Variation in Nitrate Concentrations in Streamwater of Forested Watersheds in the Northeastern Kanto Plain as a Function of Distance from the Tokyo Metropolitan Area

Yoshinaga, Shuichiro; Itoh, Yuko; Aizawa, Shuhei; Tsurita, Tatsuya

doi:10.4005/jjfs.94.84

Cited by 11 publications

(7 citation statements)

References 15 publications

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“…1 ). This range and spatial gradients of the simulated N depositions were well agreed with the observations especially in the mountainous area in previous studies 28 , 38 , 51 (See comparison in Fig. S4 ; R 2 = 0.855 and RMSE = 1.12 kg-N ha −1 ).…”

Section: Resultssupporting

confidence: 91%

“…Much attention has been paid to N deposition as a key environmental variable in water quality. However, because it has been difficult to determine multi-site N deposition rates in situ , the distance from central Tokyo has been used in studies as an explanatory variable of nitrate concentrations in forested watersheds 23 , 26 – 28 , 30 . However, when different scales and directions from the city are included in target area, the distance could not be an universal proxy index of N deposition due to the meteorological factors and topographic factors.…”

Section: Introductionmentioning

confidence: 99%

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Varying sensitivity of mountainous streamwater base-flow $${\bf{N}}{{\bf{O}}}_{{\bf{3}}}^{-}$$concentrations to N deposition in the northern suburbs of Tokyo

Nishina

Watanabe

Koshikawa

et al. 2017

Sci Rep

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Ecosystems of suburban landscapes (i.e., forest, inland water ecosystem) are threatened by high nitrogen (N) loadings derived from urban air pollutants. Forest ecosystems under high chronic N loadings tend to leach more N via streams. In the northern suburbs of Tokyo, N deposition loading on terrestrial ecosystems has increased over the past 30 years. In this region, we investigated nitrate concentrations in 608 independent small forested catchment water samples from northeastern suburbs of Tokyo. The nitrate concentrations varied from 0.07 to 3.31 mg-N L−1 in this region. We evaluated the effects of N deposition and catchment properties (e.g., meteorological and topographic factors, vegetation and soil types) on nitrate concentrations. In the random forest model, simulated N deposition rates from an atmospheric chemistry transportation model explained most of the variance of nitrate concentration. To evaluate the effects of afforestation management in the catchment, we followed a model-based recursive partitioning method (MOB). MOB succeeded in data-driven identification of subgroups with varying sensitivities to N deposition rate by vegetation composition in the catchment. According to MOB, the catchment with dominant coniferous coverage that mostly consisted of plantation with old tree age tended to have strong sensitivity of nitrate concentrations to N deposition loading.

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Section: Resultssupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Varying sensitivity of mountainous streamwater base-flow $${\bf{N}}{{\bf{O}}}_{{\bf{3}}}^{-}$$concentrations to N deposition in the northern suburbs of Tokyo

Nishina

Watanabe

Koshikawa

et al. 2017

Sci Rep

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“…Spearman's rank correlation coefficient (r) was used to examine the relationships between the logarithm NO 3 − concentration and δ 15 N and the relationships between the local urban area (LUA) and LTI at each river to evaluate denitrification in downstream in mixed land use area. All statistical analyses were carried out using an open source statistical programing language of R Version 3.3.3. in urban-or suburban-forested watersheds compared with rural-forested watersheds [10,25,26], and regional-scale spatial patterns of higher atmospheric N deposition were observed in urbanor suburban-forested areas [27][28][29]. In a previous study, river basins included suburban forests, and atmospheric N deposition was moderately high (16 kg N ha −1 year −1 in these areas [30]), which is above the threshold value that could potentially cause N leaching from a forested watershed.…”

Section: Discussionmentioning

confidence: 99%

Differences in Stream Water Nitrate Concentrations between a Nitrogen-Saturated Upland Forest and a Downstream Mixed Land Use River Basin

et al. 2017

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Nitrogen (N) saturation of upland forests has been assumed to be a substantial N source downstream. However, removal processes of N, including assimilation and denitrification in the downstream area, have not been clarified. To evaluate the N removal processes, nitrate and organic N concentrations, as well as nitrogen isotope ratio (δ 15 N) and oxygen isotope ratio (δ 18 O) of NO 3 − were measured along three rivers of Tatara River Basin, Japan where upland forests have already been N-saturated. Geographic information system (GIS) based topographical analysis was also conducted to evaluate the land use as urban area in relation to topography. In two of the three rivers, NO 3 − concentrations did not increase from upstream to downstream, despite the potential non-point N sources of urban areas. In another river, NO 3 − concentrations rather decreased.The values of δ 15 N and δ 18 O of NO 3 − and organic N concentrations suggested the presence of denitrification and assimilation over N pollutants in the river whose watersheds have a lower percentage of urban area. The lower percentage of urban area could be explained by the lower topographic index. This study concluded that the NO 3 − leaching from upland N-saturated forests was substantially assimilated or denitrified in the downstream area.

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“…High levels of N deposition that are related to industrial or other human activity have been observed in East Asia. In Japan, for example, forests close to urban areas received higher levels of N deposition than those in remote areas (Shibata et al, 2001; Yoshinaga et al, 2012). In addition, recent rapid economic growth of some countries, such as China, may cause further increases in N deposition (Liu et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

Biomass and morphology of fine roots of sugi (Cryptomeria japonica) after 3 years of nitrogen fertilization

2013

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Increasing nitrogen (N) deposition may affect carbon and nutrient dynamics in forest ecosystems. To better understand the effects of N deposition, we need to improve our knowledge of N effects on fine roots (roots <2 mm in diameter), as they are a key factor in carbon and nutrient dynamics. In this study, we fertilized 1 × 2 m plots in a sugi (Cryptomeria japonica) stand (336 kg ha-1 y-1) for 3 years and evaluated the responses of the fine roots to high N load. After fertilization, the concentration of NO3–N in the soil of N-fertilized (NF) plots was five-times as large as that in the control plots and the effect was more remarkable in the subsurface soil than in the surface soil. The biomass of fine roots <2 mm in diameter appeared to be greater in the NF plots (88 ± 19 g m-2) than in the control plots (56 ± 14 g m-2), but this difference was not statistically significant. In both plots, 76% of the biomass was accounted for by fine roots that were <1 mm in diameter. In the surface soil, the specific root length of fine roots <1 mm in diameter was significantly greater, and the diameter of those fine roots was marginally smaller, in the NF plots than in the control plots. In addition, the concentration of N in fine roots <1 mm in diameter was marginally greater in the NF plots than in the control plots. There may have been increased production of thinner fine roots or increased root branching in the NF plots. This study suggests that, in general, high N load is likely to have positive effects on sugi in terms of fine root characteristics and the effects on fine-root morphology are more evident than the effects on fine-root biomass.

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Variation in Nitrate Concentrations in Streamwater of Forested Watersheds in the Northeastern Kanto Plain as a Function of Distance from the Tokyo Metropolitan Area

Cited by 11 publications

References 15 publications

Varying sensitivity of mountainous streamwater base-flow $${\bf{N}}{{\bf{O}}}_{{\bf{3}}}^{-}$$concentrations to N deposition in the northern suburbs of Tokyo

Varying sensitivity of mountainous streamwater base-flow $${\bf{N}}{{\bf{O}}}_{{\bf{3}}}^{-}$$concentrations to N deposition in the northern suburbs of Tokyo

Differences in Stream Water Nitrate Concentrations between a Nitrogen-Saturated Upland Forest and a Downstream Mixed Land Use River Basin

Biomass and morphology of fine roots of sugi (Cryptomeria japonica) after 3 years of nitrogen fertilization

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