Assessment Comments
Assessment is based on (1) surveys of DNR Fisheries Bureau, (2) results of IDNR beach monitoring program in 2000-01, (3) results of fish tissue (RAFT) monitoring in 1997, (4) ISU lake surveys in 2000-01, & ISU plankton study.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "fully supporting." The Class B(LW) aquatic life uses remained assessed (evaluated) as fully supporting." The Class C (drinking water) uses remain "not assessed." Fish consumption uses remain assessed as "fully supporting." The sources of data for this assessment include (1) results of the IDNR-UHL beach monitoring program in summers of 2000 and 2001, (2) surveys of the IDNR Fisheries Bureau, (3) results of U.S. EPA/IDNR fish tissue monitoring, (4) results of ISU lake survey in 2000-01, and (5) 2002 ISU report on lake plankton communities.
EXPLANATION: Results of IDNR beach monitoring in 2002 and 2001 suggest full support of the Class A uses. Levels of indicator bacteria at Red Haw Lake beach were monitored once per week during the primary contact recreation seasons (May 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 Red Haw Lake 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 26 orgs/100ml in 2000 and 16 orgs/100 ml in 2001. None of the 35 weekly samples collected during 2000 and 2001 exceeded the U.S. EPA's recommended single-sample maximum value of 400 orgs/100 ml (maximum sample values were 150 orgs/100 ml in 2000 and 60 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 extremely low.
Despite the 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 levels of phosphorus may threaten full support of the Class A uses of Red Haw Lake. 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 59, 55, and 59, respectively. According to Carlson (1977), the index values for total phosphorus and secchi depth place this lake at the upper range of eutrophic lakes; the index value for chlorophyll-a is in the middle range of eutrophic lakes. These index values suggest moderately high levels of phosphorus, relatively low levels of chlorophyll-a, and relatively good water transparency. The levels of inorganic suspended solids at this lake are typical for Iowa lakes and do not suggest a strong potential for contributing to in-lake turbidity. 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 Red Haw Lake was 5.5 mg/l; this is the 70th highest median level of the 130 lakes sampled. Data from Downing et al. (2002) suggest that bluegreen algae (Cyanophyta) comprise a significant portion of the summertime phytoplankton community of this lake. Sampling in 2000 showed less than 10% of the wet mass of the phytoplankton community in late summer was bluegreens, but from 50 to over 80% was bluegreen algae in the late June and late July samplings, respectively. Although bluegreen algae tend to dominate the summertime phytoplankton community, the production of chlorophyll is relatively low at this lake, and the presence of bluegreen algae likely does not present a significant water quality impact. The eutrophic conditions at this lake, along with information from the IDNR Fisheries Bureau, suggest that the Class B(LW) aquatic life uses should be assessed as "fully supported / threatened" due to nutrient loading to the water column and siltation in the lake. 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 Class C (drinking water) uses remain "not assessed" due to lack of water quality information on which to base such an assessment. Fish consumption remain assessed as "fully supporting" based on results of U.S. EPA/IDNR fish tissue (RAFT) monitoring in 1997 (see assessment for the 1998 and 2000 reports).
