Easter Lake IA 04-LDM-1024
Polk County S19T78R23W SE edge of Des Moines.
- Cycle
- 2018
- Release Status
- Final
- Overall IR
- 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
- Trophic
- Eutrophic
- Trend
- Stable
- Created
- 10/15/2018 10:17:11 AM
- Updated
- 5/30/2019 8:55:36 AM
The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” due to 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 2012 through 2015 by Iowa State University (ISU), (2) information from the IDNR Fisheries Bureau, (3) results from the IDNR-county voluntary beach monitoring program from 2014-2015, and (4) results of U.S. EPA / IDNR fish tissue (RAFT) monitoring in 2008, 2015 and 2016.
Results of DNR beach monitoring from 2014 through 2015 suggest that the Class A1 uses are "Fully Supported." Levels of indicator bacteria at Easter Lake Park Beach were monitored once per week during the primary contact recreation seasons (May through September) of 2014 (14 samples) and 2015 (17 samples), as part of the DNR beach monitoring program. According to DNR’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) the geometric mean of the samples from each recreation season of 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 sampling season geometric mean exceeds the state criterion of 1000 orgs/100 ml during the three-year assessment period, the Class A1 uses should be assessed as “not supported.” Also, if a sampling season geometric mean exceeds the state criterion of 126 orgs/100 ml during the three-year assessment period and/or 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 Park Beach, the geometric means from 2014 and 2015 were all below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 31 E. coli orgs/100 ml in 2014 and 55 E. coli orgs/100 ml in 2015. The percentage of samples exceeding Iowa's single-sample maximum criterion (235 E. coli orgs/100 ml) was 7% in 2014 and 18% in 2015. None of these are significantly greater than 10% of the samples and therefore do not suggest impairment of the Class A1 uses. According to DNR's assessment methodology and U.S. EPA guidelines, these results suggest "Fully Supported" of the Class A1 uses. For the 2018 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Easter Lake are assessed (monitored) as "partially supported" due to poor water transparency based on information from the ISU lake survey. Using the median values from these surveys from 2012-2015 (approximately 12 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 67, 64, and 62 respectively for Easter Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Easter Lake in the Eutrophic category. 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 data show no violations of the Class A1 criterion for pH in 12 samples. Note:A TMDL for nutrients and siltation at Easter Lake was prepared by DNR and approved by EPA in 2005. Because all Section 303(d) impairments identified for the 2016 assessment/listing cycle (siltation and turbidity) are addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved). The level of inorganic suspended solids was relitivley low at Easter Lake, and does not suggest water quality problems due to non-algal turbidity. The median level of inorganic suspended solids in Easter Lake (6.25 mg/L) was ranked 104th among the 138 lakes by the ISU lake survey. Data from the 2012-2015 ISU lake survey suggest a moderately large population of cyanobacteria exists at Easter Lake. These data show that cyanobacteria comprised 71% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (19.1 mg/L) was ranked 82nd of the 138 lakes sampled
Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S.EPA/DNR fish contaminant (RAFT) monitoring at Easter Lake in 2008, 2015 and 2016. The composite samples of fillets from channel catfish and largemouth bass had low levels of contaminants. Data from the 2015 and 2008 fish contaminant monitoring show that levels of primary contaminants in the composite sample of channel catfish fillets (2015) were as follows: mercury: 0.03 ppm; total PCBs: 0.25 ppm; and technical chlordane: <0.02 ppm. Levels of primary contaminants in the composite sample of largemouth bass fillets (2008) were as follows: mercury: 0.105 ppm. Data from the 2015 and 2016 fish contaminant monitoring show that levels of primary contaminants in the composite sample of channel catfish fillets (2016) were as follows:mercury: 0.05 ppm;total PCBs: <0.06 ppm, and technical chlordane: 0.04 ppm. Levels of primary contaminants in the composite sample of largemouth bass fillets(2015) were as follows: mercury: 0.089 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 and 2008 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.