| Estuarine wetland ecosystem is especially vulnerable to global environmental and climate crisises in fast urbanization. However, even no enough attention has been paid to ecological and environmental security and protection of estuary wetland ecosystem. As a "natural wetland in city centre", the development of social economy, the growth of population and land use change bring about heavy ecological and environmental burdens to Minjiang estuarine wetland in urbanization, which cause the degradation of wetland functions and decreases of ecosystem service value. Therefore, it is urgent to scientifically study and quantitatively assess dynamic evolution of Minjiang estuarine wetland ecosystem and ecological and environmental security to find the causes and cures to its eco-challenges. In this paper, the theories and methods of urban ecology and urban ecosystem, along with remote sensing (RS), geographic information system (GIS) technology and model analysis, were applied to research the land use/cover changes and driving force, the surface temperature changes, ecological service function value and hydrodynamic-water quality changes of wetlands in Minjiang estuary, located in Fuzhou city, the capital city of Fujian province. The evolution of the wetlands in Minjiang estuary has been discussed since 1989s. Meanwhile, the conjugated control strategies of Minjiang estuary wetlands were put forward based on ecological management and ecological conservation. The results help come to a full understanding of the impact of human activities on the wetland ecosystem, grasp the space-time succession of estuarine wetland ecosystem, prevent the degradation of wetland area and system function effectively, strengthen the construction of regional ecological environment security step by step, and provide theoretical basis and scientific reference for ecological protection and management of Minjiang estuary wetlands.The main contents and achievements of this study are as followings:1. Systematical study on the land use/cover changes and its driving force of Minjiang estuary wetland ecosystemBased on time series Landsat TM/ETM+imageries and historical data, relationships between land use dynamics and natural wetland degradation from 1989 to 2009 were analyzed by using an integrated approach of RS and GIS techniques. The results showed that built-up land increased by 1.5 times, from 151.16 km2 in 1989 to 383.76 km2 in 2009. Approximately 64.25% of the newly emerging built-up land was converted from cropland (29.47%), forest and shrub (25.78%), water (3.73%), wetland (4.61%), and bare land (0.66%) during 1989 and 2009. With a remarkable decrease in cropland, the proportion of non-agricultural population increased by 23.6%. Moreover, the expansion of built-up land along the Minjiang River resulted in the eastward, southward and westward expansion. As a result, the observed environmental degradation such as loss of cropland and wetland due to heavy pressure of rapid urbanization has greatly impaired the Minjiang estuary wetland ecosystem. Additionally, the growth pattern of built-up land in the study area is highly correlated with socio-economic factors, including the gross domestic product (GDP), GDP per capita, and structure of industry, which indicated that the rapid socio-economic development of urbanization has greatly driven the land use/cover changes.2. Comprehensive analysis of the ground temperature changes in Minjiang estuary wetland ecosystemThe surface temperature inversion and standardization were performed by using thermal infrared remote sensing in Minjiang estuary wetland ecosystem. It was found that from 1994 to 2009, the high temperature areas above 29 ℃ was increasing and gathering, which mainly occured in the new extension area. It appeared densely on both sides along Minjiang River. The distribution of temperature had a close relationship with land use/cover type. And the developing trend of high temperature zones was consistent with the expansion of Fuzhou city.The random sampling statistical method was choosed to analyze temperature changes in Minjiang estuarine wetland. It was found that the internal temperature changes in wetlands were gradually increasing, and from day to night, the temperature contrasted more obviously. The larger the area of wetland takes up, the smaller surface temperature of wetland changes, and vice versa.The total area of wetlands is significantly correlated with the low temperature area of wetlands. Large wetlands played a key role in alleviating temperature rise. There were obvious linear positive correlation between the average surface temperature in wetlands and built-up land area in study area. And the expansion of built-up land was one of the most important factors which led to the rise of wetland surface temperature in urbanization.3. Scientific evaluation of the ecosystem services value and its changes in Minjiang estuarine wetland ecosystemA set of ecological evaluation was performed to quantify the allocation of ecosystem services value (ESV) associated with land use pattern and examined impacts of land use changes and socio-economic factors on spatiotemporally varying of ESV in Minjiang estuarine wetland ecosystem. The results showed that total ESV of the study area decreased from 4.332 x 109 RMB Yuan in 1989 to 3.697 x 109 RMB Yuan to 2009, mainly due to the remarkable decreases in cropland (decreased by 55.3%) and wetland (decreased by 74.2%). Forest, water and wetland played major roles in providing ecosystem services, accounting for over 90% of the total ESV. Based on time series Landsat TM/ETM+ imagery, geographic information system and historical data, analysis of the spatiotemporally varying of ESV from 1989 to 2009 was performed. It indicated that rapid expansion of urban areas along the Minjiang River resulted in significant changes in land use types, leading to a dramatic decline in ecosystem services. Meanwhile, because of land scarcity and unique ecosystem functions, the emergency of wetland and cropland protection in built-up area has become urgent task of local authorities to the local government. Furthermore, there was still a significant negative correlation between ESV of cropland and wetland and the GDP. The results suggest that future planning of land use pattern should control encroachment of urban areas into cropland and wetland in addition to scientific and rational policies towards minimizing the adverse effects of urbanization.4. Coupled simulation of the hydrodynamic and water quality changes in Minjiang estuarine wetland ecosystemIn order to support the task of water environmental protection in Minjiang estuarine wetland ecosystem, an integrated modeling system was developed based on a linked environmental fluid dynamics code (EFDC) and water quality analysis simulation program (WASP). The model system focus on the water lever of tidal reach as well as the balance of dissolved oxygen, these two indexes can reflect the character of hydrodynamic and water quality in the river section. Model calibration and model validation were conducted as well. Methods of graph and relative errors were used during the model validation to assess the results of the model validation. The result of validation showed that the developed model could be used to assist the simulation of the hydrodynamic and water quality changes in Minjiang estuarine wetland ecosystem.Three scenarios were designed in this section. Scenario analyses were conducted using the developed model system to evaluate the water quality variations influenced by sources of pollution. In Basic Scenario 1, it shows the tide downstream has a distinct influence on the hydrodynamics. The water quality in Ao Fengzhou exceed standard sometimes, and the Guangming Harbour is the most important pollution source. In Scenario 2, after taking emission-reduction measures by 50% in the main source of pollution-the Guangming Harbour, Permanganate Index (CODMn) decreases significantly, becoming no longer the major pollution index of drinking water source protection zones. In Scenario 3, if asudden pollution incident occurs in upstream of the research region, drinking water source nearby would be impacted in a period up to 34 hours with twice exceeded the water quality standard. The result shows that there is a poor diffusion condition during the process of pollutants migration in the tidal reach.5. Innovative proposing the conjugated ecological regulatory strategy system of Minjiang estuarine wetland ecosystemThe establishment of conjugated ecological regulatory strategy system was proposed to deal with the practical problems of conservation and management in Minjiang estuarine wetland ecosystem, which included total amount control and concentration control, ecological red line, ecological capacity and ecosystem services value, early warning and ecological conservation, government-leading and public engagement, etc. Conjugated ecological regulatory strategy is a critical path for the protection of Minjiang estuarine wetland ecosystem, which would provide a new train of thought and experience in future.The innovation of this paper focused on the dynamic succession Characteristics and driving mechanism of Minjiang estuarine wetland ecosystem, which differs from previous studies mainly focusing on internal structure, functional efficiency and landscape pattern changes in urbanization. Meanwhile, based on the quantitative analysis technology such as RS, GIS and coupled model simulation, the quantitative evaluation was performed for wetland ecosystem characteristics in urbanization. And the hydrodynamic-water quality coupled model, which is suitable for estuarine city area, was successfully built for the further simulation. Finally, conjugated ecological regulatory strategy system was established for estuarine wetland ecosystem protection... |
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