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Atmospheric nitrate leached from small forested watersheds during rainfall events: Processes and quantitative evaluation
Author(s) -
Osaka Ken'ichi,
Kugo Tatsuro,
Komaki Naoto,
Nakamura Takashi,
Nishida Kei,
Nagafuchi Osamu
Publication year - 2016
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2015jg003210
Subject(s) - throughfall , environmental science , leaching (pedology) , watershed , rainwater harvesting , hydrology (agriculture) , ecosystem , nitrogen , nitrate , deposition (geology) , atmospheric sciences , soil water , soil science , ecology , chemistry , geology , sediment , paleontology , geotechnical engineering , organic chemistry , machine learning , biology , computer science
To determine the availability of atmospheric NO 3 − deposition on forested ecosystems and to understand the interaction between the nitrogen cycle in a forest ecosystem and atmospheric nitrogen input/output, we quantitatively evaluated the atmospheric NO 3 − passing through forested watersheds by measuring δ 18 O NO3 leaching during rainfall events in two forest ecosystems (Su‐A and Ab‐S). Atmospheric NO 3 − leaching in rainfall events was clearly higher in Ab‐S than in Su‐A, even for a similar amount of rainfall, which demonstrated that atmospheric NO 3 − leaching differs among forested watersheds. Our observations suggest that a large part of the atmospheric NO 3 − leached from the watersheds was derived from surface soil, which was deposited before rainfall events occurred; however, direct atmospheric NO 3 − leaching via throughfall discharge also contributed, especially at the beginning of rainfall events. In Ab‐S, 2.9–37.8% (average = 15.5%) of atmospheric NO 3 − deposition passed through the watershed, accounting for 3.1–49.8% (average, 26.4%) of the total NO 3 − leached during rainfall events. The NO 3 − input was not large, and the NO 3 − pool and net nitrification rate were small; therefore, nitrogen was not saturated in the soil at Ab‐S. Nevertheless, some of the atmospheric NO 3 − deposition was not assimilated and was leached immediately. Moreover, our observations suggest that the hydrological characteristics of the watersheds, which control the ease of rainwater discharge, strongly influenced the rate of atmospheric NO 3 − leaching. This suggests that the hydrological characteristics of watersheds influence the availability of atmospheric NO 3 − deposition in forested ecosystems and the progression of nitrogen saturation.