| The Yellow River estuary located in the warm temperate zone is the youngest coastal wetland ecosystem in China. With the population growth and repaid development of industrial and agricultural production, wetland ecosystem in the Yellow River estuary depredated seriously in recent years due to the intense reclamation activities. In this paper, the coastal wetland in Yellow River estuary were selected as study objects in order to understand the response of vegetation characteristics of ecological system and ecosystem carbon sequestration to reclamation activities. The field investigation, in-situ observations and laboratory analysis were performed to study the impact of reclamation activities on wetland vegetation types, the content of organic carbon, organic carbon density, and organic carbon storage and greenhouse gas emissions. The main results were drawn as follows:(1) Reclamation activities has a significant influence on the growth of vegetation in the Yellow River estuary, vegetation type simplified and various indicators of vegetation communities are relatively low in the serious interference area(Dongying port and wuhaozhuang). However, the integrity of the vegetation was kept in the Yellow River estuary reserve. Reclamation activities had two main functions in the regulation of vegetation types. On the one hand, reclamation activities changed the key environmental factors of vegetation growth. On the other hand, vegetation element stoichiometry was influenced, which varied greatly in volatile environment and kept stable in good environment.(2) The content of organic carbon, organic carbon density and organic carbon storage had significant temporal and spatial variations, which was the result of interaction of the organic matter source, tidal effects, vegetation type, the flow-sediment regulation scheme and environmental factors. The value of organic carbon content, organic carbon density and organic carbon storage was small in the serious interference area, which due to the change of ecological system type and soil physicochemical properties. Compared with the average value of soil stoichiometric ratio in the whole country, higher C: N ratio and lower N: P ratio was found in the Yellow River estuary, and soil nitrogen content in this region is relatively low maybe the main reason.(3) The greenhouse gases fluxes under the influence of human activities also had significant temporal and spatial variations. CH4, CO2 and N2 O fluxes from the west side of the seawall(WSS), oil field(OF), Spartina alterniflora coastal wetland(SCM) and aquaculture pond(ACP) ranged from-0.0967 to 0.4107 mg CH4 m-2 h-1、from-71.14 to 583.07 mg CO2 m-2 h-1, and from-0.0091 to 0.0360 mg N2 O m-2 h-1, respectively. The fluxes of CO2 and CH4 in summer were higher than in other seasons in the four study sites, while N2 O flux varied small in the whole year. Compared with different study sites found that CH4 and CO2 fluxes from S. alterniflora coastal wetland were higher than other study sites, indicating that S. alterniflora invasion accelerated soil carbon emissions. The range of monthly average CH4 fluxes from WSS, OF, SCM and ACP were-0.0258~0.0015 mg m-2 h-1,-0.0967~0.0157 mg m-2 h-1,-0.0171~0.4107 mg m-2 h-1 and-0.0057~0.0165 mg m-2 h-1, respectively. CO2 and N2 O monthly average fluxes in the four study sites ranged from 27.08~334.69 mg CO2 m-2 h-1、13.41~197.02 mg CO2 m-2 h-1、37.22~583.07 mg CO2 m-2 h-1,-67.40~7.28 mg CO2 m-2 h-1 and-0.0091~0.0360 mg N2 O m-2 h-1、0.0082~0.0125 mg N2 O m-2 h-1、0.0015~0.0159 mg N2 O m-2 h-1 and-0.0020~0.0079 mg N2 O m-2 h-1, respectively.(4) The greenhouse gases fluxes in Yellow River estuary under human activities was higher than other natural wetlands compared with the most domestic and foreign relative results, characterized by higher CO2 and CH4 emission by the invasion of S. alterniflora and the construction of seawall blocked sea water transporting to inland which leaded to low soil moisture accelerating CO2 emission. Aquaculture ponds were significantly influenced by human activities, therefore nutrient substance content and physicochemical property of these will be different from natural water bodies(lakes, reservoirs), which could lead to differences in GHG emissions. On the whole, aquaculture ponds in the Yellow River estuary acted as an emission of CH4 and consumption of CO2.(5) The annual average CO2 emission from WSS, OF, SCM and ACP were 438826.12 mg m-2, 351516.90 mg m-2, 760624.82 mg m-2 and-126368.65 mg m-2, and the value of CH4 and N2 O were-41.39 mg m-2,-35.53 mg m-2, 496.66 mg m-2, 36.83 mg m-2 and 46.00 mg m-2, 44.18 mg m-2, 30.79 mg m-2, 36.32 mg m-2, respectively. So WSS and OF were important source of CO2 and N2 O and sink of CH4, while SCM was the source of CO2, CH4 and N2 O. Differently, ACP acted as CO2 and N2 O source and CH4 sink.(6) The main types of reclamation activities in Yellow River estuary included aquaculture pond, residential land and saltern. The reclamation intensity index maximum reached the maximum value in wuhaozhuang, while the value in the Yellow River delta reserve was small, indicating that the existence of reserve could effectively protect the ecological environment. The results of fitting and analysis between reclamation intensity index and the index of vegetation and soil indicated that the influence of reclamation activities on soil index was more significant. |
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