| Carbohydrates are the largest identified fraction of the dissolved organic carbon in the ocean, which play an important role in the marine biogeochemical cycle, and are ubiquitous in marine systems, including marine organisms, dissolved organic matter, colloids and suspended particles. They are the prime products of phytoplankton photosynthesis and the versatile molecules that serve as energy, storage and structural components of cells. Therefore studies on biogeochemical process of dissolved carbohydrates in representative shelf seas of China will contribute to the investigation on the sources, transformation and circulation of marine organic matter, and to provide the basis for understanding marine primary productivity.In this present dissertation, systematic research on the temporal and spatial distributions, concentrations and influencing factors in the surface microlayer of monosaccharides (MCHO) and polysaccharides (PCHO) in the East shelf seas of China, including the East China Sea, the South Yellow Sea and Jiaozhou Bay, were investigated. In addition, the distribution and enrichment factors of dissolved carbohydrates were detailed studied. The main findings are drawn as follows:(1) The spatial and temporal distribution of MCHO and PCHO were determined in the East China Sea and the South Yellow Sea during spring, summer, autumn and winter 2011. The results showed that the concentrations of MCHO and PCHO in the surface water ranged from 0.1 to 18.3μmol C/l and from 0.1 to 50.6μmol C/l for all samples, with the annual average values of 5.0 and 6.6μmol C/l, respectively. The concentrations of MCHO and PCHO showed a notable seasonal variation with the high average values in spring and summer and lowest value in winter, which was attributed to the seasonal variations of phytoplankton biomass, water masses and currents in the East China Sea and the South Yellow Sea. On average, TCHO accounted for 11.8% of DOC, which indicated that dissolved carbohydrates were the important fraction of DOC in the surface seawater of the East China Sea and the South Yellow Sea. The horizontal distributions of MCHO and PCHO exhibited a similar decreasing trend from inshore to offshore areas, in contrast to the various distribution patterns of MCHO and PCHO in different seasons. The vertical distributions of MCHO and PCHO during four seasons were different from each other, with the high values appearing in the upper mixed layer. Influenced by the Yangtze River effluent, the Kuroshio water and phytoplankton biomass, the vertical distributions showed a declining trend from inshore to offshore sites and from suface to bottom layer. In addition, the concentrations of MCHO and PCHO exhibited a diurnal variation in surface water of the East China Sea and the South Yellow Sea. The high concentrations of PCHO and TCHO appearing around noon time were consistent with the concentrations of Chl-a, which attributed to the production of phytoplankton. The maximum concentration of MCHO was later than the value of PCHO, which proved the hypothesis that MCHO could be partly derived from the hydrolysis of PCHO. Negative correlations between concentrations of TCHO and salinity in summer and autumn, while no relationship was shown in spring and winter, suggesting that the concentrations and distrbutions of dissolved carbohydrates were not only associated with terrestrial input. The relationships between the concentrations of dissolved carbohydrates and Chl-a were great different form each other, indicating that biological production was not the dominant source. In addition, the concentrations of MCHO, PCHO and TCHO showed no relationship with total bacterial count.(2) The spatial and temporal distribution of MCHO and PCHO were investigated in the surface microlayer of the East China Sea and the South Yellow Sea during spring, summer, autumn and winter 2011. Furthermore, the enrichment factors of MCHO and PCHO were studied in surface microlayer and the corresponding bulk water. The concentrations of MCHO and PCHO in the surface microlayer ranged from 0.8 to 29.0μmol C/l and from 0.1 to 84.8μmol C/l for all samples, with the annual mean values of 7.8 and 10.2μmol C/l, respectively. On average, TCHO in the surface microlayer accounted for 11.4% of DOC, which indicated that dissolved carbohydrates were the important fraction of DOC in the surface microlayer of the East China Sea and the South Yellow Sea. The concentrations of MCHO and PCHO in the surface microlayer showed a subtle seasonal variation with the high average values in spring and summer and low values in autumn and winter. The horizontal distributions of dissolved carbohydrates in surface microlayer exhibited the similar trend with the distribution patterns in surface water, decreasing from the coast to open seas, with the high values appearing in the northwest region of the Cheju Island, the Shandong Peninsula region and Yangtze River effluent. The concentrations of MCHO, PCHO and TCHO in the surface microlayer were significantly correlated with the values in corresponding bulk water, indicating that there was an intense and frequent water exchange between the microlayer and bulk water. The average (range) enrichment factors of MCHO and PCHO in surface microlayer were 1.9 and 2.5, respectively. Significant enrichment was observed for MCHO and PCHO in the surface microlayer, with the high average values in autumn and winter and low ones in spring and summer. The results may be associated with the properties of dissolved organic matter and sea condition of the investigated area.(3) Horizontal distributions and seasonal variations of MCHO and PCHO were studied from June 2010 to May 2011 in the surface water of Jiaozhou Bay. The concentrations of MCHO and PCHO ranged from 0.6 to 63.7 and 0.7-72.6 μmol C/1 for all samples, respectively, with the average values of 9.6 and 13.8 μmol C/1, respectively. On average, TCHO in the surface water accounted for 13.4% of DOC, suggesting that dissolved carbohydrates were an important constituent of DOC in the surface water of Jiaozhou Bay. The concentrations of MCHO showed an obvious seasonal variation with the highest average value in summer and lowest value in spring, while the highest value of PCHO was observed in spring and lowest value in autumn. The seasonal variations of MCHO and PCHO were influenced by the combination of biological activities and terrestrial input. The horizontal distributions of MCHO and PCHO in surface water of Jiaozhou Bay displayed a decreasing trend from the coast to the central region and from inner bay to outer bay, with the high values occurred in the east coast region. The high concentrations may be influenced by the industrial and domestic wastewater input, while the low values appearing in the mouth of the bay because of the strong exchange effect between inner bay water and open sea. There were significant correlations among the concentrations of PCHO, TCHO and Chl-a, indicating that the concentrations of dissolved carbohydrates were associated with phytoplankton biomass. No significant relationship between concentrations of dissolved carbohydrates and total bacteria count was found.(4) Horizontal distributions and seasonal variations of MCHO and PCHO were studied from June 2010 to May 2011 in the surface microlayer of Jiaozhou Bay. Furthermore, the enrichment factors of MCHO and PCHO were studied in surface microlayer and the corresponding bulk water. The concentrations of MCHO and PCHO ranged from 3.2 to 27.0 and 3.2 to 48.6μmol C/l for all samples, respectively, with the average values of 12.5 and 16.9μmol C/l, respectively. On average, TCHO in the surface microlayer accounted for 2.7% to 24.0% of DOC for all samples, with the annual mean value of 12.3%, which indicated that dissolved carbohydrates were the important fraction of DOC in the surface microlayer of Jiaozhou Bay. The concentrations of MCHO in surface microlayer showed a notable seasonal variation with the highest mean value in autumn and lowest one in winter, which were different from the variation in surface water of Jiaozhou Bay. Meanwhile, the maximum average concentrations of PCHO were occurred in spring and summer, and the minmum value was occurred in winter, which was consistent with the variation in surface water. There were significant relationships among the concentrations of MCHO, PCHO and TCHO which suggested that they may have the similar source and sink patterns. The annual enrichment probabilities of MCHO and PCHO in the surface microlayer were 69.1% and 56.1%, respectively, with the average enrichment factor of 1.6 and 1.8. The maximum average enrichment factor of MCHO appeared in autumn and the minmum values appeared in summer and winter. In contrast, the maximum average enrichment factor of PCHO was occurred in autumn and the minmum value was occurred in winter. The variation of microlayer enrichment factors of MCHO and PCHO were appeared during the survey, which were attributed to the biologetic productivity, carbohydrates characteristics and wind speed. |
PDF Full Text Request