Assessment Comments
Assessment is based on (1) surveys conducted by the DNR Fisheries Bureau and (2) results of IDNR beach monitoring from 2002-04, (3) ISU survey of Iowa lakes from 2000-04, (4) ISU studies of lake plankton communities from 2000-05, and (5) U.S. EPA/IDNR fish tissue monitoring in 2001 and 2005.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "not supporting" due to high levels of indicator at Nine Eagles Lake beach in 2004. The Class B(LW) aquatic life uses are assessed (evaluated) as "fully supported". The Class C (drinking water) uses are "not assessed" due to the lack of water quality information upon which to base an assessment. Fish consumption uses are assessed as "not supported" based on fish contaminant monitoring conducted in 2001 and 2005 that resulted in issuance of a fish consumption advisory for this lake in January 2006. The sources of data for this assessment include (1) the results of the IDNR-UHL beach monitoring program in summers of 2002, 2003, and 2004, (2) results of the statewide survey of Iowa lakes conducted from 2000 through 2004 by Iowa State University (ISU), (3) information from the IDNR Fisheries Bureau, (4) information on plankton communities collected from 2000 through 2005 for the ISU lakes survey, and (5) results of U.S. EPA / IDNR fish tissue monitoring in 2001 and 2005.
Note: A TMDL for turbidity at Nine Eagles Lake was prepared by IDNR and approved by EPA in 2001. Through implementation of this TMDL, water clarity at this lake had improved such that the lake was de-listed for the 2004 assessment/listing cycle. Because, however, the 2006 Section 303(d) impairments due to indicator bacteria and mercury in fish tissue at Nine Eagles Lake were not addressed in the TMDL, this waterbody was moved from IR Category 2a (fully supported) for the 2004 assessment/listing cycle to Category 5a (impaired; TMDL required) for the 2006 cycle.
EXPLANATION: Results of IDNR beach monitoring at Nine Eagles Lake from 2002 through 2004 suggest that the Class A uses are "not supported." Levels of indicator bacteria were monitored once per week during the primary contact recreation seasons (May through September) of 2002 (29 samples), 2003 (29 samples), and 2004 (14 samples) as part of the IDNR beach monitoring program. According to IDNR’s assessment methodology, two conditions need to be met for results of beach monitoring to indicate “full support” of the Class A (primary contact recreation) uses: (1) all five-sample, thirty-day geometric means for the three-year assessment period are less than the state’s geometric mean criterion of 126 E. coli orgs/100 ml and (2) not more than 10 % of the samples during any one recreation season exceeds the state’s single-sample maximum value of 235 E. coli orgs/100 ml. If a 5-sample, 30-day geometric mean exceeds the state criterion of 126 orgs/100 ml during the three-year assessment period, the Class A uses should be assessed as “not supported”. Also, if significantly more than 10% of the samples in any one of the three recreation seasons exceed Iowa’s single-sample maximum value of 235 E. coli orgs/100 ml, the Class A uses should be assessed as “partially supported”. This assessment approach is based on U.S. EPA guidelines (see pgs 3-33 to 3-35of U.S. EPA 1997b).
At Nine Eagles Lake beach, the geometric means of 3 of the 10 thirty-day periods during the summer recreation season of 2004 exceeded the Iowa water quality standard of 126 E. coli orgs/100 ml. None of the geometric means exceeded this standard during the recreational seasons of 2002 (25 geometric means) or 2003 (25 geometric means). According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest impairment (nonsupport) of the Class A (primary contact recreation) uses.
Results from the ISU statewide survey of Iowa lakes, however, suggest that the Class A uses of Nine Eagles Lake are “fully supported.” 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 51, 44, and 52, respectively. According to Carlson (1977), the index value for total phosphorus places this lake in the lower range of eutrophic lakes; the index values for chlorophyll-a is in the middle range of mesotrophic lakes, and the index value for secchi depth is in the middle range of eutrophic lakes. These index values suggest very low levels of phosphorus, extremely low production of suspended algae, and water transparency that is very good for Iowa lakes. These results suggest that this lake does not have impairments due to aesthetically objectionable conditions due either to blooms of algae or high levels of inorganic turbidity.
According to Carlson (1991), the occurrence of a low chlorophyll-a TSI value relative to those for total phosphorus and secchi depth indicates that non-algal particles or color dominate light attenuation. The ISU lake data suggest that non-algal particles do likely limit algal production at Nine Eagles 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, Nine Eagles Lake had the 55th lowest median level of inorganic suspended solids (4.2 mg/l). While this level of inorganic solids is only slightly elevated, sufficient inorganic material may be present to reduce light penetration and the production of suspended algae.
Results of ISU monitoring do not show non-phosphorus limitation due to nitrogen availability or zooplankton grazing. Based on median values from ISU sampling in 2000 through 2004, the ratio of total nitrogen to total phosphorus for Nine Eagles Lake is 26, thus suggesting that nitrogen availability does not limit algal production. This ratio, however, is considerably higher than that based on only the first two years of the ISU survey (2000 and 2001): 10. This much lower ratio, which does suggest nitrogen limitation, suggests that algal production at Nine Eagles Lake may fluctuate from being limited by phosphorus and by nitrogen.
In terms of all Iowa lakes sampled, data from the ISU survey show extremely 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 45% of the dry mass of the zooplankton community of this lake; the average per summer sample mass of Cladoceran taxa (20 mg/l) was the 8th lowest level of the 131 lakes sampled. These results suggest little if any non-phosphorus limitation due to zooplankton grazing at Nine Eagles Lake.
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 (65%) of this lake’s summertime phytoplankton community, sampling from 2000 through 2004 showed that the median per summer sample mass of bluegreen algae at Nine Eagles Lake (10.8 mg/l) was the 54th lowest of the 131 lakes sampled. This levels 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 as "fully supported". The ISU lake survey data also suggest relatively good chemical water quality at Nine Eagles Lake. Results of monitoring during summers of 2000 through 2004 show no violations of the Class B(LW) criteria for dissolved oxygen in the 13 samples collected, or for pH in the 11 samples collected.
The Class C (drinking water) uses are "not assessed" due to lack of monitoring data upon which to base an assessment. The only parameter collected as part of the ISU lake survey relevant to support of Class C (drinking water) uses is nitrate. While the results of the ISU survey from 2000-04 show that nitrate levels are very low at this lake (maximum value = 1.0 mg/l; median = 0.1 mg/l), these data are not sufficient for developing a valid assessment of support of the Class C uses.
Fish consumption uses were assessed (monitored) as “not supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Nine Eagles Lake in 2001 and in 2005. 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 (IDPH), 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 applies to the fish contaminant data generated from the RAFT sampling conducted at Nine Eagles Lake: levels of mercury in samples of largemouth bass from consecutive samplings exceeded advisory trigger levels, thus suggesting the need for a consumption advisory. The level of mercury in the samples of largemouth bass (0.26 ppm), however, exceeded the IDNR/IDPH trigger level of 0.20 ppm for a one meal per week consumption advisory (this levels is well below the “do not eat” trigger level for mercury of 1.0 ppm). According to the IDNR/IDPH advisory protocol, if two consecutive samplings show that contaminant levels are above the trigger level in fillet samples, issuance of a consumption advisory is justified. Because the level of mercury in sample of largemouth bass fillets from the 2005 sampling (0.30 ppm) also exceeded this advisory trigger level, issuance of a fish consumption advisory is justified. This advisory was issued by IDNR and IDPH in January 2006. According to IDNR’s assessment methodology, the existence of a consumption advisory indicates that fish consumption uses should be assessed as “not supported”.
