Assessment Comments
Assessment based on results of (1) IDNR beach monitoring program from 2000-02, (2) EPA/DNR fish tissue (RAFT) monitoring in 2000, (3) ISU lake survey from 2000-02, (4) ISU report on lake plankton communities, and (5) surveys by IDNR Fisheries Bureau.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation uses) are assessed (monitored) as "fully supported / threatened" due to levels of chlorophyll (algae) and inorganic suspended solids that lead to somewhat reduced water transparency. Results of IDNR beach monitoring, however, suggest “full support” of the Class A uses. The Class B(LW) aquatic life uses remain assessed (evaluated) as "fully supported / threatened" due to algal blooms and inorganic turbidity. The Class C (drinking water) uses are "not assessed" due to the lack of water quality information upon which to base an assessment. Fish consumption uses are assessed (monitored) as "fully supported" based on fish contaminant monitoring in 2000. Sources of information for this assessment include results of (1) IDNR beach monitoring from 2000 through 2002, (2) results of the statewide survey of Iowa lakes conducted in 2000 and 2001 by Iowa State University (ISU), (3) information from the IDNR Fisheries Bureau, (4) information on plankton communities at Iowa lakes in 2000 from Downing et al. (2002), and (5) results of U.S. EPA/IDNR fish tissue monitoring in 2000.
EXPLANATION: Results of IDNR beach monitoring from 2000 through 2002 suggest "full support" of the Class A uses. Levels of indicator bacteria at Lake Keomah beach were monitored once per week during the primary contact recreation seasons (April through October) of 2000, 2001, and 2002 as part of the IDNR beach monitoring program. According to U.S. EPA guidelines for determining support of primary contact recreation uses (U.S. EPA 1997b, page 3-35), the geometric mean of fecal coliform bacteria level from at least five samples collected over a thirty-day period is compared to the water quality standard of 200 fecal organisms/100ml. If a thirty-day geometric mean exceeds 200 orgs/100 ml, the primary contact recreation uses are assessed as "not supported." In addition, the U.S. EPA guidelines state that if more than 10% of the total samples taken during any thirty-day period has a bacterial density that exceeds 400 fecal coliform organsims/100 ml, the primary contact recreation uses are assessed as "partially supported." Due to the relatively low numbers of samples collected during any thirty-day period (N=5), the use of single-sample maximum values to assess beaches is problematic. With less than 10 samples collected during any thirty-day period at Iowa beaches, the occurrence of a single level of bacteria above the single-sample maximum value will result in more than 10% violation of the single-sample maximum value and thus suggest impairment of the primary contact recreation uses. The use of less than 10 samples in an assessment based on a critical value of 10% results in large probabilities (approximately 60%) of incorrectly concluding that an impairment exists. For this reason, the single-sample maximum value is not used to assess support of primary contact recreation uses with data from the IDNR beach monitoring program. At Lake Keomah beach, none of the 52 thirty-day periods during summers of 2000, 2001, and 2002 had geometric means (N = 5 samples per period) greater than 200 orgs/100ml. The maximum thirty-day geometric means were 187 orgs/100ml in 2000, 14 orgs/100 ml in 2001, and 15 orgs/100 ml in 2002. One of the weekly samples in 2000 (6% of samples) exceeded the U.S. EPA's recommended single-sample maximum value of 400 orgs/100 ml (maximum sample values were 600 orgs/100 ml in 2000, 30 orgs/100 ml in 2001, and 100 orgs/100ml in 2002). These results suggest (1) “full support” of primary contact recreation uses at this beach and (2) that levels of bacteria at this beach are generally very low.
Despite results of IDNR beach monitoring that suggest full support" of the Class A uses, results from the ISU statewide survey of Iowa lakes suggest that reduced water transparency threatens full support of these uses at Lake Keomah. Using the median values from this survey from 2000 through 2002 (approximately nine samples), Carlson's (1977) trophic state indices for total phosphorus, chlorophyll-a, and secchi depth are 75, 58, and 64, respectively. According to Carlson (1977), the index value for total phosphorus places this lake in the range of hyper-eutrophic lakes; the index value for chlorophyll-a, however, places this lake in the upper range of eutrophic lakes; the TSI value for secchi depth falls in the middle range between eutrophic and hyper-eutrophic lakes. These index values suggest (1) very high levels of phosphorus, (2) relatively low levels of chlorophyll-a, and only marginally good water transparency. According to Carlson (1991), the occurrence of a high TSI value for total phosphorus with relatively low values for chlorophyll-a and secchi depth indicate that some factor (e.g., nitrogen limitation, zooplankton grazing, or some other factor) other than phosphorus limits production of algae. Results of ISU monitoring suggest that nitrogen-limitation and possibly inorganic suspended solids combine to limit algal production at this lake. Based on median values from ISU sampling from 2000 through 2002, the ratio of total nitrogen to total phosphorus for Lake Keomah is 12. This ratio suggest the possibility that production of algae at this lake is limited by availability of nitrogen. The levels of inorganic suspended solids at this lake are somewhat elevated and suggest the potential for contributing to in-lake turbidities. The median level of inorganic suspended solids in the 131 lakes sampled for the ISU lake survey from 2000 through 2002 was 4.8 mg/l; the median level at Lake Keomah was 3.0 mg/l. The plankton sampling conducted in 2000 by Downing et al. (2002) did not produce types of zooplankton (Cladocerans) that graze on algae.
Populations of bluegreen algae at Lake Keomah are relatively low and do not likely threaten or impair designated uses. Data from Downing et al. (2002) suggest that bluegreen algae (Cyanophyta) tend to dominate the phytoplankton community of this lake in mid to late summer. Sampling in 2000 showed the percent wet mass of bluegreens ranged from less than 10% in the late June sampling, to approximately 90% in the late July sampling, and up to approximately 100% in the mid-August sampling. However, the 2000 average summer mass of bluegreen algae at Lake Keomah (8.6 mg/l) was the 58th lowest of the 131 lakes and thus does not appear to either threaten or impair designated uses.
The previous assessment of support of the Class B(LW) uses ("fully supported / threatened") was reviewed and approved by the DNR Fisheries Bureau. The IDNR fisheries biologist states that algae blooms do occur at Lake Keomah and that summer fish kills have resulted; turbidity at this lake is related primarily to colloidal clays in the watershed that tend to resist settling from the water column in the lake. Drinking water (Class C) uses were not assessed due to the lack of water quality information upon which to base an assessment. The only parameter collected as part of the ISU lake survey relevant to support of Class C (drinking water) uses is nitrate. While the results of the ISU survey from 2000-02 show that nitrate levels at Lake Keomah (maximum value = 1.4 mg/l; median = 0.2 mg/l) are very low relative to the drinking water MCL (10 mg/l), these data are not sufficient for developing a valid assessment of support of the Class C uses. Fish consumption uses are assessed (monitored) as "fully supported" based on results of EPA/DNR fish tissue (RAFT) monitoring at Lake Keomah in 2000 that showed levels of all contaminants in the composite samples of fillets from channel catfish and largemouth bass were far below ½ of the respective FDA action levels and DNR levels of concern.
