Assessment Comments
Assessment based on results of (1) IDNR beach monitorng program in 2000-01, (2) fish tissue monitoring in 2000, (3) ISU lake survey in 2000-01, (4) ISU report on lake phytoplankton communities, and (5) surveys by IDNR Fisheries Bureau.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation uses) are assessed (evaluated) as "fully supported / threatened." The Class B(LW) aquatic life uses remain assessed (evaluated) as "fully supported / threatened." Fish consumption uses are assessed as "fully supported." Sources of information for this assessment include results of (1) IDNR beach monitoring in 2000 and 2001, (2) ISU lake survey in 2000-01, (3) surveys by IDNR Fisheries Bureau, (4) ISU report on lake plankton communities, and (5) results of U.S. EPA/IDNR fish tissue monitoring in 2000. EXPLANATION: Results of IDNR beach monitoring in 2000 and 2001 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 and 2001 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 30-day period is compared to the water quality standard of 200 fecal organisms/100ml. If a 30-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 30-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 30-day period (N=5), the use of single-sample maximum values to assess beaches is problematic. With less than 10 samples collected during any 30-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 27 thirty-day periods during summers of 2000 and 2001 had geometric means (N = 5 samples per period) greater than 200 orgs/100ml. The maximum 30-day geometric means were 187 orgs/100ml in 2000 and 14 orgs/100 ml in 2001. 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 and 30 orgs/100 ml in 2001). 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 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 high levels of phosphorus threatens full support of these uses at Lake Keomah. Using the median values from this survey in 2000 and 2001 (approximately six samples), Carlson's (1977) trophic state indices for total phosphorus, chlorophyll-a, and secchi depth are 78, 53, and 60, 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 lower range of eutrophic lakes; the TSI value for secchi depth falls at the upper limit of eutrophic lakes. These index values suggest (1) extremely high levels of phosphorus, (2) low levels of chlorophyll-a, and relatively 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 or zooplankton grazing) limits production of algae. Based on median values from ISU sampling in 2000 and 2001, the ratio of total nitrogen to total phosphorus for Lake Keomah is 10. This ratio suggest the strong possibility that production of algae at this lake is limited by availability of nitrogen. The levels of inorganic suspended solids at this lake are relatively low and do not suggest the potential for impairing designated uses. The median level of inorganic suspended solids in the 130 lakes sampled for the ISU lake survey in 2000 and 2001 was 5.27 mg/l; the median level at Lake Keomah was 3.5 mg/l. Despite the indications of relatively good water quality, the high TSI value for total phosphorus suggests a threat to the full support of the Class A (primary contact) uses through the potential presence of aesthetically objectionable blooms of algae as well as the presence of nuisance algal species (i.e., bluegreen algae). For example, 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. Although bluegreen algae tend to dominate the summertime phytoplankton community, especially in late summer, the production of chlorophyll is low at this lake, and the presence of bluegreen algae likely does not cuurrently present a significant water quality impact. Although results of ISU lake monitoring in 2000 and 2001 suggest threats to full support of the designated beneficial uses of this lake, the amount of data available for characterizing water quality is not sufficient for developing an accurate assessment of support of these uses. Additional data for this lake are being generated as part of the ongoing ISU lake survey; these data will be used to improve the accuracy of future water quality assessments. The previous assessment of support of the Class B(LW) uses ("fully supported / threatened") was reviewed and approved by the DNR Fisheries Bureau. Fish consumption uses are assessed 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.
