Assessment Comments
Assessment is based on results of (1) ISU lake survey from 2000-02, (2) surveys by IDNR Fisheries Bureau, and (3) ISU report on lake plankton communities in 2000, and (4) results of U.S. EPA/IDNR fish tissue monitoring in 2001.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "partially supported" due to algal blooms and high levels of non-algal (inorganic) turbidity. The Class B(LW) aquatic life uses remain assessed (evaluated) as "partially supporting" due to nutrient loading to the water column that produces nuisance algal blooms. Fish consumption uses are "not assessed" due to the lack of recent fish contaminant monitoring at this lake. The sources of data for this assessment include (1) results of IDNR/UHL beach monitoring from 2000 through 2002, (2) results of the statewide survey of Iowa lakes conducted from 2000 through 2002 by Iowa State University (ISU), (3) information from the IDNR Fisheries Bureau, and (4) information on plankton communities at Iowa lakes in 2000 from Downing et al. (2002).
EXPLANATION: Results of IDNR beach monitoring suggest "full support" of the Class A uses. Levels of indicator bacteria at the Lower Pine Lake beach were monitored once per week during the primary contact recreation seasons (April 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 Lower Pine Lake Beach, none of the 51 thirty-day periods during summers of 2000-02 had geometric means (N = 5 samples per period) greater than 200 orgs/100ml. The maximum 30-day geometric means were 54 orgs/100ml in 2000, 24 orgs/100 ml in 2001, and 116 orgs/100 ml in 2002. Only two of the 63 weekly samples collected from 2000-02 exceeded the U.S. EPA's recommended single-sample maximum value of 400 orgs/100 ml: the sample from July 11, 2000, contained 7,500 orgs/100 ml, and the sample from May 28, 2002 contained 650 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 generally very low.
Despite results from 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 algal and non-algal turbidity impair the Class A uses of Lower Pine 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 74, 65, and 66, respectively. According to Carlson (1977), the index value for total phosphorus places this lake in the range of hyper-eutrophic lakes; the index values for chlorophyll-a and Secchi depth are in the middle range between eutrophic and hyper-eutrophic lakes. These index values suggest (1) very high levels of phosphorus in the water column, (2) somewhat elevated (but less than expected) production of suspended algae, and (3) moderately poor water transparency. The TSI values for both chlorophyll-a (65) and Secchi depth (66) suggest impairment of the designated uses. 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. The ISU lake data suggest that non-algal (inorganic) particles are likely the primary factor limiting algal production at Lower Pine Lake. The levels of inorganic suspended solids at this lake are moderately high and suggest the potential for contributing to in-lake turbidity and limiting production of suspended algae. 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 Lower Pine Lake was 5.9 mg/l; this was the 53rd highest level of the 131 lakes sampled. Other potential non-phosphorus limitation (nitrogen limitation and algal grazing) do not appear 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 Lower Pine Lake is 27. This TN:TP ratio suggests that nitrogen availability does not limit algal production at this lake. In addition, data from Downing et al. (2002) shows only moderately large populations of zooplankton species at this lake that graze on algae. Sampling in 2000 showed that Cladoceran taxa (e.g., Daphnia) comprised approximately 30% of the dry mass of the zooplankton community in the late July sample but only 10% of the late August sample. The 2000 average mass of Cladoceran grazers at this lake (15.6 mg/l) was the 58th lowest of the 131 lakes sampled. Thus, the relatively high TSI values for chlorophyll-a and secchi depth suggest impairments of the Class A (primary contact) uses through presence of blooms of algae and high levels of non-algal turbidity that violate Iowa’s narrative water quality standard protecting against aesthetically objectionable conditions.
Presence of nuisance algal species (i.e., bluegreen algae) does not appear to be a significant problem at this lake. Data from Downing et al. (2002) suggest that bluegreen algae (Cyanophyta) comprise a significant portion of the phytoplankton community of this lake in mid summer (approximately 50% by wet mass) but a relatively small portion by late summer (less than 10% by wet mass). Sampling in 2000 showed the percent wet mass of bluegreens ranged from less than 55% in the mid-July sampling, to approximately 25% in the late July sampling, and down to approximately 5% in the late August sampling. The 2000 average summer mass of bluegreen algae (2.1 mg/l) was the 21st lowest of the 131 lakes sampled. This level suggests neither a threat nor an impairment of the designated uses at this lake.
Information from the DNR Fisheries Bureau suggests that the Class B(LW) aquatic life uses should remain assessed (evaluated) as "partially supported" due to high levels of nutrients in the water column that contribute to nuisance algal blooms. Fish consumption uses are "not assessed" due to the lack of recent fish contaminant monitoring at this lake. This lake was, however, sampled in 2003 as part of the U.S. EPA/IDNR RAFT fish contaminant monitoring program. The results from this sampling, however, are not yet available.
