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), (3) information from the IDNR Fisheries Bureau, and (4) results of a fish kill investigation on March 22, 2007.
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 a fish kill in March 2007. 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 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), (3) information from the IDNR Fisheries Bureau, and (4) results of a fish kill investigation on March 22, 2007.
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 2002 through 2006 (approximately 20 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 65, 65, 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 2.6 mg/L, which was the 30th lowest of the 132 monitored lakes.
Data from the 2002-2006 ISU and UHL surveys suggest a moderate population of cyanobacteria exists at Meyers Lake, which may contribute to impairment at this lake by occasionally causing poor water clarity. These data show that cyanobacteria comprised 73% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (13.9 mg/L) was also the 55th lowest of the 132 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due to a fish kill that occurred at Meyers Lake on March 22, 2007. The fish kill was attributed to natural conditions (winter kill) and affected 200 fish. According to the IDNR 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 (2004-2007) 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 2002-2006 there were no violations of the Class B(LW) criterion for ammonia in 14 samples or of the Class B(LW) criterion for dissolved oxygen in 20 samples. There were 4 violations of the Class B(LW) criterion for pH in 20 samples (20%). 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.
