variation of reactivity of particulate and sedimentary organic matter along the Zhujiang River Estuary

To investigate organic matter source and reactivity in the Zhujiang River (Pearl River)Estuary and its adjacent areas, particulate organic carbon (POC), particulate hydrolysable amino acids (PHAA), and Chl a during two cruises in July 1999 and July 2000 were measured. The highest POC and PHAA concentration was observed in the waters with maximum Chl a. The spectra distribution,relative content (dry weight in milligram per gram), PHAA-C% POC and other indicators such as the ratios of amino acids vs. amino sugars (AA/AS) and glucosamine vs. galactosamine (Glum/Gal) suggested that particulate amino acids in the water column and sediments in the Zhujiang River Estuary were mainly derived from biogenic processes rather than transported from terrestrial erosion. In inner estuary where high turbidity was often observable, organic matter was mainly contributed by re-suspension of bottom sediments with revealed zooplankton, microbial reworked characteristics, which suggest that these organic matters were relatively “old“. In the estuarine brackish region, organic matter in water column is mainly contributed by relatively fresh, easily degradable phytoplankton derived organic matter.During physical - biological processes within the eastuary, organic matter derived from phytoplankton was subjected to alteration by zooplankton grazing and bacterial reworking.     

胶州湾沉积物中氨基酸对有机质降解及细菌源贡献的指示作用解析

基于对胶州湾表层沉积物中总可水解氨基酸（THAA）的含量、组成、构型及分布特征的系统研究,通过氨基酸碳氮归一化产率（THAA-C%,THAA-N%）、降解因子DI、反应活性指数RI以及D型氨基酸占比（D-AA%,摩尔百分比）等指标结合碳氮比（TOC/TN）、碳稳定同位素（δ13C）探析了胶州湾沉积物中有机质的来源与降解状态,利用细菌源有机质及胞外肽酶活性（EEA）探讨了微生物在有机质迁移转化过程中的作用与贡献。结果表明,胶州湾表层沉积物中氨基酸平均含量为（7.60±3.64）μmol/g,在陆源与海源混合影响下,其水平分布呈现湾内高于湾外、湾内东部高于西部的特点,表明湾内东部陆源输入对沉积物THAA具有较高贡献。THAA-C%、THAA-N%、DI、RI以及D-AA%等指示因子均显示胶州湾表层沉积物中有机质的降解程度呈现湾外高于湾内、湾内东部高于西部的变化趋势,有机质来源、微生物活性与上覆水水深共同影响了有机质的降解程度。胶州湾表层沉积物中细菌源有机碳的贡献率为（29.35±18.73）%,其水平分布显示出湾内西部与湾外相近且高于湾内东部的特点。细菌胞外肽酶活性（EEA）平均为（0.81±1.31）nmol/（g·h）（以MCA计）,整体分布趋势与细菌贡献率相反,呈现湾内东部高于湾内西部和湾外的特性。沉积物中有机质的不同海源、陆源占比决定了有机质的可降解性,而有机质的降解程度进一步影响了细菌源有机质的贡献与胞外肽酶活性。     

Sources,transport, and partitioning of organic matter at a highly dynamic continental margin

Continental shelves play a major role as transition zone during transport of multiply-sourced organic matter into the deep sea. In order to obtain a comprehensive understanding of the origin and fractionation processes of organic matter at the NW Iberian margin, 40 surface sediment samples were analyzed for a structurally diverse range of lipid biomarkers, lignin phenols, grain size distribution, organic carbon content (TOC), its stable carbon isotopic composition (δ¹³CTOC), and the organic carbon to nitrogen ratio (TOC/TN). The biomarker inventory reflected a heterogeneous mixture of organic matter from various marine and terrestrial sources. Soil- and vascular plant-derived continental organic matter, indicated by lignin phenols and plant-derived triterpenoids, was primarily associated with the silt fraction and transported by river run-off. The spatial distribution patterns of higher plant-derived waxes, long-chain n-alkanes, n-alcohols, and n-fatty acids suggested distinct different transport mechanisms and/or sources. The branched tetraether index, a molecular proxy expressing the relative abundance of branched dialkyl tetraethers vs. crenarchaeol and considered to signal soil-derived organic matter, was not as sensitive as the other molecular indicators in detecting continental organic matter. Hydrodynamic sorting processes on the shelf resulted in a separation of different types of terrestrial organic matter; grass and leaf fragments and soil organic matter were preferentially transported offshore and deposited in areas of lower hydrodynamic energy. Algal lipid biomarker distributions indicated a complex community of marine plankton contributing to organic matter. Spatial and seasonal patterns of phytoplankton growth primarily controlled the distribution of algal organic matter components. The interplay of all of these processes controls production, distribution, and deposition of organic matter and results in three distinct provinces at the Galicia–Minho shelf: (I) fresh marine organic matter dominated the inner shelf region; (II) high inputs of terrestrial organic matter and high TOC content characterized the mid-shelf deposited mudbelt; (III) lower concentrations of relatively degraded organic matter with increased proportions of refractory terrestrial components dominated the outer shelf and continental slope.     

九龙江口潮滩表层沉积物有机质的分布、来源及沉积环境指示意义

本研究旨在揭示九龙江口潮滩有机质含量及其来源的时空分异规律,寻找有效识别潮滩沉积环境的有机碳指标,以便更好地将有机碳应用于河口沉积微相识别和古环境研究。在九龙江口潮滩不同地貌单元,于夏季和冬季采集41个表层沉积物,进行粒度、总有机碳(TOC)、总氮(TN)和稳定碳同位素(δ¹³C)测试。结果显示：从高潮滩至低潮滩,沉积物粒度逐渐变粗,TOC、TN和C/N变小,δ¹³C值偏正。高潮滩有机质来源以陆源和红树林贡献为主,中潮滩以海源和互花米草贡献为主,低潮滩以海源贡献为主。九龙江口潮滩有机质的分布和来源受控于河口陆海相互作用的季节变化、潮滩沉积动力分异和潮滩植被分布。高潮滩与中–低潮滩之间,TOC存在显著性差异,TN、δ¹³C存在极显著性差异,因此参数组合TOC、TN和δ¹³C可作为高潮滩与中–低潮滩的有效判别指标。     

桑沟湾及附近海域表层沉积物碳氮同位素分析及有机质来源

Naturally existing stable carbon and nitrogen isotopes are important in the study of sedimentary organic matter sources. To identify the sources of sedimentary organic matter in Sanggou Bay and its adjacent areas, which is characterized by high-density shellfish and seaweed aquaculture, the grain size, organic carbon(OC), total nitrogen(TN), carbon and nitrogen isotopic composition(δ13C and δ15N) of organic matter in the surface sediment were determined. The results showed that, in August, sedimentary OC and TN ranged from 0.17% to 0.76% and 0.04% to 0.14%, respectively. In November, OC and TN ranged from 0.23% to 0.87% and 0.05% to 0.14%, respectively. There was a significant positive correlation between OC and TN(R=0.98, P0.0001), indicating that OC and TN were homologous. In August, the δ13C and δ15N of organic matter varied from-23.06‰ to-21.59‰ and 5.10‰ to 6.31‰, respectively. In November, δ13C and δ15N ranged from-22.87‰ to-21.34‰ and 5.13‰ to 7.31‰, respectively. This study found that the major sources of sedimentary organic matter were marine shellfish biodeposition, seaweed farming, and soil organic matter. Using a three-end-member mixed model, we estimated that the dominant source of sedimentary organic matter was shellfish biodeposition, with an average contribution rate of 65.53% in August and 43.00% in November. Thus, shellfish farming had a significant influence on the coastal carbon cycle.     

Biochemical composition and size distribution of organic matter at the Pacific and Atlantic time-series stations

Amino acids, neutral sugars and amino sugars were analyzed to investigate the chemical composition and diagenetic processing of suspended particulate organic matter (POM, > 100 nm), high-molecular-weight dissolved organic matter (HMW DOM, 1–100 nm) and low-molecular-weight dissolved organic matter (LMW DOM, < 1 nm) at the time-series stations near Bermuda (BATS) and Hawaii (HOT). Differences between BATS and HOT were principally related to location-specific biogeochemical processes and water mass ventilation ages. Concentrations of amino acids, neutral sugar and amino sugars in unfiltered seawater sharply declined with depth at both stations, indicating an upper ocean source and rapid turnover of these components. The size distribution of organic matter was heavily skewed to smaller molecular sizes. Depth comparisons showed that larger size classes of organic matter were more efficiently removed than smaller size classes. Carbon-normalized yields of amino acids, neutral sugars and amino sugars decreased rapidly with depth and molecular size. Together these biochemicals accounted for 55% of organic carbon in surface POM but only 2% of the organic carbon in LMW DOM in deep water. Chemical compositions showed distinct differences between organic matter size classes indicating the extent of diagenetic processing increased with decreasing molecular size. These findings are consistent with the size-reactivity continuum model for organic matter in which bioreactivity decreases with decreasing molecular size and diagenetic processes lead to the formation of smaller components that are resistant to biodegradation. The data also provided evidence for a size-composition continuum. Carbon-normalized yields of amino acids, neutral sugars and amino sugars were sensitive indicators of diagenetic alterations. Diagenetic indicators based on amino acid compositions revealed distinct patterns for the North Pacific and Sargasso Sea possibly indicating the influence of varying sources or diagenetic processing.     

Organic carbon and nitrogen in the northern California current system: comparison of offshore, river plume, and coastally upwelled waters

During the first year of the Northeast Pacific GLOBEC program we examined the spatial distributions of dissolved and particulate organic carbon and nitrogen in the surface waters off the Oregon and Washington coasts of North America. Eleven east–west transects were sampled from nearshore waters to 190 km offshore. Hydrographic data and the distribution of inorganic nutrients were used to characterize three distinct water sources: oligotrophic offshore water, the Columbia River plume, and the coastal upwelling region inshore of the California Current. Warm, high salinity offshore water had very low levels of inorganic nutrients, particulate organic carbon (POC) and dissolved organic carbon (DOC). Warm, low salinity water in the Columbia River plume was relatively low in nitrate, but showed a strong negative correlation between salinity and silicate. The river plume water had the highest levels of total organic carbon (TOC) (up to 180 μM) and DOC (up to 150 μM) observed anywhere in the sampling area. Cold, high salinity coastal waters had high nutrient levels, moderate to high levels of POC and particulate organic nitrogen (PON), and low to moderate levels of DOC and dissolved organic nitrogen (DON). Each of these regions has characteristic C:N ratios for particulate and dissolved organic material. The results are compared to concentrations and partitioning of particulate and dissolved organic carbon and nitrogen in other regions of the North Pacific and North Atlantic Oceans.     

Stability and composition of terrestrially derived dissolved organic nitrogen in continental shelf surface waters

A linear decrease in dissolved organic carbon and nitrogen with increasing salinity offshore from the Georgia coast suggests that organic nitrogen compounds contributed to coastal waters by rivers are stable during the period (2–3 months) of their transfer over the continental shelf. While the C/N ratio decreased with distance from shore, total dissolved organic nitrogen (DON), total amino nitrogen, and primary amino nitrogen showed similar relative decreases, suggesting that nitrogen is associated with refractory organic compounds. Measured amino nitrogen accounted for about 20% of the total DON, leaving about 80% of the organic nitrogen undefined.     

Burial of organic carbon in Holocene sediments of the Zhujiang (Pearl River) and Changjiang (Yangtze River) estuaries

The East Asian marginal seas are important sinks of terrigenous materials transported by large rivers. In this study two cores from the Changjiang (Yangtze River) and Zhujiang (Pearl River) estuaries and one core from the inner shelf off of Hong Kong were investigated to examine the burial of organic matter during the postglacial period and its possible links with paleoenvironmental changes. Based on a simple two end-member mixing model, the terrestrial organic matter supplied primarily from the Zhujiang and Changjiang dominates the estuarine areas while marine organic matter contributes more to the inner-mid shelf. The competing contributions of terrestrial and marine organic matter are responsible for the downcore variations of organic elemental compositions. The overall decreasing shifts of total organic carbon concentrations and total organic carbon to total nitrogen ratios in the Zhujiang estuarine sediments since 6.5 kaBP seems to support the notion that depth profiles of organic matter compositions deposited in the Zhujiang Estuary can aid in the reconstruction of monsoon history in the Holocene. Nevertheless, organic matter compositions in the Changjiang Estuary and inner shelf off of southeastern Hong Kong respond in a different and more complex way to freshwater discharges or precipitation changes (monsoon variability) in the catchments, owing to complex controls of deposition and preservation of organic matter in these estuarine and shelf environments. Caution is therefore needed in using organic elemental and isotopic compositions to decipher paleoenvironmental changes in East Asian continental shelves where intense river–sea interactions occur and sedimentary environments change drastically.     

Trace element and molecular markers of organic carbon dynamics along a shelf–basin continuum in sediments of the western Arctic Ocean

Molecular organic biomarkers together with trace element composition were investigated in sediments east of Barrow Canyon in the western Arctic Ocean to determine sources and recycling of organic carbon in a continuum from the shelf to the basin. Algal biomarkers (polyunsaturated and short-chain saturated fatty acids, 24-methylcholesta-5,24(28)-dien-3β-ol, dinosterol) highlight the substantial contribution of organic matter from water column and sea-ice primary productivity in shelf environments, while redox markers such as acid volatile sulfide (AVS), Mn, and Re indicate intense metabolism of this material leading to sediment anoxia. Shelf sediments also receive considerable inputs from terrestrial organic carbon, with biomarker composition suggesting the presence of multiple pools of terrestrial organic matter segregated by age/lability or hydrodynamic sorting. Sedimentary metabolism was not as intense in slope sediments as on the shelf; however, sufficient labile organic matter is present to create suboxic and anoxic conditions, at least intermittently, as organic matter is focused towards the slope. Basin sediments also showed evidence for episodic delivery of labile organic carbon inputs despite the strong physical controls of water depth and sea-ice cover. Principal components analysis of the lipid biomarker data was used to estimate fractions of preserved recalcitrant (of terrestrial origin) and labile (of marine origin) organic matter in the sediments, with ranges of 12–79%, 14–45%, and 37–66% found for the shelf, slope, and basin cores, respectively. On average, the relative preserved terrestrial organic matter in basin sediments was 56%, suggesting exchange of organic carbon between nearshore and basin environments in the western Arctic.     

Distribution, partitioning and fluxes of dissolved and particulate organic C, N and P in the eastern North Pacific and Southern Oceans

Concurrent distributions of dissolved and suspended particulate organic carbon (DOC and POC_susp), nitrogen (DON and PON_susp) and phosphorus (DOP and POP_susp), and of suspended particulate inorganic phosphorus (PIP_susp), are presented for the open ocean water column. Samples were collected along a three-station transect from the upper continental slope to the abyssal plain in the eastern North Pacific and from a single station in the Southern Ocean. The elemental composition of surface sedimentary organic matter (SOM) was also measured at each location, and sinking particulate organic matter (POM_sink) was measured with moored sediment traps over a 110-d period at the abyssal site in the eastern North Pacific only. In addition to elemental compositions, C : N, C : P and N : P ratios were also calculated. Surface and deep ocean concentrations of dissolved organic matter (DOM) and inorganic nutrients between the two sites displayed distinct differences, although suspended POM (POM_susp) concentrations were similar. Concentrations of DOM and POM_susp displayed unique C, N and P distributions, with POM_susp concentrations generally about 1–2 orders of magnitude less than the corresponding DOM concentrations. These differences were likely influenced by different biogeochemical factors: whereas the dissolved constituents may have been influenced more by the physical regime of the study site, suspended particulate matter may have been controlled to a greater extent by biological and chemical alteration. Up to 80% of total particulate P in POM_susp, POM_sink and SOM consisted of PIP. For all organic matter pools measured, elemental ratios reveal that organic P is preferentially remineralized over organic C and organic N at both sites. Increases in C : P and N : P ratios with depth were also observed for DOM at both sites, suggesting that DOP is also preferentially degraded over C and N as a function of depth. A simple one-dimensional vertical eddy diffusion model was applied to estimate the contributions of dissolved and suspended particulate organic C, N and P fluxes from the upper mixed layer into the permanent thermocline. Estimated vertical DOM fluxes were 28–63% of the total organic matter fluxes; POM_susp and POM_sink fluxes were 8–20 and 28–52% of the total.     

Direct determination of organic carbon in modern reef sediments and calcareous organisms after dissolution of carbonate

An improved method for the direct determination of organic carbon in calcareous marine sediments, organisms and particulate matter is described. Samples are dissolved in phosphoric acid to remove carbonates, purged with oxygen to remove CO₂, and the resulting acidic solution is analysed for total (dissolved and particulate) organic carbon. The method is rapid, involves minimal sample manipulation, and is both accurate (better than ± 2%) and precise (better than ± 0.2 mg organic carbon/g sediment). The method is especially suitable for modern carbonate sediments which have low levels of predominantly acid-soluble organic carbon.     

Carbon inputs and distribution in estuaries of turbid rivers: the Yang Tze and Yellow rivers (China)

Particulate and dissolved organic and inorganic carbon concentrations were measured in the Yang Tze (Changjiang) and Huanghe (Yellow) river estuaries, during two different seasons. During the winter, the organic matter in the suspended load of both estuarine systems was dominantly of terrestrial origin, while in the summer, there were significant contributions from aquatic production. In these turbid rivers, there is a strong positive correlation between the concentrations of total suspended matter and particulate organic carbon, probably because biological production is inhibited when turbidity exceeds a certain limit. Dissolved organic carbon (DOC) does not exhibit a conservative behavior in these estuarine systems. High dissolved organic carbon values in bottom water samples suggest remobilization of DOC from near-surface, bottom sediments. Dissolved inorganic carbon concentrations were very high in the Huanghe River, and the trend in the calculated saturation indices for calcite suggests precipitation of carbonate in this estuarine system. There is no such evidence for carbonate precipitation in the Yang Tze River.     

Variation of dissolved organic matter and fluorescence characteristics before,during and after phytoplankton bloom

The variation of dissolved organic matter (DOM) and fluorescence characteristics during the phytoplankton bloom were investigated in Yashima Bay, at the eastern part of the Seto Inland Sea, Japan. We found significant accumulations of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), chromophoric dissolved organic matter (CDOM) fluorescence, and UV₂₆₀ during the phytoplankton bloom period in 2005, although lower accumulations of DOC and DON and only increases of CDOM fluorescence were observed during the bloom period in 2006. Little or no correlation between DOM and phytoplankton abundance might be due to the composition of DOM, which is a complex mixture of organic materials. The 3D-EEM results revealed that the DOM produced around the phytoplankton bloom period contained tyrosine, tryptophan, and humic-like substances. Our results showed that the occurrence of phytoplankton bloom contributed to the production of DOM in coastal water but the DOM accumulation depended on the type of phytoplankton bloom, the phytoplankton species in particular. From our results, we concluded that phytoplankton have a great role in the dynamics of DOM as a producer in a coastal environment.     

A new method of evaluating the mineralization of particulate and dissolved photoassimilated organic matter

A new method of evaluating the rate of mineralization of photoassimilated organic matter is described. This method enables us to compare the rate of direct mineralization of particulate organic carbon (POC) to CO₂ with the rate of solubilization of photoassimilated organic carbon followed by the mineralization of the resultant dissolved organic carbon (DOC) under the same conditions. The direct mineralization of photoassimilated carbon from POC to CO₂ is a more significant process compared with the mineralization of extracellular released organic carbon. The first-order rate coefficients range from 0.132 to 0.434 day^–1 for direct mineralization and 0.034 to 0.189 day^–1 for solubilization.