If the present rates of biodiversity loss continue, projections suggest that within 240 years Earth may face its sixth mass extinction. Because many fishes and amphibians, as well as crustaceans, mollusks, and other aquatic macroinvertebrates, are ectotherms, temperature is an important component of water quality that directly affects their growth rate and distribution Freshwater temperature is a physical water quality parameter of critical importance, and understanding the trends in freshwater temperature is important for identifying potential threats to the biodiversity of aquatic ecosystems.
We analyzed freshwater temperature data (based on “The Water Quality Survey of Public Water Areas” of the Ministry of the Environment) from 1982 to 2016 throughout Japan to better understand how waters are warming in Japan.
We used linear regression to determine the temperature change rate and Mann-Kendall tests to identify significant temporal trends in the annual maximum and mean temperatures. Among 11,240 monitoring sites screened, 159 with fewer missing values were selected for analysis.
On the basis of this analysis, we identified and ranked the sites showing significant temporal increasing or decreasing trends for future management. At nearly half (42%) of the analyzed sites, the annual mean freshwater temperature was increasing; thus, in the future, adverse impacts from warm temperatures may increase in those aquatic ecosystems. The temperature change rate of fresh water was higher than that of air, indicating that the observed increases in freshwater temperature were not due to atmospheric warming only. Among individual sites, the annual maximum freshwater temperature change rate ranged from -1.27 to 1.91 °C/decade, and the annual mean rate ranged from -1.13 to 1.28 °C/decade. Few other studies have reported decreasing temperatures for fresh water.
We expect our results will improve understanding of how freshwater temperatures are changing at a large scale, enhance understanding of human impacts on the aquatic environment, support effective management of ecosystems experiencing temperature changes, and help to minimize the loss of biodiversity over the next half century.
(Keywords: Air temperature, Freshwater temperature, Global warming, Japan, Spatiotemporal analysis, GIS.)
Dr. Satoshi Kameyama is a Senior Chief Researcher at Biodiversity Division, National Institute for Environmental Studies; JAPAN. He is a Specially Appointed Professor at The Kyoto University (Center for the Promotion of Interdisciplinary Education and Research) and a lecturer at The University of Tokyo (The Graduate School of Agriculture and Life Science) in 2018. He is also working as visiting lecturer at VNU (Vietnam Japan University) in Vietnam National University. He received Ph.D. degrees from The Graduate School of Agriculture from The Hokkaido University in 1999. He is an editorial board member of The Remote Sensing Society of Japan from 2011. He is also a member of American Geophysical Union, American Fisheries Society, The Ecological Society of Japan, The Japanese Alpine Club etc. The main research topics of recent years are “Evaluation of ecosystem functions and services and their sustainable use” and “Watershed ecosystem restoration based on the recovery of migration pass and diadromous fish habitat using Environmental DNA” etc. The final goal (the dream) of his research is to realize sustainable regional community with high resilience to climate change harmonizing with nature.