Assessment Comments
Assessment is based on: (1) results of the IDNR-UHL beach monitoring program from 2006 through 2008, (2) results of the statewide survey of Iowa lakes conducted from 2004 through 2007 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2005 through 2008 by University Hygienic Laboratory (UHL), (4) information from the IDNR Fisheries Bureau, and (5) results from the EPA/IDNR fish tissue monitoring program in 2001, 2005, and 2007.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to levels of indicator bacteria that exceed state water quality standards. The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported.” Fish consumption uses are assessed (monitored) as “partially supported” due to the existence of a fish consumption advisory. The Class C (drinking water) uses are “not assessed” due to a lack of information upon which to base an assessment. Sources of data for this assessment include (1) results of the IDNR-UHL beach monitoring program from 2006 through 2008, (2) results of the statewide survey of Iowa lakes conducted from 2004 through 2008 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2005 through 2008 by University Hygienic Laboratory (UHL), (4) information from the IDNR Fisheries Bureau, and (5) results from the EPA/IDNR fish tissue monitoring program in 2001, 2005, and 2007.
Note: A TMDL for turbidity at Nine Eagles Lake was prepared by IDNR and approved by EPA in 2001. Through implementation of this TMDL, water clarity at this lake had improved such that the lake was de-listed for the 2004 assessment/listing cycle. Because, however, the 2006, 2008, and 2010 Section 303(d) impairments due to indicator bacteria and mercury in fish tissue at Nine Eagles Lake were not addressed in the TMDL, this waterbody remains in Category 5a (impaired; TMDL required) for the 2010 cycle.
EXPLANATION: Results of IDNR beach monitoring from 2006 through 2008 suggest that the Class A1 uses are "not supported." Levels of indicator bacteria at Nine Eagles Lake beach were monitored once per week during the primary contact recreation seasons (May through September) of 2006 (28 samples), 2007 (15 samples), and 2008 (24 samples) as part of the IDNR beach monitoring program. According to IDNR’s assessment methodology, all thirty-day geometric means for the three-year assessment period must be less than the state’s geometric mean criterion of 126 E. coli orgs/100 ml for results of beach monitoring to indicate “full support” of the Class A1 (primary contact recreation) uses. If a 5-sample, 30-day geometric mean exceeds the state criterion of 126 orgs/100 ml during the three-year assessment period, the Class A1 uses should be assessed as “not supported”. This assessment approach is based on U.S. EPA guidelines (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
At Nine Eagles Lake beach, the geometric means of 11 thirty-day periods during the summer recreation seasons of 2006, 2007 and 2008 exceeded the Iowa water quality standard of 126 E. coli orgs/100 ml: 9 of 24 geometric means violated in 2006, 0 of 11 geometric means violated in 2007, and 2 of 20 geometric means violated in 2008. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was 29% in 2006, 0% in 2007 and 21% in 2008. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest impairment (nonsupport) of the Class A1 (primary contact recreation) uses.
Results from the ISU and UHL lake surveys, however, suggest that the Class A1 uses at Nine Eagles Lake are “fully supported.” Using the median values from these surveys from 2004 through 2008 (approximately 24 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 46, 46, and 49 respectively for Nine Eagles Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Nine Eagles Lake in the mesotrophic category. These values suggest extremely low levels of chlorophyll a and suspended algae in the water, exceptional water transparency, and extremely low levels of phosphorus in the water column.
The level of inorganic suspended solids is low at this lake and does not suggest impairment due to high non-algal turbidity. The median inorganic suspended solids concentration at Nine Eagles Lake was 1.2 mg/L, which was the 9th lowest of the 132 monitored lakes.
Data from the 2004-2008 ISU and UHL surveys suggest a small population of cyanobacteria exists at Nine Eagles Lake, which does not suggest impairment at this lake. These data show that cyanobacteria comprised only 28% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (2.0 mg/L) was also the 9th lowest of the 132 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed as “fully supported” based on information from the IDNR Fisheries Bureau and results from the ISU and UHL lake surveys. The ISU and UHL lake surveys show that during 2004-2008 there were no violations of the Class B(LW) criterion for ammonia in 24 samples, for dissolved oxygen in 24 samples, or for pH in 24 samples. Based on IDNR’s assessment methodology these results suggest full support of the Class B(LW) uses at Nine Eagles Lake.
The Class C (drinking water) uses are "not assessed" due to lack of monitoring data upon which to base an assessment. The only parameter collected as part of the ISU and UHL lake surveys relevant to support of Class C (drinking water) uses is nitrate. While the results of the ISU and UHL surveys from 2004-08 show that nitrate levels are generally low at this lake (maximum value = 8.4 mg/l; median = 0.1 mg/l) compared to the drinking water MCL (10 mg/L), these data are not sufficient for developing a valid assessment of support of the Class C uses.
Fish consumption uses were assessed (monitored) as “partially supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring at Nine Eagles Lake in 2001, 2005, and 2007. 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 level of mercury in the samples of largemouth bass in 2001 (0.26 ppm) exceeded the IDNR/IDPH trigger level of 0.20 ppm for a one meal per week consumption advisory (this level is well below the “do not eat” trigger level for mercury of 1.0 ppm). According to the IDNR/IDPH advisory protocol, if two consecutive samplings show that contaminant levels are above the trigger level in fillet samples, issuance of a consumption advisory is justified. Because the level of mercury in sample of largemouth bass fillets from the 2005 sampling (0.30 ppm) also exceeded this advisory trigger level, issuance of a fish consumption advisory is justified. This advisory was issued by IDNR and IDPH in January 2006. According to IDNR’s assessment methodology, the existence of a consumption advisory indicates that fish consumption uses should be assessed as “not supported.” Follow up sampling conducted in 2007 also showed that the level of mercury in largemouth bass (0.412 ppm) was above the one meal per week consumption advisory. Therefore the consumption advisory remains at this lake and the fish consumption uses are assessed as "not supported."
