Assessment Comments
Assessment is based on results of (1) IDNR/UHL beach monitoring from 2002-04, (2) ISU lake survey from 2000-04, (3) surveys by IDNR Fisheries Bureau, (4) ISU reports on lake plankton communities, 2000-05, (5) results of EPA/DNR fish tissue (RAFT) monitoring in 1997, and (6) a UHL water supply survey in 1995.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "fully supporting" based on results of IDNR beach monitoring and ISU lake survey information. Based on information from the IDNR Fisheries Bureau, the Class B(LW) aquatic life uses assessed (evaluated) as "fully supporting". Fish consumption uses remain assessed (evaluated) as "fully supported" based on fish contaminant monitoring in 1997. The Class C (drinking water) uses are not assessed due to the lack of recent information upon which to base an assessment. The sources of data for this assessment include (1) results of IDNR/UHL beach monitoring from 2002-2004, (2) results of the statewide survey of Iowa lakes sponsored by IDNR and conducted by Iowa State University (ISU) from 2000 through 2004, (3) surveys by IDNR Fisheries Bureau, (4) information on plankton communities collected at Iowa lakes from 2000 through 2005 as part of the ISU lake survey, and (5) results of U.S. EPA/IDNR fish tissue monitoring in 1997.
EXPLANATION: Results of monitoring for indicator bacteria at both Crandalls Beach and Marble Beach suggest “full support” of the Class A uses. Results of IDNR / UHL monitoring at Crandalls Beach in from 2002-2004 suggest that the Class A (primary contact recreation) uses are "fully supported." Levels of indicator bacteria at Crandall’s Beach were monitored once per week during the primary contact recreation seasons (May through September) of 2002 (28 samples), 2003 (28 samples), and 2004 (23 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 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 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 Crandall’s Beach, the geometric means of all 67 thirty-day periods during the summer recreation seasons of 2002, 2003 and 2004 were 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 any of the three recreation seasons (2002: 7%; 2003: 4%; 2004: 4%). According to U.S. EPA guidelines, these results suggest “full support” of the Class A (primary contact recreation) uses.
Results of IDNR/UHL monitoring at Marble Beach from 2002 through 2004 also suggest that the Class A (primary contact recreation) uses are "fully supported." At Marble Beach, the geometric means of all 67 thirty-day periods during the summer recreation seasons of 2002, 2003 and 2004 were also 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 any of the three recreation seasons (2002: 4%; 2003: 7%; 2004: 0%). According to U.S. EPA guidelines, these results suggest “full support” of the Class A (primary contact recreation) uses. These results also suggest that levels of indicator bacteria at Big Spirit Lake are very low.
Similarly, results from the ISU statewide survey of Iowa lakes suggest that the Class A uses of Big Spirit 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 59, 48, and 50, respectively. According to Carlson (1977), the index value for total phosphorus places this lake in the upper range of eutrophic lakes; the index values for chlorophyll-a and Secchi depth are in the upper range of mesotrophic lakes. These index values suggest that, despite the somewhat elevated levels of total phosphorus, the production of suspended algae in this lake is extremely low, and water transparency is exceptional 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 high TSI value for total phosphorus with relatively low values for chlorophyll-a and secchi depth indicate that some factor (e.g., nitrogen limitation, zooplankton grazing, or some other factor) limits production of algae. Results of ISU monitoring, however, do not immediately suggest a non-phosphorus limitation that can account for the discrepancy between the TSI for total phosphorus (59) and those for chlorophyll-a and Secchi depth (48 and 50, respectively). Based on median values from ISU sampling from 2000-04, the ratio of total nitrogen to total phosphorus for Big Spirit Lake is 19. This ratio suggests that algal production at this lake is likely limited by availability of phosphorus (although the TN:TP ratio for the 2000-01 period was 9.7, thus suggesting that algal production at this lake may be nitrogen-limited in some years).
In terms of all Iowa lakes sampled, data from the ISU survey show relatively small populations of zooplankton species at this lake that graze on algae. Although sampling from 2000 through 2005 showed that Cladoceran taxa (e.g., Daphnia) comprised approximately 45% 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 (59.8 mg/l) was only the 88th highest of the 131 lakes sampled. These results suggest little if any non-phosphorus limitation due to zooplankton grazing at Big Spirit Lake.
The levels of inorganic suspended solids at this lake are very low and do not suggest the potential for either limiting algal production, threatening designated uses, or impairing these uses. 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 Big Spirit Lake was 2.7 mg/l; this median level was the 24th lowest of the 131 lakes sampled.
The presence of nuisance algal species (i.e., bluegreen algae) does not appear to be a significant problem at this lake. While data results of monitoring from 2000-2004 suggest that bluegreen algae (Cyanophyta) comprise approximately 60% of the wet mass of the summertime phytoplankton community of this lake, the median 2000-04 summer per sample mass of bluegreen algae at Big Spirit Lake (7.7 mg/l) is the 40th lowest of the 131 lakes sampled. The presence of bluegreen algae at this lake does not appear to either threaten or impair designated uses.
Information from the IDNR Fisheries Bureau suggests that the Class B(LW) aquatic life uses should be assessed as "fully supported". Slightly elevated levels of nutrients, however, remain a concern at this lake. The ISU lake survey data also show good chemical water quality at this lake. These data show no violations of the Class B(LW) criteria for dissolved oxygen in the 14 samples collected, or for pH in the 14 samples collected, at Big Spirit Lake during summers of 2000 through 2004.
The Class C (drinking water) uses are “not assessed” due to the lack of recent information upon which to base an assessment. In previous 305(b) assessment cycles, the Class C uses were assessed as "fully supported" based on results of sampling conducted by UHL in January 1995 (see assessment for the 1996 and 1998 reports). However, these data are now considered too old (greater than five years) to characterize current water quality conditions. The nitrate data generated through the ISU lake survey from 2000 through 2004 show no violations of the nitrate MCL (10 mg/l) in the 15 samples collected. The maximum nitrate value in these samples was 0.4 mg/l.
Fish consumption uses were assessed (evaluated) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Big Spirit Lake 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 this lake: levels of all contaminants from this monitoring were below advisory trigger levels, thus suggesting the continued “full support” of fish consumption uses.
