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Title: Environmental change in the west-central Mexican highlands over the last 1,000 years : evidence from lake sediments
Author: Davies, Sarah Jane
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2000
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Palaeoenvironmental records are presented from two lakes in the volcanic uplands of west-central Mexico, which are believed to be relatively undisturbed: Lago de Zirahuén in Michoacán (19°26'N, 101°44'W) and Laguna de Juanacatlán in Jalisco (20°37'N, 104°44'W). The principal technique employed is diatom analysis, although the analysis of mineral magnetic susceptibility and metal content in the sediments provides important additional information. The chronological framework is provided by a combination of 210Pb dating, AMS 14C dating and tephrochronology. In order to interpret effectively the diatom record from the two sites, modern diatom samples were collected from a range of sites within the Trans-Mexican Volcanic Belt. These data were combined with results from previous investigations to produce a surface sediment diatom calibration dataset for Central Mexico. The development of diatom-based transfer functions from this dataset allows the numerical reconstruction of hydrochemical variables from diatom assemblages in sediment cores. The limitations of this approach are also discussed. The record from Lago de Zirahuén extends back ca. 1,000 years. Tentative evidence is provided from the diatom record for a drier climate ca. 1,000 yrs. BP, although further work is required to confirm this. Increased soil erosion between ca. AD 1100 and AD 1550 likely relates to settlement by the Post-Classical Purépecha civilisation. This is followed by a period of catchment stability during the early Colonial Period, when the indigenous population declined steeply. The impact of Colonial development in the basin from the mid-18th century is clear, with increased soil erosion, distinct changes in the diatom flora and evidence of pollution from copper smelting. The record from Laguna de Juanacatlán is shorter, but covers at least the period since the arrival of Spanish settlers in Mexico in 1521. Evidence is provided of silver mining in the basin during the Colonial Period with associated catchment disturbance indicated by marked changes in the diatom assemblage. The most striking feature of the records from Lago de Zirahuén and Laguna de Juanacatlán, however, is the rapid and dramatic change in the diatom flora during the last 10-20 years as a result of changing land use.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available