Key Restoration Methods of a Polluted RiverEcosystem: A Systematic Review

Background: River is one of a freshwater ecosystem that plays an important role in people's living, aquatic and terrestrial living organisms, and agricultural production. Compared to other ecosystems, rivers support a disproportionately large number of plant and animal species. However, excessive human activities have busted the original ecological balance by polluting the river ecosystem. As a result, partial or total affected the structure and functions of the river ecosystem. This review aimed to investigate the major ecological restoration methods of the polluted river ecosystem. Methods: We have adopted the procedures from the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The required data were collected via a literature search of MEDLINE/PubMed, Google Scholar, Science Direct, EMBASE, HINARI, and Cochrane Library from the 9th of September, 2019 to the 5th of March, 2020 using combined terms. Articles were included in our review; only if it assessed empirically and comparison and contrast between two or more different restoration methods. This review; it is mainly included published research articles, national reports, and annual reports and excluded opinion essays. Results: Commonly used methods for restoration of polluted rivers around the globe could be categorized depending on the physical, chemical, and biological characteristics of the river. Restoration methods such as channel hydromorphic, aeration, watershed action, riparian, In-stream hydromorphic, and In-stream or wetland creation restoration account for 16%, 19%, 12%, 22%, 17% and 14% of river ecosystem restoration efficiency respectively. From the restoration methods: riparian, artificial aeration and In-stream or wetland creation are preferred for restoration of chemical characteristics. For the restoration of physical characteristics; watershed action and channel hydromorphic are preferred. While for the restoration of biological characteristics; in-stream hydromorphic is the preferred one. Conclusion: Contaminated Rivers can be restored by using different restoration methods. The selection of the preferred restoration methods depends on the physical, chemical, and biological characteristics of the river.