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) results from the IDNR-county voluntary beach monitoring program in 2006, 2007, and 2008, and (4) information from the IDNR Fisheries Bureau.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to poor water transparency caused mainly by inorganic suspended solids that violates Iowa’s narrative water quality standard protecting against aesthetically objectionable conditions. Algal turbidity also contributes to the impairment at this lake. The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported.” Excessive growth of aquatic macrophytes at this shallow lake, however, remains a concern. Fish consumption uses are “not assessed” due to a lack of information upon which to base an assessment. 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) results from the IDNR-county voluntary beach monitoring program in 2006, 2007, and 2008, and (4) information from the IDNR Fisheries Bureau.
Note: A TMDL for turbidity at Spring Lake was prepared by IDNR and approved by EPA in 2006. Because the primary Section 303(d) impairment identified for the 2010 assessment/listing cycle (turbidity) is addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved) for the 2010 cycle.
EXPLANATION: Results of IDNR county beach monitoring from 2006 through 2008 suggest that the Class A1 uses are assessed (evaluated) as "fully supported." Levels of indicator bacteria at Spring Lake beach were monitored approximately once per week during the primary contact recreation seasons (May through August) of 2006 (11 samples), 2007 (9 samples), and 2008 (5 samples) as part of the IDNR county beach monitoring program. Because a limited number of samples were collected in 2008, a 30-day geometric mean could not be calculated. Thus, these data are considered not sufficient to accurately characterize current water quality conditions, therefore the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). 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 Spring Lake beach, the geometric means of all 3 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. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was 0% in 2006 and 2008, and 22% in 2007. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest full support of the Class A1 (primary contact recreation) uses.
Results from the ISU and UHL lake surveys suggest that the Class A1 uses at Spring Lake are “not supported.” Using the median values from these surveys from 2004 through 2008 (approximately 19 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 76, 70, and 67 respectively for Spring Lake. According to Carlson (1977) the Secchi depth and chlorophyll a values place Spring Lake in the hypereutrophic category, while the total phosphorus value places Spring Lake in between the eutrophic and hypereutrophic categories. These values suggest very high levels of chlorophyll a and suspended algae in the water, extremely poor water transparency, and high levels of phosphorus in the water column.
The level of inorganic suspended solids is very high at this lake and suggests impairment due to non-algal turbidity. The median inorganic suspended solids concentration at Spring Lake was 12.0 mg/L, which was the 14th highest of the 132 monitored lakes.
Data from the 2004-2008 ISU and UHL surveys suggest a moderately large population of cyanobacteria exists at Spring Lake, which does not suggest an impairment due to nuisance aquatic life at this lake. These data show that cyanobacteria comprised only 60% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (20.0 mg/L) was also the 48th highest of the 132 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed as “fully supported” based on information from the IDNR Fisheries Bureau and results from the ISU and UHL lake surveys. Information from the IDNR Fisheries Bureau suggests that nuisance aquatic macrophytes remain a concern at this lake. The ISU and UHL lake surveys show that during 2004-2008 there were no violations of the Class B(LW) criterion for ammonia in 19 samples, or dissolved oxygen in 19 samples. There were 2 violations of the criterion for pH in 19 samples (11%). However, based on IDNR’s assessment methodology these violations were not significantly greater than 10% of the samples and therefore do not suggest impairment of the Class B(LW) uses at Spring Lake.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this lake.
