Responses of freshwater ecosystems to global change: research progress and outlook

Global change has already posed a serious threat to different freshwater ecosystems by raising water temperatures, changing precipitation patterns and water flow conditions, enhancing species invasion, and increasing extreme events. In order to identify the major works carried out and highlights of the outcomes of research in freshwater ecology in the context of global change, we conducted literature search and analysis of papers published during 1900-2018 via Web of Science. In this review, the major researches in freshwater ecology in the context of global change are categorized into: (1) the effects of various global change factors on individuals, populations, communities and ecosystems; (2) changes in biogeochemical cycles of ecosystems in the process of global change; and (3) adaptation strategies of freshwater ecosystems to global changes. Over the past 10-15 years, research in freshwater ecosystems and global change progressed rapidly and showed breakthroughs in the following aspects: (1) elucidated the response processes and mechanisms of the structure and function of freshwater ecosystems to global climate change, in particular rising water temperatures; (2) revealed that freshwater ecosystems (wetlands, lakes, rivers, etc.) are important components of the global carbon cycle, such that under the influence of global change factors organic carbon burial decreased and mineralization rate increased. In future research, it is necessary to strengthen the systematic observations and integration of the total elements of freshwater ecosystems, to conduct research on carbon transport and transformation processes mediated by the river-connected multi-systems, and to strengthen basic theoretical research for uncovering the adaptation mechanisms of freshwater ecosystems to global change.