Author:
Webster Ian T.,Ford Phillip W.,Hancock Gary
Abstract
In freshwater systems, phosphorus is adsorbed predominantly to clay within the
sediments. Assuming a linear adsorption/desorption isotherm, rapid
equilibrium adsorption, and transport by molecular diffusion, estimates are
derived for (a) the rates of exchange between the
adsorbed phosphorus pool in the sediments and the dissolved pool in the water
column and (b) time scales to re-establish equilibrium
after a step change in the water column phosphorus concentration. For oxic
sediments, the time scale is of the order of tens of days. Anoxic release is
much faster;the time scale is tens of minutes. The release of treated sewage
at Narrabri abruptly raises the phosphorus concentration in the Namoi River.
The concentration only returns to its original level 10–20 km
downstream. A sediment adsorptive-uptake model underestimates the downstream
phosphorus uptake rates. An alternative model, based on biotic uptake by
Cladophora , describes reality better. It treats
phosphorus transfer as controlled by physical transport processes and by the
phosphorus uptake capacity of the biota. We show also that carp resuspension
is faster than diffusion (6 v. 28 days) in restoring
phosphorus concentrations in the water column after perturbation by rapid
algal drawdown.
Subject
Ecology,Aquatic Science,Ecology, Evolution, Behavior and Systematics,Oceanography
Cited by
33 articles.
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