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 / threatened” due to periodic occurrence of blooms of bluegreen algae during the 2000-02 period. 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 / threatened." The Class B(WW) aquatic life uses remain assessed (monitored) as "fully supported" based on results of chemical/physical monitoring conducted from 2000-02. Fish consumption uses were assessed (monitored) as "fully supported/threatened" based on ACOE-sponsored annual fish contaminant monitoring from 2000-02. The sources of data for these assessments include (1) the results of water quality monitoring (including fish contaminant monitoring) conducted from 2000 through 2002 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 2002 by Iowa State University (ISU), (3) information from the IDNR Fisheries Bureau, and (4) information on plankton communities at Iowa lakes in 2000 from Downing et al. (2002).
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 as "fully supporting." The geometric mean of indicator bacteria (fecal coliforms) in the 24 samples collected in summers of 2000, 2001, and 2002 was 5 orgs/100 ml; no samples exceeded the EPA-recommended single sample maximum value of 400 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting, a geometric mean for fecal coliforms less than 200 orgs/100 ml, combined with less than 10% of samples exceeding the 400 orgs/100 ml single sample maximum value, suggests full support of primary contact recreation uses. (see pgs 3-33 to 3-35of U.S. EPA 1997b). Levels of indicator bacteria (fecal coliforms) at both of the reservoir beaches (North Overlook Beach and White Breast Beach) were well-below the Class A water quality criterion of 200 orgs/100 ml during recreational seasons of the 2000-02 period. These results suggest “full support” of the Class A uses at these beaches. At North Overlook Beach, none of 12 five-sample geometric means from summers of 2000 through 2002 exceeded the state water quality standard of 200 orgs/100 ml. The overall geometric mean of the 24 samples was 9 orgs/100 ml; the maximum five-sample geometric mean was 22 orgs/100 ml. The maximum daily average of the three sample sites at this beach was 335 orgs/100 ml on July 11, 2000. Similarly, at White Breast Beach, none of 12 five-sample geometric means from summers of 2000 through 2002 exceeded the state water quality standard of 200 orgs/100 ml. The overall geometric mean of the 24 samples was 13 orgs/100 ml; the maximum five-sample geometric mean was 41 orgs/100 ml. The maximum daily average of the three sample sites at this beach was 207 orgs/100 ml on June 27, 2000. Based on results of beach monitoring, the lack of violations of the Iowa’s Class A water quality standard for indicator bacteria (fecal coliforms) at North Overlook and White Breast beaches as well as from the main reservoir site from 2000-2002 suggest that the Class A uses of Red Rock Reservoir are "fully supported." The results of this monitoring suggest that bacterial levels at the Red Rock beaches and the lake in general are very low.
Results from the ISU statewide survey of Iowa lakes from 2000-02 also suggest full support of the Class A uses of Red Rock Reservoir. 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 78, 41, and 57, 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 mid to upper range of 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 2002 was 4.8 mg/l. Of 131 lakes sampled, Red Rock Reservoir has the 49th highest median level of inorganic suspended solids (5.8 mg/l), thus suggesting that non-algal turbidity likely limits the production of algae as well as contributes to in-lake turbidity. The level of chlorophyll-a at Red Rock Reservoir is extremely low (4th 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 2000-02, the ratio of total nitrogen to total phosphorus for this lake is 50; this ratio suggests that algal production at this lake is limited by the availability of phosphorus as opposed to nitrogen availability. The 2000-02 median concentration of total nitrogen at this reservoir (8.6 mg/l) was the ninth highest of the 131 lakes sampled. Data from Downing et al. (2002) show relatively small zooplankton populations at this lake, including a relatively small population of species known as algal grazers. The summer 2000 average mass of zooplankton grazers at this lake in 2000 (3.7 mg/l) was the 28th lowest of the 131 lakes sampled. The moderately high level of inorganic suspended solids at this lake, however, remains the primary non-phosphorus limitation to algal production at this lake.
Based on results of ISU/Limnology monitoring, blooms of bluegreen algae do not appear to be a problem at Red Rock Reservoir. Data from Downing et al. (2002) suggest that bluegreen algae (Cyanophyta) comprise a very small portion (approximately 2%) of the summertime phytoplankton community of this lake. The average mass of bluegreen algae in summer 2000 at this lake (0.13 mg/l) was the third lowest of the 131 lakes sampled. These results do not suggest any threats or impairments due to presence of this nuisance aquatic (e.g., algal) species. 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 for 2001 and 2002 (Lutz and Esser 2002, Lutz and Cummings 2003), 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 and in July 2002 suggests a threat to the full support of Class A uses at this reservoir.
The Class B(WW) aquatic life uses of the reservoir were assessed as "fully supported." None of the 48 samples collected during the 2000-2002 period as part of ISU/ACOE monitoring violated Class B(WW) criteria for pH or ammonia-nitrogen. One of 48 samples, however, violated the Class B(WW) criterion for dissolved oxygen: the sample from August 6, 2002 contained 4.4 mg/l of dissolved oxygen and violated the Class B(WW) criterion of 5.0 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.
Fish consumption uses were assessed as "fully supporting/threatened." Fish contaminant monitoring conducted annually in Red Rock Reservoir from 2000 through 2002 as part of the Des Moines River Water Quality Study showed that levels of organochlorine contaminants (chlordane, dieldrin, and heptachlor epoxide) in composite samples of whole-fish carp were well below respective FDA action levels. The level of dieldrin in the sample of whole-fish carp collected in May, 2001, however, contained 0.172 ppm of dieldrin. This level is above one-half the FDA action level of 0.300 ppm. Thus, based on IDNR guidelines for Section 305(b) reporting, fish consumption uses are assessed as "fully supported / threatened." Levels of organochlorine contaminants such as dieldrin tend to be higher in whole-fish versus fillet samples. Thus, levels of dieldrin in fillets could be expected to be less than one-half the FDA action level.
