Assessment Comments
Assessment is based on (1) surveys by DNR Fisheries and (2) results of fish tissue (RAFT) monitoring in 1994. See attached document for details.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (evaluated) as "partially supporting." 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 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). Further monitoring and investigation are needed to better characterize water quality conditions at this lake. EXPLANATION: Results from the ISU statewide survey of Iowa lakes suggest that high levels of algal turbidity may adversely affect the Class A and Class B(LW) uses of Lake Meyer. 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 64, 62, and 67, respectively. According to Carlson (1977), the index values for all three parameters place this lake in the range between eutrophic and hyper-eutrophic lakes. These index values suggest moderately high levels of phosphorus and chlorophyll-a and moderately poor water transparency. Based on median values from ISU sampling in 2000 and 2001, the ratio of total nitrogen to total phosphorus for this lake is 37. This TN:TP ratio, along with good agreement between the three TSI values, suggests that algal production at this lake is limited by phosphorus. The levels of inorganic suspended solids at this lake are low and do not suggest the potential for impairing designated uses. 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 Lake Meyer was 2.3 mg/l. The moderately high TSI values for total phosphorus and chlorophyll-a suggest potential impairments to the Class A (primary contact) uses through presence of aesthetically objectionable blooms of algae and due to presence of nuisance algal species (i.e., bluegreen algae). Data from Downing et al. (2002) suggest that bluegreen algae (Cyanophyta) comprise a relatively large portion of the summertime phytoplankton community, with greater than 60% wet mass in bluegreens in early summer increasing to greater than 80% bluegreens in late summer. The eutrophic conditions at this lake, along with information from the IDNR Fisheries Bureau, suggest that the Class B(LW) aquatic life uses should remain assessed as "partially supported" due to excessive nutrient loading to the water column, high levels of algal turbidity, and siltation in the 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. Fish consumption uses are "not assessed" due to the lack of recent fish contaminant monitoring. The most recent fish contaminant monitoring was conducted in 1994 (see assessment for the 1996 report above). Results of this monitoring are now considered too old (greater than five years) for characterizing current water quality conditions.
