Browns Lake IA 06-WEM-1735

Results of IDNR beach monitoring from 2012 through 2014 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 2012 (18 samples), 2013 (15 samples) and 2014 (3 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 1000 orgs/100 ml during the three-year assessment period, the Class A1 uses should be assessed as “not supported.” Also, if a sampling season geometric mean exceeds the state criterion of 126 orgs/100 ml during the three-year assessment period and/or 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).

At Browns Lake Beach, the geometric means from 2012, 2013 and 2014 were all below the Iowa water quality standard of 126 E.  coli orgs/100 ml.   The geometric mean was 17 E.  coli orgs/100 ml in 2012, 34 E.  coli orgs/100 ml in 2013 and 36 E.  coli orgs/100 ml in 2014.   The percentage of samples exceeding Iowa's single-sample maximum criterion (235 E.  coli orgs/100 ml) was 6% in 2012, 13% in 2013 and 0% in 2014.   None of these are significantly greater than 10% of the samples and therefore do not suggest impairment of the Class A1 uses.   According to IDNR's assessment methodology and U.S.  EPA guidelines, these results suggest "Fully Supported" of the Class A1 uses. 

While the Levels of indicator bacteria at Browns Lake Beach are below the impairment triggers for the 2014 reporting cycle, Browns Lake Beach was listed as "partially supporting" the Class A1 uses for the 2012 reporting cycle due to levels of indicator bacteria that exceed the state water quality criterion.   Based on 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 for two consecutive summer seasons before a lake can be removed from the state’s Section 303(d) list (IR Category 5): (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, . Therefore, Viking Lake remains assessed as "partially supported" due to high levels of algae for the 2016 assessment cycle.      

For the 2016 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Browns Lake are assessed (monitored) as "not supported" due to poor water transparency and aesthetically objectionable conditions caused by algae blooms based on information from the ISU lake survey. Using the median values from these surveys from 2010-2014 (approximately 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 73, 67, and 69 respectively for Browns Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Browns Lake in between the Eutrophic and the Hypereutrophic categories. These values suggest high levels of chlorophyll a and suspended algae in the water, very poor water transparency, and high levels of phosphorus in the water column. The data show no violations of the Class A1 criterion for pH in 15 samples.

The level of inorganic suspended solids was very high at Browns Lake, and does suggest that non-algal turbidity contributes to the impairment at this lake. The median level of inorganic suspended solids in Browns Lake (16.3 mg/L) was ranked 129th among the 138 lakes by the ISU lake survey.

Data from the 2010-2014 ISU lake survey suggest a large population of cyanobacteria exists at Browns Lake, which suggests the potential for an impairment due to nuisance aquatic life These data show that cyanobacteria comprised 78% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (41.3 mg/L) was ranked 112th of the 138 lakes sampled. This median is in the worst 25% of the 138 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 from 2010-2014. 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. 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 (monitored) as "fully supported." Results of the ISU lake survey from 2010-2014 show there were no violations of the criterion for ammonia in 15 samples(0%), no violations of the criterion for dissolved oxygen in 15 samples(0%), and no violations of the criterion for pH in 15 samples(0%). Based on IDNR's assessment methodology these violations are not significantly greater than 10% of the samples and therefore suggest (fully supported/monitored) of the Class B(LW) uses of 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.