Does Vegetation Mediate The Effects Of Climatic Change On Lake Catchment Dynamics at Lake Mugecuo, Southwest China?
Date: 28 August 2013
University of Exeter
Doctor of Philosophy in Geography
Lake sediment archives are widely used in palaeoenvironmental reconstructions on the basis that lake ecosystems are sensitive to environmental changes and they integrate changes in the surrounding landscape and atmosphere (Birks & Birks 2006; Carpenter et al., 2007; Pham et al., 2008; Williamson et al., 2008).The primary aim of this ...
Lake sediment archives are widely used in palaeoenvironmental reconstructions on the basis that lake ecosystems are sensitive to environmental changes and they integrate changes in the surrounding landscape and atmosphere (Birks & Birks 2006; Carpenter et al., 2007; Pham et al., 2008; Williamson et al., 2008).The primary aim of this research is to investigate the links between long-term changes in climate and changes in plant community dynamics, and the potential impacts of these interactions on catchment palaeo-erosion rates during the Holocene in a high relief lake catchment. There is a distinct lack of palaeo-record coverage for the Hengduan Mountains and surrounding areas including the south eastern edge of the Tibetan Plateau (Zhang & Mischke, 2009). The Lake Mugecuo MG1 record analysed here is one of the few high resolution Holocene palaeoenvironmental and palaeoecological records available for Southwestern China and one of the first for this part of the Hengduan Mountains in Sichuan Province, extending back to ~12.6 kcal.yr BP. The long-term relationship between major climatic change, vegetation change, and denudation events is complex and poorly understood (Willis et al., 1997). A PFT (plant functional type) approach was adopted to provide a method of classifying pollen taxa into plant communities in order to determine whether plant functional diversity mediates the effects of climate on lake catchment dynamics (including long-term erosion rates) at Lake Mugecuo. 10Be concentrations in bedrock and fluvial sediment samples were used as an independent proxy to estimate surface erosion rates, along with lacustrine deposits of quartz from two shallow water cores (MG3 & MG4) which are used to estimate palaeo-erosion rates for the Lake Mugecuo catchment. A published speleothem record (Wang et al., 2005; Dykoski et al., 2005) from Dongge cave (25°17′N, 108°5′E; 680 m), is used as an indicator of the general pattern of effective moisture change in this region during the Holocene in order to determine if there is a direct link between climate change and the lake deposition record and whether factoring in vegetation improves our understanding of the link between climate change and the lake deposition archive. The MG1 record provides a unique insight into the environmental and vegetation changes that took place during the Late-Glacial/Early Holocene transition. Statistical analysis of the data reveals that plant functional diversity and lake catchment dynamics (using particle-size analysis as an insight into catchment stability) respond to long-term changes (>2,800yr) in climate on in the Lake Mugecuo catchment whilst interactions between plant functional diversity and lake catchment dynamics are found to vary on shorter timescales (<2,800yr). It is argued here that apparent environmental shifts captured in the Lake Mugecuo record are primarily driven/mediated by changes in plant functional diversity and that an array of different types of species and/or functional groups play an important role in modulating and landscape evolution across millennial timescales (approximately 1,000-3,000 years). Vegetation is found to have a filtering effect on the signals of the proxies that are traditionally used as indicators for changes in erosion and deposition in palaeoenvironmental reconstructions (e.g. particle size). 10Be cosmogenic measurements provided supplementary data on past changes in landscape dynamics in the Mugecuo catchment which the conventional proxies used in palaeoenvironmental studies were unable to achieve.
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