Littlefield Lake IA 05-NSH-1439
Audubon County S17T78NR34W approx 4 mi SE of Exira.
- Cycle
- 2018
- Release Status
- Final
- Overall IR
- 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
- Trophic
- Hypereutrophic
- Trend
- Stable
- Created
- 4/9/2019 10:53:49 AM
- Updated
- 4/9/2019 10:55:26 AM
Insufficient water quality The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to aesthetically objectionable conditions caused by poor water transparency and nuisance algae blooms. The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported” although nutrient loading and the impacts of sedimentation remain concerns at this lake. Fish consumption uses remain “not assessed.” Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2012 through 2016 by Iowa State University (ISU), and (2) information from the IDNR Fisheries Bureau.
For the 2018 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Littlefield Lake are assessed (monitored) as "not supported" due to poor water transparency and aesthetically objectionable conditions caused by algae blooms based on information from the ISU lake survey. Using the median values from these surveys from 2012-2016 (approximately 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 73, 71, and 84 respectively for Littlefield Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Littlefield Lake in the Hypereutrophic category. These values suggest very high levels of chlorophyll a and suspended algae in the water, very poor water transparency, and extremely high levels of phosphorus in the water column. The data show 2 violations of the Class A1 criterion for pH in 14 samples (14%). Note:A TMDL for algae and turbidity at Littlefield Lake was prepared by DNR and approved by EPA in 2006. Because all Section 303(d) impairments identified for the 2016 assessment/listing cycle (algal growth, 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 high at Littlefield Lake, and does suggest that non-algal turbidity contributes to the impairment at this lake. The median level of inorganic suspended solids in Littlefield Lake (11.2 mg/L) was ranked 124th among the 138 lakes by the ISU lake survey. Data from the 2012-2016 ISU lake survey suggest a moderately large population of cyanobacteria exists at Littlefield Lake. These data show that cyanobacteria comprised 88% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (29.7 mg/L) was ranked 101st of the 138 lakes sampled. The Class B(LW) (aquatic life) uses are assessed (monitored) as "fully supported." Results of the ISU lake survey from 2012-2016 show there were no violations of the criterion for ammonia in 14 samples(0%), one violation of the criterion for dissolved oxygen in 15 samples(7%), and 2 violations of the criterion for pH in 14 samples(14%). Based on DNR's assessment methodology these violations are not significantly greater than 10% of the samples and therefore suggest (fully supported/monitored) of the Class B(LW) uses of Littlefield Lake. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake.