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 from the IDNR-county voluntary beach monitoring program from 2004 through 2006, and (5) results of U.S. EPA / IDNR fish tissue (RAFT) monitoring in 2005.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” due poor water transparency that violates Iowa’s narrative criteria protecting against aesthetically objectionable conditions. The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due to siltation impacts at this lake. Fish consumption uses are assessed (monitored) 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 from the IDNR-county voluntary beach monitoring program from 2004 through 2006, and (5) results of U.S. EPA / IDNR fish tissue (RAFT) monitoring in 2005.
Note: A TMDL for nutrients and siltation at Easter Lake was prepared by IDNR and approved by EPA in 2005. Because all Section 303(d) impairments identified for the 2008 assessment/listing cycle (siltation 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 Easter Lake beach were monitored approximately once per week during the primary contact recreation seasons (May through August) of 2004 (11 samples), 2005 (14 samples), and 2006 (14 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 Easter Lake beach, the geometric means of all 14 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: 0%, 2005: 7%, 2006: 7%. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest full support of the Class A1 (primary contact recreation) uses.
For the 2008 reporting cycle, the Class A1 (primary contact recreation) uses for Easter Lake are assessed (monitored) as “partially supported” based on results from the ISU statewide survey of lakes and the UHL ambient lake monitoring program. 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 67, 64, and 64 respectively for Easter Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Easter Lake in between the eutrophic and the hypereutrophic categories. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, poor water transparency, and moderately high levels of phosphorus in the water column.
The levels of inorganic suspended solids at this lake were high and suggest non-algal turbidity contributes to poor water clarity at this lake. The median level of inorganic suspended solids in Easter Lake (7.1 mg/L) was the 35th highest median of the 132 lakes sampled by the ISU and UHL programs.
Data from the 2002-2006 ISU and UHL surveys suggest a moderate population of cyanobacteria exists at Easter Lake, which may cause occasional nuisance algae blooms. These data show that cyanobacteria comprised 99% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (23.7 mg/L) was the 52nd highest of the 132 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due the impacts of siltation at this lake. Results from the ISU and UHL lake surveys from 2002-2006 show no violations of the Class B(LW) criteria for ammonia in 16 samples. The data show two violations of the criterion for dissolved oxygen in 22 samples (9%), and 3 violations of the pH criterion in 23 samples (13%). Based on IDNR’s assessment methodology, these violations are not significantly greater than 10% of the samples and therefore do not suggest an impairment of the aquatic life uses at this lake.
Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring at Easter Lake in 2005. The composite samples of fillets from channel catfish and largemouth bass had low levels of contaminants. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.0512 ppm; total PCBs: <0.09 ppm; and technical chlordane: 0.026 ppm. Levels of primary contaminants in the composite sample of largemouth bass fillets were as follows: mercury: 0.172 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. 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 2005 RAFT sampling conducted at Easter Lake show that the levels of contaminants do not exceed any of the advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.
