Assessment Comments
Assessment is based on (1) surveys of DNR Fisheries Bureau, (2) results of IDNR beach monitoring program from 2000-02, (3) results of fish tissue (RAFT) monitoring in 1997, (4) ISU lake surveys from 2000-02, and (5) the ISU study of lake plankton communities in 2000.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "fully supporting/ threatened" due to reduced water transparency related primarily to moderately high levels of inorganic suspended solids. The Class B(LW) aquatic life uses remain assessed (evaluated) as “fully supporting / threatened" due to nutrient loading to the water column and to siltation impacts. The Class C (drinking water) uses remain "not assessed" due to the lack of information upon which to base an assessment. Fish consumption uses remain assessed (evaluated) as "fully supporting" based on results of fish contaminant monitoring in 1997. The sources of data for this assessment include (1) results of the IDNR-UHL beach monitoring program in summers of from 2000 through 2002, (2) surveys of the IDNR Fisheries Bureau, (3) results of U.S. EPA/IDNR fish tissue monitoring in 1997, (4) results of ISU lake survey from 2000-02, and (5) 2002 ISU report on lake plankton communities (Downing et al. 2002).
EXPLANATION: Results of IDNR beach monitoring in 2000, 2001, and 2002 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 2000-02 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 45 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 30-day geometric means were 26 orgs/100ml in 2000, 16 orgs/100 ml in 2001, and 19 orgs/100 ml in 2002. None of the 57 weekly samples collected during 2000-02 exceeded the U.S. EPA's recommended single-sample maximum value of 400 orgs/100 ml. 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 moderately high levels of inorganic suspended solids may threaten full support of the Class A uses of Red Haw Lake. 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 58, 57, and 62, respectively. According to Carlson (1977), the index values for total phosphorus and chlorophyll-a place this lake at the upper range of eutrophic lakes; the index value for Secchi depth is in the lower range between eutrophic and hyper-eutrophic lakes. These index values suggest relatively low levels of phosphorus, relatively low levels of chlorophyll-a, but only marginally good water transparency. According to Carlson (1991), the occurrence of a high TSI value for secchi depth relative to that for chlorophyll-a suggests that non-algal turbidity limits algal production. The levels of inorganic suspended solids at this lake are moderately high relative to other Iowa lakes and do suggest the potential for contributing to in-lake turbidity and thus limiting algal production. 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 Red Haw Lake was 5.0 mg/l; this is the 61st highest median level of the 131 lakes sampled. Based on median values from ISU sampling from 2000 through 2002, the ratio of total nitrogen to total phosphorus for Red Haw Lake is 23. This TN:TP suggests that algal production at this lake is not limited by nitrogen availability. In addition, data from Downing et al. (2002) show that the zooplankton community of Red Haw Lake has moderately large populations of species (Cladocerans) known as algal grazers. The summer 2000 average mass of Cladocerans at this lake (19.6 mg/l) was the 63rd highest of the 131 lakes sampled. At this level, zooplankton grazers may have some impact on algal production at this lake. Thus, the results of ISU monitoring from 2000-02 suggest a threat to full support of the Class A uses from slight reductions in water transparency due primarily to turbidity caused by the moderately high levels of inorganic suspended solids.
Data from Downing et al. (2002) suggest that bluegreen algae (Cyanophyta) comprise a significant portion of the summertime phytoplankton community of this lake but that the mass of bluegreens is low relative to those of other Iowa lakes. 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. The summer 2000 average mass of bluegreens (3.8 mg/l) was the 35th lowest of the 131 lakes sampled. At this level, 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. The Class C (drinking water) uses remain "not assessed" due to lack of water quality information on which to base such 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 are very low at this lake (maximum value = 0.4 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 remain assessed (evaluated) 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).
