Assessment Comments
Assessment is based on results of (1) ISU lake survey from 2000-04, (2) ISU reports on lake plankton communities from 2000-05, 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 (suggesting excellent water quality) do not agree well with information provided by the IDNR Fisheries Bureau regarding siltation impacts. 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 sponsored by IDNR and conducted by Iowa State University (ISU) from 2000 through 2004, (2) surveys by IDNR Fisheries Bureau, and (3) information on plankton communities collected at Iowa lakes from 2000 through 2005 as part of the ISU lake survey.
Note: A TMDL for siltation at Yellow Smoke Lake was prepared by IDNR and approved by EPA in 2002; thus, this waterbody was placed into IR Category 4a (TMDL approved) for the 2004 assessment/listing cycle. Because all Section 303(d) impairments identified for the 2006 assessment/listing cycle (siltation) are addressed by the TMDL, this waterbody remains in IR Category 4a.
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 2004 (approximately 15 samples), Carlson's (1977) trophic state indices for total phosphorus, chlorophyll-a, and secchi depth are 56, 53, and 42, respectively. This lake has some of the consistently 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 range of eutrophic 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 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, inorganic turbidity, or reduced water transparencies. Of the 131 lakes sampled from 2000 through 2004 as part of the ISU survey, Yellow Smoke Lake ranked 13th best for median total phosphorus (36 ug/l), 25th best for median chlorophyll-a (10 ug/l), and third best for median Secchi depth (3.5 meters).
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, however, do not immediately suggest an obvious 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 2004, the ratio of total nitrogen to total phosphorus for Yellow Smoke Lake is 22. 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 very 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 5.2 mg/l; the median level at Yellow Smoke Lake was 2.5 mg/l (the 20th best median of all 131 lakes).
In terms of all Iowa lakes sampled, data from the ISU survey show relatively small populations of zooplankton species at this lake that graze on algae. Sampling from 2000 through 2005 showed that Cladoceran taxa (e.g., Daphnia) comprised a large percentage (about 65%( of the dry mass of the zooplankton community of this lake. The average per summer sample mass of Cladoceran taxa over the 2000-2005 period (69 mg/l), however, was the 52nd lowest of the 131 lakes sampled. These results suggest little if any non-phosphorus limitation due to zooplankton grazing at Yellow Smoke Lake.
The levels of nuisance (=noxious) algal species (i.e., bluegreen algae) at this lake do not suggest an impairment of Class A uses. Data from the ISU survey from 2000 through 2004 suggest that bluegreen algae (Cyanophyta) comprise a relatively small portion (approximately 35%) of this lake’s summertime phytoplankton community. This sampling showed that the median per summer sample mass of bluegreen algae at Yellow Smoke Lake (2.3 mg/l) was the 12th lowest of the 131 lakes sampled. This level is in the lowest 10% of the 131 Iowa lakes sampled. The presence of a this very small population of bluegreen algae at this lake does not suggest a potential violation of Iowa’s narrative water quality standard protecting against occurrence of nuisance aquatic life. This assessment, however, is based strictly on a distribution of the lake-specific median bluegreen algae values for the 2000-2004 monitoring period. Median levels less than the 75th percentile of this distribution (~29 mg/l) were arbitrarily considered by IDNR staff to not represent an impairment of the Class A uses of Iowa lakes. No criteria exist, however, upon which to base a more accurate identification of impairments due to bluegreen algae. Thus, while the ability to characterize the levels of bluegreen algae at this lake has improved over that of the previous (2004) assessment due to collection of additional data, the assessment category for assessments based on level of bluegreen algae nonetheless remains, of necessity, "evaluated" (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).
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.
The ISU lake survey data show good chemical water quality at Yellow Smoke Lake. Results of this monitoring show no violations of the Class B(LW) criteria for dissolved oxygen in the 12 samples collected during summers of 2000 through 2004. One of 13 samples, however, (8%) exceeded the Class B(LW) criterion for pH (maximum = 9.2; minimum = 8.4 pH units). This single violation does not indicate impairment of designated uses.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake.
