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Microcystins in Eagle Creek Reservoir

Citizens Water in partnership with CEES-IUPUI has been monitoring the water quality of Eagle Creek Reservoir that provides drinking water to the city of Indianapolis. Between 2009 and 2013, a total of 474 samples were analyzed for the detection of microcystins (cyanobacterial toxins) in the reservoir’s raw water. Toxin analyses were realized using the ELISA-ADDA method with a Limit Of Detection (LOD) of 0.15 μg/L. The percent of microcystin detections is variable between years and ranges from 3.9% to 37.8%. In average, 20% of the samples were positive for microcystins over the last five years of monitoring in Eagle Creek Reservoir (see Table below). The average concentration of all detections is 0.31 μg/L; with a maximum value of 1.53 μg/L that occurred in November 2009.

 

Year

N

Detect

%Detect

Range (μg/L)*

2009

74

28

37.8

ND-1.53

2010

97

32

33.0

ND-0.88

2011

97

8

8.2

0.19-0.40

2012

104

23

22.1

ND-0.32

2013

102

4

3.9

0.20-0.51

Total

474

95

20.0

ND-1.53

*ND = Non-Detected

Most occurrences of microcystins are found during the spring (April to June) and the fall (September to November). These months correspond to periods when the reservoir is fully mixed. During the summer months (July and August), despite elevated algal cell densities (>100,000 cells/mL) in the water, no toxins are detected (below LOD – see chart below). Recreation advisories regarding Indiana Lakes and Reservoirs are posted weekly on IDEM website (http://www.in.gov/idem/algae/).

The State of Indiana uses the recreational water guidance value of 20 μg/L for high risk exposure to microcystins. Eagle Creek Reservoir never experienced such elevated concentrations in its raw waters since the beginning of the monitoring program.

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