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, and (4) results of a fish kill investigation on August 16, 2007.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to aesthetically objectionable conditions caused by nuisance algae blooms and non-algal turbidity. Violations of Iowa’s water quality criterion for pH also contribute to the impairment at this lake. Large populations of cyanobacteria potentially suggest an additional impairment of the Class A1 uses due to presence of nuisance (noxious) aquatic plant life. The Class B(LW) (aquatic life) uses are assessed (monitored) as “partially supported” due to violations of Iowa’s water quality criterion for pH. Nuisance blooms of algae, nutrients, and re-suspension of sediment also remain concerns at this lake. A fish kill in August of 2007 also suggests partial support of hte Class B(LW) uses. Fish consumption uses remain “not assessed” due to a lack of fish contaminant monitoring at this lake. 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, and (4) results of a fish kill investigation on August 16, 2007.
Note: A TMDL for algae and turbidity at Ingham Lake was prepared by IDNR and approved by EPA in 2005. Because all Section 303(d) impairments identified for the 2008 assessment/listing cycle (algae, pH, turbidity) are addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved).
EXPLANATION: For the 2008 reporting cycle, the Class A1 (primary contact recreation) uses for Ingham Lake are assessed (monitored) as “not supported” due to aesthetically objectionable conditions caused by poor water transparency due to algal and non-algal turbidity. Using the median values from the ISU and UHL lake surveys from 2002 through 2006 (approximately 23 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 77, 79, and 75 respectively for Ingham Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Ingham Lake in the hypereutrophic category. These values suggest extremely high levels of chlorophyll a and suspended algae in the water, extremely poor water transparency, and extremely high levels of phosphorus in the water column.
The levels of inorganic suspended solids at this lake were very high and suggest that non-algal turbidity contributes to the impairment at this lake. The median level of inorganic suspended solids in Ingham Lake (8.6 mg/L) was the 29th highest median of the 132 lakes sampled by the ISU and UHL programs.
Data from the 2002-2006 ISU and UHL surveys suggest a large population of cyanobacteria exists at Ingham Lake, which contributes to impairment at this lake. These data show that cyanobacteria comprised 99% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (98.3 mg/L) was also the 8th 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 “partially supported” based on information from IDNR’s Fisheries Bureau and results from the ISU and UHL lake surveys. Nuisance blooms of algae, nutrients, and re-suspension of sediment remain concerns at this lake. 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 23 samples. The pH data, however, show 8 violations of the Class A1,B(LW) criterion for pH in 22 samples (36%). Based on IDNR’s assessment methodology these violations are significantly greater than 10% of the samples and therefore suggest impairment of the Class B(LW) uses at Ingham Lake. These violations likely reflect primary productivity at Ingham Lake and do not reflect the input of pollutants into this lake.
A fish kill that occurred in this lake on or before August 16, 2007 also suggests "impairment" of the Class B(LW) uses. The kill was identified as a natural kill resulting from high temperatures and low dissolved oxygen. The kill mainly affected carp and occurred in the goose pen area off Ingham Lake. The total number of fish killed was 10. According to the IDNR assessment/listing methodology, the occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or waterbody reach during the most recent assessment period (2004-2007) indicates a severe stress to the aquatic community and suggests that the aquatic life uses should be assessed as “impaired.” If a cause of the kill was not identified during the IDNR investigation, or if the kill was attributed to non-pollutant causes (e.g., winterkill), the assessment type will be considered “evaluated.” Such assessments, although suitable for Section 305(b) reporting, lack the degree of confidence to support addition to the state Section 303(d) list of impaired waters (IR Category 5). Waterbodies affected by such fish kills will be placed in IR subcategories 2b or 3b and will be added to the state list of waters in need of further investigation. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this lake.
