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 plankton communities in 2000.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation uses) are assessed (monitored) as "partially supported" due to presence of aesthetically objectionable conditions related to blooms of algae and to high levels of inorganic turbidity that contribute to poor water transparency. The presence of nuisance (=noxious) aquatic life (bluegreen algae) presents an additional impairment of the Class A uses. The Class B(LW) aquatic life uses are assessed (evaluated) as "fully supported / threatened" due to nutrient loading to the water column and to algal blooms. Fish consumption uses are "not assessed" due to the lack of fish contaminant monitoring at this lake. 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: 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 lakes. 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 are 75, 68, and 69, respectively, for Cold Springs Lake. According to Carlson (1977), these index values place this lake in the range of hyper-eutrophic lakes and suggest extremely high levels of phosphorus in the water column, moderately high levels of chlorophyll-a, and moderately poor water transparency. The TSI for Secchi depth suggests an impairment of the Class A (primary contact recreation) uses through presence of aesthetically objectionable conditions (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, zooplankton grazing, or some other factor) other than phosphorus limits production of algae. The ISU lake data suggest that algal production at Cold Springs Lake is limited by nitrogen availability, zooplankton grazing, and by inorganic turbidity. Based on median values from ISU sampling from 2000 through 2002, the ratio of total nitrogen to total phosphorus for this lake is 11. This ratio suggest the possibility that algal production at this lake may be limited by nitrogen availability. In addition, Downing et al. (2002) show relatively large populations of zooplankton species (Cladocerans) at this Cold Springs Lake that graze on algae. Sampling in 2000 showed that Cladoceran taxa (e.g., Daphnia) comprised approximately 70% of the dry mass of the zooplankton community at this lake. The average summer mass of these zooplankton grazers (33.0 mg/l) in 2000 was the 38th highest of the 131 lakes sampled. Data from the ISU survey also 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 131 lakes sampled for the ISU lake survey from 2000 through 2002 was 4.8 mg/l. The median level of inorganic suspended solids at Cold Springs Lake was relatively high (9.1 mg/l). This was the 37th highest value of the 131 lakes sampled, thus suggesting that non-algal turbidity likely limits the production of suspended algae as well as contributes to the poor water transparency at this lake. The TSI for chlorophyll-a (68) indicates moderately high levels of suspended algae that contribute to impairments of the Class A uses through reduced water transparency and through contribution to aesthetically objectionable blooms of algae at this lake. Information from the IDNR Fisheries Bureau is supports the impairment of designated uses at this lake due to blooms of 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 community in the mid-June sample, 20% of the mid-July sample, and 75% of the early August samples were bluegreen algae. The 2000 summer average mass of bluegreen algae at Cold Springs Lake (50.7 mg/l) was the 20th highest of the 131 lakes sampled. The presence of this very large population of bluegreen algae suggests an impairment of support of the designated uses of this lake due to the potential for violating Iowa’s narrative water quality standard protecting against presence of nuisance aquatic life. Although results of plankton sampling in 2000 suggest that this narrative standard is violated such that designated uses are impaired, the amount of data available for characterizing algal populations at this lake (one season) is not sufficient for developing a more accurate assessment of support of these uses. Thus, the assessment category is considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). Additional data on plankton have been collected at this lake as part of the ongoing ISU lake survey and will be used to improve the accuracy of future water quality assessments.
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.
