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Despite of the importance for tracking sources and fates of organics in determining carbon cycling and assessing the overall health of lacustrine ecosystems, little is known of organics behaviors in shallow eutrophic lakes. In this study, for relating the benthic organics to pelagic sources, an ecosystem-level investigation was performed in hypereutrophic Lake Taihu, China, by using source-specific fatty acid biomarkers on the molecular level. Results exhibited the unexpected asymmetric phenomena of organics between surface water and sediments. In the abundance, the dominant organics shifted from cyanobacteria in surface water to terrestrial plants in sediments. In the spatial pattern, as opposed to terrestrial plants, cyanobacteria were found not site-to-site symmetrical, although both of their spatial distributions varied strongly. Essentially, these asymmetric phenomena ascribed to a more considerable loss of cyanobacteria compared to terrestrial plants during sinking, caused by aquatic animal consumption and microbial utilization with different degree. Combined dual stable isotopes (δ13C and δ15N) and fatty acid biomarkers revealed that there were only subtle differences in the diets of benthic and pelagic animals and cyanobacteria were their main food source. Concomitantly, results of δ13C of bacteria-specific fatty acids demonstrated that bacteria equally and profoundly affected organics accumulation or preservation in the sediments, because they preferentially utilized labile cyanobacteria as their carbon source instead of terrestrial plants (>95% within these two sources). Consequently, these novel findings clarify that not only in deep lakes, but also shallow eutrophic ones, the extensive losses of autochthonous organic matter can be expected during sedimentation coupling with the dramatical modifications of biogeochemical processes.

Although an understanding of the quantity and quality of sedimentary organic matter (SOM) pools is necessary to design sound environmental management strategies for lacustrine systems, the characterization of organic matter sources and the assessment of their relative contributions to eutrophic and inland lake sediments remain insufficient. In this study, the contribution of potential organic matter sources to sediments in shallow and hypereutrophic lake Taihu, China was assessed on the molecular level using source-specific fatty acid biomarkers. The results indicated that SOM was composed mainly of terrestrial plants with a maximal contribution of 45.3 ± 2.4% to the total organic carbon, which accounted for approximately 66% among the determined organic matter sources. Evidence suggests the terrestrial plants remained in a fresh state in surface sediments: the correlation ( R 2 = 0.62, p R 2 = 0.60, p

The quantity and quality of sedimentary organic matter (SOM) in relation to material and energy flows are crucial for understanding the current state and future development of lake systems, yet, characterization of organic matter sources and assessment of their relative contributions in different trophic-state lakes caused by anthropogenic impacts are scarcely known. In this study, for obtaining information concerning the source of SOM and its compositional diversity along different trophic gradients, a total of thirty-one sampling sites from four freshwater lakes located in China and Japan were performed by the molecular level analysis using source-specific fatty acid biomarkers. Results indicated that SOM in these lakes was composed of microalgae-, aquatic plant-, terrestrial plant- and bacteria-derived organic matters based on their fatty acid profiles. The scatter plot matrix exhibited correlations between these sources, however, only terrestrial plant-derived organic carbon was a well predictor for sediment TOC with strong, spatiotemporal dynamics. The source and composition of SOM were evidently influenced by lake trophic state with redundancy analysis. Moreover, increase of lake trophic state led to the relatively higher contribution of aquatic organic matter sources to SOM pool compared with terrigenous sources, as evidenced by significant correlations between the trophic state index [TSI (TP)] and the ratio of terrigenous to aquatic fatty acids (TARFA ratio). Yet, this changing trend became more gradual with higher trophic state and prevented the occurrence of regime shift from allochthonous to autochthonous dominant state by a threshold (0.683) of TARFA ratio. Together, a conceptual diagram was proposed, which highlighted the prevailing state of allochthonous source and implicated sedimentary organics in biogeochemistry cycle within freshwater lakes.

The effects of bacterial activity on the degradation of estrone (E1), estradiol (E2), estriol (E3) and ethinylestradiol (EE2) in nitrifying activated sludge (NAS) were studied with different substrates and organic loading rates (OLRs) and low temperature conditions. Heterotroph was shown to have utilized glucose prior to E1 for metabolism. The co-metabolism of ammonia oxidizing bacteria (AOB) dominated the degradation of E1, E2 and EE2 in NAS. The higher the organic loading, the higher the rate of organic matter transformation, with less ammonia oxidation and less degradation of E1, E2 and EE2. The degradation of E3 in NAS was shown to be largely due to heterotroph metabolism. On the basis of the difference of apparent activity between heterotroph and AOB at 4 degrees C, the process of estrogen degradation via the co-metabolism of AOB was able to be identified.

The mechanism thought to be responsible for the observed fortnightly modulation of estuarine circulation in Tokyo Bay was investigated in December 1998 using a two-layer theoretical model, which was verified using a three-dimensional non-hydrostatic model. The influence of the difference in kinetic energy between the upper and lower layers on estuarine circulation was clarified in terms of vorticity, which was defined by the difference in the velocities of the two layers. The ratio of the difference in kinetic energy between the two layers to the baroclinic energy was attributed to the change in strength of estuarine circulation. Thus, the mechanism for fortnightly modulations of estuarine circulation may be due to the suppression of upper-water withdrawal during spring tide, when the ratio is more than 1, and the enhancement of upper-water withdrawal during neap tide, when the ratio is close to 0.

Sea surface current observations with the use of two high-frequency radars were carried out near the mouth of Tokyo Bay, Japan from 1 December to 23 December 1998. A peculiar fortnightly variability of residual flow was found near the mouth of Tokyo Bay, that is, sea surface residual flow was weak and southward in spring tide but it was strong and formed a clockwise circulation in neap tide. Strong sea surface residual flow resulted from large vertical shears of estuarine circulation and small vertical viscosity by weak tidal currents in neap tide. The clockwise circulation was produced by an expansion of horizontal circulation from the river mouth to the bay mouth.