Assessment Comments
Assessment is based on: (1) results of the IDNR-UHL beach monitoring program in summers of 2006, 2007, and 2008, (2) results from the IDNR-county voluntary beach monitoring program in 2006, 2007, and 2008, (3) results of the statewide survey of Iowa lakes conducted from 2004 through 2007 by Iowa State University (ISU), (4) results of the statewide ambient lake monitoring program conducted from 2005 through 2008 by University Hygienic Laboratory (UHL), (5) information from the IDNR Fisheries Bureau, and (6) results of a fish kill investigation in August 2009.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to violations of the state water quality criteria for indicator bacteria at Marble Beach. The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” based on results of a fish kill investigation in August 2009. The Class C (drinking water) uses are “not assessed” due to a lack of recent information upon which to base an assessment. Fish consumption uses are "not assessed" due to a lack of recent information upon which to base an assessment. Sources of data for this assessment include (1) results of the IDNR-UHL beach monitoring program in summers of 2006, 2007, and 2008, (2) results from the IDNR-county voluntary beach monitoring program in 2006, 2007, and 2008, (3) results of the statewide survey of Iowa lakes conducted from 2004 through 2007 by Iowa State University (ISU), (4) results of the statewide ambient lake monitoring program conducted from 2005 through 2008 by University Hygienic Laboratory (UHL), (5) information from the IDNR Fisheries Bureau, and (6) results of a fish kill investigation in August 2009.
EXPLANATION: Results of IDNR beach monitoring at Crandall’s Beach on Big Spirit Lake from 2006 through 2008 suggest that the Class A1 uses should be assessed (monitored) as “fully supported." Levels of indicator bacteria were monitored once per week during the primary contact recreation seasons (May through September) of 2006 (28 samples), 2007 (15 samples), and 2008 (27 samples) at Crandall's Beach and Marble Beach as part of the IDNR 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 Crandall’s beach, the geometric means of all 58 thirty-day periods during the summer recreation seasons of 2006, 2007 and 2008 were below the Iowa water quality standard of 126 E. coli orgs/100 ml. These results suggest generally low levels of indicator bacteria at this lake. Also, there were no violations of the single-sample maximum criterion in 2007 or 2008 and the percentage of samples exceeding the single-sample maximum criterion was 7% in 2006. Thus, these results do not suggest an impairment of the Class A1 uses of Big Spirit Lake.
Results of IDNR beach monitoring from 2006 through 2008 at Marble Beach suggest that the Class A1 uses are "not supported." At Marble beach, the geometric means of 2 thirty-day periods during the summer recreation season of 2006 exceeded the Iowa water quality standard of 126 E. coli orgs/100 ml. No geometric means violated the criteria in 2007 or 2008. There were also no violations of the single-sample maximum criterion in 2007 or 2008 and the percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was 7% in 2006. According to IDNR’s assessment methodology and U.S. EPA guidelines, the violations of the geometric mean criterion suggest impairment (nonsupport) of the Class A1 (primary contact recreation) uses.
Results of IDNR-county beach monitoring from 2006 suggest that the Class A1 uses are assessed (evaluated) as "fully supported." Levels of indicator bacteria at Orleans Beach at Big Spirit Lake were monitored approximately once per week during the primary contact recreation seasons (May through August) of 2006 (16 samples) as part of the IDNR county beach monitoring program. At Orleans beach, the geometric means of all 12 thirty-day periods during the summer recreation season of 2006 were below the Iowa water quality standard of 126 E. coli orgs/100 ml. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was 13% in 2006. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest "full support" of the Class A1 (primary contact recreation) uses. Due to limited data (only one year) this assessment is considered "evaluated" rather than "monitored" indicating an assessment of lower confidence.
Results from the ISU and UHL lake surveys, however, suggest that the Class A1 uses of Big Spirit Lake are assessed (monitored) as “fully supported." Using the median values from these surveys from 2004 through 2008 (approximately 25 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 54, 56, and 58 respectively for Big Spirit Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Big Spirit Lake in the eutrophic category. These values suggest relatively low levels of chlorophyll a and suspended algae in the water, very good water transparency, and relatively low levels of phosphorus in the water column.
The levels of inorganic suspended solids were relatively low at this lake and do not suggest water quality problems due to non-algal turbidity. The median level of inorganic suspended solids in Big Spirit Lake (2.0 mg/L) was the 17th lowest median concentration among the 132 lakes sampled by the ISU and UHL lake surveys.
Data from the 2004-2008 ISU and UHL surveys suggest a relatively large population of cyanobacteria exists at Big Spirit Lake. These data show that cyanobacteria comprised 81% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (36.0 mg/L) was also the 29th highest of the 132 lakes sampled. This median is in the worst 25% of the 132 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 for the 2004-2008 period. 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. The assessment category for 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 (evaluated) as “partially supported” based on results of a fish kill investigation in August 2009. The kill occurred on or before August 13, 2009. Approximately 600 walleye were killed along the southeast shoreline of Spirit Lake. Results of the investigation indicate that low levels of dissolved oxygen likely caused by algae and aquatic plant decomposition caused the kill. According to the IDNR assessment/listing methodology, the occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or waterbody reach during the most recent assessment period (2006-2009) indicates a severe stress to the aquatic community and suggests that the aquatic life uses should be assessed as “impaired.” If a cause of the kill was not identified during the IDNR investigation, or if the kill was attributed to non-pollutant causes (e.g., winterkill), the assessment type will be considered “evaluated.” Such assessments, although suitable for Section 305(b) reporting, lack the degree of confidence to support addition to the state Section 303(d) list of impaired waters (IR Category 5). Waterbodies affected by such fish kills will be placed in IR subcategories 2b or 3b and will be added to the state list of waters in need of further investigation.
Information from the IDNR Fisheries Bureau and results from the ISU and UHL lake surveys suggest that the Class B(LW) uses should be assessed as "fully supported." The ISU and UHL lake survey results show good chemical water quality at Big Spirit Lake. During 2004-2008 there were no violations of the Class B(LW) criterion for ammonia (25 samples), or dissolved oxygen (25 samples), and only one violation of the pH criterion in 25 samples. Based on IDNR’s assessment methodology, the one violation of the pH criterion does not constitute an impairment of the Class A1,B(LW) uses at Big Spirit Lake.
The Class C (drinking water) uses are “not assessed” due to the lack of recent information upon which to base an assessment. In previous 305(b) assessment cycles, the Class C uses were assessed as "fully supported" based on results of sampling conducted by UHL in January 1995 (see assessment for the 1996 and 1998 reports). However, these data are now considered too old (greater than ten years) to characterize current water quality conditions. 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 2004-08 show that nitrate levels are extremely low at this lake (maximum value = 0.6 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 were “not assessed” due to a lack of recent fish contaminant monitoring at this lake. The most recent fish tissue monitoring was conducted in 1997. While these results suggest that levels of contaminants were low at Big Spirit Lake, they are now too old (greater than 10 years) to be used for an assessment.
