Assessment Comments
Assessment based on results of (1) ISU lake survey in 2000-01, (2) ISU report on lake phytoplankton communities, (3) results of U.S. EPA / IDNR fish tissue (RAFT) monitoring in 2000 and (4) surveys by IDNR Fisheries Bureau.
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 uses are assessed as "fully supported." 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, (3) information on phytoplankton communities at Iowa lakes in 2000 from Downing et al. (2002), and (4) the results of U.S. EPA/IDNR fish tissue (RAFT) monitoring in July 2000. 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 Lower Gar 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 76, 67, and 72, respectively. According to Carlson (1977), the index values total phosphorus and secchi depth place this lake in the range of hyper-eutrophic lakes; the index value for chlorophyll-a is in the range between eutrophic and hyper-eutrophic lakes. These index values suggest excessive levels of phosphorus in the water column, moderately high, but somewhat less than expected production of suspended algae, and poor water transparency. 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. Of 130 lakes sampled, Lower Gar Lake had the 18th highest median level of inorganic suspended solids (17.4 mg/l), thus suggesting that non-algal turbidity limits the production of algae as well as contributes to impairments of both the primary contact recreation and aquatic life uses. Also, the relatively low ratio of total nitrogen to total phosphorus for this lake (9) suggests at least the potential for nitrogen limitation at this lake. These conditions indicate potential 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 Lower Gar Lake, especially in early and mid-summer). Sampling in 2000 showed the percent wet mass of bluegreens was 100% in the mid-June and mid-July samples and dropped to approximately 60% in the early August sampling. The Class B(LW) aquatic life uses remain assessed as "partially supported" based on information from the IDNR Fisheries Bureau. See assessment for previous Section 305(b) reports above. Fish consumption are assessed as "fully supported" based on results of U.S. EPA / IDNR fish tissue monitoring in July 2000. Levels of all contaminants in the composite samples of fillets from channel catfish were well-below the respective FDA action levels and IDNR levels of concern. The levels of the primary contaminants of Iowa fish (i.e., chlordane, DDE, dieldrin, ,mercury and PCBs) were all very low in the sample from Lower Gar Lake.
