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) results of the IDNR-UHL beach monitoring program in 2008, 2009, and 2010, and (4) information from the IDNR Fisheries Bureau.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” due to high levels of indicator bacteria at the beach and aesthetically objectionable conditions caused by algal blooms. The Class B(LW) aquatic life uses are assessed (monitored) as “fully supported.” The Class C (drinking water) uses remain “not assessed” due to a lack of information upon which to base an assessment. Fish consumption uses remain “not assessed” due to the 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 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) results of the IDNR-UHL beach monitoring program in 2008, 2009, and 2010, and (4) information from the IDNR Fisheries Bureau. Note: this lake was drained and its fishery was renovated by IDNR in 2006, and watershed improvements were also made (e.g., installation of silt-retention structures). Positive changes in water quality may result from this renovation which will affect future assessments.
EXPLANATION: Results of IDNR beach monitoring from 2008 through 2010 suggest that the Class A1 uses are “partially supported." Levels of indicator bacteria at Viking Lake beach were monitored once per week during the primary contact recreation seasons (May through September) of 2008 (27 samples), 2009 (26 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 Viking 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 42 E. coli orgs/100 ml in 2008, 78 E. coli orgs/100 ml in 2009, and 75 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 19% in 2008, 23% in 2009 and 19% in 2010. The number of samples exceeding the single-sample maximum criterion was significantly greater than 10% in 2009 and therefore suggests impairment. 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 the Class A1 uses at Viking Lake should be assessed as “partially supported” due to elevated levels of chlorophyll a. Using the median values from these surveys from 2006 through 2010 (approximately 20 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 60, 60, and 61 respectively for Viking Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Viking Lake in between the eutrophic and hypereutrophic categories. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, moderately poor water transparency, and moderately high levels of phosphorus in the water column.
While the TSI values for Viking Lake are below the impairment trigger of 65 for the 2012 reporting cycle, Viking Lake was listed as "partially supporting" the Class A1 uses for the 2010 reporting cycle due to algal turbidity. Based on IDNR's assessment methodology, median-based TSI values for both chlorophyll-a and Secchi depth must be 63 or less for two consecutive summer seasons before a lake can be removed from the state’s Section 303(d) list (IR Category 5). Therefore, Viking Lake remains assessed as "partially supported" due to high levels of algae for the 2012 assessment cycle.
The level of inorganic suspended solids is relatively low at Viking Lake and suggests that non-algal turbidity does not contribute to the impairment at this lake. The median inorganic suspended solids concentration at Viking Lake was 2.0 mg/L, which was the 43rd lowest of the 134 monitored lakes.
Data from the 2006-2010 ISU and UHL surveys suggest a moderate population of cyanobacteria exists at Viking Lake, which does not cause an impairment due to nuisance aquatic life. These data show that cyanobacteria comprised 80% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (33.8 mg/L) was the 43rd highest of the 134 lakes sampled.
The Class B(LW) (aquatic life) uses at Viking Lake are assessed (monitored) as “fully supported.” Information from the IDNR Fisheries Bureau suggests that since the fishery renovation in 2006 the water quality and fishery at this lake are greatly improved although algae still remains a problem at this lake. Results from the ISU and UHL lake surveys show moderately good chemical water quality at Viking Lake. During 2006-2010 there were no violations of the Class B(LW) criterion for ammonia in 20 samples and no violations of the pH criterion in 20 samples. There was 1 violation of the dissolved oxygen criterion in 20 samples (5%). Based on IDNR’s assessment methodology this violation is not significantly greater than 10% of the samples and therefore do not suggest an impairment of the Class B(LW) uses at Viking Lake.
The Class C (drinking water) uses remain “not assessed” due to lack of water quality information upon which to base such 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 very low at this lake (maximum value = 1.4 mg/l; median = 0.1 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 remain "not assessed" due to the lack of fish contaminant monitoring in this lake.
