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, (4) results of the IDNR-county voluntary beach monitoring program from 2004 through 2006, and (5) results of U.S. EPA/IDNR fish tissue monitoring in 1997.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to aesthetically objectionable conditions caused by poor water clarity and nuisance algae (cyanobacteria). The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported.” Fish consumption uses remain 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, (4) results of the IDNR-county voluntary beach monitoring program from 2004 through 2006, and (5) results of U.S. EPA/IDNR fish tissue monitoring in 1997.
Note: A TMDL for algae and turbidity at Lake Cornelia was prepared by IDNR and approved by EPA in 2006. Because all Section 303(d) impairments identified for the 2008 assessment/listing cycle (algal growth and turbidity) are addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved).
EXPLANATION: Results of IDNR-county beach monitoring from 2004 through 2006 suggest that the Class A1 uses are assessed (monitored) as "fully supported." Levels of indicator bacteria at Lake Cornelia beach were monitored approximately once per week during the primary contact recreation seasons (May through August) of 2004 (13 samples), 2005 (16 samples), and 2006 (16 samples) as part of the IDNR county beach monitoring program. According to IDNR’s assessment methodology, two conditions need to be met for results of beach monitoring to indicate “full support” of the Class A1 (primary contact recreation) uses: (1) all thirty-day geometric means for the three-year assessment period are less than the state’s geometric mean criterion of 126 E. coli orgs/100 ml and (2) not more than 10 % of the samples during any one recreation season exceeds the state’s single-sample maximum value of 235 E. coli orgs/100 ml. 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.” Also, if significantly more than 10% of the samples in any one of the three recreation seasons exceed Iowa’s single-sample maximum value of 235 E. coli orgs/100 ml, the Class A1 uses should be assessed as “partially supported.” This assessment approach is based on U.S. EPA guidelines (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
At Lake Cornelia beach, the geometric means of all 33 thirty-day periods during the summer recreation seasons of 2004, 2005 and 2006 were below the Iowa water quality standard of 126 E. coli orgs/100 ml. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was also less than 10% in the all of following recreation seasons: 2004: 8%, 2005: 0%, 2006: 6%. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest full support of the Class A1 (primary contact recreation) uses.
However, based on results from the ISU statewide survey of lakes and the UHL ambient lake monitoring program the Class A1 uses for Lake Cornelia are assessed as “not supported” due to poor water clarity caused by non-algal turbidity and nuisance algal blooms. Using the median values from these surveys from 2002 through 2006 (approximately 23 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 70, 63, and 65 respectively for Lake Cornelia. According to Carlson (1977) the Secchi depth value places Lake Cornelia in the hypereutrophic category, while the chlorophyll a and total phosphorus values place Lake Cornelia in between the eutrophic and hypereutrophic categories. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, very poor water transparency, and high levels of phosphorus in the water column.
The level of inorganic suspended solids was very high at this lake and suggests that non-algal turbidity contributes to the impairment at this lake. Based on data from the ISU and UHL surveys in 2002 through 2006, the median concentration of inorganic suspended solids was 9.3 mg/L, which was the 25th highest concentration of the 132 lakes monitored by these programs.
Data from the 2002-2006 ISU and UHL surveys suggest a large population of cyanobacteria exists at Lake Cornelia, which contributes to the impairment at this lake. These data show that cyanobacteria comprised 99% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (92.5 mg/L) was also the 10th highest of the 132 lakes sampled. This median is in the worst 25% of the 132 lakes sampled. The presence of a large population of cyanobacteria at this lake suggests a potential violation of Iowa’s narrative water quality standard protecting against the occurrence of nuisance aquatic life. This assessment is based strictly on the distribution of the lake-specific median cyanobacteria values from 2002-2006. Median levels greater than the 75th percentile of this distribution were arbitrarily considered to represent potential impairment. No other criteria exist, however, upon which to base a more accurate identification of impairments due to cyanobacteria. The assessment category for assessments based on level of cyanobacteria will be considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence) to account for this lower level of confidence.
The Class B(LW) (aquatic life) uses are assessed as “fully supported.” The ISU and UHL lake surveys data from 2002-2006 show no violations of the Class B(LW) criteria for ammonia in 16 samples or dissolved oxygen in 22 samples. The data show one violation of the criterion for pH in 23 samples (4%). Based on IDNR’s assessment methodology, this violation is not significantly greater than 10% of the samples and therefore does not suggest an impairment of the aquatic life uses at this lake.
Fish consumption uses were assessed (evaluated) as “fully supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring at Lake Cornelia in 1997. 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 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 1997 RAFT sampling conducted Lake Cornelia show that levels of all contaminants from this monitoring were below advisory trigger levels, thus suggesting the continued “full support” of fish consumption uses.
