TY - JOUR A1 - Tian, Fang A1 - Herzschuh, Ulrike A1 - Mischke, Steffen A1 - Schluetz, Frank T1 - What drives the recent intensified vegetation degradation in Mongolia - Climate change or human activity? JF - The Holocene : an interdisciplinary journal focusing on recent environmental change N2 - This study examines the course and driving forces of recent vegetation change in the Mongolian steppe. A sediment core covering the last 55years from a small closed-basin lake in central Mongolia was analyzed for its multi-proxy record at annual resolution. Pollen analysis shows that highest abundances of planted Poaceae and highest vegetation diversity occurred during 1977-1992, reflecting agricultural development in the lake area. A decrease in diversity and an increase in Artemisia abundance after 1992 indicate enhanced vegetation degradation in recent times, most probably because of overgrazing and farmland abandonment. Human impact is the main factor for the vegetation degradation within the past decades as revealed by a series of redundancy analyses, while climate change and soil erosion play subordinate roles. High Pediastrum (a green algae) influx, high atomic total organic carbon/total nitrogen (TOC/TN) ratios, abundant coarse detrital grains, and the decrease of C-13(org) and N-15 since about 1977 but particularly after 1992 indicate that abundant terrestrial organic matter and nutrients were transported into the lake and caused lake eutrophication, presumably because of intensified land use. Thus, we infer that the transition to a market economy in Mongolia since the early 1990s not only caused dramatic vegetation degradation but also affected the lake ecosystem through anthropogenic changes in the catchment area. KW - central Mongolia KW - grain size KW - human impact KW - lake eutrophication KW - pollen KW - vegetation degradation Y1 - 2014 U6 - https://doi.org/10.1177/0959683614540958 SN - 0959-6836 SN - 1477-0911 VL - 24 IS - 10 SP - 1206 EP - 1215 PB - Sage Publ. CY - London ER - TY - JOUR A1 - Struck, Martin A1 - Andermann, Christoff A1 - Hovius, Niels A1 - Korup, Oliver A1 - Turowski, Jens M. A1 - Bista, Raj A1 - Pandit, Hari P. A1 - Dahal, Ranjan K. T1 - Monsoonal hillslope processes determine grain size-specific suspended sediment fluxes in a trans-Himalayan river JF - Geophysical research letters N2 - Sediments in rivers record the dynamics of erosion processes. While bulk sediment fluxes are easily and routinely obtained, sediment caliber remains underexplored when inferring erosion mechanisms. Yet sediment grain size distributions may be the key to discriminating their origin. We have studied grain size-specific suspended sediment fluxes in the Kali Gandaki, a major trans-Himalayan river. Two strategically located gauging stations enable tracing of sediment caliber on either side of the Himalayan orographic barrier. The data show that fine sediment input into the northern headwaters is persistent, while coarse sediment comes from the High Himalayas during the summer monsoon. A temporally matching landslide inventory similarly indicates the prominence of monsoon-driven hillslope mass wasting. Thus, mechanisms of sediment supply can leave strong traces in the fluvial caliber, which could project well beyond the mountain front and add to the variability of the sedimentary record of orogen erosion. KW - Himalayas KW - erosion KW - grain size KW - suspended sediments KW - landslide KW - river transport Y1 - 2015 U6 - https://doi.org/10.1002/2015GL063360 SN - 0094-8276 SN - 1944-8007 VL - 42 IS - 7 SP - 2302 EP - 2308 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Brooke, Sam A. S. A1 - Whittaker, Alexander C. A1 - Armitage, John J. A1 - Watkins, Stephen E. A1 - D'Arcy, Mitchell T1 - Quantifying sediment transport dynamics on alluvial fans from spatial and temporal changes in Grain Size, Death Valley, California JF - Journal of geophysical research : Earth surface N2 - How information about sediment transport processes is transmitted to the sedimentary record remains a complex problem for the interpretation of fluvial stratigraphy. Alluvial fan deposits represent the condensed archive of sediment transport, which is at least partly controlled by tectonics and climate. For three coupled catchment-fan systems in northern Death Valley, California, we measure grain size across 12 well-preserved Holocene and late-Pleistocene surfaces, mapped in detail from field observations and remote sensing. Our results show that fan surfaces correlated to the late Pleistocene are, on average, 30-50% coarser than active or Holocene fan surfaces. We adopt a self-similar form of grain size distribution based on the observed stability of the ratio between mean grain size and standard deviation downstream. Using statistical analysis, we show that fan surface grain size distributions are self-similar. We derive a relative mobility function using our self-similar grain size distributions, which describes the relative probability of a given grain size being transported. We show that the largest mobile grain sizes are between 20 and 35mm, a value that varies over time and is clearly lower in the Holocene than in the Pleistocene; a change we suggest is due to a drier climate in the Holocene. These results support recent findings that alluvial fan sedimentology can record past environmental change and that these landscapes are potentially sensitive to climatic change over a glacial-interglacial cycle. We demonstrate that the self-similarity methodology offers a means to explore changes in relative mobility of grain sizes from preserved fluvial deposits. Plain Language Summary A key challenge in Earth Science is understanding how landscapes respond to climate. It may be possible to observe measurable differences in certain landscapes settings such as alluvial fans in desert regions. Alluvial fans are believed to be effective recorders of climate, representing a cumulative store of material transported downstream by rainfall-sensitive river systems. In northern Death Valley, California, we measure at high resolution grain size on three alluvial fans with surfaces that date from the Holocene and the arid climate of today to the 20-40% wetter late-Pleistocene epoch. We find that older late-Pleistocene surfaces are coarser on average than surfaces deposited during the modern and Holocene dry period, suggesting a changing sediment transport regime potentially in response to precipitation. We also show that measured grain size distributions within and between surfaces can be successfully normalized based on the decay in mean grain size and variance downstream, exhibiting a self-similar pattern. Finally, we employ a grain size relative mobility model using our field data to establish which grain sizes are likely to be in transport or locked in the substrate. This model predicts that during the wetter late-Pleistocene mobile grain sizes are up to 40% larger than during the Holocene. KW - alluvial fans KW - grain size KW - sediment transport KW - self-similarity KW - fluvial geomorphology KW - Death Valley Y1 - 2018 U6 - https://doi.org/10.1029/2018JF004622 SN - 2169-9003 SN - 2169-9011 VL - 123 IS - 8 SP - 2039 EP - 2067 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Roda-Boluda, Duna C. A1 - McDonald, Jordan A1 - Whittaker, Alexander C. A1 - D'Arcy, Mitchell T1 - Lithological controls on hillslope sediment supply BT - insights from landslide activity and grain size distributions JF - Earth surface processes and landforms : the journal of the British Geomorphological Research Group N2 - The volumes, rates and grain size distributions of sediment supplied from hillslopes represent the initial input of sediment delivered from upland areas and propagated through sediment routing systems. Moreover, hillslope sediment supply has a significant impact on landscape response time to tectonic and climatic perturbations. However, there are very few detailed field studies characterizing hillslope sediment supply as a function of lithology and delivery process. Here, we present new empirical data from tectonically-active areas in southern Italy that quantifies how lithology and rock strength control the landslide fluxes and grain size distributions supplied from hillslopes. Landslides are the major source of hillslope sediment supply in this area, and our inventory of similar to 2800 landslides reveals that landslide sediment flux is dominated by small, shallow landslides. We find that lithology and rock strength modulate the abundance of steep slopes and landslides, and the distribution of landslide sizes. Outcrop-scale rock strength also controls the grain sizes supplied by bedrock weathering, and influences the degree of coarsening of landslide supply with respect to weathering supply. Finally, we show that hillslope sediment supply largely determines the grain sizes of fluvial export, from catchments and that catchments with greater long-term landslide rates deliver coarser material. Therefore, our results demonstrate a dual control of lithology on hillslope sediment supply, by modulating both the sediment fluxes from landslides and the grain sizes supplied by hillslopes to the fluvial system. KW - lithology KW - hillslopes KW - landslides KW - grain size KW - sediment supply Y1 - 2018 U6 - https://doi.org/10.1002/esp.4281 SN - 0197-9337 SN - 1096-9837 VL - 43 IS - 5 SP - 956 EP - 977 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Radosavljevic, Boris A1 - Lantuit, Hugues A1 - Knoblauch, Christian A1 - Couture, Nicole A1 - Herzschuh, Ulrike A1 - Fritz, Michael T1 - Arctic nearshore sediment dynamics - an example from Herschel Island - Qikiqtaruk, Canada JF - Journal of marine science and engineering N2 - Increasing arctic coastal erosion rates imply a greater release of sediments and organic matter into the coastal zone. With 213 sediment samples taken around Herschel Island-Qikiqtaruk, Canadian Beaufort Sea, we aimed to gain new insights on sediment dynamics and geochemical properties of a shallow arctic nearshore zone. Spatial characteristics of nearshore sediment texture (moderately to poorly sorted silt) are dictated by hydrodynamic processes, but ice-related processes also play a role. We determined organic matter (OM) distribution and inferred the origin and quality of organic carbon by C/N ratios and stable carbon isotopes delta C-13. The carbon content was higher offshore and in sheltered areas (mean: 1.0 wt.%., S.D.: 0.9) and the C/N ratios also showed a similar spatial pattern (mean: 11.1, S.D.: 3.1), while the delta C-13 (mean: -26.4 parts per thousand VPDB, S.D.: 0.4) distribution was more complex. We compared the geochemical parameters of our study with terrestrial and marine samples from other studies using a bootstrap approach. Sediments of the current study contained 6.5 times and 1.8 times less total organic carbon than undisturbed and disturbed terrestrial sediments, respectively. Therefore, degradation of OM and separation of carbon pools take place on land and continue in the nearshore zone, where OM is leached, mineralized, or transported beyond the study area. KW - permafrost KW - Arctic Ocean KW - stable carbon isotopes KW - nitrogen KW - sediment KW - chemistry KW - sediment dynamics KW - Beaufort Sea KW - grain size Y1 - 2022 U6 - https://doi.org/10.3390/jmse10111589 SN - 2077-1312 VL - 10 IS - 11 PB - MDPI CY - Basel ER - TY - JOUR A1 - Cordeiro, Andre M. A1 - Andrade, Luis A1 - Monteiro, Catarina C. A1 - Leitao, Guilherme A1 - Wigge, Philip Anthony A1 - Saibo, Nelson J. M. T1 - Phytochrome-interacting factors BT - a promising tool to improve crop productivity JF - Journal of experimental botany N2 - Review exploring the regulation of PHYTOCHROME-INTERACTING FACTORS by light, their role in abiotic stress tolerance and plant architecture, and their influence on crop productivity. Light is a key determinant for plant growth, development, and ultimately yield. Phytochromes, red/far-red photoreceptors, play an important role in plant architecture, stress tolerance, and productivity. In the model plant Arabidopsis, it has been shown that PHYTOCHROME-INTERACTING FACTORS (PIFs; bHLH transcription factors) act as central hubs in the integration of external stimuli to regulate plant development. Recent studies have unveiled the importance of PIFs in crops. They are involved in the modulation of plant architecture and productivity through the regulation of cell division and elongation in response to different environmental cues. These studies show that different PIFs have overlapping but also distinct functions in the regulation of plant growth. Therefore, understanding the molecular mechanisms by which PIFs regulate plant development is crucial to improve crop productivity under both optimal and adverse environmental conditions. In this review, we discuss current knowledge of PIFs acting as integrators of light and other signals in different crops, with particular focus on the role of PIFs in responding to different environmental conditions and how this can be used to improve crop productivity. KW - Cold KW - drought KW - grain size KW - heat KW - light signaling KW - phytochrome KW - PIF KW - plant architecture KW - plant breeding KW - plant yield KW - salinity Y1 - 2022 U6 - https://doi.org/10.1093/jxb/erac142 SN - 0022-0957 SN - 1460-2431 VL - 73 IS - 12 SP - 3881 EP - 3897 PB - Oxford Univ. Press CY - Oxford ER -