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The Sources, Transportations And Transformations Of Dissolved And Particulate Terrestrial Organic Matter In Typical River And Estuary Systems

Posted on:2014-01-22Degree:DoctorType:Dissertation
Country:ChinaCandidate:H Y BaoFull Text:PDF
GTID:1220330395955787Subject:Estuarine and coastal science
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Rivers and estuaries are the major link between land and ocean. Terrestrial organic matter (OM) is a major food source for the marine organism. It plays an important role in the global biogeochemical cycle. Under the background of global climate change, the extreme climate events such as storms, typhoon may increase, in the meantime, the human impact on the natural process increased in the past decades. The study of the sources, composition and fluxes of fluvial organic carbon would help us to understand how the human activities would influence the biogeochemical cycles. Due to the dam constructions in many river systems, dissolved organic matter (DOM) became the dominated. Though there were studies focused on the fluvial OM transportation in China, however, the systematically, quantified and molecular level studies are scarce, especially for DOM. Here we carried out studies that focused on Changijang, small tropical estuary in Hainan Island and Zhejiang small river systems. Bulk properties (carbon to nitrogen molar ratio (C/N), stable carbon isotope (δ13C)) and biomarker (lignin phenols), field observation and lab incubation were used in present studies. Our objectives were1) to trace the sources of both particulate and dissolved organic matter in different river and estuary systems;2) to understand how the human activities and natural process affected the composition and transportation of terrestrial OM.The particulate organic matter (POM) in Changjiang was mainly composed of soil OM, higher plant tissue and phytoplankton. Stable carbon isotope (δ13C) and lignin phenols were used to quantify the contribution of contribution from different OM sources. The results showed that soil OM is the major OM sources of particulate organic matter in Changjiang, it contribute approximately50%-70%to the total OM. The contribution from soil OM did not show significant seasonal variation can be observed. The contribution from higher plant tissue and phytoplankton was variable temporally and spatially. The contribution from phytoplankton was higher in dry season than in flooding period. The dominant OM sources in tributaries of Changjiang were different and also with seasonal variation. Special notice should be put into Dongting Lake and Poyang Lake. In rainy season, the OM in the two lakes was predominated by in situ production. The contribution from phytoplankton was approximately80%. However, in dry season, phytoplankton only contributed approximately20%to the total OM. The seasonal OM sources variation in Hanjiang was close to that of Changjiang. The dissolved lignin phenols concentrations varied from6.1μg/L to11.6μg/L in2009sampling campaign, and varied from10.8μg/L to19.2μg/L in2010. Utilizing the vanillyl (Ⅴ) end-member value derived from Hernes et al.(2007), it can be calculated that the contribution from higher plant to DOM was approximately12%-36%and24%-32%in August-October2009and July August2010, respectively. Moreover, the contribution from higher plant tissue was higher in upper reach DOM samples (24.5±8.3%) than that in middle and lower reach (15.4±2.4%), higher in the flooding period (27.0±4.0%) than in non-flooding rainy season (15.4±2.4%).Seasonal TSM variation of Changjiang, TGD impoundment, input from two lakes and channel erosion in middle and lower Changjiang are the major factors that influenced the composition and flux of OM in Changjiang. Specially, after the impoundment of TGD, approximately80%of the sediment from upper reach was trapped within TGR. However, the water discharge from upper Changjiang was almost unaffected (except during the impoundment period, which is mainly during the middle Spetember and middle Octorber), which makes the channel erosion and lakes become more important in determining the Changjiang OM composition and fluxes. The geomorphology, TSM and sewage input was the major factors affecting DOC concentration in the mainstream, while the compositions and fluxes of dissolved terrestrial OM was influenced by its sources, turbidity of the water column, residence time, TGD impoundment, flocculation as well as the interaction between POM and DOM.The photochemical degradation and dark incubation experiment carried out in different samples indicated that the OM source is the major factor that would influence their bioavailability and photochemical degradation character. The less degraded mangrove pore water from Hainan Wenchang/Wenjiao Estuary had much higher degradation rate than that of dissolved lignin phenols from Three Gorges Reservoir (TGR) which might have experienced longer degradation process. The different compounds of lignin phenols had different degradation rates, syringyl (S) degraded faster than V. The variation of mass ratios of vanillic acid to vanillin ((Ad/Al)v) was also related to the sources of lignin phenols, the increase of (Ad/Al)v of mangrove pore water samples were significant, however, in the TGR samples, it was more variable. The comparison between the fluorescence spectroscopy and lignin phenols in the TGR sample showed that the photochemical degradation rates of lignin phenols were similar to UVC humic-like substance, which is similar to other’s study. The similar degradation rates further indicated that lignin phenols in TGR were pre-degraded.The seasonal observation of813C and A8in Wenchang River/Estuary showed that the major OM source in the Wenchang River was in situ production. Utilizing the V yield of dissolved lignin phenols, it can be calculated that the contribution of higher plant tissues to DOC was approximately14%-40%in Bamen Bay and7%-16%in the coastal region. The contrition of higher plant tissue to DOC in Wenchang River was higher than in Changjiang during "impoundment" period, however, lower than Changjiang during flooding period. The contribution of mangrove forest was different between POM and DOM. The contribution of mangrove to POM was insignificant, however, the higher dissolved lignin phenols concentration in Bamen Bay and the relatively lower (Ad/Al)v revealed the input from mangrove forest to DOM, this is similar to the results in other regions. The impact of extreme events was higher than seasonal variation. During the typhoon "Kammuri", the increase of TSM in Bamen bay was higher than the seasonal variation. Large amount of soil derived terrestrial OM could be transported to the coastal region during the typhoon period. The hydrodynamic process, typhoon, photochemical degradation, seasonal variation, mangrove and aquaculture ponds all had effect on the composition of POM and DOM in the Wenchang/Wenjiao Estuary in different extends.The observation of POM and DOM in both dry season and rainy season in Zhejiang river showed that soil is the major POM source, the contribution from higher plant tissue is less; the contribution of plant tissues to DOM varied from10%-50%in different river systems. Unlike in Changjiang, DOC in the Zhejiang Rivers was strongly affected by the human activities, which was caused by their small drainage basins and higher population densities. The statistical (SPSS) analysis indicated that the difference of bulk properties between two seasons was insignificant. However, significant difference could be found for lignin phenol concentration (∑8). Higher∑8in the rainy season suggested that POM in rainy season contained higher portion of terrestrial OM, this is similar to the seasonal OM composition variation in Changjiang. The statistical results further suggested that lignin phenols were more sensitive to the OM sources change than bulk properties. Moreover, the human impact was more significant in dry season.The present study showed that human activities and natural process played different roles during the fluvial transport of POM and DOM. However, their roles were affected by the drainage basin scales as well as the geomorphology of the drainage basin. Due to the human impact, some natural processes become more important, e.g., because of the dam construction, photochemical degradation, freshwater flocculation might be more significant in the river systems. More efforts should be put into those process based studies.
Keywords/Search Tags:particulate organic matter, dissolved organic matter, lignin phenols, river-estuary system, human activities, photochemical degradation
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