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 (monitored) as "partially supported." The Class B(LW) aquatic life uses remain assessed (evaluated) as "fully supported /threatened." Fish consumption remain "not assessed. Sources of data for this assessment include (1) results of the IDNR-UHL beach monitoring program in summers of 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). EXPLANATION: Results of monitoring conducted by ISU in 2000 and 2001 as part of the statewide survey of Iowa lakes suggest that the Class A (primary contact) uses are only "partially supported." Using the median values from this survey in 2000 and 2001 (approximately six samples), Carlsons's (1977) trophic state indices for total phosphorus, chlorophyll-a, and secchi depth are 83, 72, and 73, respectively, for Ingham Lake. According to Carlson (1977), these index values place this lake in the range of hyper-eutrophic lakes and suggests (1) excessive phosphorus loading to the water column, (2) excessive, but less than expected, production of suspended algae, and (3) poor water transparency. These conditions indicate impairments to the Class A (primary contact) uses through presence of nuisance blooms of algae and presence of nuisance algal species (i.e., bluegreen algae) (data from Downing et al. (2002) suggest that bluegreen algae (Cyanophyta) tend to dominate the summertime phytoplankton community of Ingham Lake). The TSI value for chlorophyll-a (72) is low relative to the the TSI for total phosphorus (83), and this difference suggests that other factors, incuding nitrogen limitation or high levels of non-algal turbidity, limit the production of suspended algae. Based on median values from ISU sampling in 2000 and 2001, the ratio of total nitrogen to total phosphorus for this lake is 9. Data on inorganic suspended solids from the ISU survey suggest that this lake is subject to occasional episodes of high levels of non-algal turbidity. For example, levels of inorganic suspended solids were relatively high during the three sampling events in 2000 (14.5, 207, and 28.8 mg/l) but were relatively low during 2001 (5.0, 2.7, and 3.0 mg/l). 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 Ingham Lake was 9.8 mg/l; this is the 36th highest median value of the 130 lakes sampled. Thus, the "turbidity" impact identified in previous Section 305(b) reports (assessment for the 1994 report above) is likely due to both suspended algae and suspended inorganic material. Based on this information, turbidity-related impacts to the primary contact and aquatic life uses at this lake will be attributed to both suspended algae and re-suspended inorganic material. 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 "fully supported / threatened" due to excessive nutrient loading to the water column, nuisance blooms of algae, and re-suspension of sediment. Fish consumption remain "not assessed" due to the lack of recent fish contaminant monitoring at this lake.
