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), (3) information from the IDNR Fisheries Bureau, and (4) results of U.S. EPA/IDNR fish tissue (RAFT) monitoring in 2009 and 2010.
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 (monitored) as “partially supported” based on results of fish tissue monitoring in 2009 and 2010. 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), (3) information from the IDNR Fisheries Bureau, and (4) results of U.S. EPA/IDNR fish tissue (RAFT) monitoring in 2009 and 2010.
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 the Section 303(d) impairment for mercury in fish tissue was not addressed by the TMDL, this waterbody will be moved to IR Category 5a (impaired; TMDL needed) for the 2012 assessment/listing cycle.
EXPLANATION: For the 2012 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 2006 through 2010 (approximately 16 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 73, 65, and 72 respectively for Lake Miami. According to Carlson (1977) the Secchi depth and total phosphorus values place Lake Miami in the hypereutrophic category while the chlorophyll a value places Lake Miami in between the eutrophic and hypereutrophic categories. These values suggest high levels of chlorophyll a and suspended algae in the water, very 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 8.5 mg/L, which was the 23rd highest of the 134 monitored lakes.
Data from the 2006-2010 ISU and UHL surveys suggest a moderately large population of cyanobacteria exists at Lake Miami. These data show that cyanobacteria comprised 60% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (18.3 mg/L) was the 59th lowest of the 134 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. Information from the IDNR Fisheries Bureau suggests that turbidity remains an issue at this 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 2006 through 2010, there were no violations of the Class B(LW) criterion for ammonia in 16 samples, no violations of the Class B(LW) criterion for dissolved oxygen in 16 samples, and no violations of the Class B(LW) criterion for pH in 16 samples. Based on IDNR’s assessment methodology these results do not suggest impairment of the Class B(LW) uses.
Fish consumption uses are assessed (monitored) as “partially supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Lake Miami in 2009 and 2010. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes. The fish contaminant data generated from the 2009 RAFT sampling conducted at Lake Miami show that levels of mercury are sufficiently high for concern and thus justify follow-up monitoring. Results from the 2009 sampling show that the level of mercury in the sample of largemouth bass fillets (0.353 ppm) exceeds the 1 meal/week trigger level (0.30 ppm) as defined in Iowa’s revised (2007) fish consumption advisory protocol. According to IDNR’s assessment methodology, the single occurrence of contaminant above an advisory trigger level neither warrants issuance of an advisory nor indicates impairment of the fish consumption uses: two consecutive samplings that show contaminant levels are above the trigger level in fillet samples are needed to justify issuance of an advisory. Follow-up sampling conducted in 2010 showed that levels of mercury in largemouth bass (0.394 ppm) again exceeded the 1 meal/week trigger level (0.30 ppm). Thus a one meal per week fish consumption advisory was issued for Lake Miami and the fish consumption uses are assessed as “partially supported.” Levels of primary contaminants in channel catfish were all below the advisory trigger levels: mercury: 0.109 ppm; total PCBs: 0.09 ppm; technical chlordane: <0.03 ppm.
