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 phytoplankton communities.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation uses) are assessed (evaluated) as "partially supported." The Class B(LW) aquatic life uses remain assessed (evaluated) as "partially supported". Fish consumption remain "not assessed." Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted in 2000 and 2001 by Iowa State University (ISU), (2) information from the IDNR Fisheries Bureau, and (3) information on phytoplankton communities at Iowa lakes in 2000 from Downing et al. (2002). EXPLANATION: For the 2002 reporting cycle, the level of support of the Class A (primary contact recreation) uses are assessed (evaluated) as "partially supported" based on results from the ISU statewide survey of Iowa 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 82, 59, and 68, respectively, for Indian Lake. 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 upper range of eutrophic lakes, and the index value for secchi depth is in the upper range between eutrophic and hyper-eutrophic lakes. These index values suggest excessive levels of phosphorus in the water column, relatively low (and less than expected) levels of chloropohyll-a (suspended algae), and 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) limits production of algae. Based on median values from ISU sampling in 2000 and 2001, the ratio of total nitrogen to total phosphorus for Indian Lake is 8. This TN:TP ratio, as well as the dominance of the phytoplankton community by bluegreen algae, suggest the possibility that the production of algae at this lake is limited by the availability of nitrogen. Carlson (1991) also suggest that the occurrence of a high TSI value for secchi depth relative to that for chlorophyll-a suggests that non-algal turbidity limits algal production. At Indian Lake, the low chlorophyll-a TSI (59) relative to that for secchi depth (68) may be related, in part, to non-algal turbidity. During the 2000 and 2001 ISU surveys, however, levels of inorganic suspended solids were typical (median =5.0 mg/l) compared to other Iowa lakes. This median level suggests that contributions of inorganic suspended solids to in-lake turbidity are likely minor. These conditions suggest impairments to the Class A (primary contact) uses through presence of non-algal turbidity, aesthetically objectionable blooms of algae and presence of nuisance algal species (i.e., bluegreen algae). Data from Downing et al. (2002) suggest that bluegreen algae (Cyanophyta) dominate the summertime phytoplankton community of Indian Lake. Sampling in 2000 showed the percent wet mass of bluegreens comprised from 95% to 100% of the phytoplankton community in the three summer samples from this lake. Although results of ISU lake monitoring in 2000 and 2001 suggest that nutrient-related impairments may exist, neither the amount of data available for characterizing water quality nor the magnitude of the TSI values are sufficient for identifying impairments with the level of confidence necessary to justify adding this lake to Iowa's Section 303(d) list. Thus, further investigation and monitoring are needed to (1) better characterize current water quality conditions and (2) verify that such impairments exist. 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 hyper-eutrophic conditions at this lake, along with information from the IDNR Fisheries Bureau, suggest that the Class B(LW) aquatic life uses are "partially supported" due to excessive nutrient loading to the water column, nuisance blooms of algae, and impacts from organic enrichment in the lake. Fish consumption remain "not assessed" due to the lack of fish contaminant monitoring in this lake.
