TRACE-ELEMENT ACCUMULATION BY HYGROHYPNUM-OCHRACEUM IN THE UPPER RIO-GRANDE BASIN, COLORADO AND NEW-MEXICO, USA

Accumulation of 12 trace elements by transplanted aquatic bryophytes ( Hygrohypnum ochraceum) was determined at 13 sites in the Rio Grande an d tributary streams in southern Colorado and northern New Mexico as pa rt of the U.S. Geological Survey's National Water-Quality Assessment P rogram. The purposes of the study were to determine the spatial distri bution of trace elements in relation to land-use practices in the uppe r Rio Grande Basin, compare accumulation rates of metals ill bryophyte s at sites contaminated by trace elements, and evaluate transplanted a quatic bryophytes as a tool for examining the bioavailability of trace elements in relation to concentrations in water and bed sediment. Con centrations of Cd, Cu, Pb, and Zn in bryophytes, water, and bed sedime nt were significantly higher at sites that receive drainage from minin g areas than at sites near agricultural or urban activities. Concentra tions of most trace elements were lower in a tributary stream below an urban source than at sites near mining or agricultural use. Concentra tions of Cu and Zn in bryophytes correlated with concentrations in wat er and bed sediment. In addition, bryophyte concentrations of As, Cd, and Pb correlated with concentrations in bed sediment. Transplanted br yophytes can provide an indication of bioavailability. Rates of accumu lation were related to the magnitude of ambient trace-element concentr ations; maximal uptake occurred during the first 10 d of exposure. Tra ce-element concentrations in transplanted bryophytes could potentially be used to predict water and sediment concentrations that represent a n integration of conditions over short to intermediate lengths of time , rather than instantaneous conditions as measured using water samples .