Assessment Comments
Assessment is based on results of (1) ISU lake survey in 2000-01, (2) surveys by IDNR Fisheries Bureau, and (3) ISU report on lake phytoplankton communities.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (evaluated) as "fully supporting / threatened." The Class B(LW) aquatic life uses are assessed (evaluated) as "fully supporting / threatened." Fish consumption uses are "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). Further monitoring and investigation are needed to better characterize water quality conditions at this lake. EXPLANATION: According to the IDNR Fisheries Bureau, Lake Smith previously suffered from nuisance blue-green algae blooms. During the winter of 2000-2001, however, Lake Smith 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 has been very good: the water is clear and submergent vegetation is starting to get 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 in 2000 and 2001 (approximately six samples), Carlson's (1977) trophic state indices for total phosphorus, chlorophyll-a, and secchi depth were 79, 66, and 68, respectively. According to Carlson (1977), the index value for total phosphorus places this lake in range of hyper-eutrophic lakes; the index values for chlorophyll-a and secchi depth are in the range between eutrophic and hyper-eutrophic lakes. These index values suggest excessive levels of phosphorus in the water column, moderately high levels of chlorophyll-a (suspended algae), and moderately poor 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 or zooplankton grazing) limits production of algae (based on median values from ISU sampling in 2000 and 2001, the ratio of total nitrogen to total phosphorus for Lake Smith is 20, thus suggesting that nitrogen is not a limiting nutrient in this lake. Data from Downing et al. (2002), however, showed moderately large populations of zooplankton in Lake Smith 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 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, Lake Smith had the 27th highest median level of inorganic suspended solids (12.7 mg/l), thus suggesting that non-algal turbidity may have limited the production of algae as well as contributed to impairments of 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. These conditions indicate the potential for future impairments to the Class A (primary contact) uses of this lake 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) 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. Based, however, on more recent information from the IDNR Fisheries Bureau, these conditions are believed to have improved, and the Class A uses are thus assessed as "fully supporting / threatened." 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." Further investigation and monitoring are needed to better characterize current water quality conditions and to determine any changes in the improved water quality that followed the winter kill of 2000-2001 and chemical renovation by the IDNR Fisheries Bureau. 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. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring a this lake.
