Quantifying the effects of clear-cutting and strip-cutting on nitrate dynamics in a forested watershed using triple oxygen isotopes as tracers
Quantifying the effects of clear-cutting and strip-cutting on nitrate dynamics in a forested watershed using triple oxygen isotopes as tracers
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DOI：
10.5194/bg-11-5411-2014
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发表时间：
2014-10
期刊：
影响因子：
4.9
通讯作者：
U. Tsunogai;D. Komatsu;T. Ohyama;A. Suzuki;F. Nakagawa;I. Noguchi;K. Takagi;M. Nomura;Karibu Fukuzawa;H. Shibata
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文献类型：
--
作者：
U. Tsunogai;D. Komatsu;T. Ohyama;A. Suzuki;F. Nakagawa;I. Noguchi;K. Takagi;M. Nomura;Karibu Fukuzawa;H. Shibata
测定了从冷温性森林流域（8公顷）溶出的河水中硝酸盐稳定同位素组成的时间变化，以量化树木皆伐和随后的林下植被矮秆竹条伐的生态地球化学效应（Sasa senanensis），特别强调的变化，在大气中的硝酸盐的命运，已沉积到流域的基础上的1 - 17 O值的硝酸盐。2004年春季，溪流硝酸盐浓度显著增加至15 µmol L 1，这与硝酸盐的117 O值显著增加有关。117 O值高达+14.3 ‰，表明直接排放的NO3--N占森林流域NO3--N输出总量的50%以上。2005年春季，两种浓度和117 O值也有类似的增加.相反，在其他季节观察到低于+1.5 ‰的低117 O值，而不管溪流硝酸盐浓度的增加，这表明在春季以外的季节，从森林流域输出的硝酸盐大多数是微生物化的硝酸盐：那些保留在森林生态系统中的有机N或铵，然后通过微生物硝化作用转化为硝酸盐。与带状采伐前相比，2004年大气硝酸盐和矿化硝酸盐的年出口量分别增加了16倍和4倍，2005年分别增加了13倍和5倍。林下植被（Sasa）对提高大气硝态氮的生物消耗尤为重要.
Temporal variations in the stable isotopic com- positions of nitrate dissolved in stream water eluted from a cool-temperate forested watershed (8 ha) were measured to quantify the biogeochemical effects of clear-cutting of trees and subsequent strip-cutting of the understory vegeta- tion, dwarf bamboo (Sasa senanensis), with special empha- sis on changes in the fate of atmospheric nitrate that had been deposited onto the watershed based on 1 17 O values of nitrate. A significant increase in stream nitrate concentra- tion to 15 µmol L 1 in spring of 2004 was correlated with a significant increase in the 1 17 O values of nitrate. Addi- tionally, the high 1 17 O values of +14.3 ‰ suggest that the direct drainage of atmospheric nitrate accounted for more than 50 % of total nitrate exported from the forested water- shed peaking in spring. Similar increases in both concentra- tions and 1 17 O values were also found in spring of 2005. Conversely, low 1 17 O values less than +1.5 ‰ were ob- served in other seasons, regardless of increases in stream nitrate concentration, indicating that the majority of nitrate exported from the forested watershed during seasons other than spring was remineralized nitrate: those retained in the forested ecosystem as either organic N or ammonium and then been converted to nitrate via microbial nitrification. When compared with the values prior to strip-cutting, the annual export of atmospheric nitrate and remineralized ni- trate increased more than 16-fold and fourfold, respectively, in 2004, and more than 13-fold and fivefold, respectively, in 2005. The understory vegetation (Sasa) was particularly im- portant to enhancing biological consumption of atmospheric nitrate.