High sediment export from a trans-Himalayan semi-desert driven by late Holocene climate change and human impact

Johanna Menges, Niels Hovius, Christoff Andermann, Michael Dietze, Charlie Swoboda, Kirsten Cook, Andrea Vieth-Hillebrand, Stephane Bonnet, T. Reimann, Dirk Sachse

Research output: Contribution to conferenceAbstractAcademic

Abstract

Sediment export rates are sensitive to changes in climate, vegetation and human impact, but the direct response of a given landscape to such changes is difficult to unravel. Here, we report a strong landscape response to a disturbance
of a stable, soil covered landscape in a trans-Himalayan valley, which was pushed over an eco-geomorphic tipping point resulting in fast and widespread erosion. We then identify potential drivers for this transition. The upper Kali Gandaki (KG) river valley in Nepal drains the southern edge of the Tibetan plateau in the rain shadow of the High Himalayas, where a scarcely vegetated semi-desert is dissected by deep gullies. These badlands formed in a graben structure storing large amounts of unconsolidated sediments which provide a source of erosion product to the high stream-power river. Due to the high erodibility of this material, the region is particularly sensitive to changes in climate and land use. At the outlet of the upper valley, we estimate that river
suspended sediment concentrations are up to two orders of magnitude higher for a given river discharge than downstream in the monsoon dominated High Himalayan river segment. Even though precipitation rates are low in the upper valley (160 mm/yr to 250 mm/yr) and discharges rarely exceed 100 m3/s, we show that modern erosion efficiency is around five times higher than in the steep and wet, landslide dominated southern part of the catchment. In stark contrast to this modern setting, widespread occurrence of paleosol horizons reflects the persistence of geomorphologically stable conditions during the Holocene until 2.4 ka based on OSL and 14C ages. What pushed this landscape from a soil covered stable state into the erosional state observed today?We investigated human land use and climate change as possible drivers of this transition. Human impact on the landscape has been suggested from 5.4 ka onwards (Miehe et al., 2009) and an increased occurence of archeological sites and evidence of
grazing animals has been reported from 3 ka (Simons et al.,1994). We estimated paleo-hydrological conditions using the hydrogen isotopic composition of plant lipids (Dwax) extracted from the paleosol horizons in the upper KG valley (3500 - 4100 m asl., n=24). Dwax values range from 214 h to 236 h which is offset by 40 h 6 h from the Dwax values of modern shrub leaves sampled at the paleosol sites and modern topsoils sampled along the wetter fringes of the valley. This strongly suggests that soil formation took place under substantially wetter conditions, i.e. an enhanced monsoonal precipitation in the past. The subsequent Late Holocene drying trend combined with human land use likely reduced vegetation cover which then initiated the transition to badland development observed today. Current erosion rates suggest a catchment-average surface lowering rate of one meter per 1000 years, resulting in a strong and irreversible degradation of the landscape and its soils.
Original languageEnglish
Pages21-21
Number of pages1
Publication statusPublished - 2019
EventEGU General Assembly 2019 - Vienna, Austria
Duration: 7 Apr 201912 Apr 2019

Conference

ConferenceEGU General Assembly 2019
CountryAustria
Period7/04/1912/04/19

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anthropogenic effect
desert
Holocene
valley
climate change
paleosol
sediment
badlands
erosion
river
catchment
land use
archaeological evidence
soil
erodibility
climate
gully
erosion rate
river discharge
graben

Cite this

Menges, J., Hovius, N., Andermann, C., Dietze, M., Swoboda, C., Cook, K., ... Sachse, D. (2019). High sediment export from a trans-Himalayan semi-desert driven by late Holocene climate change and human impact. 21-21. Abstract from EGU General Assembly 2019, Austria.
Menges, Johanna ; Hovius, Niels ; Andermann, Christoff ; Dietze, Michael ; Swoboda, Charlie ; Cook, Kirsten ; Vieth-Hillebrand, Andrea ; Bonnet, Stephane ; Reimann, T. ; Sachse, Dirk. / High sediment export from a trans-Himalayan semi-desert driven by late Holocene climate change and human impact. Abstract from EGU General Assembly 2019, Austria.1 p.
@conference{09bec5763ba64759b6654596a9bde8c8,
title = "High sediment export from a trans-Himalayan semi-desert driven by late Holocene climate change and human impact",
abstract = "Sediment export rates are sensitive to changes in climate, vegetation and human impact, but the direct response of a given landscape to such changes is difficult to unravel. Here, we report a strong landscape response to a disturbanceof a stable, soil covered landscape in a trans-Himalayan valley, which was pushed over an eco-geomorphic tipping point resulting in fast and widespread erosion. We then identify potential drivers for this transition. The upper Kali Gandaki (KG) river valley in Nepal drains the southern edge of the Tibetan plateau in the rain shadow of the High Himalayas, where a scarcely vegetated semi-desert is dissected by deep gullies. These badlands formed in a graben structure storing large amounts of unconsolidated sediments which provide a source of erosion product to the high stream-power river. Due to the high erodibility of this material, the region is particularly sensitive to changes in climate and land use. At the outlet of the upper valley, we estimate that riversuspended sediment concentrations are up to two orders of magnitude higher for a given river discharge than downstream in the monsoon dominated High Himalayan river segment. Even though precipitation rates are low in the upper valley (160 mm/yr to 250 mm/yr) and discharges rarely exceed 100 m3/s, we show that modern erosion efficiency is around five times higher than in the steep and wet, landslide dominated southern part of the catchment. In stark contrast to this modern setting, widespread occurrence of paleosol horizons reflects the persistence of geomorphologically stable conditions during the Holocene until 2.4 ka based on OSL and 14C ages. What pushed this landscape from a soil covered stable state into the erosional state observed today?We investigated human land use and climate change as possible drivers of this transition. Human impact on the landscape has been suggested from 5.4 ka onwards (Miehe et al., 2009) and an increased occurence of archeological sites and evidence ofgrazing animals has been reported from 3 ka (Simons et al.,1994). We estimated paleo-hydrological conditions using the hydrogen isotopic composition of plant lipids (Dwax) extracted from the paleosol horizons in the upper KG valley (3500 - 4100 m asl., n=24). Dwax values range from 214 h to 236 h which is offset by 40 h 6 h from the Dwax values of modern shrub leaves sampled at the paleosol sites and modern topsoils sampled along the wetter fringes of the valley. This strongly suggests that soil formation took place under substantially wetter conditions, i.e. an enhanced monsoonal precipitation in the past. The subsequent Late Holocene drying trend combined with human land use likely reduced vegetation cover which then initiated the transition to badland development observed today. Current erosion rates suggest a catchment-average surface lowering rate of one meter per 1000 years, resulting in a strong and irreversible degradation of the landscape and its soils.",
author = "Johanna Menges and Niels Hovius and Christoff Andermann and Michael Dietze and Charlie Swoboda and Kirsten Cook and Andrea Vieth-Hillebrand and Stephane Bonnet and T. Reimann and Dirk Sachse",
year = "2019",
language = "English",
pages = "21--21",
note = "EGU General Assembly 2019 ; Conference date: 07-04-2019 Through 12-04-2019",

}

Menges, J, Hovius, N, Andermann, C, Dietze, M, Swoboda, C, Cook, K, Vieth-Hillebrand, A, Bonnet, S, Reimann, T & Sachse, D 2019, 'High sediment export from a trans-Himalayan semi-desert driven by late Holocene climate change and human impact' EGU General Assembly 2019, Austria, 7/04/19 - 12/04/19, pp. 21-21.

High sediment export from a trans-Himalayan semi-desert driven by late Holocene climate change and human impact. / Menges, Johanna; Hovius, Niels; Andermann, Christoff; Dietze, Michael; Swoboda, Charlie ; Cook, Kirsten ; Vieth-Hillebrand, Andrea; Bonnet, Stephane; Reimann, T.; Sachse, Dirk.

2019. 21-21 Abstract from EGU General Assembly 2019, Austria.

Research output: Contribution to conferenceAbstractAcademic

TY - CONF

T1 - High sediment export from a trans-Himalayan semi-desert driven by late Holocene climate change and human impact

AU - Menges, Johanna

AU - Hovius, Niels

AU - Andermann, Christoff

AU - Dietze, Michael

AU - Swoboda, Charlie

AU - Cook, Kirsten

AU - Vieth-Hillebrand, Andrea

AU - Bonnet, Stephane

AU - Reimann, T.

AU - Sachse, Dirk

PY - 2019

Y1 - 2019

N2 - Sediment export rates are sensitive to changes in climate, vegetation and human impact, but the direct response of a given landscape to such changes is difficult to unravel. Here, we report a strong landscape response to a disturbanceof a stable, soil covered landscape in a trans-Himalayan valley, which was pushed over an eco-geomorphic tipping point resulting in fast and widespread erosion. We then identify potential drivers for this transition. The upper Kali Gandaki (KG) river valley in Nepal drains the southern edge of the Tibetan plateau in the rain shadow of the High Himalayas, where a scarcely vegetated semi-desert is dissected by deep gullies. These badlands formed in a graben structure storing large amounts of unconsolidated sediments which provide a source of erosion product to the high stream-power river. Due to the high erodibility of this material, the region is particularly sensitive to changes in climate and land use. At the outlet of the upper valley, we estimate that riversuspended sediment concentrations are up to two orders of magnitude higher for a given river discharge than downstream in the monsoon dominated High Himalayan river segment. Even though precipitation rates are low in the upper valley (160 mm/yr to 250 mm/yr) and discharges rarely exceed 100 m3/s, we show that modern erosion efficiency is around five times higher than in the steep and wet, landslide dominated southern part of the catchment. In stark contrast to this modern setting, widespread occurrence of paleosol horizons reflects the persistence of geomorphologically stable conditions during the Holocene until 2.4 ka based on OSL and 14C ages. What pushed this landscape from a soil covered stable state into the erosional state observed today?We investigated human land use and climate change as possible drivers of this transition. Human impact on the landscape has been suggested from 5.4 ka onwards (Miehe et al., 2009) and an increased occurence of archeological sites and evidence ofgrazing animals has been reported from 3 ka (Simons et al.,1994). We estimated paleo-hydrological conditions using the hydrogen isotopic composition of plant lipids (Dwax) extracted from the paleosol horizons in the upper KG valley (3500 - 4100 m asl., n=24). Dwax values range from 214 h to 236 h which is offset by 40 h 6 h from the Dwax values of modern shrub leaves sampled at the paleosol sites and modern topsoils sampled along the wetter fringes of the valley. This strongly suggests that soil formation took place under substantially wetter conditions, i.e. an enhanced monsoonal precipitation in the past. The subsequent Late Holocene drying trend combined with human land use likely reduced vegetation cover which then initiated the transition to badland development observed today. Current erosion rates suggest a catchment-average surface lowering rate of one meter per 1000 years, resulting in a strong and irreversible degradation of the landscape and its soils.

AB - Sediment export rates are sensitive to changes in climate, vegetation and human impact, but the direct response of a given landscape to such changes is difficult to unravel. Here, we report a strong landscape response to a disturbanceof a stable, soil covered landscape in a trans-Himalayan valley, which was pushed over an eco-geomorphic tipping point resulting in fast and widespread erosion. We then identify potential drivers for this transition. The upper Kali Gandaki (KG) river valley in Nepal drains the southern edge of the Tibetan plateau in the rain shadow of the High Himalayas, where a scarcely vegetated semi-desert is dissected by deep gullies. These badlands formed in a graben structure storing large amounts of unconsolidated sediments which provide a source of erosion product to the high stream-power river. Due to the high erodibility of this material, the region is particularly sensitive to changes in climate and land use. At the outlet of the upper valley, we estimate that riversuspended sediment concentrations are up to two orders of magnitude higher for a given river discharge than downstream in the monsoon dominated High Himalayan river segment. Even though precipitation rates are low in the upper valley (160 mm/yr to 250 mm/yr) and discharges rarely exceed 100 m3/s, we show that modern erosion efficiency is around five times higher than in the steep and wet, landslide dominated southern part of the catchment. In stark contrast to this modern setting, widespread occurrence of paleosol horizons reflects the persistence of geomorphologically stable conditions during the Holocene until 2.4 ka based on OSL and 14C ages. What pushed this landscape from a soil covered stable state into the erosional state observed today?We investigated human land use and climate change as possible drivers of this transition. Human impact on the landscape has been suggested from 5.4 ka onwards (Miehe et al., 2009) and an increased occurence of archeological sites and evidence ofgrazing animals has been reported from 3 ka (Simons et al.,1994). We estimated paleo-hydrological conditions using the hydrogen isotopic composition of plant lipids (Dwax) extracted from the paleosol horizons in the upper KG valley (3500 - 4100 m asl., n=24). Dwax values range from 214 h to 236 h which is offset by 40 h 6 h from the Dwax values of modern shrub leaves sampled at the paleosol sites and modern topsoils sampled along the wetter fringes of the valley. This strongly suggests that soil formation took place under substantially wetter conditions, i.e. an enhanced monsoonal precipitation in the past. The subsequent Late Holocene drying trend combined with human land use likely reduced vegetation cover which then initiated the transition to badland development observed today. Current erosion rates suggest a catchment-average surface lowering rate of one meter per 1000 years, resulting in a strong and irreversible degradation of the landscape and its soils.

M3 - Abstract

SP - 21

EP - 21

ER -

Menges J, Hovius N, Andermann C, Dietze M, Swoboda C, Cook K et al. High sediment export from a trans-Himalayan semi-desert driven by late Holocene climate change and human impact. 2019. Abstract from EGU General Assembly 2019, Austria.