Processes Regulating the Growth and Distribution of Phytoplankton, and the
Production of Taste and Odour Compounds in Drinking Water Reservoirs
John-Mark Davies, Ph.D. Candidate
NSERC-IRC Program, University of Victoria
Background: Sustaining clean and safe drinking water sources is increasingly becoming a global priority. The means of attaining and maintaining clean drinking water
sources requires effective policies that identify, document, and reduce watershed risks (Davies & Mazumder 2003). Phytoplankton naturally occur in all lakes and reservoirs
(Figure 1); however, they can increase the risk to human health by producing toxins and by increasing disinfection byproduct formation during water treatment. Water
purveyors are also keen to reduce unnecessary costs associated with treating water for aesthetic purposes, such as removing unpleasant tastes & odours and filter clogging
algae. Therefore, understanding processes that regulate phytoplankton distribution is a vital component for the environmental management of drinking water sources. This
knowledge has the potential to reduce the cost of supplying water by removing or delaying the need for additional treatment plants and optimizing or reducing the occurrence of
taste and odour events.
Odour Production: Phytoplankton biomass is a strong predictor of odour in source water (Figure 2; Davies et al #1 in review). Furthermore, the type of odour (e.g.
earthy/beets, decomposing vegetation, or grassy) in source water is also dependent on biomass. Our study examining the principle source of odours in the City of Victoria’s
drinking water (e.g. source water vs. distribution system) will allow for more effective management of this important drinking water issue.
Figure 1: Some common phytoplankton.
n=4
Top (left to right): Chrysosphaerella,
Dinobryon, and Mallomonas
FPA Odour Intensity
n = 44
Species in this group (chrysophytes) can
produce taste and odour compounds
and can clog filters.
Bottom (left to right): Microcystis,
Anabaena, and Aphanizomenon
Species in this group (Cyanobacteria)
can produce taste and odour compounds
and toxins
4
n = 41
3
n = 96
2
n = 76
1
n = 13
0
0
Nutrients: One of the most studied and understood concepts regarding phytoplankton growth is the relationship
2
4
6
µ g L-1)
Chlorophyll a (µ
between the concentration of phosphorus and phytoplankton biomass. However, the plankton community can be deficient
in more than one nutrient, and major deficiencies may be predicable from phytoplankton species size (Davies et al #2 in
review). Understanding the strength of these deficiencies, in combination with other growth and death processes, will help
us predict changes in species composition.
Figure 2: Relationship between phytoplankton
biomass (chlorophyll a) and odour (FPA = flavour
profile analysis) compounds in our study lakes
(1999-2002)
Growth and Death: Linking process that affect phytoplankton growth and death, such as nutrient availability
and nutrient stress, light, temperature, composition of herbivores and plankton sinking rates will lead to a better
understanding of which factors are most important for determining phytoplankton species composition in our lakes
and reservoirs.
Conclusion: The effectiveness of management and policy development are dependent upon a concerted scientific
effort to understand all aspects of drinking water systems. Ideally drinking water protection should focus on raising
the quality of source water rather than increasing the sophistication of treatment since treatment alone is not failsafe
(Davies & Mazumder 2003). Phytoplankton are only one component of drinking water systems; however, because of
their established importance in defining water quality, understanding phytoplankton dynamics remains a critical goal
to the management of drinking water sources.
Percent difference from annual mean
Photosynthesis: Many studies rely on static measurements; however, determining when phytoplankton communities have maximal rates of photosynthesis is vital to
understanding the timing of major annual species compositional changes. By studying many lakes it is possible to understanding why processes are different between lakes.
Our recent work (Davies et al #3 in review) implicates the size of food webs (i.e. zooplankton size) as an important predictor of when phytoplankton photosynthesis is greatest
in coastal lakes (Figure 3).
250
Sooke Lake Reservoir
Maxwell Lake
200
150
100
50
0
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Davies, J.M. and A. Mazumder. 2003. Health and environmental policy issues in Canada: the role of watershed management in
sustaining clean drinking water quality at surface sources. Journal of Environmental Management. 68:273-286
Davies, J.M. M. Roxborough, and A. Mazumder. Origins and implications of drinking water odours in BC lakes and reservoirs.
#1 In Review
Davies, J.M. W.H. Nowlin and A. Mazumder. Temporal changes in nitrogen and phosphorus co-deficiency of plankton in Coastal
and Interior British Columbia. #2 In Review
Davies, J.M. W.H. Nowlin and A. Mazumder. Variations in temporal 14C-plankton photosynthesis between warm-monomictic lakes
of coastal British Columbia. #3 In Review
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Figure 3: Timing of maximal photosynthesis in
drinking water lakes for the City of Victoria
(Sooke) and Ganges (Maxwell). Sooke has large
Daphnia,whereas Maxwell has small zooplankton