Assessment Comments
Assessment is based on results of (1) ISU lake survey in 2000-01, (2) surveys by IDNR Fisheries Bureau, and (3) ISU report on lake plankton communities, 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 (evaluated) as "fully supporting / threatened." The Class B(LW) aquatic life uses remain assessed (evaluated) as "partially supporting." Fish consumption uses are "not assessed." The sources of data for this assessment include (1) results of IDNR/UHL beach monitoring in 2000 and 2001, (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, and (4) information on phytoplankton communities at Iowa lakes in 2000 from Downing et al. (2002). Further monitoring and investigation are needed to better characterize water quality conditions at this lake.
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 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 Lower Pine Lake Beach, none of the 26 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 54 orgs/100ml in 2000 and 24 orgs/100 ml in 2001. Only one 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: the sample from July 11, 2000, contained 7,500 orgs/100 ml (the next highest sample contained 120 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 may threaten the Class A uses of Lower Pine 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 74, 59, 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 is in the upper range of eutrophic lakes, and the index value for secchi depth is 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) relatively low (and much less than expected) production of suspended algae, and (3) moderately poor 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) other than phosphorus limits production of algae. Based on median values from ISU sampling in 2000 and 2001, the ratio of total nitrogen to total phosphorus for Lower Pine Lake is 45. This TN:TP ratio suggests that nitrogen does not limit algal production at this lake. In addition, data from Downing et al. (2002) show 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. 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, however, are moderately high and suggest at least the potential for contributing to in-lake turbidity and limiting production of suspended algae. 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 Lower Pine Lake was 6.5 mg/l. The relatively high TSI values for total phosphorus, chlorophyll-a, and secchi depth suggest potential threats to the Class A (primary contact) uses through presence of aesthetically objectionable blooms of algae and high levels of non-algal turbidity. 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 Class B(LW) aquatic life uses remain assessed as "partially supported" based on review of the previous (2000) assessments by the DNR Fisheries Bureau. 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. Fish consumption uses are "not assessed" due to the lack of recent fish contaminant monitoring at this lake (see assessment for the 2000 report above).
