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 (monitored) as "partially supported." The Class B(LW) aquatic life uses are assessed (evaluated) as "fully supported / threatened". Fish consumption are "not assessed." 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: The level of support of the Class A (primary contact recreation) uses are assessed as "partially supported" based on results from the ISU statewide survey of Iowa lake. Using the median values from this survey in 2000 and 2001 (approximately six samples), Carlsons's (1977) trophic state indices for total phosphorus, chlorophyll-a, and secchi depth are 78, 73, and 70, respectively, for Cold Springs Lake. According to Carlson (1977), these index values place this lake in the range of hyper-eutrophic lakes and suggest excessive phosphorus loading to the water column, excessive production of suspended algae, and poor water transparency. These conditions indicate impairments to the Class A (primary contact recreation) uses 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) comprise a significant portion (approximately one-third) of the summer phytoplankton community of Cold Springs Lake. Sampling in summer 2000 showed that approximately 35% of wet mass of the phytoplankton commmunity in the mid-June sample, 20% of the mid-July sample, and 75% of the early August samples were bluegreen algae. Based on median values from ISU sampling in 2000 and 2001, the ratio of total nitrogen to total phosphorus for this lake is 10. Data from the ISU survey suggest that this lake has moderately high levels of inorganic suspended solids and thus has potential problems with high levels of non-algal turbidity. 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 of inorganic suspended solids at Cold Springs Lake was 9.3 mg/l. This was the 37th highest value of the 130 lakes sampled, thus suggesting that non-algal turbidity may present some limitation to the production of suspended algae. The hyper-eutrophic conditions at this lake, along with information from the IDNR Fisheries Bureau, suggest that the Class B(LW) aquatic life uses are fully supported but threatened due to excessive nutrient loading to the water column and nuisance blooms of algae. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake.
