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), 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 aesthetically objectionable conditions caused by algae blooms. 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 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), 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 2012 assessment/listing cycle (algae growth) are potentially addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved).
EXPLANATION: For the 2012 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 2006 through 2010 (approximately 16 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 60, 65, and 65 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, moderately 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 2.0 mg/L, which was the 28th lowest of the 134 monitored lakes.
Data from the 2006-2010 ISU and UHL surveys suggest a relatively small population of cyanobacteria exists at Lake Meyer, which does not cause an additional impairment due to nuisance aquatic life at this lake. These data show that cyanobacteria comprised 16% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (6.7 mg/L) was the 13th lowest of the 134 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due nutrient loading and eutrophic conditions at Lake Meyer. This BPJ-based potential impairment is not appropriate for Iowa’s Section 303(d) list of impaired waters (Integrated Report Category 5) but is appropriate for IR Category 3b of Iowa’s Integrated Report and Iowa’s list of waters in need of further investigation. Results of the ISU and UHL lake surveys, however, suggest good chemical water quality at Lake Meyer. Based on data from the ISU and UHL lake surveys from 2006 through 2010, there were no violations of the Class B(LW) criterion for ammonia in 16 samples. There was one violation of the Class B(LW) criterion for dissolved oxygen in 16 samples (6%). Based on IDNR's assessment methodology these violations are not significantly greater than 10% of the samples and therefore do not constitute an impairment of the Class B(LW) uses. Data from the ISU and UHL surveys show that there were 2 violations of the Class A1,B(LW) criterion for pH in 16 samples (12%). 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.
