Assessment Comments
Assessment is based on: (1) results of the IDNR beach monitoring program in summers of 2010-2012, (2) results of the statewide survey of Iowa lakes conducted from 2009-2012 by Iowa State University (ISU), (3) information from the IDNR Fisheries Bureau, and (4) IDNR fish contaminant monitoring in 2013 and 2014.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” (IR 5a) due to violation's of the state's indicator bacteria criteria. The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported” (IR 2a). Fish consumption uses are assessed as “partially supported" (IR 5a) due to high levels of mercury in predator fish. Sources of data for this assessment include (1) results of the IDNR beach monitoring program in summers of 2010-2012, (2) results of the statewide survey of Iowa lakes conducted from 2009-2012 by Iowa State University (ISU), (3) information from the IDNR Fisheries Bureau, (4) IDNR fish contaminant monitoring in 2013 as part of Iowa's statwide fish tissue monitoring program and in 2014 as part of an Iowa DNR study on levels of mercury in Iowa fish. NOTE: Lake Wapello was drawn down in 2008 to eliminate gizzard shad populations in the lake and repair the dam.
EXPLANATION: Results of IDNR beach monitoring from 2010-2012 suggest that the Class A1 uses are “partially supported." Levels of indicator bacteria at Lake Wapello beach were monitored once per week during the primary contact recreation seasons (May through September) of 2010 (16 samples), 2011 (15 samples), and 2012 (15 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 2014 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 Lake Wapello beach, the geometric means from 2010-2012 were below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 74 E. coli orgs/100 ml in 2010, 36 E.coli orgs/100 ml in 2011, and 8 E. coli orgs/100 ml in 2012. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was 38% in 2010, 20% in 2011, and 0% in 2012. The number of samples exceeding the single-sample maximum in 2010 was significantly greater than 10% of the samples and therefore suggests impairment of the Class A1 uses. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest “partial support” of the Class A1 uses.
NOTE: Results of indicator bacteria monitoring at the state park beaches showed high numbers of exceedences of the E. coli single-sample maximum standard at almost all beaches in 2010. These high results at most beaches were likely due to the timing of sample collection related to rainfall events. On multiple dates in 2010, rainfall events occurred on Sunday or Monday immediately prior to regularly scheduled sample collections on Monday. Lake Wapello has generally shown very low levels of indicator bacteria at the beach.
For the 2014 assessment/listing cycle, results from the ISU and UHL lake surveys indicate that the Class A1 (primary contact recreation) uses of Lake Wapello should be assessed (monitored) as “fully supported.” Using the median values from these surveys from 2008-2012 (approximately 12 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 63, 56, and 59 respectively for Lake Wapello. According to Carlson (1977) the chlorophyll a and total phosphorus values all place Lake Wapello in the eutrophic category and the Secchi depth index values places Lake Wapello in between the eutrophic and hypereutrophic categories. These values suggest relatively low levels of chlorophyll a and suspended algae in the water, moderately poor transparency, and relatively low levels of phosphorus in the water column.
Based on data from the ISU and UHL lake surveys, the level of inorganic suspended solids was moderately high at this lake but does not suggest impairment due to high non-algal turbidity. The median inorganic suspended solids concentration at Lake Wapello was 8.3 mg/L, and ranked 102nd of the 134 monitored lakes.
Data from the 2006-2010 ISU and UHL surveys suggest a moderately large of cyanobacteria exists at Lake Wapello. These data show that cyanobacteria comprised approximately 92% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (27.1 mg/L) and ranked 95th of the 134 lakes sampled. These results suggest full support of the Class A1 uses at Lake Wapello.
The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported” based on data from the ISU and UHL lake surveys and information from IDNR’s Fisheries Bureau. Results of the ISU and UHL lake surveys from 2008-2012 show no violations of the Class B(LW) criterion for ammonia in 12 samples, pH in 12 samples, or for dissolved oxygen in 12 samples.
The Class C (drinking water) uses remain "not assessed" due to a lack of water quality 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 extremely low at this lake (maximum value = 0.3 mg/l; median = 0.2 mg/l), these data are not sufficient for developing a valid assessment of support of the Class C uses.
Fish consumption uses are assessed (monitored) as “partially supported” based on results of IDNR fish contaminant monitoring at Lake Wapello in 2013 and 2014. 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 2013 RAFT sampling conducted at Lake Wapello showed that levels of contaminants in the sample of channel catfish fillets were below advisory thresholds (total PCBs <0.6 ppm; total chlordane <0.2 ppm). Levels of mercury in largemouth bass, however, were sufficiently high for concern and thus justified follow-up monitoring. Results from the 2013 sampling showed that the average level of mercury in tissue samples from five largemouth bass exceeded the threshold for a "do not eat" fish consumption advisory of 1.0 ppm. The average level of mercury was 1.2 ppm (SD = 0.13 ppm; max. = 1.34 ppm, min = 1.02 ppm). These levels of mercury were unusually high for an Iowa lake or river. According to IDNR’s assessment methodology, the single occurrence of contaminant above an advisory trigger level neither warrants issuance of an advisory nor indicates 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.
Thus, follow-up monitoring was conducted in August 2014 as part of an Iowa DNR study on levels of mercury in Iowa fish. Tissue samples from 13 largemouth bass from Lake Wapello were analyzed for mercury. The length of the fish ranged from 8.8 to 19.9 inches. The average level of mercury in the 13 samples was 0.5 ppm (SD=0.28 ppm) with a maximum concentration of 0.82 ppm. Nine of the 13 samples contained levels of mercury above Iowa's 1 meal/week advisory threshold of 0.3 ppm, but none of the samples contained mercury above "do not eat" advisory threshold of 1.0 ppm. Based on the results monitoring in 2013 and the results of this follow-up monitoring in 2014, a 1 meal/week advisory was issued for this lake. The existence of this advisory suggests that the fish consumption uses at Lake Wapello should be assessed as "partially supporting".
