Assessment Comments
Assessment is based on results of (1) ISU lake survey in 2000-01, (2) ISU report on lake phytoplankton communities, and (3) surveys by IDNR Fisheries Bureau.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (evaluated) as "fully supporting." The Class B(LW) aquatic life uses remain assessed (evaluated) as "partially supporting." Fish consumption uses remain "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). 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 in 2000 and 2001 (approximately six samples), Carlson's (1977) trophic state indices for total phosphorus, chlorophyll-a, and secchi depth are 59, 44, and 43, respectively. According to Carlson (1977), the index value for total phosphorus is in the upper range of eutrophic lakes; the index values for chlorophyll-a and secchi depth are in the middle to lower range of mesotrophic lakes. These index values suggest (1) relatively low levels of phosphorus, (2) 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 blooms of algae. 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 or zooplankton grazing) may limit production of algae. Based on median values from ISU sampling in 2000 and 2001, the ratio of total nitrogen to total phosphorus for Yellow Smoke Lake is 23.6. This ratio suggests that algal production at this lake is only slightly limited by the availability of nitrogen. In addition, data from Downing et al. (2002) 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. This suggests that the presence of zooplankton grazers may also limit production of algae at this lake. 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 130 lakes sampled for the ISU lake survey in 2000 and 2001 was 5.27 mg/l; the median level at Yellow Smoke Lake was 2.3 mg/l. This median value is the 17th lowest of the 130 lakes sampled. 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. Although bluegreen algae can comprise a significant portion of the mid-summer phytoplankton community, the production of chlorophyll is extremely low at this lake, and thus the presence of bluegreen algae likely does not present a water quality impact. Although results of ISU lake monitoring in 2000 and 2001 suggest full support of the designated primary contact uses of this lake, the amount of data available for characterizing water quality is not sufficient for developing an accurate assessment of support of these uses. Additional data for this lake are being generated as part of the ongoing ISU lake survey; these data will be used to improve the accuracy of future water quality assessments.
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.
