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 poor water clarity caused primarily by algal turbidity. The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due to eutrophic conditions and nutrient loading at this lake. Fish consumption uses remain “not assessed.” 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.
Note: A TMDL for nutrients and siltation at Lake Meyer was prepared by IDNR and approved by EPA in 2005. Because all Section 303(d) impairments identified for the 2006 and 2008 assessment/listing cycle (algal growth and turbidity) are potentially addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved).
EXPLANATION: For the 2008 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Lake Meyer are assessed as “partially supported” based on information from the ISU lake survey and UHL lake monitoring program. 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 67 respectively for Lake Meyer. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Lake Meyer in between the eutrophic and the hypereutrophic categories. These values suggest high levels of chlorophyll a and suspended algae in the water, poor water transparency, and high levels of phosphorus in the water column.
Based on data from the ISU and UHL lake surveys, the level of inorganic suspended solids was relatively low at this lake and does not suggest impairment due to high non-algal turbidity. The median inorganic suspended solids concentration at Lake Meyer was 3.0 mg/L, which was the 45th lowest of the 132 monitored lakes.
Data from the 2002-2006 ISU and UHL surveys suggest a moderately large population of cyanobacteria exists at Lake Meyer, which contributes to occasional algal blooms and impairment at this lake. These data show that cyanobacteria comprised 92% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (20.8 mg/L) was the 61st highest of the 132 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due nutrient loading and eutrophic conditions at Lake Meyer. Results of the ISU and UHL lake surveys suggest good chemical water quality at Lake Meyer. Based on data from the ISU and UHL lake surveys from 2002 through 2006, there were no violations of the Class B(LW) criterion for ammonia in 14 samples or the Class B(LW) criterion for dissolved oxygen in 19 samples. Data from the ISU and UHL surveys show that there were three violations of the Class A1,B(LW) criterion for pH in 20 samples (15%). Based on IDNR’s assessment methodology, however, these violations are not significantly greater than 10% of the samples and therefore do not constitute an impairment of the Class B(LW) uses of Lake Meyer.
Fish consumption uses are "not assessed" due to the lack of recent fish contaminant monitoring at this lake. The most recent fish contaminant monitoring was conducted in 1994 as part of the U.S. EPA/IDNR (RAFT) program. Although results of the 1994 RAFT monitoring at Lake Meyer indicated very low levels of contaminants and “full support” of the fish consumption uses, these data are now considered too old (greater than ten years) to characterize current water quality conditions.
