Open AccessRole of stormflow in reducing N retention in a suburban forested watershed, western Japan
Author(s) -
Chiwa Masaaki,
Maruno Ryoko,
Ide Jun'ichiro,
Miyano Takeaki,
Higashi Naoko,
Otsuki Kyoichi
Publication year - 2010
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2009jg000944
Subject(s) - throughfall , watershed , hydrology (agriculture) , environmental science , nitrate , stemflow , mineralization (soil science) , nitrification , soil water , leaching (pedology) , precipitation , nitrogen , soil science , geology , chemistry , geography , meteorology , geotechnical engineering , organic chemistry , machine learning , computer science
To evaluate the role of stormflow in reducing N retention in forested watersheds, we investigated the inorganic N budget of a Japanese suburban forested watershed for 4 years where the proportion of direct flow to precipitation is considerably high (mean is 33%; range is 25–42%). Soil net N mineralization and net nitrification were also measured at middle and lower positions of a slope within the watershed to evaluate nitrate (NO 3 − ) pool size. Annual mean N deposition via throughfall plus stemflow was 15.5 kg N ha −1 yr −1 (13.6–17.1 kg N ha −1 yr −1 ), which exceeded the threshold value to potentially induce N leaching from forested watersheds. Net nitrification at the middle position was comparable with the lower position. This suggests that the NO 3 − rich area is large, which could be partly caused by comparable soil moisture conditions with the lower position due to rising groundwater levels during storm events. Annual mean N export was 10.4 kg N ha −1 yr −1 (7.8–12.5 kg N ha −1 yr −1 ), and subsequent N retention was distinctly low 33% (12–53%). Stormflow accounted for more than 80% of total annual N export. Furthermore, N retention was lower (12 and 27%) in years with higher proportions of direct flow than in years with lower proportions (36 and 53%). Therefore, stormflow is a significant factor in reducing N retention in forested watersheds. The effect of stormflow observation on the comparison of N budgets in other watersheds with different climate and/or hydrologic conditions is discussed.