| Summary: | <p><p>I investigated the usefulness of phytoplankton for the removal of surface water
contaminants. Three experiments, consisting of nine large mesocosms (92.2 m<sup>3</sup>) were
suspended in the flooded DJX uranium pit at Cluff Lake (Saskatchewan, Canada), and
filled with contaminated mine water. During the summer of 2003, each mesocosm was
fertilized with a different amount of phosphorus throughout the 35 day experiment to
stimulate phytoplankton growth, and to create a range in phosphorus load (g) to examine
how contaminants may be affected by different nutrient regimes. Algal growth was
rapid in fertilized mesocosms as demonstrated by chlorophyll a profiles. As phosphorus
loads increased there were significant declines in the surface water concentrations of As,
Co, Cu, Mn, Ni, and Zn. This decline was near significant for uranium. The surface
water concentrations of Ra<sup>226</sup>, Mo, and Se showed no relationship to phosphorus load.
Contaminant concentrations in sediment traps suspended at the bottom of each
mesocosm generally showed the opposite trend to that observed in the surface water,
with most contaminants (As, Co, Cu, Mn, Ni, Ra<sup>226</sup>, U, and Zn) exhibiting a significant positive relationship (<i>P</i> < 0.05) with phosphorus load. Sediment trap concentration of Se
and Mo did not respond to nutrient treatments.</p>
<p>Similar experiments were repeated during the mid- and late-summer of 2004,
with 5 mesocosms being fertilized with phosphorus, and another 4 with both phosphorus
and ammonium to create different nutrient gradients. Results from these experiments
were much more variable than those seen in the experiment conducted in 2003, and small samples (<i>n</i> = 5 for phosphorus treatments and <i>n</i> = 4 for both phosphorus and
ammonium treatments) yielded insufficient statistical power to effectively determine
statistically significant trends. However, contaminant sedimentation tended to respond to
phosphorus treatments in a similar manner as results from 2003; phosphorus-with-ammonium
treatments had little positive effect on contaminant sedimentation rates.</p>
<p>My results suggest that phytoremediation has the potential to lower many surface
water contaminants through the sedimentation of phytoplankton. Based on our results
from 2003, we estimate that the Saskatchewan Surface Water Quality Objectives
(SSWQO) for the DJX pit would be met in approximately 45 weeks for Co, 65 weeks
for Ni, 15 weeks for U, and 5 weeks for Zn if treated using phytoremediation.</p><p>Note:</p><p>Appendix A content (pages 92-95) contains copyrighted material which has been removed. It can be viewed in the original thesis upon request.</p>
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