Assessment Comments
Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2009-2012 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted in 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 2009-2012 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program in 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 2014 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 2014 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 2008-2012(approximately 14 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 61, 63, 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 moderatley high of chlorophyll a and suspended algae in the water, moderately poor water transparency, and moderately high levels of phosphorus in the water column. The Secchi depth and chlorophyll a index values are both below the impairment trigger of 65, however, Lake Meyer was listed as "partially supporting" the Class A1 uses for the 2012 assessment/listing cycle for elevated levels of chlorophyll a (TSI = 65). Based on IDNR's assessment methodology, median-based TSI values for both chlorophyll a and Secchi depth must be 63 of less for two consecutive assessment/listing cycles before a lake can be removed from the states Section 303(d) list. Therefore, the Class A1 will remain listed as "partially supported" due to algae for the 2014 IR cycle.
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 2.3 mg/L, and ranked 16th of the 134 monitored lakes.
Data from the 2008-2012 ISU and UHL surveys suggest a large 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 93% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (34.7 mg/L) was and ranked 106th 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 2008-2012, there were no violations of the Class B(LW) criterion for ammonia in 14 samples. There were two violations of the Class B(LW) criterion for dissolved oxygen in 14 samples (14%). 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 was 1 violation of the Class A1,B(LW) criterion for pH in 14 samples (7%). 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.
