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ORIGIN OF THE TASTE AND ODOR PROBLEM
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- 2.3 ORIGIN OF THE TASTE AND ODOR PROBLEM 2.3.1 Reservoirs
- Lake Pleasant 0 20 40 60 80 100 120
- Dec-00 Feb-01 Apr-01 Jun-01 Aug-01 Oct-01 Dec-01 Feb-02
- Blue-green count, /mL Epilimnion-MIB Blue-greens, /mL
- Bartlett Lake 0 10 20 30 40 50 60
- Aug-99 Oct-99 Dec-99 Feb-00 Apr-00 Jun-00 Aug-00 Oct-00
- Apr-02 MIB, ng/L 0 50 100 150 200 250
- May-01 Jul-01 Sep-01 Nov-01 Jan-02 Mar-02 Change in MIB, ng/L
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2.3.1 Reservoirs
The reservoirs were major sources of MIB produced by planktonic or shallow periphytic blue-green algae. MIB concentrations in the epilimnion were generally greater than in the hypolimnion when the reservoirs were stratified (usually May through October) (Figures 2-6 through 2-8). In some instances, peaks in numbers of blue-green algae were associated with MIB peaks, whereas in other cases there did not appear to be a relationship. The algae blooms associated with peak MIB levels were mainly composed of filamentous forms in the family Oscillatoriaceae (see Figure 4-1).
The culprit organisms tended to favor elevated temperatures typical of the summer and early fall. They produce MIB or geosmin that accumulates in the cells. Although these compounds may leak from the living cells, the cells retain much higher concentrations than the surrounding aqueous environment. When cells die and lyse, larger quantities of MIB or geosmin are released into the water. Some of these organisms also appear to be capable of turning MIB/geosmin production/release on and off. Furthermore, production can be influenced by environmental conditions.
MIB production in the reservoirs is not always a problem for downstream water users. During summer stratification, MIB is produced in the epilimnion and water is released from the hypolimnion. If the stratification is strong enough to prevent vertical mixing, water being released from the bottom may have low MIB concentrations, even when MIB concentrations in the epilimnion are very high. When stratification breaks down and the reservoir mixes, MIB concentrations in the outlet water often increase. Predicting where and when MIB releases from reservoirs occur is discussed in Section 4.
0 20 40 60 80 100 120 Aug-99 Oct-99 Dec-99 Feb-00 Apr-00 Jun-00 Aug-00 Oct-00 Dec-00 Feb-01 Apr-01 Jun-01 Aug-01 Oct-01 Dec-01 Feb-02 Apr-02 MIB, ng/L 0 20 40 60 80 100 Blue-green count, #/mL Epilimnion-MIB Blue-greens, #/mL
Figure 2-6. MIB and blue-green algae numbers for Lake Pleasant. 12
0 10 20 30 40 50 60 Aug-99 Oct-99 Dec-99 Feb-00 Apr-00 Jun-00 Aug-00 Oct-00 Dec-00 Feb-01 Apr-01 Jun-01 Aug-01 Oct-01 Dec-01 Feb-02 Apr-02 MIB, ng/L 0 50 100 150 200 250 300 Blue-green count, #/mL Epilimnion-MIB Blue-greens, #/mL
Figure 2-7. MIB and blue-green algae numbers for Bartlett Lake.
0 20 40 60 80 100 120 Aug-99 Oct-99 Dec-99 Feb-00 Apr-00 Jun-00 Aug-00 Oct-00 Dec-00 Feb-01 Apr-01 Jun-01 Aug-01 Oct-01 Dec-01 Feb-02 Apr-02 MIB, ng/L 0 50 100 150 200 250 300 Blue-green counts, #/mL Epilimnion-MIB Blue-greens, #/mL
Figure 2-8. MIB and blue-green algae numbers for Saguaro Lake. 2.3.2 Arizona Canal
MIB is also produced within the Arizona Canal. On many occasions, the Arizona Canal was the predominate source of MIB. MIB production in Figures 2-9 and 2-10 was calculated by subtracting the MIB concentration at the head of the Arizona Canal below the CAP inlet (site R13) from the MIB concentration at WTPs. “MIB production,” therefore, refers to MIB produced by culprit algae growing in the Arizona Canal above each of the water treatment plants.
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10 20 30 40 50 60 Sep-99 Nov-99 Jan-00 Mar-00 May-00 Jul-00 Sep-00 Nov-00 Jan-01 Mar-01 May-01 Jul-01 Sep-01 Nov-01 Jan-02 Mar-02 Change in MIB, ng/L Figure 2-9. MIB production within the Arizona Canal above the Squaw Peak WTP, ng/L.
0 10 20 30 40 50 60 Sep-99 Nov-99 Jan-00 Mar-00 May-00 Jul-00 Sep-00 Nov-00 Jan-01 Mar-01 May-01 Jul-01 Sep-01 Nov-01 Jan-02 Mar-02 Change in MIB, ng/L Figure 2-10. MIB production within the Arizona Canal above the Deer Valley WTP, ng/L
During the winter and early spring, there was little MIB production in the Arizona Canal above the Squaw Peak WTP (Figure 2-9), and occasionally even a net loss. Peak MIB production in the Arizona Canal above the Squaw Peak WTP (10-20 ng/L) generally occurred in September and October.
MIB was produced in the Arizona Canal above the Deer Valley WTP almost every month of the year (Figure 2-10). Average MIB production often exceeded 20 ng/L from August through November. During some years, MIB production in the Arizona Canal above the Deer Valley WTP exceeded 50 ng/L.
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