季节性缺氧湖泊氮的生物地球化学循环

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	季节性缺氧湖泊氮的生物地球化学循环
其他题名	nitrogen biogeochemical cycles in a seasonally anonxic lake
	肖化云
	2002
学位授予单位	中国科学院地球化学研究所
学位授予地点	中国科学院地球化学研究所
学位名称	博士
学位专业	环境地球化学
关键词	氮同位素氮循环季节性缺氧红枫湖
摘要	红枫湖是在河流上筑坝而形成的人造湖泊,水动力较大.湖泊夏季水体出现明显的热分层现象,而在秋后又往往发生“黑潮”事件,因而红枫湖是一个典型的季节性缺氧湖泊.该文通过对其进行季节性采样分析,对湖泊全年氮的生物地球化学循环以及外源氮输入（雨水和河流）及其特征进行了系统研究.该论文不仅研究了不同形态氮含量的季节性变化规律,而且进行了多种氮同位素的测试和特征研究.
其他摘要	Hongfeng Lake has a strong hydraulic power, formed by damming rivers. Thermal stratification occurred in the water columns of summer and "black tide" was often found in the late autumn. Therefore, Hongfeng Lake is a typical seasonally anoxic lake. In this thesis, samples were collected seasonally from the lake and other pertinent waters. Based on the analytical results, nitrogen biogeochemical cycles in the lake have been discussed. Additionally, characteristics of exterior N sources (rains and rivers) were also studied. By using the nitrogen isotopic techniques and other methods, some significant innovations has been obtained. 1. N Sources from Rains and its Characteristics Lake waters in Hongfeng Lake mainly come from rain waters, so the studies on N in rains help to the understanding of the real N sources of the lake. In order determine nitrogen and sulfur isotopic compositions in rains, two different types of rains (<5mm for flurries and >100mm for storms) were sampled. The sources of nitrogen and sulfur have been also studied. For both species a significant difference in mean sulfur and nitrogen isotopic composition was seen in this study between samples collected from flurries (-4.90±2,76%o for sulfate and +2.O±4.4%o for nitrate) and storms (J-4.5S±5.02%o for sulfate and +4.1±4.0%o for nitrate), supporting that sulfur and nitrogen in the two types of rains were of difference sources. For sulfate, the negative 534S values in flurries are associated with Local sources (coal combustion and biogenic sulfur) while sulfur in storms, caused by typhoon form Pacific Ocean, with positiveδ~(34)S values are of maritime origin. For nitrate, the sources in flurries are not much clear because of a wide range ofδ~(15)N values (-3.8%o ~ +10.7%o), but the higherδ~(15)N values (>+6.0%o) in the range are probably related to dry deposition or coal-fired power plants; the meanδ~(15)N value of +4.1%0 in storms may also be a reflection of maritime origin. Measurements ofδ~(15)N values for ammonium in flurries show thatδ~(15)N values are v/ell related with ammonium concentrations (R~2=0.92). The lower values in the range ofδ~(15)N values (-1.7%o ~ -22.0%o) for ammonium are due to the less incorporation of 15N by cloud water, which probably has a 6Ii;N value of about -22.0%o. But the higher concentrations (averaged 1.25mg I"1, relative to that of New York) arid the lower 815N values (averaged -12.2±6.7%o) indicated that sources of ammonium are widespread agricultural use of excretory wastes and the release of NH3 from soils. By compared nitrogen isotopic compositions in rains with those in lake waters, I concluded that the contributions of N in rains to the lake are small. 2. N Sources from Rivers and its Characteristics The water supply of the lake by rains is by the way of rivers. It had been believed that N in rivers, especially in those that seriously polluted by industrial wastewaters, was the main N sources of the kike. In the thesis, different types of rivers and some industrial wastewaters have been discussed for their characteristics of N pollution. In dry seasons, Yangchang River, which polluted by industrial wastewaters and was characteristic of high nitrate and ammonium concentrations, hadδ~(15)N values that lie in the range of industrial wastewaters (>+10%o). But in wet seasons, the nitrogen concentrations decreased. And their concentrations and 815N values were similar to those in agricultural rivers. It was the result of the decreased scale of industrial wastewaters in rivers. Therefore, the N distributions of industrial wastewaters to the river can be ignored. Industrial wastewaters had high nitrate and ammonium concentrations and highδ~(15)N values (>+10%o). Higher ammonium concentrations have been found in production times than in other times, but the nitrate concentrations kept constant. N contributions of rivers to Hongfeng Lake varied with time. In summer, water fluxes in rivers are large, but their N concentrations are low. So the contributions are small. However, an opposition occurred to rivers, in winer-spring because of the small fluxes and higher N concentrations. 3. Seasonal N Biogeochemical Characters in Lake Waters Season variations of nitrate concentrations in Hongfeng Lake waters are the results of biogeochemical processes. From early spring to early summer, algae grew weakly and few nitrate was consumed. In the meantime, the decomposition of organic matters was weak and few nitrate was also produced. So, nitrate concentrations kept constant in this time. Although algae in surface waters assimilated substantial nitrate in summer, however, the decomposition of organic matters (nitrification) is strong and this makes the nitrate concentrations increase. The phenomena did not found before. The strong denitrtification occurred in late summer- early autumn resulted in the rapid fall of nitrate concentrations. It persisted until the thermal stratification disappeared. After the disappearance, denitrification was obviously limited and thus the nitrate concentrations rose again. The increase of nitrate concentrations in summer was not the result of exterior sources. Variations of nitrate and TN concentrations at different profiles of Hongfeng Lake are large. From the inlet of rivers downstream to the dam, nitrate and TN concentrations increased step by step, suggesting that nitrate did not come from exterior sources. On the contrary, they come from the lake somewhere. The nitrogen isotopic data also strongly proved that nitrate was interiorly produced, The interior sources are the decomposition of organic matters (nitrification). In summer, production of organic matters is always companied with decomposition. Some of these organic matters stems from aquatic algae; some are land-derived. Because the inlet of rivers is just the site where organic matters sank and where the surface waters with high DO concentrations from epilimnion went down, substantial land-derived organic metter were lost. Effects of N in exterior rivers on Hongfeng Lake are dominant in winter-spring. The high load of exterior nitrate increased again after the fall of nitrate concentrations by denitrification in autumn. And decomposition of organic matters (nitrification) also provided nitrate for these seasons. Results of nitrogen isotopic traces showed that mixing of exterior rivers with lake waters is evident in the inlet, and the middle-downstreara parts of the lake dominated the decomposition. Nitrate produced by decomposition in winter waters is largest in middle layers of water columns, consistent with the rich sinking organic matters in the layers. Denitrificatiort and nitrification occurred simultaneously in the lake in autumn, but the latter is weaker than the former due to the low nitrate concentrations. Nitrification mainly occurred in surface waters and denitrification in the surface sediments. Nitrate produced by nitrification and inherited from summer waters strengthen denitrification. Substantial N2O, a green house gas, was produced and released to the atmosphere. 4. Nitrogen Isotopic Compositions in Lake Sediments and Their Significances According to the organic C and N content, C:N values, distribution of bacteria in sediments and isotopic compositions, stage of sediments of Hongfeng lake can be divided into: surface sediments (0-llcm) - loosed accumulation - rapid decomposing stage, middle sediments (ll-19cm) - extrusion - slow decomposing stage and bottom sediments - close accumulation - steady stage. Decomposition of sedimentary organic matters occurred in the surface sediments and is most important to water environments. As a whole, 515N values for sedimentary organic N (+4.37%o~ +8.2l%o, average +6.52%o) and for absorbed ammonium (+7.25%o - +20.96%o, average +3.69%o) increased from the bottom to the surface, indicating that the inflow fluxes of wastewater increase from 1961 to 2001. However, extent of the increase varied with years. Nitrogen isotopic data showed that the fluxes are steady in the early times, and rapid increases in 1990s' was found after a small decrease in the middle-late of 1980s'. Nitrogen isotopic data for sedimentary organic N and absorbed ammonium can be used to trace the history of N pollution id lakes. They all showed a good relationship with inflow fluxes of wastewater, suggesting nitrogen isotopic techniques for lake sediments is an efficient methods to reconstruct the revolution of N pollution id lakes. The method by using nitrogen isotopic data for absorbed ammonium is one of the innovations in the thesis. No correlative reports can be found before. 5. Other Innovations Effects of damming rivers on transportation of N in vivers are not clear. The studies on N biogeochemical processes help to understand them. In the past, decreases of N loads after damming are believed. But this did not occur to Hongfeng Lake. I believed that it was due to the strong hydraulic power, which carried the surface waters with high DO concentrations to the thermocline and caused substantial organic matters decomposed. Transformation between land-derived and aquatic organic matters occurred when inorganic N produced by decomposition of land-derived organic matters was provided to aquatic algae. The transformadon weakened the ability to reconstruct the revolution of land vegetation types (C_3 and C_4) and of aquatic algae.
页数	131
语种	中文
文献类型	学位论文
条目标识符	http://ir.gyig.ac.cn/handle/352002/3604
专题	研究生_研究生_学位论文环境地球化学国家重点实验室
推荐引用方式 GB/T 7714	肖化云. 季节性缺氧湖泊氮的生物地球化学循环[D]. 中国科学院地球化学研究所. 中国科学院地球化学研究所,2002.

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