Assessment Comments
Assessment is based on results of (1) ISU lake survey from 2000-02, (2) surveys by IDNR Fisheries Bureau, and (3) ISU report on lake phytoplankton communities in 2000.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "fully supporting / threatened" due to somewhat elevated levels of chlorophyll-a (suspended algae) and due to marginally good water transparency. The Class B(LW) aquatic life uses are assessed (evaluated) as "fully supporting / threatened." Fish consumption uses are "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: According to the IDNR Fisheries Bureau, Lake Smith previously suffered from nuisance blue-green algae blooms. During the winter of 2000-2001, however, this lake suffered a severe winterkill. Because the sportfish population was reduced dramatically, IDNR Fisheries chemically renovated the lake in September of 2001. Both common carp and grass carp were successfully eliminated. The water quality in 2002 was very good: the water was clear and submergent vegetation was reestablished. Although the relative permanence of these positive changes is difficult to determine, the IDNR Fisheries does not consider this lake to be currently "impaired" for aquatic life uses. Results from the ISU statewide survey of Iowa lakes, which includes data collected before and after the fish kill, suggest that high levels of algal turbidity may have adversely affected the Class A and Class B(LW) uses of Lake Smith. 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 were 75, 64, and 65, respectively. According to Carlson (1977), the index value for total phosphorus continues to places this lake in range of hyper-eutrophic lakes; the index values for chlorophyll-a and secchi depth are in the middle range between eutrophic and hyper-eutrophic lakes. These index values suggest very high levels of phosphorus in the water column, somewhat elevated levels of chlorophyll-a (suspended algae), and marginally good water transparency. 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 limits production of algae. The ISU lake data suggest that algal production at Lake Smith is limited primarily by inorganic turbidity but also (potentially) by zooplankton grazing. 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. Of 131 lakes sampled, Lake Smith had the 40th highest median level of inorganic suspended solids (7.3 mg/l), thus suggesting that non-algal turbidity may limit the production of algae as well as contribute to threats to both the primary contact recreation and aquatic life uses previously identified for this lake. These high levels of inorganic suspended solids may have been related to the presence of common carp in this lake prior to the fish kill in winter 2000-2001. The drop in overall medians for ISS from the 2000-01 period (12.7 mg/l) to the 2000-02 period (7.3 mg/l) does suggest improving water quality at this lake. Data from Downing et al. (2002) showed moderately large populations of zooplankton in Lake Smith (Cladocerans) that graze on algae. Based on sampling in summer 2000, approximately 30% of the dry mass of the zooplankton community were comprised of species known as algal grazers. The 2000 average summer mass of Cladocerans at Lake Smith (37.2 mg/l) was the 34th highest of the 131 lakes sampled and thus suggests at least the potential for algal grazing to limit algal production. Based on median values from ISU sampling from 2000 through 2002, the ratio of total nitrogen to total phosphorus for Lake Smith is 19, thus suggesting that nitrogen is not likely a limiting nutrient in this lake.
Levels of bluegreen algae at Lake Smith are somewhat elevated but do not appear to either threaten or impair designated uses at this lakes. Data from Downing et al. (2002) suggest that bluegreen algae (Cyanophyta) tend to dominate the summertime phytoplankton community of Lake Smith in mid to late summer. Sampling in 2000 showed the percent wet mass of bluegreens ranged from less than 10% in the mid-June sampling, to approximately 60% in the mid-July sampling, and up to approximately 80% in the early August sampling. The 2000 average summer mass of bluegreen algae at this lake (10.5 mg/l) was the 61st highest of the 131 lakes sampled. This level is not believed to present either a threat or impairment to designated uses.
Recent information from the IDNR Fisheries Bureau suggests that water quality of this lake is improving, with a shift from a turbid, algae-dominated system to one with clear water and abundant rooted aquatic vegetation. Results from the ISU lake survey that show declines in TSI values from the 2000-01 period to the 2000-02 period support this conclusion. Information from the IDNR Fisheries Bureau suggests that the Class B(LW) aquatic life uses should, due to recent improvements in water quality at this lake, be assessed as "fully supported / threatened." Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring a this lake.
