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 phytoplankton communities in 2002.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "partially supported" due to algal blooms and due to high levels of inorganic turbidity (poor water transparencies) related to high levels of suspended algae and to high levels of inorganic suspended solids. Large populations of bluegreen algae 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 remain assessed (evaluated) as "fully supported /threatened" due to nuisance blooms of algae, nutrients, and re-suspension of sediment. 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 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: Results of monitoring conducted by ISU from 2000 through 2002 as part of the statewide survey of Iowa lakes suggest that the Class A (primary contact) uses are only "partially supported" due to turbidity (poor water transparency) caused by suspended algae and inorganic suspended solids. 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 76, 73, and 75, 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) very 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 2002, the ratio of total nitrogen to total phosphorus for this lake is 15. 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. For example, levels of inorganic suspended solids were high during the three sampling events in 2000 (14.5, 207, and 28.8 mg/l) but were relatively low during 2001 (5.0, 2.7, and 3.0 mg/l). 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 at Ingham Lake was 11.2 mg/l. This median was the 25th highest median value of the 131 lakes sampled and suggests that inorganic suspended solids contribute to the very poor water transparencies at this lake. Data from Downing et al. (2002), however, show relatively low populations of zooplankton species at this lake that graze on algae. Sampling in 2000 showed that Cladoceran taxa (e.g., Daphnia) comprised less than 10% of the dry mass of the zooplankton community in both the mid-July and early August samples. The 2000 average summer mass of Cladocerans at this lake (16.5 mg/l) was the 60th lowest of the 131 lakes sampled, is relatively low, and does not suggest a non-phosphorus limitations due to algal grazing.
The presence of nuisance aquatic (algal) life at this lake may indicate an additional impairment to the lake’s designated uses. Data from Downing et al. (2002) suggest that bluegreen algae (Cyanophyta) tend to dominate the summertime phytoplankton community of Ingham Lake. The 2000 average summer mass of bluegreen algae at this lake (81.5 mg/l) was the 14th highest of the 131 lakes sampled. This level of bluegreen algae suggests a strong potential for impairment designated uses due to violation of the Iowa narrative water quality standard protecting against nuisance aquatic (algal) life. Although results of plankton sampling in 2000 suggest impairment of designated uses, 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. 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. These conditions indicate impairments to the Class A (primary contact) uses through presence of algal blooms and inorganic turbidity that lead to aesthetically objectionable conditions that violate Iowa’s narrative water quality standards. 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 suggest an additional impairment due to violations of the Iowa water quality standard protecting against nuisance aquatic life.
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 / threatened" due to excessive nutrient loading to the water column, nuisance blooms of algae, and re-suspension of sediment. Fish consumption remain "not assessed" due to the lack of fish contaminant monitoring at this lake.
