Assessment Comments
Assessment is based on results of (1) ISU lake survey from 2000-04, (2) surveys by IDNR Fisheries Bureau, and (3) ISU reports on lake phytoplankton communities from 2000-05.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation uses) are assessed (monitored) as "partially supported" due to algal turbidity and algal blooms that create aesthetically objectionable conditions. Large populations of nuisance aquatic life (bluegreen algae) potentially suggest an additional impairment of the Class A uses at this lake. Levels of inorganic suspended solids are typical for Iowa lakes but are sufficiently high to contribute to poor water transparency at this lake. The Class B(LW) aquatic life uses remain assessed (evaluated) as "partially supported" due to nutrient, nuisance algal blooms, and occasional fish kills (organic enrichment) that sometimes follow algal die-off. Frequent violations of Iowa’s water quality criterion for pH suggest that both the Class A and Class B(LW) uses should be assessed (monitored) as “partially supported”. Fish consumption remain "not assessed" due to the lack of fish contaminant monitoring at this lake. Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes sponsored by IDNR and conducted by Iowa State University (ISU) from 2000 through 2004, (2) surveys by IDNR Fisheries Bureau, and (3) information on plankton communities collected at Iowa lakes from 2000 through 2005 as part of the ISU lake survey.
Note: A TMDL for organic enrichment and noxious aquatic plants (cyanobacteria) at Indian Lake was prepared by IDNR and approved by EPA in 2005. Because all Section 303(d) impairments identified for the 2006 assessment/listing cycle (algal growth, pH, turbidity, and potentially cyanobacteria) are addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved).
EXPLANATION: The Class A (primary contact recreation) uses are assessed (monitored) as "partially supported" based on results from the ISU statewide survey of Iowa lakes. Using the median values from this survey from 2000 through 2004 (approximately 15 samples), Carlson's (1977) trophic state indices for total phosphorus, chlorophyll-a, and secchi depth are 82, 70, and 70, respectively, for Indian Lake. According to Carlson (1977), the index value for total phosphorus places this lake well into the range of hyper-eutrophic lakes. The index values for chlorophyll-a and Secchi depth are at the upper boundary of the range between eutrophic and hyper-eutrophic lakes.. These index values suggest extremely high levels of phosphorus in the water column, relatively high levels of chlorophyll-a (suspended algae), and relatively poor water transparency.
According to Carlson (1991), the occurrence of a high TSI value for total phosphorus with relatively lower 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. Results of ISU monitoring suggest that nitrogen availability and zooplankton grazing may serve as non-phosphorus limitations to algal production at this lake.
Based on median values from ISU sampling from 2000 through 2004, the ratio of total nitrogen to total phosphorus for Indian Lake is 8. This TN:TP ratio suggests a good possibility that the production of algae at this lake is at times limited by the availability of nitrogen.
Results of the 2000-04 ISU survey, however, shows that the level of inorganic suspended solids at Indian Lake (4.9 mg/l) was approximately equal to the overall median level (5.2 mg/l) for the 131 lakes sampled. This median level suggests that inorganic suspended solids contribute to in-lake turbidity and may also limit algal production to some degree.
These water quality conditions suggest impairments to the Class A (primary contact) uses primarily through presence of algal turbidity and blooms that violate Iowa’s narrative water quality standards protecting against aesthetically objectionable conditions. The IDNR Fisheries Bureau concurs with this assessment.
The presence of nuisance (=noxious) algal species (i.e., bluegreen algae) may also present an impairment of the Class A uses at this lake. Data from the ISU survey from 2000 through 2004 suggest that bluegreen algae (Cyanophyta) dominate this lake’s summertime phytoplankton community. Sampling from 2000 through 2004 showed that the percent wet mass of bluegreen algae in the phytoplankton community of Indian Lake in summers of the 2000-2004 period was over 90%. Also, the median per summer sample mass of bluegreen algae at this lake (46 mg/l) was the 16th highest of the 131 lakes sampled. This median is in the worst 25% of the 131 Iowa lakes sampled. The presence of a large population of bluegreen algae at this lake suggests the potential violation of Iowa’s narrative water quality standard protecting against occurrence of nuisance aquatic life. This assessment, however, is based strictly on a distribution of the lake-specific median bluegreen algae values for the 2000-2004 monitoring period. Median levels greater than the 75th percentile of this distribution (~29 mg/l) were arbitrarily chosen by IDNR staff to represent the condition of “potential impairment: partially supported.” No criteria exist, however, upon which to base a more accurate identification of impairments due to bluegreen algae. Thus, while the ability to characterize the levels of bluegreen algae at this lake has improved over that of the previous (2004) assessment due to collection of additional data, the assessment category for assessments based on level of bluegreen algae nonetheless remains, of necessity, "evaluated" (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).
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 (i.e., fish kills following algal die-off) in the lake. The ISU lake survey data suggest an impairment due to high levels of pH at this lake. Only one violation of the Class B(LW) criteria for dissolved oxygen occurred in the 15 samples collected during summers of 2000 through 2004. Based on IDNR’s assessment methodology, the occurrence of this single violation does not suggest an impairment of aquatic life uses at this lake. Seven of 15 samples, however, violated the Class A,B(LW) criterion for pH (maximum = 9.7; minimum = 7.8 pH units). Based on IDNR’s assessment methodology, these results suggest that significantly more than 10% of the samples exceed Iowa’s pH criteria and thus suggest an impairment of the Class A and Class B(LW) uses of this lake. These violations likely reflect primary productivity at Indian Lake and do not reflect the input of pollutants into this lake.
Fish consumption remain "not assessed" due to the lack of fish contaminant monitoring in this lake.
