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" due to presence of aesthetically objectionable blooms of algae and presence of nuisance algal species (i.e., bluegreen algae). 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 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), Carlsons's (1977) trophic state indices for total phosphorus, chlorophyll-a, and secchi depth are 90, 67, and 74 respectively, for East Lake. According to Carlson (1977), the index value for total phosphorus places this lake in the upper range of hyper-eutrophic lakes; the value for chlorophyll-a places is in the range between eutrophic and hyper-eutrophic lakes, and the index value for secchi depth is in the lower range of hyper-eutrophic lakes. These index values suggest extremely high levels of phosphorus in the water column, moderately high, but somewhat less than expected production of suspended algae, and poor water poor water transparency. The difference in TSI values for total phosphorus and chlorophyll-a may be due, in part, to non-algal turbidity. During the 2000 and 2001 ISU surveys, however, levels of inorganic suspended solids were relatively low (median =5.0 mg/l) compared to other Iowa lakes. The relatively low ratio of total nitrogen to total phosphorus (6), and the dominance of bluegreen algae, suggest that production of algae at this lake is limited by nitrogen. These conditions indicate impairments to the Class A (primary contact) uses through presence of 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 this lake. Sampling in 2000 showed the percent wet mass of bluegreens ranged from approximately 75% in the late June sampling, to approximately 90% in the late July sampling, and approximately 89% in the late August sampling. 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.
