Assessment Comments
Assessment is based on results of (1) ISU lake survey from 2000-02, (2) surveys by IDNR Fisheries Bureau (3) ISU report on lake plankton communities in 2000, and (4) results of U.S. EPA/IDNR fish tissue (RAFT) monitoring in 2001.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "partially supporting" due to presence aesthetically objectionable conditions caused by non-algal (inorganic) turbidity and blooms of algae. The Class B(LW) aquatic life uses are assessed (evaluated) as "partially supported" due to excess algal production and due to reduced water transparency related to presence of common carp populations and to sedimentation problems in the lake. Fish consumption uses remain assessed (monitored) as "fully supported" based on results of fish contaminant monitoring in 2001. The 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, (3) information on plankton communities collected at Iowa lakes from 2000 through 2005 as part of the ISU lake survey, and (4) results of U.S. EPA / IDNR fish tissue (RAFT) monitoring in 2001.
Note: A TMDL for siltation and nutrients at Lake Miami was prepared by IDNR and approved by EPA in 2001; thus, this lake was placed into IR Category 4a (TMDL approved) for the 2004 assessment/listing cycle. Because all the Section 303(d) impairments identified for the 2006 assessment/listing cycle (turbidity, algal growth) are addressed by the TMDL, this waterbody remains in IR Category 4a.
EXPLANATION: Results from the ISU statewide survey of Iowa lakes suggest that high levels of algal and non-algal (inorganic) turbidity impair the Class A and Class B(LW) uses of Lake Miami. 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, 67, and 71, respectively. According to Carlson (1977), the index values for total phosphorus and secchi depth place this lake in the range of hyper-eutrophic lakes; the index value for chlorophyll-a is in the range between eutrophic and hyper-eutrophic lakes. These index values suggest extremely high levels of phosphorus in the water column, moderately high (but less than expected) production of suspended algae, and very poor water transparency.
According to Carlson (1991), the occurrence of a high TSI value for total phosphorus with relatively lower values for chlorophyll-a and secchi depth indicates 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 Lake Miami may be limited by non-algal turbidity and by nitrogen limitation; zooplankton grazing does not appear to limit algal production as this lake. 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. Of 131 lakes sampled, Lake Miami had the 25th highest median level of inorganic suspended solids (11.6 mg/l), thus suggesting that non-algal turbidity limits the production of algae as well as contributes to the very poor water transparency that impairs of both the primary contact recreation and aquatic life uses.
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 does suggest that algal production is limited, at least to some degree, by nitrogen availability.
In terms of all Iowa lakes sampled, data from the ISU survey show very small 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 25% of the dry mass of the zooplankton community of this lake; the average per summer sample mass of Cladoceran taxa (43 mg/l) was the 22nd lowest level of the 131 lakes sampled. These results suggest little if any non-phosphorus limitation due to zooplankton grazing at Lake Miami.
These conditions indicate continued impairments to the Class A (primary contact) uses at this lake through presence of aesthetically objectionable conditions related to (1) high levels of non-algal turbidity (inorganic suspended solids) and (2) blooms of algae.
The levels of nuisance (=noxious) algal species (i.e., bluegreen algae) at this lake do not suggest an impairment of Class A uses. While data from the ISU survey from 2000 through 2004 suggest that bluegreen algae (Cyanophyta) comprise a significant portion (almost 80%) of this lake’s summertime phytoplankton community, sampling from 2000 through 2004 showed that the median per summer sample mass of bluegreen algae at Lake Miami (11.9 mg/l) was the 63rd lowest of the 131 lakes sampled. This level is in the lower half of the 131 Iowa lakes sampled. The presence of a relatively small population of bluegreen algae at this lake does not suggest 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 less than the 75th percentile of this distribution (~29 mg/l) were arbitrarily considered by IDNR staff to not represent an impairment of the Class A uses of Iowa lakes. 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
Information from the IDNR Fisheries Bureau suggests that the Class B(LW) aquatic life uses should be assessed (evaluated) as impaired due to excess algal production and due to reduced water transparency related to presence of common carp populations and to sedimentation problems in the lake. Results of ISU monitoring from 2000 through 2004 suggest generally good chemical water quality at this lake. Results of this monitoring show that only 1 of the 15 samples collected exceeded the Class B(LW) criteria for dissolved oxygen and that only 2 of the 15 samples collected exceeded Iowa’s Class A,B(LW) criteria for pH (maximum = 10.1; minimum = 7.6 pH units). Based on IDNR’s assessment methodology, these results do not suggest violation frequencies are significantly greater than 10% for either parameter and thus do not suggest impairment of either the Class A and Class B(LW) uses of Lake Miami.
Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Lake Miami in 2001. The composite samples of fillets from channel catfish and largemouth bass had low levels of contaminants. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses. Prior to 2006, IDNR used action levels published by the U.S Food and Drug Administration to determine whether consumption advisories should be issued for fish caught as part of recreational fishing in Iowa. In an effort to make Iowa’s consumption more compatible with the various protocols used by adjacent states, the Iowa Department of Public Health, in cooperation with Iowa DNR, developed a risk-based advisory protocol. This protocol went into effect in January 2006 (see http://www.iowadnr.gov/fish/news/consump.html for more information on Iowa’s revised fish consumption advisory protocol). Because the revised (2006) protocol is more restrictive than the previous protocol based on FDA action levels; fish contaminant data that previously suggested “full support” may now suggest either a threat to, or impairment of, fish consumption uses. This scenario, however, does not apply to the fish contaminant data generated from the 2001 RAFT sampling conducted at Lake Miami: the levels of contaminants do not exceed any of the new (2006) advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.
