Assessment Comments
Assessment is based on: (1) results of the IDNR-UHL beach monitoring program from 2004 through 2006, (2) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), (4) information from the IDNR Fisheries Bureau, and (5) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2003.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” due to poor water transparency caused by algae blooms and non-algal turbidity and violations of the Class A1 criterion for pH. The Class B(LW) (aquatic life) uses are assessed (monitored) as “partially supported” due to violations of the Class B(LW) criterion for pH. The Class C (drinking water) uses are “not assessed” due to a lack of information upon which to base an assessment. Fish consumption uses are assessed (monitored) as “fully supported” based on fish tissue monitoring in 2003. Sources of data for this assessment include: (1) results of the IDNR-UHL beach monitoring program from 2004 through 2006, (2) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), (4) information from the IDNR Fisheries Bureau, and (5) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2003.
EXPLANATION: Results of IDNR beach monitoring at Prairie Rose Lake from 2004 through 2006 suggest that the Class A1 uses should be assessed (monitored) as “fully supported.” Levels of indicator bacteria were monitored once per week during the primary contact recreation seasons (May through September) of 2004 (22 samples), 2005 (23 samples), and 2006 (28 samples) as part of the IDNR 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 Prairie Rose Lake beach, the geometric means of all 61 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. These results suggest generally low levels of indicator bacteria at this lake. Also, the percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was less than 10% in all three recreation seasons: 2004: 5%, 2005: 0%, 2006: 4%. Thus, these results do not suggest an impairment of the Class A1 uses of Prairie Rose Lake. Prairie Rose Lake had been listed on the 2006 impaired waters list for indicator bacteria. There were 5 violations of the Class A1 geometric mean criteria in 2002, however, there have been no violations of the geometric mean criteria from 2003 through 2007. Therefore, the indicator bacteria impairment is being removed and Prairie Rose Lake is assessed as “fully supported” based on indicator bacteria.
Results from the ISU and UHL lake surveys, however, suggest that the Class A1 uses at Prairie Rose Lake are “partially supported” due to poor water transparency caused by algae blooms and non-algal turbidity and violations of the Class A1 criterion for pH. 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 66, 65, and 67 respectively for Prairie Rose Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Prairie Rose Lake in between the eutrophic and hypereutrophic categories. These values suggest high levels of chlorophyll a and suspended algae in the water, poor water transparency, and high levels of phosphorus in the water column.
The level of inorganic suspended solids is high at this lake, and suggests that non-algal turbidity contributes to the impairment at this lake. The median inorganic suspended solids concentration at Prairie Rose Lake was 7.0 mg/L, which was the 37th highest of the 132 monitored lakes.
Data from the 2002-2006 ISU and UHL surveys suggest a relatively large population of cyanobacteria exists at Prairie Rose Lake, which may also contribute to impairment at this lake. These data show that cyanobacteria comprised 76% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (25.7 mg/L) was the 48th highest of the 132 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed as “partially supported” based on information from the IDNR Fisheries Bureau, results from the ISU and UHL lake surveys, and results of physical/chemical monitoring associated with the IDNR beach monitoring program. The ISU and UHL lake surveys show that during 2002-2006 there were no violations of the Class B(LW) criterion for ammonia in 17 samples, or dissolved oxygen in 23 samples. There were 5 violations of the Class A1,B(LW) criterion for pH in 23 samples (22%). Based on IDNR’s assessment methodology these violations are significantly greater than 10% of the samples and therefore suggest impairment (partial support/monitored) of the Class B(LW) uses of Prairie Rose Lake. Results of physical/chemical monitoring associated with the IDNR beach monitoring program from 2004-06 also suggest that the Class B(LW) uses at Prairie Rose Lake be assessed as “partially supported.” Using this data there was one violation of the Class B(LW) criterion for dissolved oxygen in 70 samples (1%). Based on IDNR’s assessment methodology this one violation is not significantly greater than 10% of the samples and therefore does not suggest impairment of the Class B(LW) uses. However, there were 10 violations of the Class A1,B(LW) criterion for pH in 70 samples (14%). Combined with data from the ISU and UHL lake surveys these results are significantly greater than 10% of the samples and therefore suggest impairment of the Class B(LW) uses at Prairie Rose Lake. The pH violations at Prairie Rose Lake likely reflect the excessive primary productivity at the lake and do not reflect the input of pollutants into this lake.
Drinking water uses remain "not assessed" due to lack of information upon which to base an assessment. The only parameter collected as part of the ISU and UHL lake surveys relevant to support of Class C (drinking water) uses is nitrate. While the results of the ISU and UHL surveys from 2002-06 show that nitrate levels are low at Prairie Rose Lake (maximum value = 3.8 mg/l; median = 0.2 mg/l) relative to the MCL (10 mg/L), these data are not sufficient for developing a valid assessment of support of the Class C uses.
Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring at Prairie Rose Lake in 2003. The composite samples of fillets from channel catfish and largemouth bass had very low levels of contaminants. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: <0.0181 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm. Levels of primary contaminants in the composite sample of largemouth bass fillets were as follows: mercury: <0.0181 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 2003 RAFT sampling conducted at Prairie Rose 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.
