Assessment Comments
Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), and (3) information from the IDNR Fisheries Bureau.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” due to violations of the Class A1 criterion for pH. The Class B(LW) (aquatic life) uses are assessed (monitored) as “partially supported” due to violations of the Class B(LW) criterion for pH. Fish consumption uses are “not assessed” due to a lack of fish contaminant monitoring at this lake. Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), and (3) information from the IDNR Fisheries Bureau.
EXPLANATION: For the 2008 reporting cycle, the Class A1 (primary contact recreation) uses for Center Lake are assessed as “partially supported” due to violations of the Class A1 criterion for pH. Additional results from the ISU statewide survey of lakes and the UHL ambient lake monitoring program, however, do not suggest impairment of the Class A1 uses at Center Lake. Using the median values from these surveys from 2002 through 2006 (approximately 23 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 61, 62, and 70 respectively for Center Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus index values all place Center Lake in the between the eutrophic and hypereutrophic categories. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, moderately poor water transparency, and very high levels of phosphorus in the water column.
The levels of inorganic suspended solids at this lake were moderately high and do not suggest an impairment due to non-algal turbidity. The median level of inorganic suspended solids in Center Lake (3.6 mg/L) was the 56th lowest median of the 132 lakes sampled by the ISU and UHL surveys.
Data from the 2002-2006 ISU and UHL surveys suggest that a moderately large population of cyanobacteria exists at Center Lake. These data show that cyanobacteria comprised 99% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (19.6 mg/L) was also the 64th highest of the 132 lakes sampled.
The Class B(LW) (aquatic life) uses for Center Lake are assessed (monitored) as “partially supported” due to violations of the Class A1,B(LW) criterion for pH. The ISU and UHL lake surveys data from 2002-2006 show no violations of the Class B(LW) criterion for ammonia in 16 samples, or dissolved oxygen in 23 samples. The data for pH, however, show 5 violations of the Class A1,B(LW) criterion for pH in 22 samples (23%). Based on IDNR’s assessment methodology, these violations are significantly greater than 10% of the samples and therefore constitute an impairment (partial support/monitored) of the Class A1,B(LW) uses of Center Lake. These violations likely reflect the high levels of primary productivity at Center Lake and do not reflect the input of pollutants into this lake.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this lake.
