Socio-ecological dimensions of sustainable tropical lake management: lessons learned from interdisciplinary research in Lake Maninjau, Indonesia

Abstract

Growing anthropogenic influence on the environment has accelerated the environmental crisis. An integrated approach to ecosystem-based management (EBM) has been hailed to overcome inadequacies of a single disciplinary perspective to address the wicked problems unfolding in the crisis. While the importance and success of EBM has been demonstrated in some marine ecosystems, its application to inland water ecosystems is still rare.

One of the fundamental reasons for the rare successful application of EBM is the inadequacy of underpinning research on integrated human and ecological systems. While integration between social and ecological research is imperative, on an operational level it is hampered by epistemological and methodological differences between disciplines. Although there are an increasing number of frameworks to conduct interdisciplinary research, very few explicitly address how to integrate these differences across disciplines. This study fills this knowledge gap by introducing a research framework which embraces the epistemological pluralism concept to help the integration.

In this thesis, I elaborate on the lessons learned from my PhD research, which incorporates environmental-social science, ecology, and ecological economics to analyse cage aquaculture management in my case study: Lake Maninjau. I use my analysis of the lake to support the development of inland water EBM in Indonesia. The case study is representative of many lakes in Indonesia and other tropical Global South lakes where a single disciplinary approach has been used to guide the management, resulting in the failure to achieve the management goal. Lake Maninjau has a long history of environmental degradation due to cage aquaculture proliferation and social conflict. The local government has voiced their inability to solve the problems. Chapter 1 of the thesis elucidates the introduction of the problem, the research questions, objectives, methodological approaches, outline, novelties, and theoretical and practical contributions of the thesis. It specifies the applied and theoretical contributions of the thesis and its chapters.

In Chapter 2, I engaged the Institutional Analysis and Development (IAD) framework to provide an institutional perspective on the challenges of developing environmentally sustainable cage culture farming in the lake. I found that the lack of trust between the systems' participants and contrasting formal and customary regulations are the main challenges for the development of working rules-in-use at the operational level. I provide suggestions for local stakeholders and local and national governments seeking legitimacy to build strong rules-in-use to govern the cage aquaculture. Applying the framework in this case study is particularly interesting as the cage aquaculture represents private properties encompassing a common pool resource.

In Chapter 3, I developed a Maximum Entropy species distribution model to obtain a new and relatively more affordable monitoring effort for the impact of cage farming on the native fish species. The models were validated by cross-validation with independent data. The effects of cage aquaculture on providing habitat services to the native fish were then tested using Maximum Likelihood Mixed Effects Models on the relative abundance data. The results show that cage farms provide habitat services that are at least similar to the services offered by the natural habitat. Thus, the chapter provides evidence of a positive synergy between provisioning services related to cage aquaculture and native species habitat.

In Chapter 4, I conceptualised and quantified the lake's ecological response to the introduction of several management intervention scenarios by developing a Bayesian Belief Networks model. The scenarios are business as usual, reduced cages, epilimnetic aeration, reduction of internal phosphorus loading (IPL), and a combination of epilimnetic aeration and IPL control.

I validated the model using independent observational data. Both epilimnetic aeration and IPL control make a significant contribution to the reduction of mass fish kills and temporary forgone production of a native species, Gobiopterus sp. The combination of both technologies generated the best result. Further, the model also emphasised the importance to control IPL in deep tropical lakes, which has not been considered thus far by lake managers in tropical Global South Countries.

Chapter 5, which is a synthesis chapter, presents the economic appraisal of several management intervention scenarios. I used the obtained ecosystem services trade-offs between cage aquaculture, water quality, and native species habitat provisioning services revealed in previous chapters. I engaged both deterministic models and Monte Carlo Simulation to analyse the data. The results indicate that technological interventions are essential to compensate the lost economic value if a cage reduction policy is implemented. It is also shown that cage eradication as proposed by the environmentalists is not economically desirable. Further, the explicit inclusion of uncertainties of the human and biophysical system is vital for lake management's decision-making process.

Chapter 6, the last principal chapter, describes the alignment between previous chapters. I illustrate the perspectives obtained from each discipline, and highlight the perspectives arising from their integration. Further, the integrated perspectives are used to generate recommendations for improving Lake Maninjau's management. Additionally, the lessons learned for future interdisciplinary research to develop inland water EBM in Indonesia and other Global South Countries are summarised. A research framework assisting the integration between the social and natural scientists is developed and discussed in relation to previously proposed conceptual and research frameworks.

I expect that the individual chapters and research framework advanced in this thesis can contribute to theory and knowledge development in the inland water management area. It is also hoped that the lessons learned from this research can be practically helpful to assits decision-making process in the study area and other lake regions in Indonesia, as well as supporting researchers working on similar interdisciplinary research.