Estimating streamwater concentrations of aluminium released from streambeds during 'acid episodes'
Title:
Estimating streamwater concentrations of aluminium released from streambeds during 'acid episodes'
Author:
Tipping, E. Hopwood, J.
Appeared in:
Environmental technology
Paging:
Volume 9 (1988) nr. 7 pages 703-712
Year:
1988-07
Contents:
Rates of release of monomeric aluminium - Alm - were determined for streambed materials placed in a laboratory channel and exposed to acid water, and values of the release rate coefficient, R (μmol Al released per m2 of bed per second) were calculated. Estimates of R were also made from the reported results of experiments in which streams were artificially acidified. The values of R ranged from 0.1 to 3.2 μmol m-2 s-1. They decreased with increase in pH, and were greater for beds containing substantial amounts of the liverwort Nardia compressa than for pebble and/or gravel (mineral) beds. Calculations, using, the estimates of R, were performed to assess the contribution of bed-derived Al to streamwater concentrations, under conditions where acid water enters stream channels having exchanged negligible H+ for Al3+ or base cations in the soil. For typical high-discharge conditions, considerable concentrations of Al are possible. For a liverwort-rich bed exposed to water of initial pH 3.5 there may be as much as 60 μM Al in the streamwater. At the other extreme, a mineral bed subjected to pH 4.5 water would yield less than 1 μM Alm. Streambed stores of releasable Al appear sufficient to supply Al to the water for significant lengths of time.
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