Assessment Comments
Assessment is based on results of (1) ISU lake surveys from 2000-04, (2) surveys by IDNR Fisheries Bureau, and (3) ISU reports on lake plankton communities from 2000-05.
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 primarily to high levels of inorganic turbidity and secondarily to blooms of algae that contribute to poor water transparency. The frequency of violations of Iowa’s water quality criterion for pH also suggest “partial support” of the Class A uses. The presence of nuisance (=noxious) aquatic life (bluegreen algae) presents an additional (evaluated) impairment of the Class A uses. The Class B(LW) aquatic life uses are assessed (monitored) as "partially supported" due to the frequency of violations of Iowa’s water quality criterion for pH. 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 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: the fish populations of this lake was renovated in Fall 2006 to remove common carp and grass carp that were believed to have adverse impacts on water quality. The IDNR Fisheries Bureau expects that lake water quality will improve as a result of the renovation.
EXPLANATION: The level of support of the Class A (primary contact recreation) uses are assessed (monitored) as "partially supported" based on results from the ISU statewide survey of Iowa lakes. 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 68, 66, and 69, respectively, for Cold Springs Lake. According to Carlson (1977), these index values place this lake in the range between eutrophic and hyper-eutrophic lakes and suggest high levels of phosphorus in the water column, moderately high levels of chlorophyll-a, and 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 2004, the ratio of total nitrogen to total phosphorus for this lake is 20. This ratio suggests that algal production at this lake is limited by the availability of phosphorus.
Data from the ISU survey show relatively large populations of zooplankton species at this lake that graze on algae. Sampling from 2000 through 2005 showed that Cladoceran taxa (e.g., Daphnia) comprised about two-thirds of the dry mass of the zooplankton community. Cold Springs Lake had the 16th highest per summer sample mass of zooplankton (Cladoceran) grazers of the 131 lakes sampled. This level of zooplankton grazers may be able to suppress algal production.
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 2004 was 5.2 mg/l. The median level of inorganic suspended solids at Cold Springs Lake was moderately high (8.3 mg/l). This was the 38th 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 (66) 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 nearly the entire (approximately 90%) of the summer phytoplankton community of Cold Springs Lake.
Data from the ISU survey from 2002-2004 suggest that the presence of nuisance aquatic species (i.e., bluegreen algae) may present an impairment of the Class A uses at this lake. Summer sampling during this period showed the percent wet mass of bluegreens was approximately 90%, thus dominating the phytoplankton community of this lake. In addition, Cold Springs Lake had the 11th highest median per summer sample mass (65.4 mg/l) of bluegreen algae of the 131 lakes sampled. This median exceeds the 90th percentile median value of bluegreen algae for the 131 Iowa lakes (59 mg/l). The presence of a large population of bluegreen algae at this lake suggests 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 greater than the 90th percentile of this distribution (~59 mg/l) were arbitrarily chosen by IDNR staff to represent the condition of “potential impairment; not supported.” No criteria exist, however, upon which to base a more accurate identification of impairments due to bluegreen algae. Thus, while the , 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, of necessity, remains "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 suggests that the Class B(LW) aquatic life uses are “fully supported”. Nutrient loading to the water column and nuisance blooms of algae, however, remain water quality concerns at this lake. The ISU lake survey data show no violations of the Class B(LW) criteria for dissolved oxygen in the 14 samples collected during summers of 2000 through 2004. Five of 15 samples, however, exceeded the Class B(LW) criterion for pH of 9.0 pH units (maximum value = 10.1; minimum value = 8.0 pH units). Based on IDNR’s assessment methodology, these results suggest that significantly more than 10 percent of the samples exceed Iowa’s pH criteria. Thus, these results suggest an impairment (partial support/monitored) of the Class A and Class B(LW) uses of this lake. These violations likely reflect the high levels of primary productivity at Cold Springs Lake and do not reflect the input of pollutants into this lake.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake.
