I have given a possible alternative writing of your text.  This might help make it more understandable.

A study of regional development

In the south of Leipzig, a huge landscape transformation took place: former surface mines have turned into lakes. Many resources have been devoted to this process whose results are supposed to exist for thousands of years.  (I am not sure what you mean by this sentence.  Perhaps you mean “Many factors led to this process.  The result of this process will likely exist for thousand of years.”) Via six semi-structured expert interviews, this study aims to observe how local stakeholders (I am not sure what you mean by “stakeholders”.  Maybe you mean “residents”) assess the landscape change. Challenges and possible solutions are investigated and the findings are discussed on the basis of the sustainability concept. Cooperation between policy makers is the most significant characteristic, which helps the regional individuals to implement their ideas. However, low budgets limit the realization of many projects. Also, regional progress may decrease as constructive debates among policy makers and the support of the population declines. Although people strive to balance current ecological, social and economic aspects, considerations about long-term trends and consequences were rarely expressed in the interviews. Research and better assistance at a higher political level might help municipalities to anticipate and handle potential developments in the future.

Study on regional development