Assessment Comments
Assessment is based on results of (1) ISU lake survey from 2000-04, (2) surveys by IDNR Fisheries Bureau, and (3) ISU reports on lake phytoplankton communities from 2002-05.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "not supported" due to poor water transparency caused by algal blooms and by high levels of inorganic turbidity. Large populations of bluegreen algae potentially suggest an additional impairment of the Class A uses due to presence of nuisance (noxious) aquatic plant life. The Class B(LW) aquatic life uses are assessed (monitored) as "partially supported" due to frequent violations of Iowa’s water quality criterion for pH. Nuisance blooms of algae, nutrients, and re-suspension of sediment also remain concerns regarding support of the Class B(LW) aquatic life uses at this lake. Fish consumption remain "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: A TMDL for algae and turbidity at Ingham Lake was prepared by IDNR and approved by EPA in 2005. Because all Section 303(d) impairments identified for the 2006 assessment/listing cycle (algae, pH, turbidity) are addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved).
EXPLANATION: Results of monitoring conducted by ISU from 2000 through 2004 as part of the statewide survey of Iowa lakes suggest that the Class A (primary contact) uses are "not supported" due to turbidity (poor water transparency) caused by a combination of suspended algae and inorganic suspended solids. 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 76, 73, and 77, respectively, for Ingham Lake. According to Carlson (1977), these index values place this lake in the range of hyper-eutrophic lakes and suggests (1) extremely high levels of phosphorus in the water column, (2) very high levels of chlorophyll-a, and (3) extremely poor water transparency. These TSI values are roughly similar and do not suggest any significant non-phosphorus limitation on algal production at this lake.
Based on median values from ISU sampling from 2000 through 2004, the ratio of total nitrogen to total phosphorus for this lake is 18. This ratio does not suggest significant limitations on algal production due to nitrogen availability.
Data on inorganic suspended solids from the ISU survey suggest that this lake is subject to occasional episodes of very 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 at Ingham Lake over this time was 12.8 mg/l. This median was the 22nd highest median value of the 131 lakes sampled and suggests that inorganic suspended solids contribute to the very poor water transparencies at this lake.
Monitoring from 2000 through 2005 shows the presence of extremely large populations of zooplankton at Ingham Lake that graze on algae. In terms of all Iowa lakes sampled, data from the ISU survey show an extremely large population of zooplankton species at this lake that graze on algae. Sampling from 2000 through 2005 showed that Cladoceran taxa (e.g., Daphnia) comprised approximately 65% of the dry mass of the zooplankton community of this lake. The average per summer sample mass of Cladoceran taxa over the 2000-2005 period (520 mg/l) was the third highest of the 131 lakes sampled. Despite the extremely high levels of Cladocerans at this lake, the TSI values for total phosphorus, chlorophyll-a, and Secchi depth do not suggest a significant non-phosphorus limitation to algal production.
The presence of nuisance (=noxious) algal species (i.e., bluegreen algae) may also present an impairment of the Class A uses at this lake. Data from the ISU survey from 2000 through 2004 suggest that bluegreen algae (Cyanophyta) dominate this lake’s summertime phytoplankton community. Sampling from 2000 through 2004 showed that the percent wet mass of bluegreen algae in the phytoplankton community of Ingham Lake in summers of the 2000-2004 period was approximately 90%. Also, the median per summer sample mass of bluegreen algae at this lake (58.6 mg/l) was the 15th highest of the 131 lakes sampled. This median is approaching the worst 10% of the 131 Iowa lakes sampled. 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 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 remains, of necessity, "evaluated" (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).
These conditions indicate impairments to the Class A (primary contact) uses through presence of algal blooms and inorganic turbidity that lead to violations Iowa’s narrative water quality standards protecting against aesthetically objectionable conditions. Based on the ISU information, turbidity-related impacts to the primary contact and aquatic life uses at this lake will be attributed to both suspended algae and re-suspended inorganic material. The very high levels of bluegreen (nuisance) algae potentially suggest an additional impairment due to violations of the Iowa water quality standard protecting against nuisance aquatic life.
Iinformation from the IDNR Fisheries Bureau suggests that the Class B(LW) aquatic life uses are "fully supported". Nutrient loading to the water column, nuisance blooms of algae, and re-suspension of sediment, however, remain concerns for the continued support of the Class B(LW) uses at Ingham Lake. The ISU lake survey data, however, suggest an impairment due to high levels of pH at this lake. Only one violation of the Class B(LW) criteria for dissolved oxygen occurred in the 15 samples collected during summers of 2000 through 2004. Based on IDNR’s assessment methodology, the occurrence of this single violation does not suggest an impairment of aquatic life uses at this lake. Five of 15 samples, however, violated the Class A,B(LW) criterion for pH (maximum = 9.2; minimum = 8.1 pH units). Based on IDNR’s assessment methodology, these results suggest that significantly more than 10% of the samples exceed Iowa’s pH criteria and thus suggest an impairment of the Class A and Class B(LW) uses of this lake. These violations likely reflect high levels of primary productivity at Ingham Lake and do not reflect the input of pollutants into this lake.
Fish consumption remain "not assessed" due to the lack of fish contaminant monitoring at this lake.
