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) information from the IDNR Fisheries Bureau, (4) results from the IDNR-county voluntary beach monitoring program in 2008, 2009, and 2010, (5) results of Syngenta’s voluntary atrazine monitoring program (VMP) from 2004-2006, and (5) results of U.S. EPA/IDNR fish contaminant monitoring in 2005, 2006, and 2008.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” due to poor water clarity caused by non-algal turbidity. Due to low levels of chlorophyll (algae) over the last two IR cycles, the previous impairment due to algal turbidity is proposed for de-listing. The Class B(LW) (aquatic life) uses are assessed (monitored) as “partially supported” due to high turbidity that is adversely affecting the lake's fish populations. The Class C (drinking water) uses are assessed (evaluated) as "partially supported" due to increased levels of turbidity. Fish consumption uses are assessed (monitored) as “fully supported.” 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) information from the IDNR Fisheries Bureau, (4) results from the IDNR-county voluntary beach monitoring program in 2008, 2009, and 2010, (5) results of Syngenta’s voluntary atrazine monitoring program (VMP) from 2004-2006, and (5) results of U.S. EPA/IDNR fish contaminant monitoring in 2005, 2006, and 2008.
EXPLANATION: Results of IDNR city/county beach monitoring from 2008 through 2010 suggest that the Class A1 uses are “fully supported." Levels of indicator bacteria at Little River Lake beach were monitored once per week during the primary contact recreation seasons (May through September) of 2008 (13 samples), 2009 (8 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 Little River 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 57 E. coli orgs/100 ml in 2008, 20 E. coli orgs/100 ml in 2009, and 61 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 23% in 2008, 13% in 2009 and 25% in 2010. 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 “full support” of the Class A1 uses.
For the 2012 assessment/listing cycle, results from the ISU and UHL lake surveys, however, indicate that the Class A1 (primary contact recreation) uses of Little River Lake are assessed as “partially supported” due to high levels of turbidity in the lake. Using the median values from these surveys from 2006 through 2010 (approximately 16 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 67, 56, and 67 respectively for Little River Lake. According to Carlson (1977) the Secchi depth and total phosphorus scores place Little River Lake in between the eutrophic and hypereutrophic categories while the chlorophyll a score places Little River Lake at the upper end of the eutrophic category. These values suggest relatively low levels of chlorophyll a and suspended algae in the water, poor water transparency, and high levels of phosphorus in the water column.
NOTE: Little River Watershed Lake was assessed (monitored) as "partially supporting" (IR Category 5a) due to algae for the 2008 and 2010 assessment/listing cycles based on information from the DNR Fisheries Bureau. Data from the ISU and UHL lake monitoring programs for 2006-10, however, suggest low levels of chlorophyll a (TSI = 56) and cyanobacteria (39th lowest median among 134 monitored lakes). In addition, levels of chlorophyll for the previous (2010) assessment cycle were also low (TSI = 59). Therefore, because the chlorophyll TSI values have been less than the impairment threshold of 63 for two consecutive Integrated Reporting cycles (2010 and 2012), the chlorophyll/algae impairment is proposed for de-listing.
Based on data from the ISU and UHL lake surveys, the level of inorganic suspended solids was high at this lake and suggests that non-algal turbidity contributes to the impairment at this lake. The median inorganic suspended solids concentration at Little River Lake was 5.0 mg/L, which was the 55th highest of the 134 monitored lakes.
Data from the 2006-2010 ISU and UHL surveys suggest a relatively small population of cyanobacteria exists at Little River Lake. These data show that cyanobacteria comprised 70% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (12.0 mg/L) was the 39th lowest of the 134 lakes sampled. These results suggest full support of the Class A1 uses at Little River Lake.
The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” based on information from IDNR’s Fisheries Bureau. Information from the IDNR Fisheries Bureau indicates that Little River Lake experiences high turbidity and algae blooms. The water treatment plant at Little River Lake recorded the most turbid water clarity season during 2007 and the fishery is struggling to produce quality sportfish due to suppression of sportfish feeding and reproduction due to increased turbidity in the lake. Increasing turbidities in this lake are attributed to both the silt dam failure in 2007 and due to loss of silt-storage capacity behind the silt dam. An increasing population of common carp also impact water quality in this lake. A watershed improvment grant has been obtained to address soil loss in the watershed.
Data from the ISU and UHL lake surveys from 2006 through 2010 show no violations of the Class B(LW) criterion for ammonia in 16 samples, no violations of the Class B(LW) criterion for dissolved oxygen in 16 samples, and no violations of the Class A1,B(LW) criterion for pH in 16 samples. Based on IDNR’s assessment methodology these results suggest "full support" of the Class B(LW) uses of Little River Lake.
The Class C (drinking water) uses remain assessed (evaluated) as “partially supported” due to increasing turbidities in the lake following the failure of a silt dam at the upper end of the lake in 2007.
Results of Syngenta's "Iowa Voluntary Atrazine Monitoring Program" from 2004 through 2006, however, show low levels of atrazine in this lake and no impact to the Class C drinking water uses. NOTE: Little River Lake was not monitored as part of the Syngenta Voluntary Atrazine monitoring program in 2007 or 2008. The monitoring from 2004 through 2006 showed that the time-weighted mean levels of atrazine in the samples collected in calendar years 2004, 2005, and 2006 were well-below the MCL of 3.0 ug/l. The mean and median atrazine level over this three-year period (N=78) were 1.2 ug/L and 1.1 ug/L, respectively. The maximum value for this period was 2.7 ug/l. None of the 65 moving annual averages for atrazine for the years 2004, 2005, and 2006 at Little River Lake exceeded the MCL (maximum average = 1.6 ug/l). Based on DNR's Section 305(b) assessment methodology, if the average contaminant level in source water is less than the MCL, the Class C (drinking water) uses of the source water should be assessed as "fully supported." In addition, results of the ISU and UHL lake surveys from 2006-2010 show that nitrate levels are low at this lake (maximum: 7.1 mg/L, median: 0.3 mg/L) relative to the MCL (10 mg/L).
Fish consumption uses are assessed (monitored) as “fully supported” based on fish contaminant monitoring in 2005, 2006, and 2008. 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 composite samples of fillets from channel catfish and white crappie in 2005 had generally low levels of contaminants. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.92 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. Levels of primary contaminants in the composite sample of white crappie fillets were as follows: mercury: 0.12 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. The level of mercury in the sample of channel catfish fillets, however, exceeds the IDNR/IDPH trigger level of 0.30 ppm for a one meal per week consumption advisory. According to the IDNR/IDPH advisory protocol, 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 was conducted in 2006. The level of mercury in channel catfish was 0.186 ppm. The level of mercury in largemouth bass was 0.174 ppm. Both of these levels were below the trigger level for a fish consumption advisory, therefore Little River Lake is assessed as “fully supporting” the fish consumption uses. Follow up sampling was again conducted in 2008. The level of technical chlordane (<0.15 ppm) in channel catfish was below the trigger level for a fish consumption advisory. The level of total PCBs in the fillets of channel catfish was <0.45 ppm. Due to interference when analyzing the sample, the detection limit for this sample was above the advisory trigger level (0.2 ppm). Because the level of total PCBs is below the detection limit and past levels of PCBs in this lake were very low (<0.09 ppm) this result does not suggest cause for concern. Also the likelihood of high levels of PCBs at this lake is low, therefore this lake will remain assessed as "fully supporting" the fish consumption uses. Additional follow-up monitoring will be conducted in the future.
