Assessment Comments
Assessment is based on results of (1) ISU lake survey from 2000-02, (2) ISU report on lake plankton communities, and (3) surveys by IDNR Fisheries Bureau.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "fully supporting." The Class B(LW) aquatic life uses remain assessed (evaluated) as "partially supporting" due to impacts of siltation. Assessments based on results from the ISU lake survey do not agree well with information provided by the IDNR Fisheries Bureau. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake. The sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2000 through 2002 by Iowa State University (ISU), (2) information from the IDNR Fisheries Bureau, and (3) information on plankton communities at Iowa lakes in 2000 from Downing et al. (2002).
EXPLANATION: Results from the ISU statewide survey of Iowa lakes suggest that the Class A uses of Yellow Smoke Lake are "fully supported." Using the median values from this survey from 2000 through 2002 (approximately nine samples), Carlson's (1977) trophic state indices for total phosphorus, chlorophyll-a, and secchi depth are 56, 50, and 42, respectively. This lake has some of the best trophic state numbers of any lake in Iowa. According to Carlson (1977), the index value for total phosphorus is in the middle range of eutrophic lakes; the index value for chlorophyll-a is at the lower boundary between eutrophic and mesotrophic lakes, and the index value for Secchi depth is in the lower range of mesotrophic lakes. These index values suggest (1) relatively low levels of phosphorus, (2) very low to extremely low levels of chlorophyll-a, and (3) water transparency that is exceptional for Iowa lakes. These results suggest that this lake does not have impairments due to aesthetically objectionable conditions related either to blooms of algae or inorganic turbidity and reduced water transparencies. According to Carlson (1991), the occurrence of a high TSI value for total phosphorus with relatively low values for chlorophyll-a and secchi depth indicate that some factor (e.g., nitrogen limitation, zooplankton grazing, or some other factor) other than phosphorus may limit production of algae. Results of ISU monitoring suggest that zooplankton grazing is the most readily apparent non-phosphorus limitation on algal production at this lake. Neither inorganic turbidity nor nitrogen limitation appear to limit algal production at this lake. Based on median values from ISU sampling from 2000 through 2002, the ratio of total nitrogen to total phosphorus for Yellow Smoke Lake is 21. This ratio suggests that algal production at this lake is likely limited by the availability of phosphorus. The levels of inorganic suspended solids at this lake are relatively low and do not suggest the potential for impairing designated uses. The median level of inorganic suspended solids in the 131 lakes sampled for the ISU lake survey from 2000 through 2002 was 4.8 mg/l; the median level at Yellow Smoke Lake was 2.3 mg/l. This median value is the 22nd lowest of the 131 lakes sampled. Data from Downing et al. (2002) do, however, show relatively large populations of zooplankton species at Yellow Smoke Lake that graze on algae. Sampling in 2000 showed that Cladoceran taxa (e.g., Daphnia) comprised approximately 35% of the dry mass of the zooplankton community in the mid-July sample and 70% of the early September sample. The summer 2000 average mass of Cladocerans at this lake (23.0 mg/l) was the 51st highest of the 131 lakes sampled, thus suggesting that the presence of zooplankton grazers may limit production of algae at this lake.
This lake does not appear to have problems due to presence of nuisance algal species (i.e., bluegreen algae). Data from Downing et al. (2002) suggest that bluegreen algae (Cyanophyta) generally comprise a relatively small portion of the summertime phytoplankton community of this lake. Sampling in 2000 showed that bluegreen algae comprised less than 10% of the wet mass of the mid-June and early August samples but did increase to approximately 50% in the mid-July sample. The summer 2000 average mass of bluegreens at this lake (3.9 mg/l) is relatively low and thus does not likely present a water quality impact.
Information from the IDNR Fisheries Bureau, however, suggests that the Class B(LW) aquatic life uses should remain assessed as "partially supported" due to siltation impacts in the lake. According to IDNR's December 13, 2001 TMDL for Yellow Smoke Lake, the primary water quality impact at this lake is accumulated sediment and its interference with reproduction and growth of fish and other aquatic life; this impact occurs primarily in the eastern portion of the lake. The lake has steep sides and a hard clay bottom; these conditions present less than optimal conditions for spawning of species such important fish species as bluegill and largemouth bass. Prior to sedimentation impacts, however, the east arm of the lake was shallow and was ideal as spawning habitat for these and other fish species. That area is now covered with several feet of fine silt that make successful spawning almost impossible. Although this is a very small portion of the lake overall (under 10% of the total surface area of the lake), it is a key habitat (50%-70% of available spawning habitat). The deposition of sediment in the east arm has severely limited the fishery in the entire lake. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake.
