Hydrological Responses and Flow Pathways in an Acrisol on a Forested Hillslope with a Monsoonal Subtropical Climate

Sørbotten, Lars-Erik; Stolte, Jannes; Wang, Yanhui; Mulder, Jan

doi:10.1016/s1002-0160(17)60447-8

Cited by 15 publications

(10 citation statements)

References 41 publications

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“…Soils on HS are acidic (pH = 3.7–4.1), loamy yellow mountain soils (Acrisols; WRB, ), with a thin O horizon (0–3 cm). Generally, HS soils are well drained, with considerable interflow over the B horizon following rainfall (Sørbotten et al ., Accepted). In the GDZ, the soils are developed from colluvium (Cambisols; WRB, ) derived from the surrounding HS and their hydraulic conductivity is smaller than that of the surface horizons of HS soils.…”

Section: Methodsmentioning

confidence: 99%

Multiyear dual nitrate isotope signatures suggest that N‐saturated subtropical forested catchments can act as robust N sinks

Zhu

Mulder

et al. 2016

Global Change Biology

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In forests of the humid subtropics of China, chronically elevated nitrogen (N) deposition, predominantly as ammonium (NH ), causes significant nitrate (NO ) leaching from well-drained acid forest soils on hill slopes (HS), whereas significant retention of NO occurs in near-stream environments (groundwater discharge zones, GDZ). To aid our understanding of N transformations on the catchment level, we studied spatial and temporal variabilities of concentration and natural abundance (δ N and δ O) of nitrate (NO ) in soil pore water along a hydrological continuum in the N-saturated Tieshanping (TSP) catchment, southwest China. Our data show that effective removal of atmogenic NH and production of NO in soils on HS were associated with a significant decrease in δ N-NO , suggesting efficient nitrification despite low soil pH. The concentration of NO declined sharply along the hydrological flow path in the GDZ. This decline was associated with a significant increase in both δ N and δ O of residual NO , providing evidence that the GDZ acts as an N sink due to denitrification. The observed apparent N enrichment factor (ε) of NO of about -5‰ in the GDZ is similar to values previously reported for efficient denitrification in riparian and groundwater systems. Episode studies in the summers of 2009, 2010 and 2013 revealed that the spatial pattern of δ N and δ O-NO in soil water was remarkably similar from year to year. The importance of denitrification as a major N sink was also seen at the catchment scale, as largest δ N-NO values in stream water were observed at lowest discharge, confirming the importance of the relatively small GDZ for N removal under base flow conditions. This study, explicitly recognizing hydrologically connected landscape elements, reveals an overlooked but robust N sink in N-saturated, subtropical forests with important implications for regional N budgets.

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Section: Methodsmentioning

confidence: 99%

Multiyear dual nitrate isotope signatures suggest that N‐saturated subtropical forested catchments can act as robust N sinks

Zhu

Mulder

et al. 2016

Global Change Biology

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“…We established two experimental sites on a northeast‐facing hillslope, one on the top of the hillslope (Upper site) and one at the foot of the hillslope (Lower site, Figure B). Soil moisture and organic matter contents are higher at the Lower than at the Upper sites, because the hillslope experiences considerable interflow over the Bt horizon following rain episodes …”

Section: Methodsmentioning

confidence: 98%

“…Soil moisture and organic matter contents are higher at the Lower than at the Upper sites, because the hillslope experiences considerable interflow over the Bt horizon following rain episodes. 25…”

Section: Site Descriptionmentioning

confidence: 99%

Nitrification is the primary source for NO in N‐saturated subtropical forest soils: Results from in situ¹⁵N labeling

Kang

Dörsch

et al. 2020

Rapid Comm Mass Spectrometry

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Rationale Acidic subtropical forest soils that receive high atmospheric nitrogen (N) deposition have been identified as important sources of nitric oxide (NO). The relative importance of major processes producing NO is unclear. Methods To partition NO sources, we conducted an in situ tracing experiment with 15NH4NO3 and NH415NO3 in well‐drained acid soils of an N‐saturated subtropical forest in Chongqing, southwest China. Results In the 15NH4NO3 treatment, the 15N signature of NO emitted from the foot of the hillslope (Lower site) was similar to that of the NH4+ pool, indicating predominant autotrophic nitrification for NO formation. In the NH415NO3 treatment, the 15N enrichment of NO was smaller than that of the NO3− pool, suggesting minor contribution of denitrification to NO production (~15%). Conclusions Nitrification is the main process responsible for NO emissions, even in monsoonal summers when soil water‐filled pore space values are relatively high.

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“…

δ^{15} N_{{NO}_{3} - input}

and

δ^{15} N_{{NO}_{3} - soil}

were determined as concentration‐weighted averages of

δ^{15} N_{{NO}_{3}}

on hillslopes (plots A and B) and across whole catchments (plots A to D), respectively. We did not capture changes of

δ^{15} N_{{NO}_{3}}

with soil depths, but previous studies of

δ^{15} N_{{NO}_{3}}

in southern Chinese forest catchments demonstrated the vertical transport and transformation of NO 3 − is negligible because of limited infiltration in the argic B horizon (Sørbotten, Stolte, Wang, & Mulder, ; Yu et al, ). Concentration‐weighted averages of

δ^{15} N_{{NO}_{3}}

in stream water were taken as indicative for

δ^{15} N_{{NO}_{3} - L}

.…”

Section: Methodsmentioning

confidence: 99%

Denitrification as a major regional nitrogen sink in subtropical forest catchments: Evidence from multi‐site dual nitrate isotopes

Mulder

Zhu

et al. 2019

Global Change Biology

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Increasing nitrogen (N) deposition in subtropical forests in south China causes N saturation, associated with significant nitrate (NO3−) leaching. Strong N attenuation may occur in groundwater discharge zones hydrologically connected to well‐drained hillslopes, as has been shown for the subtropical headwater catchment “TieShanPing”, where dual NO3− isotopes indicated that groundwater discharge zones act as an important N sink and hotspot for denitrification. Here, we present a regional study reporting inorganic N fluxes over two years together with dual NO3− isotope signatures obtained in two summer campaigns from seven forested catchments in China, representing a gradient in climate and atmospheric N input. In all catchments, fluxes of dissolved inorganic N indicated efficient conversion of NH4+ to NO3− on well‐drained hillslopes, and subsequent interflow of NO3− over the argic B‐horizons to groundwater discharge zones. Depletion of 15N‐ and 18O–NO3− on hillslopes suggested nitrification as the main source of NO3−. In all catchments, except one of the northern sites, which had low N deposition rates, NO3− attenuation by denitrification occurred in groundwater discharge zones, as indicated by simultaneous 15N and 18O enrichment in residual NO3−. By contrast to the southern sites, the northern catchments lack continuous and well‐developed groundwater discharge zones, explaining less efficient N removal. Using a model based on 15NO3− signatures, we estimated denitrification fluxes from 2.4 to 21.7 kg N ha−1 year−1 for the southern sites, accounting for more than half of the observed N removal. Across the southern catchments, estimated denitrification scaled proportionally with N deposition. Together, this indicates that N removal by denitrification is an important component of the N budget of southern Chinese forests and that natural NO3− attenuation may increase with increasing N input, thus partly counteracting further aggravation of N contamination of surface waters in the region.

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Hydrological Responses and Flow Pathways in an Acrisol on a Forested Hillslope with a Monsoonal Subtropical Climate

Cited by 15 publications

References 41 publications

Multiyear dual nitrate isotope signatures suggest that N‐saturated subtropical forested catchments can act as robust N sinks

Multiyear dual nitrate isotope signatures suggest that N‐saturated subtropical forested catchments can act as robust N sinks

Nitrification is the primary source for NO in N‐saturated subtropical forest soils: Results from in situ¹⁵N labeling

Denitrification as a major regional nitrogen sink in subtropical forest catchments: Evidence from multi‐site dual nitrate isotopes

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Hydrological Responses and Flow Pathways in an Acrisol on a Forested Hillslope with a Monsoonal Subtropical Climate

Cited by 15 publications

References 41 publications

Multiyear dual nitrate isotope signatures suggest that N‐saturated subtropical forested catchments can act as robust N sinks

Multiyear dual nitrate isotope signatures suggest that N‐saturated subtropical forested catchments can act as robust N sinks

Nitrification is the primary source for NO in N‐saturated subtropical forest soils: Results from in situ15N labeling

Denitrification as a major regional nitrogen sink in subtropical forest catchments: Evidence from multi‐site dual nitrate isotopes

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Nitrification is the primary source for NO in N‐saturated subtropical forest soils: Results from in situ¹⁵N labeling