| It is important that the natural ecosystem is as the environment of human survive, and close combination of agriculture and natural ecosystem. The reason that the agricultural development depends on natural ecosystem, and the soil, rivers, gas and so on could be affected virtually by Agriculture. In this regard, Agriculture has double effects on natural ecosystem, not only destroys mildly, but protects mostly. Studies on agricultural multi-function, both assuring sustainable development and keeping the ecosystem balance.Rice production shows an important status in food production in our country, which not only offers essential rice, but also has multi-functionalities, for example, flood prevention, water source self-control, organic waste processing, atmospheric regulation, education and scientific research and so many kinds of public welfare functions. And several proposal and strategy was given in paddy field to endurance public welfare function. Emphatically research the human activity influence on the public welfare function of paddy field and its mechanism, which is not only significant theory breakthrough, but also the important basis of paddy field management.Basing on the analysis of assessment research of the value about the ecosystem services provided by paddy field ecosystem at home and abroad and present situation, estimated and surveyed on the function of hydrologic cycle and gas regulatory in paddy ecosystem of Four-lake basin. According to the data obtained from Four-lake basin paddy field survey, collection of materials, and indoor sample analyses, estimated the values of paddy ecosystem mitigation flood, recharge groundwater, microclimate regulation, fixed microclimate and releasing oxygen, greenhouse gas, application ecology, ecological Economics and so on. Through analyzing the study findings, the results were as followed:(1) Mitigation flood:Investigation on the water head between lower and higher of water-gate at three discharge zone in Four-lakes Watershed, the result as the upper discharge zone> the middle> the down. Wetlands in discharge zone could absorb into flood gradually, to weaken the flood volume and protect the Lower Reaches roughly; the area of paddy field was forty thousand hectare approximate, and that was to be equivalent to six hundred million cubic metre of the reservoir. The area of paddy field had a change during ten years gradually, the medium rice area is as a primary key now.The potential monetary value of flood mitigation function is estimated by using SCM (Substitute cost method). That is a same scenario to construct a dam or reservoir in place of a paddy field in terms of flood mitigation function from financial aspect. In other words, the water-storing capacity of paddy field is equivalent to that of a multipurpose dam. Consequently, we substitute the functional value of paddy fields using the annual cost of construction and maintenance of a flood control dam or reservoir.Thus the potential monetary value of flood mitigation function in four-lake Watershed was430million yuan of2011, and the medium rice of that was occupied57%.(2) Groundwater recharge:Investigation on the soil infiltration rate among the periodically waterlogged soil, Submerged type, Gleyed type and bog type, and the difference was significant (P>0.05) among four infiltration rate. And analysis of the soil mechanical composition on the same Profile, Submerged type> periodically waterlogged soil> Gleyed type> bog type based on the contents of sand particle.The area of middle rice was been analyzed on the six available HJ-CCD images in2011, and calculated the magnitude of groundwater recharge was222million cubic metre. Groundwater recharge of submerged type was up to93million cubic metre. Thus the potential monetary value of groundwater recharge function by SCM in four-lake Watershed was150million yuan of2011.(3) Cooling summer temperature:Investigation the temperature and humidity on the different underlying surface such as paddy field, upland and cement at7to8of2011, the result was showed paddy field<upland<cement at temperature and paddy field> upland> cement at humidity. Comparing to cement, paddy field could decrease temperature at0.3℃to1.4℃and increase humidity at1.1%to11.2%; upland could decrease temperature at0.2℃to1.1℃and increase humidity at0.4%to6.5%.The potential monetary value of cooling summer temperature function is estimated by using SCM. The early rice of that was16million yuan, the middle rice was52million yuan, the late rice was18million yuan.(4) Carbon Fixation and Oxygen Release:Daily assimilation measuring based on LI-6400XT was to estimate the annual carbon fixation and oxygen release of rice.Daily assimilation of early rice was86.2mmol, middle rice was99.4mmol, late rice was78.5mmol. Annual carbon fixation of early rice was63thousand t, middle rice was560thousand t and late rice was80thousand t; Annual oxygen release of early rice was45thousand t, middle rice was410thousand t, late rice was59thousand t. The potential monetary value of Carbon Fixation function is estimated by using SCM. The value of oxygen release of rice paddy was19million yuan, Carbon fixation of rice was15million yuan. And the value of middle rice was higher among those.(5) Greenhouse gas:Investigation the daily emission of CO2、CH4and N2O on the different crop-system in Four-lakes Watershed were to estimate the annual emission of CO2、CH4and N2O.On the daily emission of CO2, early rice-watermelon was higher; On the daily emission of CH4, middle rice-winter fallow field was much higher; On the daily emission of N2O; watermelon-late rice was higher. On the annual emission, middle rice-wheat of CO2emission was higher, middle rice-winter fallow field of CH4emission was higher, late rice of N2O emission was higher. On the global warming potential, middle rice-winter fallow field was much higher.The potential monetary value of greenhouse gas emission function is estimated by using SCM. The total value of greenhouse gas emission was130million yuan.In view of present research situation of paddy field public welfare function, pointing out that the rice paddy public welfare function value, assessment research should with emphasis emphatically in the theory exploration and the method perfect aspect in future, considered fully in the influencing factors of the public welfare function value, the improvement assessment way, the method and the technology, cause the appraisal result to have measurability and usability, provide theory basis and technical support for reasonable development and using the agricultural resource, manages the paddy field ecosystem, realizes the agriculture sustainable development. |
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