Author

Ruth Indrick

Publication Date

2008

Document Type

Honors Thesis

Department

Geosciences

Abstract

In viticulture, the terroir, or growing environment, of the grapevine determines the characteristics and quality of the wine that is produced. Terroir is influenced by all the interactions that take place between the atmosphere, lithosphere, and biosphere within the critical zone of the earth. The critical zone extends from the upper reach of vegetation to the lower limits of groundwater. This study examines the relationships between three components of the critical zone, rocks, soils, and plants, in vineyards in the region west of Milton-Freewater, Oregon to determine the sources of the elements found in the soil and the plants and the processes of selection that occur through weathering, exchange, and plant uptake. Samples of soil and leaves were collected from three sites at each of nine vineyards to the northwest of Milton-Freewater, Oregon, and cobbles were also collected from four of these sites. The bulk composition of Columbia River Flood Basalt cobbles in the soil was measured in order to compare the soil composition to its basaltic parent material. The soils were analyzed for organic and inorganic carbon, bulk composition, and exchangeable cations. An acid leach from the grape leaves was analyzed to determine the relative chemical composition of the leaves of the plant. The major and trace element compositions of the soils and cobbles were relatively consistent across all sampled sites. The chemical composition of the soils was similar to that of the cobbles. In all the vineyards, certain elements were concentrated (A1) or depleted (Ca, MG, K, P) as a result of modification of the soil through weathering and plant uptake. Lead and zinc were the only two elements with values that fluctuated widely both between and within vineyards. This variation is likely due to the use of lead arsenate pesticides when the land was previously cultivated in orchards. The concentration of exchangeable cations in the soil are also relatively consistent across all sites. Although these concentrations differ from those found in the bulk composition of the soil, the changes can be explained through selection during weathering and cation exchange. The chemical compositions of the grapevine leaves are also relatively consistent across the vineyards, and the differences between the composition of the plants and soils can be explained through the mechanisms of selective uptake and transport within the plant. Humans appear to have little impact on the critical zone interactions that influence the elemental compositions of the soil and plants, and individual decisions made by the vineyard managers about the best way to manage vines did little to change the composition of the plants. The place and its specific geologic setting and climate, not the human management, have a larger influence on the plant composition and the terroir of the region

Comments

vi, 71 leaves : col. ill. Thesis (Honors)--Smith College, Northampton, Mass., 2008. Includes bibliographical references (leaves 67-71)

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