11:05 AM - 11:25 AM
[ACG48-07] Spatial Distribution of Stream Chemistry and Regulating Factors throughout Japan ~Challenge of Citizen Science for Extensive Survey~
★Invited Papers
Keywords:stream, chemistry, Citizen Science, nitrogen
Since streamwater chemistry determines the fundamental properties of surface water and affects the river and downstream ecosystems, it is important to elucidate its spatial distribution and regulating mechanisms. For example, nitrogen (N) is important for forest growth, but when atmospheric N deposition exceeds the forest's demand, it causes soil acidification, biodiversity loss, and nitrate (NO3-) leaching. Since N is an essential element for phytoplankton as well, NO3- supply affects the river biota. However, the effects of N loading on forests may vary depending on forest conditions and environmental factors such as climate and topography. Therefore, the purpose of this study was to clarify the spatial distribution of streamwater chemistry and regulating factors under various environments throughout Japan.
Mountain stream surveys in a wide area require enormous time and effort. "Mountain Health Checkup" project, a collaboration between Field Science Education and Research Center of Kyoto University (FSERC, Kyoto-U) and Montbell, Inc., conducted a nationwide mountain stream survey from June to November 2022 in the form of Citizen Science involving the general public. Water samples were collected at the points mapped on the project's website with no rice paddies, fields, orchards, buildings, or other human influences upstream. The samples were filtered through a 0.45 um disc filter to remove particulate matter and microorganisms, then stored in bottles, immediately mailed to FSERC, Kyoto-U, and stored in a refrigerator (4C). The concentrations of major inorganic ions in the samples were measured using an ion chromatograph.
The data were mapped using a geographic information system (ArcMap 10.8.2, ESRI). In addition, environmental factor data such as atmospheric N deposition, climate, topography, vegetation, soil, and geology were extracted for each watershed. Finally, we identified the regulating factors using Random Forest regression analysis, one of machine learning.
Finally, 1428 water samples were collected from all over Japan. NO3- concentrations tended to be at higher levels in the suburbs of urban areas such as Tokyo, Osaka, and Fukuoka but lower on the Japan-sea side, where the northwestern monsoon brings air pollutants from the Asian continent and causes high N deposition. This is probably because, on the Japan-sea side with heavy rain and snow in winter, N was not incorporated into the ecosystem but was flushed out at once during rainfall and snow melt, resulting in the low stream NO3- concentration at baseflow condition.
Stream NO3- concentrations tended to be at higher levels in the Kunisaki Peninsula in northeastern Kyushu and Kagawa Prefecture too with no large cities nearby. The low precipitation along the Seto Inland Sea, including Kagawa, and therefore low N flush during rainfall have probably contributed to the high stream NO3- concentration at baseflow conditions.
Stream Calcium (Ca2+) and magnesium (Mg2+) concentrations tended to be at higher levels in the area above the Fossa Magna, and Ca2+ concentrations were higher in the area above the Median Tectonic Line too. Since the slope and terrain-ruggedness-index were the regulating factors for Ca2+ and Mg2+ concentrations, the weathering may have been stronger in the steep and uneven Fossa Magna area. On the other hand, potassium (K+) concentrations were lower in steeper slopes and uneven surface areas and more significantly regulated by topographic-wetness-index, suggesting that the K+ leaching due to biological effects and ion exchange may have been stronger than the weathering one. Other factors' contributions such as climate and rocks were also revealed for each element.
Citizen Science, in which citizens participate in the survey, researchers analyze the samples, and return the outcome to the public, broadened the scope of research, and furthermore, is expected to have provided an opportunity for citizens to consider environmental issues.
Mountain stream surveys in a wide area require enormous time and effort. "Mountain Health Checkup" project, a collaboration between Field Science Education and Research Center of Kyoto University (FSERC, Kyoto-U) and Montbell, Inc., conducted a nationwide mountain stream survey from June to November 2022 in the form of Citizen Science involving the general public. Water samples were collected at the points mapped on the project's website with no rice paddies, fields, orchards, buildings, or other human influences upstream. The samples were filtered through a 0.45 um disc filter to remove particulate matter and microorganisms, then stored in bottles, immediately mailed to FSERC, Kyoto-U, and stored in a refrigerator (4C). The concentrations of major inorganic ions in the samples were measured using an ion chromatograph.
The data were mapped using a geographic information system (ArcMap 10.8.2, ESRI). In addition, environmental factor data such as atmospheric N deposition, climate, topography, vegetation, soil, and geology were extracted for each watershed. Finally, we identified the regulating factors using Random Forest regression analysis, one of machine learning.
Finally, 1428 water samples were collected from all over Japan. NO3- concentrations tended to be at higher levels in the suburbs of urban areas such as Tokyo, Osaka, and Fukuoka but lower on the Japan-sea side, where the northwestern monsoon brings air pollutants from the Asian continent and causes high N deposition. This is probably because, on the Japan-sea side with heavy rain and snow in winter, N was not incorporated into the ecosystem but was flushed out at once during rainfall and snow melt, resulting in the low stream NO3- concentration at baseflow condition.
Stream NO3- concentrations tended to be at higher levels in the Kunisaki Peninsula in northeastern Kyushu and Kagawa Prefecture too with no large cities nearby. The low precipitation along the Seto Inland Sea, including Kagawa, and therefore low N flush during rainfall have probably contributed to the high stream NO3- concentration at baseflow conditions.
Stream Calcium (Ca2+) and magnesium (Mg2+) concentrations tended to be at higher levels in the area above the Fossa Magna, and Ca2+ concentrations were higher in the area above the Median Tectonic Line too. Since the slope and terrain-ruggedness-index were the regulating factors for Ca2+ and Mg2+ concentrations, the weathering may have been stronger in the steep and uneven Fossa Magna area. On the other hand, potassium (K+) concentrations were lower in steeper slopes and uneven surface areas and more significantly regulated by topographic-wetness-index, suggesting that the K+ leaching due to biological effects and ion exchange may have been stronger than the weathering one. Other factors' contributions such as climate and rocks were also revealed for each element.
Citizen Science, in which citizens participate in the survey, researchers analyze the samples, and return the outcome to the public, broadened the scope of research, and furthermore, is expected to have provided an opportunity for citizens to consider environmental issues.