Geoarchaeological Investigations in the Upper Senegal River Watershed of Southeast Senegal.

A geoarchaeological study was recently completed as part of the Sabadala Gold Mine Project, the first systematic cultural resources management project conducted in Senegal. Research objectives of this study included: (1) modeling the potential for buried archaeological sites in proposed impact areas (e.g., proposed mining, tailing piles, reservoirs, and haul roads); and (2) evaluating the anthropogenic effects of traditional agricultural management practices on soil quality and agricultural sustainability. A map of buried site sensitivity was produced for different landforms, based on interpretations of soil development and geomorphic process associated with different landforms and landscape positions. Buried site probability was interpreted as highest for the floodplains, but the site types there are most likely dominated by agricultural fields that leave few archaeological traces. An ethnopedology study was completed to document: (1) traditional agricultural management practices and conservation measures for different farming systems (e.g., rain-fed, runoff, and floodwater recession systems); (2) an indigenous classification of agricultural soils and landforms; and (3) strategies that farmers use for recognizing soil degradation. Anthropogenic effects on soil quality were quantified by measuring and comparing soil properties (e.g., pH, organic carbon, nitrogen, calcium, potassium, magnesium, available phosphorus, particle-size distributions, and unsaturated hydraulic conductivity) for 14 agricultural fields relative to eight control fields from nearby uncultivated areas in analogous soil and landform settings. Soil test data identified no evidence of soil degradation in the fields. Malinke farmers have developed a number of techniques for recognizing early stages of degradation that prompt their slash and burn fields to be shifted; these techniques rely on observations of: (1) a weed known as lanlango that is the first plant to grow and die in fields; (2) growth of a grass known as tenengene kotio that migrates into fields and quickly becomes dominant over the crops; (3) formation of a gray acidic soil known as dougou khoto khouno; and (4) poor crop growth. Floodplains have the highest nutrient status but because floodplain soils are poorly aerated during the growing season, the gravelly and loamy soils of the first terraces are the prime agricultural land for the main crops (e.g., sorghum, maize, and peanuts). Mitigating the loss of agricultural land to industrial mining activities will require careful consideration of indigenous crops and management practices. If agriculture is expanded and intensified on marginal farm land outside of alluvial valleys, where top soils are thinner, less resilient and more erodible, soil degradation risks will be increased.