Assessment Comments
Assessment is based on: (1) the results of the IDNR-UHL beach monitoring program in summers of 2008, 2009, and 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 tissue monitoring in 1996, 2006, 2008 and 2009.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” due to high levels of bacteria that exceed the Class A1 standard. High levels of pH that exceed the state water quality criterion also contribute to an impairment at this lake. High levels of cyanobacteria also contribute to a potential impairment due to nuisance aquatic life. The Class B(LW) (aquatic life) uses are assessed (monitored) as “partially supported” due to high levels of pH that exceed the state water quality criterion. The Class C (drinking water) uses remain “not assessed” due to a lack of information upon which to base an assessment. Fish consumption uses are assessed (monitored) as “partially supported” due to the issuance of a fish consumption advisory at this lake. Sources of data for this assessment include (1) the results of the IDNR-UHL beach monitoring program in summers of 2008, 2009, and 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 tissue monitoring in 1996, 2006, 2008 and 2009.
Note: A TMDL for bacteria and pH at Geode Lake was prepared by IDNR and approved by EPA in 2009. Because not all of the Section 303(d) impairments identified for the 2012 assessment/listing cycle (mercury) are addressed by the TMDL, this waterbody remains in IR Category 5a (impaired; TMDL required) for the 2012 assessment/listing cycles.
EXPLANATION: Results of IDNR beach monitoring from 2008 through 2010 suggest that the Class A1 uses are “partially supported." Levels of indicator bacteria at Geode Lake beach were monitored once per week during the primary contact recreation seasons (May through September) of 2008 (25 samples), 2009 (27 samples), and 2010 (17 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 Geode 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 61 E. coli orgs/100 ml in 2008, 123 E. coli orgs/100 ml in 2009, and 81 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 24% in 2008, 48% in 2009 and 24% in 2010. These results are all significantly greater than 10% of the samples and therefore suggest impairment of the Class A1 uses at Lake Geode. 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 lake survey and the UHL ambient lake monitoring program suggest that the Class A1 (primary contact recreation) uses for Lake Geode be assessed (monitored) as “partially supported” for the 2012 reporting cycle due to high levels of pH. Other than high pH, the ISU and UHL data show exceptional water quality for Lake Geode. Using the median values from these surveys from 2006 through 2010 (approximately 23 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 51, 57, and 63 respectively for Lake Geode. According to Carlson (1977) the Secchi depth and chlorophyll a values place Lake Geode in the eutrophic category, while the total phosphorus value places Lake Geode in between the eutrophic and hypereutrophic categories. These values suggest relatively low levels of chlorophyll a and suspended algae in the water, very good water transparency, and moderately high levels of phosphorus in the water column.
The level of inorganic suspended solids was low at Lake Geode and does not suggest an impairment due to non-algal turbidity. Based on data from the ISU and UHL surveys in 2006 through 2010, the median concentration of inorganic suspended solids at Lake Geode was 2.0 mg/L, which was the 23rd lowest concentration of the 134 lakes monitored by these programs.
Data from the 2006-2010 ISU and UHL surveys suggest a large population of cyanobacteria exists at Lake Geode. These data show that cyanobacteria comprised 100% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (53.3 mg/L) was the 23rd highest of the 134 lakes sampled. This median is in the worst 25% of the 134 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 for the 2006-2010 period. 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 results from the ISU and UHL lake surveys. The ISU and UHL lake surveys data from 2006-2010 show no violations of the Class B(LW) criteria for ammonia in 23 samples or dissolved oxygen in 23 samples. The data, however, show 9 violations of the criterion for pH in 23 samples (39%). Based on IDNR’s assessment methodology, these violations are significantly greater than 10% of the samples and therefore suggest an impairment (partial support/monitored) of the Class A1,B(LW) uses at this lake. Information from the IDNR Fisheries Bureau suggests that nutrients and short-lived algae blooms are a concern at this lake, but are being addressed by a watershed and lake restoration project.
The Class C (drinking water) uses remain "not assessed" due to the lack of water quality information. 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 these surveys from 2006-10 show that nitrate levels at this lake are low relative to the drinking water MCL (10 mg/l) (maximum sample value = 4.8 mg/l; median = 1.6 mg/l), these data are not sufficient for developing a valid assessment of the Class C uses.
Fish consumption uses were assessed (monitored) as “partially supported” based on results of U.S.EPA/IDNR fish tissue monitoring in 1996, 2006, 2008 and 2009. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes. The fish contaminant data generated from the 1996 RAFT sampling conducted at Lake Geode show that levels of mercury are sufficiently high for concern and thus justify follow-up monitoring. Results from the 1996 sampling showed that the level of mercury in the sample of largemouth bass fillets (0.348 ppm) exceeded the 1 meal/week trigger level (0.30 ppm) as defined in Iowa’s revised (2007) fish consumption advisory protocol. According to IDNR’s assessment methodology, the single occurrence of contaminant above an advisory trigger level neither warranted issuance of an advisory nor indicated impairment of the fish consumption uses: two consecutive samplings that show contaminant levels are above the trigger level in fillet samples are needed to justify issuance of an advisory. Follow-up sampling conducted in 2006 showed that levels of mercury in largemouth bass (0.51 ppm) again exceeded the 1 meal/week trigger level (0.30 ppm). Thus a one meal per week fish consumption advisory was issued for Lake Geode and the fish consumption uses were assessed as “partially supported.” Follow-up fish tissue monitoring is now conducted every other year at Lake Geode. Follow-up sampling was conducted in 2008. The level of mercury in the sample of largemouth bass fillets (0.267 ppm) was less than the 1 meal/week advisory trigger level (0.30 ppm). Because the level of mercury was less than the advisory trigger level in 2008, follow-up sampling was conducted again in 2009. The level of mercury in the sample of largemouth bass fillets (0.437 ppm) was again above the advisory trigger level. Therefore the fish consumption advisory will remain at Geode Lake and the lake will be assessed as "partially supported" for the 2012 assessment/listing cycle.
In addition to fish tissue, turtle tissue was also analyzed for levels of primary contaminants. The composite samples of shoulder tissue from snapping turtle had low levels of contaminants. Levels of primary contaminants in the composite sample of snapping turtle shoulder tissue were as follows: mercury: 0.284 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm.
