Sarah L. O'Hara

Accelerated soil erosion around a Mexican highland lake caused by prehispanic agriculture

THE severely degraded landscape of the volcanic highlands of central Mexico has been the focus of considerable debate1–5. Although it is widely believed that the Spanish encountered an almost pristine landscape in AD 1521 (refs 1–3), some archival and palaeolimnological studies have suggested that extensive land clearance began before European contact, during the Preclassic to Postclassic periods (˜3,500–350 14C yr before present, BP) 5–11. Here we analyse sediment cores from Lake Pátzcuaro, Michoacán (Fig. 1), to derive a quantitative estimate of variations in soil erosion in central Mexico since 4,000 yr BP. We identify three periods of accelerated erosion and conclude that erosion rates during both the late Preclassic/early Classic periods (2,500–1,200 yr BP) and the later Postclassic period (850–350 yr BP) were at least as high as those after the Spanish conquest. One implication of these results is that soil erosion caused by the Spanish introduction of plough agriculture was apparently no more severe than that associated with traditional agricultural methods; it is therefore questionable whether a return to traditional methods would have significant environmental benefits.

Exposure to airborne dust contaminated with pesticide in the Aral Sea region.

The Aral Sea region is one of the worlds foremost ecological disaster zones and there is increasing local concern for the health of millions of people living in this region. We have found that dust deposition rates across eastern Turkmenistan are among the highest in the world and that the dust is contaminated with pesticide.

Degradation, Drought, and Dissent: An Environmental History of Colonial Michoacán, West Central Mexico

Environmental degradation of the central Mexican highlands has traditionally been attributed to colonial land-use change, specifically the introduction of livestock and the use of the plow. Some investigations, however, suggest that the Spanish encountered an already modified or degraded landscape in many locations, and as such, the environmental impacts of Spanish colonization have been overstated. In this paper, we present evidence as to the post-Conquest environmental impacts in Michoacan, west central Mexico, drawn from a range of historical sources, including colonial archives. The findings indicate that there was a period of landscape recovery in the immediate post-Conquest period as a result of indigenous depopulation and a consequent reduction in the intensity of land use. Contrary to conventional belief that the introduction of livestock precipitated an immediate and deleterious impact on the landscape, it is clear that the Spanish introduced conservative livestock-raising practices. A case can b...

Central Asia's Water Resources: Contemporary and Future Management Issues

The collapse of the Soviet Union in 1991 meant that overnight the newly independent Central Asian Republics (CARs) had to assume responsibility for the management and maintenance of a huge, poorly managed and maintained water distribution and irrigation system. Problems emerged almost immediately with a lack of funds virtually halting maintenance programmes. The decline of the system has been marked and it is likely that major failures will occur in the near future. Tension over access to water is also increasing and despite public assurance regarding regional cooperation over water-resource allocation a number of recent incidents suggest this is more political rhetoric than reality. The situation is likely to deteriorate as government backed policies coupled with predicted population increases mean that water resources will become stressed and demand will far outstretch supply. This paper presents a brief review of past water-management strategies, outlines current problems and highlights the challenges which Central Asias leaders face as they strive to develop a water-management strategy to ensure the economic and social well-being of the region into the 21st century .

On the arid margin: The relationship between climate, humans and the environment. A review of evidence from the highlands of central Mexico

There has long been speculation as to the relationship between climate, humans and the environment. Until recently, however, it has proved difficult to establish the degree to which these factors are interlinked. Here we draw on evidence that has recently emerged from a series of investigations in central México to evaluate the long-term human impact on the environment and to establish the impact that late Holocene changes in the climate have had on the indigenous populations that lived on the arid frontier of Mesoamerica. Data from these studies indicate that: 1) the indigenous peoples of central México had a significant and often detrimental impact on the landscape, causing widespread land degradation; 2) The onset of anthropogenic accelerated erosion coincided with the introduction of sedentary agriculture in this region; 3) Fluctuations in the climate of central México over the last 4,000 years have had a significant impact on the subsistence strategies of the population which extended its territory into the northern arid lands during wetter periods, but rapidly abandoned these areas when the climate became drier.

Conflicts Over Water in 'The Little Drought Age' in Central Mexico

M?xico represents one of the most climatically sensitive regions of the world. Over the Colonial period, prolonged drought episodes had severe impacts on all sectors of society, particularly indigenous rural populations. This paper employs a variety of colonial historical records to document the nature and extent of these impacts within the context of prevailing social, political and economic condi tions. It is clear that access to water has long been a source of contention especially during drought episodes. Resource monopolisation by individuals and institutions such as the church served to exacerbate this situation particularly during the 18th century.

Corona Remotely-Sensed Imagery in Dryland Archaeology: The Islamic City of al-Raqqa, Syria

Abstract Satellite remote sensing has seen some use in archaeological research, although its effectiveness has been restricted by the low spatial resolution and the high cost of available imagery. In 1995 the United States declassified 860,000 high-resolution Corona satellite photographs, acquired for intelligence purposes between 1960 and 1972. Corona offers global coverage with an emphasis on areas of strategic significance to the United States. The imagery has been released into the public domain at low cost of acquisition. In this paper we explore the potential of Corona imagery in archaeological investigations using as an example the topography and cultural landscape of the early Islamic city of al-Raqqa in northern Syria.

Irrigation and Water Management in Turkmenistan: Past Systems, Present Problems and Future Scenarios

FOR THE FORMER SOVIET REPUBLIC OF TURKMENISTAN agriculture is the single most important economic activity in that more than 40% of the population is directly in its employ. For a greater number of people it represents a major secondary income source, which in the economic crisis of the post-independence period has assumed even greater significance. With agriculture in Turkmenistan being almost totally dependent on irrigation, access to water is essential and the control and management of the regions water resources has long been an important factor in Turkmen history. Archaeological and historical records indicate that the amount of land irrigated in the region has varied considerably over time. During periods of political stability, often when a single polity ruled over the area, irrigation flourished, but declined after periods of invasion or when internal political conditions were unstable. It was during the 70 years that Turkmenistan was part of the Soviet Union, however, that the regions irrigation...

Drought and disputes, deluge and dearth: climatic variability and human response in colonial Oaxaca, Mexico

Abstract ‘Extreme’ weather events such as droughts, floods, hurricanes, frosts and unusually high or low temperatures can have immense and immediate social, economic and environmental impacts. Investigations of historical extreme weather events, and the nature of the social responses to them, afford insight into the way in which societies have been affected by and have adapted to these events in the past. Historical documents represent invaluable sources to investigate these themes. In this paper we use a range of archival sources to investigate how society in colonial Oaxaca, southern Mexico, was affected by and responded to different types of extreme weather event. Our findings indicate that while drought contributed to antagonism over water supplies between users, it was also used opportunistically to support or challenge cases of water deprivation in legal proceedings. Flooding appears to have been a relatively frequent phenomenon in colonial Oaxaca, but a number of particularly devastating flood events are recorded in the archives. The impact of these events appears to have been determined as much by the timing of the events and level of socio-economic preparedness, as by scale of the flood itself. We then analyse harvest losses due to a range of different climatic phenomena. We highlight how different cross-sections of the community and the local administration responded to these events and suggest that some of the documented harvest losses might have actually been encouraged by high risk agricultural practices.

The climate of Mexico since the Aztec period

Fluctuations in the climate of Mexico since the Aztec period (1345–1994) are established using a variety of primary and secondary historical sources. Drought conditions prevailed when the Aztecs entered the Basin of Mexico, but the climate became wetter shortly after this time and the period 1345–1640 appears to have been relatively wet. From 1640 to 1915 the country experienced a series of prolonged and devastating droughts which were extremely severe in the mid to late 1700s and the late 1800s. This interval coincides with periods of adverse weather conditions elsewhere in the world and may represent the period of the Little Ice Age. Since the early 1900s there has been a shift towards somewhat wetter conditions in Mexico. Variations in precipitation over this period can be explained by changes in the strength of the summer monsoon.