Assessment Comments
Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2004 through 2007 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, (4) results of the IDNR-county voluntary beach monitoring program in 2006, 2007, and 2008, and (5) results of U.S. EPA/IDNR fish contaminant monitoring in 2002.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to levels of indicator bacteria that exceed Iowa’s water quality standards and aesthetically objectionable conditions caused by elevated levels of algae (chlorophyll a). The Class B(LW) (aquatic life) uses are assessed (evaluated) as "partially supported" due to violations of the Class B(LW) criterion for ammonia. Fish consumption uses remain assessed (monitored) as “fully supported.” Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2004 through 2007 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, (4) results of the IDNR-county voluntary beach monitoring program in 2006, 2007, and 2008, and (5) results of U.S. EPA/IDNR fish contaminant monitoring in 2002.
EXPLANATION: Results of IDNR county beach monitoring from 2006 through 2008 suggest that the Class A1 uses are assessed (monitored) as "not supported." Levels of indicator bacteria at Lake Pahoja beach were monitored approximately once per week during the primary contact recreation seasons (May through August) of 2006 (15 samples), 2007 (11 samples), and 2008 (13 samples) as part of the IDNR county beach monitoring program. According to IDNR’s assessment methodology, all thirty-day geometric means for the three-year assessment period must be less than the state’s geometric mean criterion of 126 E. coli orgs/100 ml for results of beach monitoring to indicate “full support” of the Class A1 (primary contact recreation) uses. 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”. This assessment approach is based on U.S. EPA guidelines (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
At Lake Pahoja beach, the geometric means of 2 thirty-day periods during the summer recreation seasons of 2004, 2005, and 2006 exceeded the Iowa water quality standard of 126 E. coli orgs/100 ml. All of the geometric mean exceedences occurred in 2008. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was 20% in 2006, 9% in 2007, and 23% in 2008. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest nonsupport of the Class A1 (primary contact recreation) uses.
For the 2010 assessment/listing cycle, results from the ISU and UHL lake surveys indicate that the Class A1 (primary contact recreation) uses of Lake Pahoja are assessed (monitored) as “partially supported.” Using the median values from these surveys from 2004 through 2008 (approximately 20 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 64, 69, and 71 respectively for Lake Pahoja. According to Carlson (1977) the Secchi depth and chlorophyll a values place Lake Pahoja in between the eutrophic and hypereutrophic categories while the total phosphorus value places Lake Pahoja in the hypereutrophic category. These values suggest high levels of chlorophyll a and suspended algae in the water, moderately poor water transparency, and very high levels of phosphorus in the water column.
Based on data from the ISU and UHL lake surveys, the level of inorganic suspended solids was relatively low at this lake and does not suggest impairment due to high non-algal turbidity. The median inorganic suspended solids concentration at Lake Pahoja was 3.0 mg/L, which was the 51st lowest of the 132 monitored lakes.
Data from the 2004-2008 ISU and UHL surveys suggest a moderate population of cyanobacteria exists at Lake Pahoja, which contributes to the aesthetically objectionable conditions caused by algae blooms at this lake. These data show that cyanobacteria comprised 70% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (19.6 mg/L) was the 51st highest of the 132 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due to violations of the Class B(LW) chronic criterion for ammonia. Results of the ISU and UHL lake surveys from 2004 through 2008 show 2 violations of the Class B(LW) chronic criterion for ammonia in 20 samples. Based on IDNR’s 2008 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. Because, however, more than one violation of the chronic criterion for ammonia occurred, this potential impairment will be added to Iowa's list of waters in need of further investigation. Note: Based on consultation with other Region 7 states and U.S. EPA Region 7 staff in 2007, IDNR's methodology for assessing impairments due to violations of chronic criteria for toxic parameters (e.g., ammonia and toxic metals) was changed. Prior to the 2008 listing cycle, IDNR followed a U.S. EPA recommendation (U.S. EPA 1997b, page 3-18) that more than one violation of a water quality criterion for a toxic pollutant in an abundant data set indicates an impairment of aquatic life uses. Because no state in Region 7 collects ambient data with the frequency necessary to accurately identify compliance with a chronic criterion (i.e., to allow calculation of a short-term (4-day or 30-day averages)), Region 7 states concluded that another assessment approach (e.g., the 10% rule) was more appropriate. Thus, for the 2008 and current (2010) listing cycle, IDNR identified aquatic life impairments for toxic parameters when significantly more than 10% of the samples exceeded a chronic criterion.
Data from the ISU and UHL surveys show no violations of the Class B(LW) criterion for dissolved oxygen in 20 samples. Data for pH show 4 violations of the Class A1,B(LW) criterion for pH in 20 samples (20%). Based on IDNR’s assessment methodology, however, these violations are not significantly greater than 10% of the samples and therefore do not suggest impairment of the Class B(LW) uses of Lake Pahoja due to pH.
Fish consumption uses were assessed (evaluated) as “fully supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring at Lake Pahoja in 2002. The composite samples of fillets from channel catfish had low levels of contaminants: mercury: 0.036 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.030 ppm. A predator sample was not collected as part of the 2002 RAFT sample. Typically, samples of both bottom-feeding fish (e.g., common carp) and predator species (e.g., largemouth bass) are collected at RAFT status sites such as the 2002 sampling at Lake Pahoja. Predator species, however, are sometimes difficult to capture, and RAFT status samples occasionally contain only the bottom-feeder sample. Because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). 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 2002 RAFT sampling conducted at Lake Pahoja 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.
