Assessment Comments
Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, and (4) results of a fish kill investigations in March 2007 and March 2008.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” due to aesthetically objectionable conditions caused primarily by algae blooms. The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due to fish kills in March 2007 and March 2008. Fish consumption uses remain “not assessed” due to a lack of information on which to base an assessment. Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, and (4) results of a fish kill investigations in March 2007 and March 2008.
EXPLANATION: Results from the ISU and UHL lake surveys suggest that the Class A1 uses at Meyers Lake are “partially supported.” Using the median values from these surveys from 2006 through 2010 (approximately 16 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 65, 69, and 72 respectively for Meyers Lake. According to Carlson (1977) the Secchi depth and chlorophyll a values place Meyers Lake in between the eutrophic and hypereutrophic categories, while the total phosphorus value places Meyers Lake in the hypereutrophic category. These values suggest high levels of chlorophyll a and suspended algae in the water, poor water transparency, and very high levels of phosphorus in the water column.
The level of inorganic suspended solids is relatively low at this lake and does not suggest impairment due to high non-algal turbidity. The median inorganic suspended solids concentration at Meyers Lake was 3.0 mg/L, which was the 56th lowest of the 134 monitored lakes.
Data from the 2006-2010 ISU and UHL surveys suggest a moderate population of cyanobacteria exists at Meyers Lake. These data show that cyanobacteria comprised 48% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (11.6 mg/L) was also the 33rd lowest of the 134 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due to fish kills that occurred at Meyers Lake on March 22, 2007 and March 25, 2008. The first fish kill was attributed to natural conditions (winter kill) and affected 200 fish. The 2008 fish kill was also attributed to natural conditions (winter kill) and affected 2800 fish. According to IDNR’s assessment/listing methodology, the occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or waterbody reach during the most recent assessment period (2008-2011) indicates a severe stress to the aquatic community and suggests that the aquatic life uses should be assessed as “impaired.” If a cause of the kill was not identified during the IDNR investigation, or if the kill was attributed to non-pollutant causes (e.g., winterkill), the assessment type will be considered “evaluated.” Such assessments, although suitable for Section 305(b) reporting, lack the degree of confidence to support addition to the state Section 303(d) list of impaired waters (IR Category 5). Waterbodies affected by such fish kills will be placed in IR subcategories 2b or 3b and will be added to the state list of waters in need of further investigation.
Information from the IDNR Fisheries Bureau supports that the Class B(LW) uses are partially supported due to the lake’s susceptibility to fish kills due to its shallow depth and nutrient concentrations. Results from the ISU and UHL lake surveys suggest the Class B(LW) uses of Meyers Lake are “fully supported.” The ISU and UHL lake survey results show generally good chemical water quality at Meyers Lake. During 2006-2010 there were no violations of the Class B(LW) criterion for ammonia in 16 samples or of the Class B(LW) criterion for dissolved oxygen in 16 samples. There was 1 violation of the Class B(LW) criterion for pH in 16 samples (6%). Based on IDNR’s assessment methodology, however, these violations are not significantly greater than 10% of the samples and therefore do not suggest an impairment of the Class B(LW) uses of Meyers Lake.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this lake.
