Assessment Comments
Assessment based on (1) results of IDNR beach monitoring program from 2002 to 2003, (2) ISU lake survey from 2000-03, (3) ISU reports on lake plankton from 2002-05, and (4) EPA/IDNR fish tissue monitoring in 1997.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "fully supporting". The slightly elevated levels of chlorophyll and algal-related turbidity at this lake, however, remain of concern. The Class B(LW) aquatic life uses are assessed (evaluated) as "fully supporting." Fish populations were renovated in Fall 2003 due to an increasingly large population of yellow bass at this lake. Fish consumption uses remain assessed (monitored) as "fully supported" based on fish contaminant monitoring conducted in 1997. The sources of data for this assessment include (1) results of the IDNR-UHL beach monitoring program in summers of 2002 and 2003, (2) results of the statewide survey of Iowa lakes conducted from 2000 through 2003 by Iowa State University (ISU), (3) information from the IDNR Fisheries Bureau, (4) ISU reports on lake plankton communities from 2000-05, and (5) results of U.S. EPA/IDNR fish contaminant monitoring in 1997. This assessment primarily reflects water quality conditions prior to the chemical renovation of the lake's fish population in Fall 2003. Due to the potential influence of fish populations on water quality, changes in water quality at this lake can be expected for the 2004-2006 period.
EXPLANATION: Results of IDNR beach monitoring at Lake Anita in 2002 and 2003 suggest that the Class A uses are "fully supported." Levels of indicator bacteria were monitored once per week during the primary contact recreation seasons (May through September) of 2002 (19 samples) and 2003 (20 samples) as part of the IDNR beach monitoring program (this lake’s beach was not monitored during the 2004 recreational season; this lake was drained and renovated in Fall, 2003). 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. This assessment approach is based on U.S. EPA guidelines (see pgs 3-33 to 3-35of U.S. EPA 1997b).
At Lake Anita beach, the geometric means of all 31 thirty-day periods during the summer recreation seasons of 2002 and 2003were below the Iowa water quality standard of 126 orgs/100 ml. Also, the percentage of samples exceeding Iowa’s single-sample maximum criterion did not exceed 10% in either of the two recreation seasons (2002: 0%; 2003: 5%). According to U.S. EPA guidelines and IDNR’s assessment methodology, these results suggest “full support” of the Class A (primary contact recreation) uses. These results suggest that levels of bacteria at this beach are very low.
Results from the ISU statewide survey of Iowa lakes suggest full support of the Class A uses at Lake Anita. 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 63, 64, and 62, respectively. According to Carlson (1977), all three index values are in the range between eutrophic and hyper-eutrophic lakes. These index values suggest somewhat elevated levels of phosphorus and chlorophyll-a and marginally good water transparency. Based on median values from ISU sampling from 2000 through 2004, the ratio of total nitrogen to total phosphorus for this lake is 19, thus suggesting that phosphorus is the nutrient that limits production of suspended algae at this lake.
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 approximately 40% of the dry mass of the zooplankton community of this lake. The average per summer sample mass of Cladoceran taxa (61 mg/l) was the 45th lowest level of the 131 lakes sampled. These results suggest little if any non-phosphorus limitation due to zooplankton grazing at Lake Anita.
The levels of inorganic suspended solids at this lake are relatively low and do not suggest a strong potential for either limiting algal production or for increasing lake turbidity. The median level of inorganic suspended solids in the 131 lakes sampled for the ISU lake survey from 2000 through 2005 was 5.2 mg/l; the median level at Lake Anita was 4.0 mg/l. The somewhat elevated TSI value for chlorophyll-a suggests a threat to full support of the Class A (primary contact) uses through presence of aesthetically objectionable conditions related to 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 (approximately 70%) 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 Ahquabi (13.6 mg/l) was the 74th lowest of the 131 lakes sampled. This level is in the lowest two-thirds of the 131 Iowa lakes sampled. The presence of a moderately high 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." While the water quality of this lake has remained good, the recreational fishery had declined markedly since the accidental introduction of yellow bass (Morone mississippiensis) in 1995. According the DNR Fisheries Bureau, the increasingly large population of yellow bass reduced the bluegill population by 85%, the crappie population by 70%, and the largemouth bass population by 60%. In 2002, the density of yellow bass was estimated at 8,000 fish per acre; the combined panfish density was estimated at less than 300 fish per acre (information from "Iowa Outdoors," February 4, 2003, http://www.iowadnr.com/news/io.html). The DNR Fisheries Bureau chemically renovated the fish population of this lake in Fall 2003. Because the adverse impacts from yellow bass at this and other lakes are related to inter-specific competition versus degraded water quality (as caused, for example, by common carp), the their adverse impact at Lake Anita is not considered a water quality impact in the context of Section 305(b) reporting or Section 303(d) listing.
The ISU lake survey data show no violations of the Class B(LW) criteria for dissolved oxygen in the 10 samples collected during summers of 2000 through 2003. One of 11 samples exceeded the Class A,B(LW) criterion for pH (maximum = 9.5; minimum = 8.0 pH units). Based on IDNR’s assessment methodology, however, these results do not suggest that significantly more than 10 percent of the samples exceed Iowa’s pH criteria and thus do not suggest an impairment of the Class A and Class B(LW) uses of this lake. This violation likely reflects the high levels of primary productivity at Lake Anita and does not reflect the input of pollutants into this lake.
Fish consumption uses were assessed (evaluated) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Lake Anita in 1997. Because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes. 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 1997 RAFT sampling conducted at Lake Anita: levels of all contaminants from this monitoring were below advisory trigger levels, thus suggesting the continued “full support” of fish consumption uses.
