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 Saylorville Reservoir were assessed (monitored) as "fully supported / threatened” due to slight reductions in water transparency caused by moderately high levels of inorganic turbidity and due to presence of blooms of bluegreen algae (noxious aquatic plants) in summers of 2001 and 2002. The primary contact recreation uses at the reservoir's two beaches, as measured by levels of indicator bacteria, however, 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 are assessed (monitored) as "fully supported / threatened" due to (1) slight reductions in water transparency and (2) the occurrence of several violations of the Iowa water quality standard for dissolved oxygen. Fish consumption uses remain assessed (monitored) as "fully supported" based on ACOE-sponsored fish contaminant monitoring from 2000-02. The sources of data for these assessments include (1) the results of water quality monitoring conducted from 2000 through 2002 at Saylorville 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/Limnology), (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 25 samples collected in summers of 2000, 2001, and 2002 was 4 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 (Sandpiper and Oak Grove beaches) 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 Sandpiper 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 18 orgs/100 ml; the maximum five-sample geometric mean was 44 orgs/100 ml. The maximum daily average of the three sample sites at this beach was 623 orgs/100 ml on July 24, 2001. Similarly, at Oak Grove Beach, none of 11 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 8 orgs/100 ml; the maximum five-sample geometric mean was 13 orgs/100 ml. The maximum daily average of the three sample sites at this beach was 160 orgs/100 ml on August 24, 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 Sandpiper and Oak Grove beaches as well as from the main reservoir site from 2000-2002 suggest that the Class A uses of Saylorville Reservoir are "fully supported." The results of this monitoring suggest that bacterial levels at the Saylorville beaches and the lake are, in general, very low.
Results from the ISU/Limnology statewide survey of Iowa lakes from 2000-02 also suggest full support of the Class A uses of Saylorville 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 76, 50, and 64, 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 at the boundary between mesotrophic and eutrophic lakes, and the value for Secchi depth is in the middle range between eutrophic and hyper-eutrophic lakes. These index values suggest (1) extremely high levels of phosphorus in the water column, (2) very low (and much lower than expected) levels of chlorophyll-a and production of suspended algae, and (3) marginally 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/Limnology lake data suggest that non-algal particles do likely limit algal production at Saylorville Reservoir. The median level of inorganic suspended solids in the 131 lakes sampled for the ISU/Limnology lake survey from 2000 through 2002 was 4.8 mg/l. Of 131 lakes sampled, Saylorville Reservoir has the 44th highest median level of inorganic suspended solids (6.7 mg/l), thus suggesting that non-algal turbidity likely limits the production of algae. The moderately high level of inorganic suspended solids at this reservoir, and the marginally good water transparency suggested by TSI value for Secchi depth (64), suggests a threat to the full support of the Class A (primary contact) uses primarily due to the potential for levels of turbidity that may violate Iowa’s narrative water quality standard protecting against aesthetically objectionable conditions.
The level of chlorophyll-a at Saylorville Reservoir is extremely low (15th lowest of the 131 lakes sampled) and does not appear to contribute to impairments at this lakes. Based on median values from ISU/Limnology sampling from 2000-02, the ratio of total nitrogen to total phosphorus for this lake is 71; this ratio suggests that algal production at this lake is limited by the availability of phosphorus and that levels of nitrogen are very high. The 2000-02 median concentration of total nitrogen at this reservoir (10.4 mg/l) was the fifth highest of the 131 lakes sampled. Data from Downing et al. (2002) show moderately large zooplankton populations at this lake, including large population of species known as algal grazers. The median summer mass of zooplankton grazers at this lake in 2000 (31.8 mg/l) was the 32nd highest of the 131 lakes sampled; this level of zooplankton grazers may, in combination with inorganic turbidity, limit algal production.
Based on results of ISU/Limnology monitoring, blooms of bluegreen algae do not appear to be a problem at Saylorville Reservoir. Data from Downing et al. (2002) suggest that bluegreen algae (Cyanophyta) comprise a very small portion of the summertime phytoplankton community of this lake. The average mass of bluegreen algae in summer 2000 at this lake (1.01 mg/l) was the 13th lowest of the 131 lakes sampled. These results do not suggest any impairments due to presence of nuisance aquatic species (e.g., bluegreen algae) at this reservoir. Results of ISU/ACOE monitoring, however, do suggest that blooms of bluegreen algae do occasionally occur at Saylorville 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 since 1990. The occurrence of a bluegreen blooms June to September of 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 / threatened" due violations of the Iowa water quality standard for dissolved oxygen. While none of the 50 samples collected during the 2000-2002 period violated Class B(WW) criteria for pH or ammonia-nitrogen, four of the 50 sampled (8%) violated the Class B(WW) criterion for dissolved oxygen of 5.0 mg/l. The dates and violations were as follows: August 24, 2000 (4.9); August 21, 2001 (4.3 mg/l); August 6, 2002 (4.8 mg/l); and August 13, 2002 (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. Nonetheless, the occurrence of these violations, although very slight, suggest a concern and a potential threat to the Class B(WW) uses at this lake.
Fish consumption uses were assessed as "fully supporting." Fish contaminant monitoring conducted in Saylorville 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.
