Presentation Information
[O12-P32]Investigating the Multifaceted Functions of Forest Watersheds in Northern Kyoto: Toward Detailed Soil Mapping
*Takumu Kosuge1, *Teruma Ueda1, *Akari Kajimura1, *Reon Shigemitsu1, Miku Saeki1, Sota Nakamura1, Yuna Hirano1, Kairi Tadano1, Meilin Ding1, Natsumu Kataoka1, Sayaka Seno1, Yuma Urabe1, Yusaku Okuda1, Hiroi Kanda1, Yusuke Iwasaki1, Rurina Yuasa1, Kanna Kawauchi1, Amika Kijima1, Seiji Ukai1, Anna Shimizu1, Sasane Nishikiori1, Hiroto Hayashi1, Yuri Kisaka1, Kiyora Nagata1, Fumitaka Nakamura1 (1. Kyoto Prefectural Sagano High School)
Keywords:
soil classification,terraced ice field ruins,rounded pebbles,a buried A layer,topographical factors
1. Introduction
Forests provide a wide array of ecosystem services, including water resource conservation and soil stabilization. Soil maps allow us to investigate differences in soil properties and their geographical distribution. This study aimed to examine the multifaceted functions of forest watersheds by conducting soil surveys at representative locations within those watersheds.
2. Method
Field investigations were conducted in July 2025 within a small watershed located in TANGO ECO-FUTURE PARK. This area lies within the Sea of Japan climatic region. The study site covers 8,918 m², with elevations ranging from 108 to 151 m a.s.l. The survey items included visual inspection, soil profile survey, and soil penetration strength measurements (Daitou Techno Green H-60).
3. Results and Discussion
The five factors influencing soil formation are parent material, climate, biotic factors, topography, and time. In this study, we focused on topographical factors and conducted soil surveys. Visual inspections confirmed the presence of flat surfaces and traces of terraced fields. Soil profile surveys were conducted at four locations: the upper part of the ridge, the middle of the ridge, and the upper and lower sections of the terraced field ruins within the small watershed.
The results of the soil profile survey at the upper part of the ridge indicated that the soil type was clay loam and that the soil was dry. According to the Comprehensive Soil Classification System of Japan, it was classified as Lithic Haplic Brown Forest soil.
The results of the soil profile survey at the middle of the ridge showed that the soil texture in the lower layers was light clay. Additionally, weathered round pebbles were observed in the C layer.
At the upper part of the terraced field site, a surface layer approximately 8 cm thick was identified. This is considered shallow for a topsoil layer. Oka et al. (2020) reported the possibility of Horton surface runoff occurring in nearby terraced fields. This suggests that the topsoil layer may have been lost during the period of terraced field use. Although the paddy field has been abandoned for a long time, it appeared to be temporarily flooded by rainfall even now. Based on the above results, the soil was classified as fine-textured Typic Paleudults soil.
In the lower part of the terraced field site, a distinct gley layer was identified. The soil texture below this layer was heavy clay. Based on these results, the soil was classified as fine-textured Typic Epiaquepts soil.
Regarding soil penetration strength, the soil softness (S value, cm/drop) was less than 0.7 at the ridge crest, making it difficult for many roots to penetrate. Conversely, at the terraced field site, the S value was greater than 4.0, indicating that the soil may have low bearing capacity for plants. In particular, a soft layer was confirmed at a depth of 40-50 cm. This layer was thought to be a buried A layer.
4. Conclusion
Although the watershed covers less than one hectare, a variety of soil types were observed. The discovery of a buried A layer in the terraced field ruins and weathered round pebbles in the C layer on the ridges suggests the need for further investigation of the underlying layers.
Forests provide a wide array of ecosystem services, including water resource conservation and soil stabilization. Soil maps allow us to investigate differences in soil properties and their geographical distribution. This study aimed to examine the multifaceted functions of forest watersheds by conducting soil surveys at representative locations within those watersheds.
2. Method
Field investigations were conducted in July 2025 within a small watershed located in TANGO ECO-FUTURE PARK. This area lies within the Sea of Japan climatic region. The study site covers 8,918 m², with elevations ranging from 108 to 151 m a.s.l. The survey items included visual inspection, soil profile survey, and soil penetration strength measurements (Daitou Techno Green H-60).
3. Results and Discussion
The five factors influencing soil formation are parent material, climate, biotic factors, topography, and time. In this study, we focused on topographical factors and conducted soil surveys. Visual inspections confirmed the presence of flat surfaces and traces of terraced fields. Soil profile surveys were conducted at four locations: the upper part of the ridge, the middle of the ridge, and the upper and lower sections of the terraced field ruins within the small watershed.
The results of the soil profile survey at the upper part of the ridge indicated that the soil type was clay loam and that the soil was dry. According to the Comprehensive Soil Classification System of Japan, it was classified as Lithic Haplic Brown Forest soil.
The results of the soil profile survey at the middle of the ridge showed that the soil texture in the lower layers was light clay. Additionally, weathered round pebbles were observed in the C layer.
At the upper part of the terraced field site, a surface layer approximately 8 cm thick was identified. This is considered shallow for a topsoil layer. Oka et al. (2020) reported the possibility of Horton surface runoff occurring in nearby terraced fields. This suggests that the topsoil layer may have been lost during the period of terraced field use. Although the paddy field has been abandoned for a long time, it appeared to be temporarily flooded by rainfall even now. Based on the above results, the soil was classified as fine-textured Typic Paleudults soil.
In the lower part of the terraced field site, a distinct gley layer was identified. The soil texture below this layer was heavy clay. Based on these results, the soil was classified as fine-textured Typic Epiaquepts soil.
Regarding soil penetration strength, the soil softness (S value, cm/drop) was less than 0.7 at the ridge crest, making it difficult for many roots to penetrate. Conversely, at the terraced field site, the S value was greater than 4.0, indicating that the soil may have low bearing capacity for plants. In particular, a soft layer was confirmed at a depth of 40-50 cm. This layer was thought to be a buried A layer.
4. Conclusion
Although the watershed covers less than one hectare, a variety of soil types were observed. The discovery of a buried A layer in the terraced field ruins and weathered round pebbles in the C layer on the ridges suggests the need for further investigation of the underlying layers.