Assessment Comments
Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, and (4) results of U.S. EPA/IDNR fish contaminant monitoring in 2003.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to (1) poor water transparency caused by a combination of high levels of chlorophyll-a (suspended algae) and high levels of inorganic suspended solids and (2) high levels of pH that exceed the Class A1 water quality criterion. The Class B(LW) (aquatic life) uses are assessed (monitored) as “partially supported” primarily due to violations of the Class B(LW) criterion for pH and secondarily due to algal blooms, sediment re-suspension, and nutrient loading to the water column. 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 2006 through 2010 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, and (4) results of U.S. EPA/IDNR fish contaminant monitoring in 2003.
Note: A TMDL for turbidity and algae at Little Spirit Lake was prepared by IDNR and approved by EPA in 2005. Because all Section 303(d) impairments identified for the 2012 assessment/listing cycle (algal growth, pH, and turbidity) are addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved).
EXPLANATION: For the 2012 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Little Spirit Lake are assessed (monitored) as “not supported” based on information from the ISU lake survey and UHL lake monitoring program. Using the median values from these surveys from 2006 through 2010 (approximately 22 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 68, 68, and 77 respectively for Little Spirit Lake. According to Carlson (1977) the Secchi depth and chlorophyll a values place Little Spirit Lake in between the eutrophic and hypereutrophic categories, while the total phosphorus value places Little Spirit Lake in the hypereutrophic category. These values suggest high levels of chlorophyll a and suspended algae in the water, poor water transparency, and extremely high levels of phosphorus in the water column.
Based on data from the ISU and UHL lake surveys, 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. The median inorganic suspended solids concentration at Little Spirit Lake was 7.9 mg/L, which was the 27th highest of the 134 monitored lakes.
Data from the 2006-2010 ISU and UHL surveys suggest a moderately large population of cyanobacteria exists at Little Spirit Lake, which contributes to occasional algal blooms and aesthetically objectionable conditions at this lake. These data show that cyanobacteria comprised 69% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (30.3 mg/L) was the 49th highest of the 134 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed (monitored) as “partially supported” due to violations of the Class B(LW) criterion for pH as well as algal blooms, sediment re-suspension, and nutrient loading to the water column. Results of the ISU and UHL lake surveys from 2006 through 2010 show there were no violations of the Class B(LW) criterion for ammonia in 21 samples. There was one violation of the Class B(LW) criterion for dissolved oxygen in 22 samples (5%). Based on IDNR’s assessment methodology this violation is not significantly greater than 10% of the samples and therefore does not suggest impairment of the Class B(LW) uses at Little Spirit Lake. There were 4 violations of the Class A1,B(LW) criterion for pH in 22 samples (18%). Based on IDNR’s assessment methodology these violations are not significantly greater than 10% of the samples and therefore do not suggest impairment of the Class A1 and B(LW) uses of Little Spirit Lake. However, Little Spirit Lake was assessed as “partially supporting” in the 2010 assessment/listing cycle due to significant violations of the pH criteria and therefore remains “partially supported” due to the continued violations. Based on IDNR’s assessment methodology 2 consecutive assessment/listing cycles without significantly greater than 10% of the samples violating the criterion are necessary to propose delisting based on pH violations. The pH violations at Little Spirit Lake likely reflect the excessive primary productivity at the lake and do not reflect the input of pollutants into this lake.
Fish consumption uses were assessed (evaluated) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Little Spirit Lake in 2003. The composite samples of fillets from common carp and walleye had low levels of contaminants. Levels of primary contaminants in the composite sample of common carp fillets were as follows: mercury: 0.019 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm. Levels of primary contaminants in the composite sample of walleye fillets were as follows: mercury: 0.04 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm. 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 the degree to which Iowa’s lakes and rivers support their fish consumption uses. The fish contaminant data generated from the 2003 RAFT sampling conducted at this 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.
