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 U.S. EPA/IDNR fish tissue (RAFT) monitoring in 2001.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to poor water clarity caused by both algal and non-algal turbidity. The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due to excessive algal production, reduced water transparency related to presence of common carp populations, and sedimentation problems in the lake. Fish consumption uses are assessed (evaluated) as “fully supported.” 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 U.S. EPA/IDNR fish tissue (RAFT) monitoring in 2001.
Note: A TMDL for siltation and nutrients at Lake Miami was prepared by IDNR and approved by EPA in 2001; thus, this lake was placed into IR Category 4a (TMDL approved) for the 2004 assessment/listing cycle. Because all the Section 303(d) impairments identified for the 2008 assessment/listing cycle (turbidity, algal growth) are addressed by the TMDL, this waterbody remains in IR Category 4a.
EXPLANATION: For the 2008 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Lake Miami are assessed (monitored) as “not 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 67, 71, and 72 respectively for Lake Miami. According to Carlson (1977) the chlorophyll a and total phosphorus values place Lake Miami in the hypereutrophic category, while the Secchi depth value places Lake Miami in between the eutrophic and hypereutrophic categories. These values suggest very high levels of chlorophyll a and suspended algae in the water, poor water transparency, and very 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 high at this lake and suggests that non-algal turbidity contributes to poor water clarity and the impairment at this lake. The median inorganic suspended solids concentration at Lake Miami was 7.0 mg/L, which was the 38th highest of the 132 monitored lakes.
Data from the 2002-2006 ISU and UHL surveys suggest a moderately large population of cyanobacteria exists at Lake Miami, which contributes to occasional algal blooms and the impairment for poor water clarity at this lake. These data show that cyanobacteria comprised 84% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (16.5 mg/L) was the 72nd highest of the 132 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due to reduced water transparency related to the presence of common carp populations and sedimentation problems in the lake. Results of the ISU and UHL lake surveys suggest good chemical water quality at Lake Miami. 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, one violation of the Class B(LW) criterion for dissolved oxygen in 20 samples (5%), and one violation of the Class B(LW) criterion for pH in 20 samples (5%). Based on IDNR’s assessment methodology none of these violations are significantly greater than 10% of the samples and therefore do not constitute an impairment of the Class B(LW) uses of Lake Miami.
Fish consumption uses were assessed (evaluated) as “fully supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring at Lake Miami in 2001. Because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). The composite samples of fillets from channel catfish and largemouth bass had low levels of contaminants. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses. The fish contaminant data generated from the 2001 RAFT sampling conducted at Lake Miami show that the levels of contaminants do not exceed any of the advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.
