Research On Adaptive Mechanism To Drought And Integrated Regulation In Baiyangdian Wetland

Wetlands all over the world are facing an abrupt degraded trend due to the diversion of ecological water and ecological land and the extensive occurring of droughts with high frequency, large scale and long duration. Nowadays, on the basis of systematically identifying the degradation mechanism of wetlands and particularly the impact mechanism of extreme events, it is a hot spot and cutting-edge issue in resources and environmental field to come up with comprehensive measures, especially measures in the condition combined of "the most disadvantages". Based on objectively assessing the characteristics of water scarcity of wetlands in the context of drought, some measures such as establishing rational allocation and regulation of water resources and ensuring emergency responses oriented to wetlands ecological security would be key problems. It should be noted that, drought in wetlands were not only influenced by the precipitation in the wetland area, but also wholly constrained by water cycle in watershed. As a new issue, drought in wetlands appeared when responses to climate change and wetlands protection and restoration has entered into a new stage. Unfortunately, there is neither systematic research aimed at drought in wetlands, nor indexes or evaluation methodology of drought in wetlands has been established, home and abroad. Correlational studies mainly focused on aspects as wetlands hydrological characteristics, ecological water requirement, ecological impact of extreme hydrological events, and emergency water supply to wetlands, etc. Usually, researchers studied drought in wetlands from various aspects such as how drought affected plants, aquatic animals, microorganisms, and they mainly acquired these information through experiments, remote sensing and field monitoring and investigation. Or they studied water quality, element behavior in wetlands while drought occurs. There were a few researches about adaptive mechanism of wetland to drought in a systematical view.Based on the theory of hydrology and ecology, and combined with research achievements on wetland ecohydrology, this paper made a comprehensive analysis on ecohydrological characteristics of wetland in the context of drought. Accordingly, we proposed the connotation and assessment method of drought depending on the evolution of drought in Baiyangidan Wetland, which formed an easy description of wetland drought as well as its characteristics. The laboratory experiment, prototype observation, mathematical statistics and geographic information technology, etc. were used on systematic identification of the influence and adaptive mechanism about typical plants in wetland at different drought scenes, then gave assessments on the recovery capability of the plants at different drought scenes as well. Furthermore, proposed the integrated regulation measures which based on the functional orientation of Baiyangdian Wetland, so as to provide a theoretical and application support to the rate of water make-up at different drought scenes and brought ecological water use of wetland into basin water resources allocation.The conclusions are as follows:(1) Due to climate change and human activities, the frequency of drought occurs in wetlands increase. It altered hydrological characteristics first, then influenced vegetation and ecosystem of wetland, lead to the reducing of water level, water area, biodiversity and biomass. At last, it changed landscape of wetland.(2) Drought resulted in the reducing of growth rate, net photosynthetic rate, stomatal conductance, transpiration rate and biomass of reed and typha. As to the water use efficiency, it became highest at one drought scene. When the water content exceeded or below this standard, water use efficiency of reed and typha would decrease. The adaptability to drought of reed was higher than that of typha. And the adaptive threshold of reed and typha were at serious drought scene (soil water content20-30%) and moderate drought scene (soil water content30-40%), respectively. Same as the adaptability, the recovery capability of reed was higher than typha. And they both showed the highest recovery capability at moderate drought scene.(3) Based on the functional orientation of Baiyangdian Wetland and the studies in previous chapters, we put forward the protected object and threshold of the wetland, they were:object in mild drought-a water level standard at7.61m; object in moderate drought-a water level standard at7.08m; object in serious drought-a water level standard at6.91m; object in mega drought-a water level standard at6.88m. According to the protected objects, we could calculate the rate of water make-up at different drought scenes and different period, and propose the integrated regulation measures in Baiyangdian Wetland.