Late Holocene environmental change in the Basin of Pátzcuaro, Michoacán, México
This thesis describes late Holocene environmental changes in the Basin of Pátzcuaro, Michoacán, Mexico. Using palaeolimnological evidence it is possible to conclude that the Basin of Pátzcuaro has suffered at least three episodes of disturbance within the last 3,600 years. A minor episode of erosion began about 3,500 years ago and is believed to have been triggered by the onset of sedentary agriculture within the basin. A second, more severe phase of disturbance, occurred between about 2,500 and 1,200 years B.P. during which time there was extensive degradation in the northern part of the catchment; widespread gullying is believed to have occurred at this time. The recent, most intense period of erosion began about 850 years B.P., coinciding with the arrival of the Purépecha in the basin. There is no evidence to suggest that degradation within the catchment intensified after the arrival of the Spanish 470 years B.P. However, a change in the style of erosion from predominantly sheet-wash to gully erosion occurred at approximately 400-500 years B.P. and may reflect the introduction of new agricultural techniques by the Spanish. Fluctuations in the level of Lake Pátzcuaro have been used to infer late Holocene climatic change. Prior to 4,000 years B.P. dry conditions prevailed. An abrupt change to wetter conditions occurred between about 3,600 and 3,200 years B.P. before becoming more arid. Wetter conditions between 2,500 and 1,200 years B.P. can be inferred from the lake sediment record. The driest period in the record occurred between 1,200 and 850 B.P. Fluctuations in the level of the lake over the last 600 years have been determined from historical records. The lake rose between 600 and 470 years B.P. and remained high until approximately 300 years B.P. after which time the lake level fell once again.