Seasonal and spatial patterns of metals at a restored copper mine site II. Copper in riparian soils and Bromus carinatus shoots

Soil and plants were sampled throughout winter and spring near a perennial stream traversing a restored mine site in a winter–rainy climate. Within 1 m of an acidic reach of the stream, soil had pH 3–5 and 50–100 μg/g “bioavailable” copper (extractable with 0.01 M CaCl2). Soil 2–3 m from the stream had pH 5–8 and lower (less than 3 μg/g) bioavailable copper. “Oxide-bound” copper (extractable with 2 N HCl) was 50–100 μg/g at most locations. Copper concentrations in the shoots of field-collected Bromus carinatus declined from 20 μg/g in winter to 2 μg/g in spring at all sampling sites. A similar temporal pattern was found in plants grown under controlled conditions. Thus B. carinatus has a developmental program for control of shoot copper concentration, causing a seasonally-varying pattern of copper phytoaccumulation over a large range of copper availability in the soil.