Lakes and their watersheds provide important habitat for human beings. Over the past two decades, deterioration of lake ecosystems and lake eutrophication associated with rapid socio-economic development in China has acquired much attention by the public and the government. With the growing problems of lake ecosystem, the importance of integrated management of ecosystems, environmental resources, and social systems at the watershed scale have been highlighted. Studies have shown that lakes and their watersheds should be viewed as a holistic system from a management perspective. The idea of watershed ecosystem management has been the focus of related studies since 1990s and considered to be an effective way to deal with ecological and environmental problems at the watershed scale. 

(1) A systematic survey of watershed ecosystem management studies

The necessity of systematic studies on lake-watershed ecosystem management (LWEM) was present based on the analysis of ecological and environmental problems at the watershed scale in China. Four challenges were identified for the LWEM studies in China, which can be viewed as the basis of LWEM on theories, research methodologies and case study. The research developments were surveyed on lake-watershed ecosystem dynamics and modeling, integrated ecosystem assessment, and watershed ecosystem management. The research advances were proposed.

(2) Proposition of the theoretical system for LWEM

Based on surveys about watershed ecosystem management, management definitions and principles are presented in this paper. Further, the differences between traditional water environmental protection, integrated watershed management and watershed ecosystem management are analyzed. Ecosystem ecology, watershed ecology, ecosystem health and the watershed approach are considered to be the fundamental theories for LWEM. Ecosystem approach and watershed analysis are taken as the methodological basis for LWEM. The theoretical system for LWEM was proposed, including the ecosystem management goals, management principles, management framework, management foundations, key problems in the management process, and the benefits and obstructions in the LWEM. Three core issues are identified for LWEM; uncertainties and obstacles in the process, the effects of land use/cover change to the aquatic ecosystems, and the linkage between social and ecological systems.

(3) Development of the research methodological system for LWEM
In light of previous studies on ecosystem management, four steps were developed for the research methodological system of LWEM, including management basis, management goals, management models, and management implementation. The Integrated Model for Lake-Watershed Ecosystem Management (IMLWEM) was developed. The IMLWEM was consisted with lake-watershed ecosystem dynamics modeling (EDMLW), integrated ecosystem assessment (IEA) model, ecological-economic optimization modeling (IMLOPOEEW), and optimal modeling for management alternatives based on inexact chance-constrained linear programming (ICCLP).

A practical detailed process for LWEM is given in this thesis. It consists of six steps. The first is scoping of object, area and stakeholders. Second, fundamental data collection and analysis and primary judgment of ecological issues are performed. The third step is goal setting, including operational goals. Fourth, systems in the lake-watershed ecosystem are synthesized, including ecosystem dynamics modeling of lake and the watershed (EDMLW) and scenario analysis and assessment. Next, integrated assessment of the lake-watershed ecosystem, in which ecosystem health and integrity are taken as indictors for assessing ecosystem structure, is performed; ecosystem service is valued to reflect ecosystem function and ecological capacity is measured as a token of supporting capacity of the ecosystems. Adaptive management is the last step in the process, including the formulation of collaborative action and rules, optimal selection of actions and preferential sites, implementation and enforcement, and monitoring, evaluation and feedback.

(4) Case study: Ecosystem management for Lake Qionghai Watershed, Southwestern China
The IMLWEM has been successfully applied to a practical case, Lake Qionghai Watershed where ecological restoration and economic development are of a high priority. The case studies include overview of the study area, the analysis of watershed characters, diagnosis of ecological problems in Lake Qionghai Watershed, management goals, the IMLWEM for Lake Qionghai Watershed, and the adaptive management mechanism.
The preliminary ecosystem assessment demonstrated that Lake Qionghai was in the process toward eutrophication and phosphorus (P) was the limiting factors. The land coverage in the watershed was relatively low. There was a high risk of soil losses and potential debris flows. Fifteen goals were identified for the ecosystem management in Lake Qionghai watershed based on the results of above diagnosis. Four scenarios were developed and assessed for Lake Qionghai watershed. The model results of EDMLW based on the preferable scenario showed that the total phosphorus (TP) loading to the lake will be 89.70 t·a–1. The corresponding TP and Chla concentrations will increase to 0.121mg·l–1 and 75.865 mg·m-3, respectively. The management goals can not be ensured. According to the ecological fragility assessment, Lake Qionghai watershed was in middle-strong fragility degree. The integrated ecosystem health index has decreased from 0.984 in 1988 to 0.580 in 2001 and 0.567 in 2004. Lake Qionghai is in the process of ecological deterioration. The RBFNNs model based IEA assessment of Lake Qionghai watershed in 1988, 1990, 1995, 2001 and 2005 showed the decreasing trend of the ecological conditions. The IEA assessment results for the five years are 2.633, 2.6309, 2.6114, 2.5949 and 2.6133.
The IMLOPOEEW model was developed for Lake Qionghai watershed based on EDMLW. The optimal results on the plant structure, water resource allocation, pollutants discharging, forest expanding and soil erosion were considered in the study. Watershed approach was viewed as the framework for the pollution control and ecological restoration measures, which were brought out based on the results of IMLOPOEEW and EDMLW model. The main procedures of the watershed approach include: (1) dividing watershed into sub-watersheds and forecasting pollutant loading from each sub-watershed to the lake; (2) designing pollution control and ecological restoration strategies consisting of source prevention, process elimination, endpoint control and sink improvement; (3) calculating the reduction rate of pollutant loading; (4) recommending the desired strategy. The main pollution control and ecological restoration measures were brought out after the stakeholders and experts’ discussion, including point and non-point sources control, preventive engineering of soil loss and debris flows, dredging of lake sediments, restoration of natural wetlands in riparian areas, ecological restoration of riparian areas, water level control, ecosystem approach for fishery in Lake Qionghai, forest maintenance and rural ecological engineering.
The ICCLP model was applied to Lake Qionghai watershed for better water quality improvement at a possibly minimum total cost after the decision of the preferable alternative strategies. A three-period optimization was conducted based on the alternative strategies and the model parameters from field investigation. Five probability levels were considered in the model, as qi =0.01, 0.25, 0.50, 0.90 and 0.99. The model results showed that the total optimized costs was between $[55710.86, 80691.81] ×104 to $[72151.39, 101338.6] ×104 under different probability levels. The model results indicated that soil erosion treatment, NPS controlling measures and rural wastes treatment have the much higher cost than other strategies. The changes in qi resulted in different temporal and spatial distributions of management strategies in the watershed. Then an adaptive ecosystem management process was developed for the study area.