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-county voluntary beach monitoring program in 2008, 2009, and 2010, (4) information from the IDNR Fisheries Bureau, and (5) results of U.S. EPA/IDNR fish and turtle contaminant (RAFT) monitoring in 2010.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” due to levels of indicator bacteria that exceed the state water quality criterion. Poor water transparency due to non-algal turbidity also causes an impairment at this lake. The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported.” Fish consumption uses are assessed (monitored) as "fully supported" based on results of fish and turtle contaminant monitoring in 2010. 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-county voluntary beach monitoring program in 2008, 2009, and 2010, (4) information from the IDNR Fisheries Bureau, and (5) results of U.S. EPA/IDNR fish and turtle contaminant (RAFT) monitoring in 2010.
EXPLANATION: Results of IDNR city/county beach monitoring from 2008 through 2010 suggest that the Class A1 uses are “partially supported." Levels of indicator bacteria at Browns Lake beach were monitored once per week during the primary contact recreation seasons (May through September) of 2008 (14 samples), 2009 (12 samples), and 2010 (12 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 Browns 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 79 E. coli orgs/100 ml in 2008, 77 E. coli orgs/100 ml in 2009, and 71 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 29% in 2008, 8% in 2009 and 25% in 2010. The percentage of samples exceeding the single-sample maximum was significantly greater than 10% in 2008 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.
For the 2012 reporting cycle, the Class A1 (primary contact recreation) uses for Browns Lake are assessed (monitored) as “partially supported” based on results from the ISU statewide survey of lakes and the UHL ambient lake monitoring program. Using the median values from these surveys from 2006 through 2010 (approximately 17 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 67, 64, and 67 respectively for Browns Lake. According to Carlson (1977) the Secchi depth, chlorophyll a and total phosphorus values place Browns 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 levels of inorganic suspended solids at this lake were very high and suggest that non-algal turbidity contributes to the impairment at this lake. The median level of inorganic suspended solids in Browns Lake (10.0 mg/L) was the 20th highest median of the 134 lakes sampled by the ISU and UHL surveys.
Data from the 2006-2010 ISU and UHL surveys also suggest that a small population of cyanobacteria exists at Browns Lake that do not likely cause an impairment due to nuisance aquatic life. These data show that cyanobacteria comprised 49% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (14.2 mg/L) was also the 45th lowest of the 134 lakes sampled.
The Class B(LW) (aquatic life) uses for Browns Lake are assessed (monitored) as “fully supported” based on information from the IDNR Fisheries Bureau and 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) criterion for ammonia in 17 samples, dissolved oxygen in 16 samples, or pH in 17 samples. Based on IDNR’s assessment methodology, these results suggest "full support" of the Class B(LW) uses at Browns Lake.
Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring at Browns Lake in 2010. 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: 0.0247 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: 0.149 ppm. In addition to fish tissue samples, turtle tissue was also collected from snapping turtle at Browns Lake. Levels of primary contaminants in the sample of shoulder tissue from snapping turtle were as follows: mercury: 0.0582 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 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 and turtle contaminant data generated from the 2010 RAFT sampling conducted at this 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.
