Assessment Comments
Assessment is based on: (1) results of the IDNR-UHL beach monitoring program from 2008 through 2010, (2) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 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 and 2007.
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. In addition, violation's of the state's water quality standard for indicator bacteria also suggest an impairment at Prairie Rose Lake: this is a new impairment for this lake. 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 and 2007. Sources of data for this assessment include: (1) results of the IDNR-UHL beach monitoring program from 2008 through 2010, (2) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 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 and 2007.
EXPLANATION: Results of IDNR beach monitoring from 2008 through 2010 suggest that the Class A1 uses are “partially supported." Levels of indicator bacteria at Prairie Rose Lake beach were monitored once per week during the primary contact recreation seasons (May through September) of 2008 (15 samples), 2009 (17 samples), and 2010 (16 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) 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 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).
NOTE: Based on consultation with EPA Region 7 staff in 2011, IDNR’s methodology for assessing impairments based on the geometric mean water quality criterion was changed. Prior to the 2012 listing cycle, IDNR calculated geometric means for lakes based on a 30-day periods within the recreational season. Any violation of one of these 30-day periods within 3 years resulted in an impairment of the Class A1 uses of that lake. Because water quality standards do not identify a 30 day period but instead a recreational season, Region 7 concurred that the approach used for rivers and streams with less frequent bacteria data (seasonal geometric means) would be appropriate for identifying §303(d) impairments at lake beaches. Thus, for the 2012 listing cycle, IDNR identified primary contact recreation impairments for lakes when the geometric mean of all samples from the recreation season of a given year exceeded the geometric mean criterion. This does not impact the way IDNR assesses beaches for closure to protect the recreating public in the short term.
At Prairie Rose Lake beach, the geometric means from 2008, 2009, and 2010 were all below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 62 E. coli orgs/100 ml in 2008, 85 E. coli orgs/100 ml in 2009, and 90 E. coli orgs/100 ml in 2010. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was 7% in 2008, 29% in 2009 and 31% in 2010. The number of samples exceeding the single-sample maximum criterion was significantly greater than 10% in 2009 and 2010. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest “partial support” of the Class A1 uses.
Results from the ISU and UHL lake surveys 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 2006 through 2010 (approximately 22 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 66, 64, 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 moderately 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 6.8 mg/L, which was the 34th highest of the 134 monitored lakes.
Data from the 2006-2010 ISU and UHL surveys suggest a relatively large population of cyanobacteria exists at Prairie Rose Lake, which may also contribute to aesthetically objectionable conditions and the algae impairment at this lake. These data show that cyanobacteria comprised 66% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (38.1 mg/L) was the 36th highest of the 134 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed as “partially supported” based on information from the IDNR Fisheries Bureau, and results from the ISU and UHL lake surveys. Information from the IDNR Fisheries Bureau suggests that algae is a concern at this lake. The ISU and UHL lake surveys show that from 2006-2010 there was 1 violation of the Class B(LW) criterion for ammonia in 22 samples (5%). Based on IDNR’s 2012 Section 303(d) listing methodology, however, these results do not suggest that significantly more than 10 percent of the samples exceed Iowa’s chronic criterion for ammonia and thus do not suggest an impairment of the Class B(LW) aquatic life uses. There were no violations of the Class B(LW) criterion for dissolved oxygen in 21 samples. There were 3 violations of the Class A1,B(LW) criterion for pH in 22 samples (14%). 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 Prairie Rose Lake. However, Prairie Rose Lake was assessed as "partially supporting" the Class A1,B(LW) uses due to violations of the pH criteria for the 2010 assessment/listing cycle. Based on IDNR's assessment methodology, two consecutive assessment/listing cycles without significantly greater than 10% of the samples exceeding the criteria are necessary to suggest de-listing of the pH impairment. Therefore, Prairie Rose Lake remains assessed as "partially supporting" the Class A1,B(LW) uses.
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 2006-10 show that nitrate levels are low at Prairie Rose Lake (maximum value = 6.1 mg/l; median = 0.5 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 and 2007. 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. Follow up sampling in 2007 also showed low levels of primary contaminants. Data from 2007 show the composite samples of fillets from channel catfish and largemouth bass had low levels of contaminants. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.0273 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: 0.091 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 and 2007 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.
