Assessment Comments
Assessment is based on results of (1) monitoring of water quality, fish contaminants, and indicator bacteria at beaches conducted by Iowa State Univ. as part of the ACOE's Des Moines R./Saylorville Res./Red Rock Res. water quality study, (2) the statewide survey of Iowa lakes conducted from 2000-02 by Iowa State University, (3) information from the IDNR Fisheries Bureau, and (4) information on plankton communities at Iowa lakes in 2000.
Basis for Assessment
SUMMARY: Class A (primary contact recreation) uses of the Red Rock Reservoir were assessed (evaluated) as "fully supported” although occasional blooms of algae during summer months remains a concern. The primary contact recreation uses at the reservoir's two beaches remain assessed (monitored) as fully supported. The overall assessment of Class A uses for the reservoir is thus "fully supported”. The Class B(WW) aquatic life uses are assessed (monitored) as "fully supported". Fish consumption uses were assessed (monitored) as "fully supported " based on ACOE-sponsored annual fish contaminant monitoring from 2002-04. The sources of data for these assessments include (1) the results of water quality monitoring (including fish contaminant monitoring) conducted from 2002 through 2004 at Red Rock Reservoir by Iowa State University under contract with the U.S. Army Corps of Engineers as part of the Des Moines River Water Quality Study, (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, and (4) information on plankton communities collected from 2000 through 2005 for the ISU lakes survey, and.
EXPLANATION: Results of water quality monitoring at the ISU/ACOE long-term station on the main reservoir near the dam suggest that the Class A uses should be assessed (monitored) as "fully supporting." The geometric mean level of indicator bacteria (E. coli) in the 25 samples collected at this station during the recreational seasons of 2002 through 2004 (5 orgs/100ml) is well below the Iowa Class A water quality criterion of 126 orgs/100ml. None of the 25 samples exceeded Iowa’s single-sample maximum value of 235 orgs/100 ml (maximum sample value = 43 orgs/100 ml). Due to recent changes in Iowa’s Water Quality Standards, Iowa’s 2006 assessment methodology for indicator bacteria has changed. Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A criterion for indicator bacteria (fecal coliforms) designed to protect primary contact recreation uses: the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) did not apply "when the waters [were] materially affected by surface runoff." Due to a change in the Standards in July 2003, E. coli is now the indicator bacterium, and the high flow exemption was eliminated and replaced with language stating that the Class A criteria for E. coli apply when Class A1, A2, or A3 uses “can reasonably be expected to occur.” Because the IDNR Technical Advisory Committee on WQ Standards could not agree on what flow conditions would define periods when uses would not be reasonably expected to occur, all monitoring data generated for E. coli during the assessment period, regardless of flow or lake level conditions during sample collection, will be considered for determining support of Class A uses for purposes of the 2006 Section 305(b) assessments and Section 303(d) listings.
Similarly, results of ACOE beach monitoring from 2002 through 2004 at North Overlook and White Breast beaches also suggest that the Class A uses are "fully supported." Levels of indicator bacteria at North Overlook and White Breast beaches were monitored approximately three times per month during the primary contact recreation seasons (May through September) of 2002 and 2003 as part of the ACOE/Iowa State University “Des Moines River Water Quality Studies”. This monitoring program began weekly monitoring at the Red Rock beaches in summer 2004. 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 North Overlook Beach, the geometric means of all 23 thirty-day periods during the summer recreation seasons of 2002 (3 geometric means), 2003 (4 geometric means) and 2004 (16 geometric means) 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: 0%; 2003: 0%; 2004: 10%). According to U.S. EPA guidelines and IDNR’s assessment methodology, these results suggest “full support” of the Class A (primary contact recreation) uses.
Similarly, at White Breast Beach, the geometric means of all 23 thirty-day periods during the summer recreation seasons of 2002 (3 geometric means), 2003 (4 geometric means) and 2004 (16 geometric means) 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: 0%; 2003: 0%; 2004: 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.
Results from the ISU statewide survey of Iowa lakes from 2000-04 also suggest full support of the Class A uses of Red Rock Reservoir. 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 79, 42, and 61, respectively. According to Carlson (1977), the index value for total phosphorus places this reservoir in the range of hyper-eutrophic lakes; the index value for chlorophyll-a, however, is in the lower range of mesotrophic lakes, and the value for secchi depth is in the lower range between eutrophic and hyper-eutrophic lakes. These index values suggest (1) extremely high levels of phosphorus in the water column. (2) extremely low (and much lower than expected) levels of chlorophyll-a, and production of suspended algae, and (3) relatively good water transparency.
According to Carlson (1991), the occurrence of a low chlorophyll-a TSI value relative to those for total phosphorus and secchi depth indicate non-algal particles or color dominate light attenuation. The ISU lake data suggest that non-algal particles do likely limit algal production at Red Rock Reservoir. 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, Red Rock Reservoir has the 43rd highest median level of inorganic suspended solids (7.2 mg/l), thus suggesting that non-algal turbidity likely limits the production of algae as well as contributes to in-lake turbidity. The median level of chlorophyll-a at Red Rock Reservoir is extremely low (3rd lowest of the 131 lakes sampled) and does not suggest either threats or impairments to support of designated uses at this lakes. Based on median values from ISU sampling from 2000-04, the ratio of total nitrogen to total phosphorus for this lake is 51; this ratio suggests that algal production at this lake is limited by the availability of phosphorus as opposed to nitrogen availability. The 2000-04 median concentration of total nitrogen at this reservoir (9.2 mg/l) was the eighth highest of the 131 lakes sampled.
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. Although 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 over the 2000-2005 period (37 mg/l) was the 16th lowest of the 131 lakes sampled. These results suggest little if any non-phosphorus limitation due to zooplankton grazing at Red Rock Lake.
The moderately high level of inorganic suspended solids at this lake, however, remains the primary non-phosphorus limitation to algal production at this 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 (approximately 60%) of this lake’s summertime phytoplankton community, sampling from 2000 through 2004 showed that the median per summer sample mass of bluegreen algae at Red Rock Lake (1.3 mg/l) was the 8th lowest of the 131 lakes sampled. This levels is in the lowest 10% 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 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). Results of ISU/ACOE monitoring, however, do suggest that blooms of bluegreen algae occasionally occur at Red Rock Lake. According to the ISU/ACOE annual monitoring reports (e.g., Lutz and Esser 2002, Lutz and Cummings 2003, Lutz 2004, and Lutz et al. 2005), blooms of bluegreen algae typically occur during July and August, especially under elevated pool conditions. These reports contain a summary of when these blooms have occurred at Red Rock Lake since 1990. The occurrence of bluegreen blooms from June to September 2001, July 2002, June 29, 2004, and July 6, 2004 suggests a threat to the full support of Class A uses at this reservoir (no algal blooms were observed at this reservoir in 2003).
The Class B(WW) aquatic life uses of the reservoir were assessed as "fully supported". None of the 51 samples collected during the 2002-2004 period as part of ISU/ACOE monitoring violated Class B(WW) criteria for pH or ammonia-nitrogen. Three of 51 samples (6%), however, violated the Class B(WW) criterion for dissolved oxygen: all these violations occurred in late summer and all were relatively minor (rage from 4.4 to 4.9 mg/l). According to U.S. EPA guidelines for Section 305(b) reporting (U.S. EPA 1997b: page 3-17), however, a violation frequency for conventional parameters (including dissolved oxygen) of 10% or less does not suggest an impairment of aquatic life uses.
The ISU lake survey data also show good chemical water quality at this lake. Results of this monitoring show no violations of the Class A,B(LW) criteria for pH in the 14 samples collected during summers of 2000 through 2004 (maximum = 8.7; minimum = 8.0 pH units). Two of 14 samples exceeded the Class B(LW) criterion for dissolved oxygen. Based on IDNR’s assessment methodology, however, these results do not suggest that significantly more than 10 percent of the samples exceed Iowa’s dissolved oxygen criteria and thus do not suggest an impairment of the Class B(LW) uses of Red Rock Lake.
Fish consumption uses were assessed (monitored) as “fully supported” based on results of ACOE/ISU fish contaminant monitoring at Red Rock Lake in 2002, 2003, and 2004. The composite samples of whole-fish common carp and the sample of catfish fillets had low levels of contaminants (the ACOE/ISU samples are not analyzed for mercury or PCBs). Levels of total chlordane in the composite samples were as follows: 2002: 23.9 ppb; 2003: 4.4 ppb; 2004: 4.6 ppb. The level of total chlordane in the sample of channel catfish fillets was 32.3 ppb. None of these levels approach the new (2006) advisory trigger level of 600 ppb for chlordane. 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 ACOE/ISU fish contaminant sampling conducted at Red Rock Lake: the levels of contaminants do not exceed any of the new (2006) advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.
