Assessment Comments
Assessment is based on results of (1) water quality (including fish tissue) monitoring conducted as part of the UI/ACOE "Coralville Water Quality Study from 2002-04, (2) ISU statewide surveys of lakes from 2000-04, (3) ISU studys on plankton communities from 2000-05, and (4) information from the IDNR Fisheries Bureau.
Basis for Assessment
SUMMARY: Class A (primary contact recreation) uses of the reservoir were assessed (monitored) as "partially supported” due to poor water transparency caused by high levels of inorganic suspended solids in this reservoir. The primary contact recreation uses at the reservoir's three beaches and for the non-beach portions of the lake are assessed (monitored) as "fully supported". The Class B(WW) aquatic life uses are assessed (monitored) as "fully supported". Fish consumption uses were assessed as "fully supported" based on ACOE-sponsored fish contaminant monitoring from 2003-04. The sources of data for these assessments include (1) the results of water quality monitoring conducted from 2002 through 2004 at Coralville Reservoir by the University of Iowa (under contract with the U.S. Army Corps of Engineers (ACOE)) as part of the Coralville Reservoir Water Quality Study, (2) results of the statewide survey of Iowa lakes conducted from 2002 through 2004 by Iowa State University (ISU), (3) information from the IDNR Fisheries Bureau, and (4) information on plankton communities collected at Iowa lakes from 2000 through 2005 as part of the ISU lake survey.
EXPLANATION: Results of water quality monitoring at the UI/ACOE long-term station at the MaHaffey Bridge on the main reservoir suggest that the Class A uses should be assessed (monitored) as "fully supporting". The geometric mean of indicator bacteria (E. coli) in the 18 samples collected in the main reservoir in summers of 2002, 2003, and 2004 was 11 orgs/100 ml and was far below Iowa’s geometric mean standard of 126 orgs/100 ml. Also, none of the 18 samples exceeded Iowa’s single sample maximum value of 235 orgs/100 ml (maximum sample value = 40 orgs/100 ml). According to IDNR’s assessment methodology for Section 305(b) reporting, a geometric mean for E. coli less than 126 orgs/100 ml, combined with less than 10% of samples exceeding the 235 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).
Mean levels of indicator bacteria (fecal coliforms) at all three of the reservoir’s beaches (West Overlook, Sugar Bottom, and Sandy Beach) were well-below the Class A water quality criterion of 126 E. coli orgs/100 ml during recreational seasons of 2003 and 2004 period (beach monitoring was not conducted during 2002). None of the combined 15 thirty-day geometric means (N=5) for each beach during summers of 2003 and 2004 exceeded 126 E. coli orgs/100 ml; the maximum thirty-day geometric means were as follows: West Overlook: 47 orgs/100 ml; Sugar Bottom: 31 orgs/100 ml; Sandy Beach: 93 orgs/100 ml. The percentage of individual samples that exceeded Iowa’s single-sample maximum criterion (235 orgs/100 ml) were as follows: West Overlook: 0% in 2003; 14% (2 of 14 samples) in 2004; Sugar Bottom Beach: 0% in both 2003 and 2004; Sandy Beach: 11% (1 of 9 samples) in 2003; 15% (2 of 13 samples) in 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). All geometric means for the reservoir’s beaches were below Iowa’s geometric mean criterion of 126 orgs/100 ml. Also, based on IDNR’s assessment methodology, the percentage of samples that exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml was not significantly greater than 10% during the assessment period. According to IDNR’s assessment methodology, at least 4 violations in sample sizes from 12 to 14 are needed to demonstrate that significantly more than 10% of the samples exceed the single-sample maximum criterion (with 90% confidence).
Results from the ISU statewide survey of Iowa lakes from 2003-04, however, suggest impairments to the Class A uses of Coralville Reservoir due to high levels of non-algal turbidity. Using the median values from this survey from 2002 through 2004 (approximately 15 samples), Carlson’s (1977) trophic state indices for total phosphorus, chlorophyll-a, and secchi depth are 82, 54, and 67, respectively. According to Carlson (1977), the index value for total phosphorus places this reservoir in the upper range of hyper-eutrophic lakes; the index value for chlorophyll-a is in the middle range of eutrophic lakes, and the value for secchi depth is in the middle range between eutrophic and hyper-eutrophic lakes. These index values suggest extremely high levels of phosphorus in the water column, relatively low (and much less than expected) production of suspended algae, and moderately poor 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 Coralville 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, Coralville Reservoir eighth highest median level of inorganic suspended solids (21.9 mg/l), thus suggesting that non-algal turbidity limits the production of algae and is the primary cause of the moderately poor water transparency. These conditions suggest an suggest impairment of the Class A (primary contact) uses primarily due to presence high levels of inorganic turbidity that reduce water transparency such that Iowa’s narrative water quality standard protecting against aesthetically objectionable conditions is violated. The level of chlorophyll-a at Coralville Reservoir is very low (26th lowest of the 131 lakes sampled) and does not appear to contribute to impairments at this lakes. The IDNR Fisheries Bureau concurs that turbidity-related impairments exist at this lake.
Based on median values from ISU sampling from 2000-02, the ratio of total nitrogen to total phosphorus for this lake is 40; this ratio suggests that algal production at this lake is not limited by the availability of nitrogen. The 2000-02 median concentration of total nitrogen at this reservoir (9.0 mg/l) was the ninth highest of the 131 lakes sampled.
The results of ISU plankton monitoring from 2000 through 2005 show a relatively small population of zooplankton grazers at Coralville Reservoir. This lake had the second lowest per summer sample mass of zooplankton (Cladoceran) grazers of the 131 lakes sampled. This low level of zooplankton grazers would likely be unable to suppress algal production.
The extremely high level of inorganic suspended solids at this lake remains the primary non-phosphorus limitation to algal production at this lake. The application of the TSI assessment methodology developed to Iowa lakes to Iowa’s four federal flood control reservoirs, however, may not be appropriate. That is, these waterbodies, by design, have extremely high watershed-to-surface area ratios. Thus, the occurrence of higher inorganic turbidities in these reservoirs is not unexpected. Nonetheless, the high levels of inorganic suspended solids in this reservoir, and the poor water transparency that results, suggest a water quality concern.
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 (~50%) of this lake’s summertime phytoplankton community, sampling from 2000 through 2004 showed that the median per summer sample mass of bluegreen algae at Coralville Reservoir (15.9 mg/l) was only the 50th highest of the 131 lakes sampled. This levels is in the lowest two-thirds 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, 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).
The Class B(WW) aquatic life uses of the reservoir were assessed as "fully supported". None of the approximately 68 samples collected during the 2002-2004 period as part of ACOE monitoring violated Class B(WW) criteria for pH or ammonia-nitrogen. Two of 66 samples (3%), however, violated the Class B(WW) criterion for dissolved oxygen: the sample from August 20, 2003 contained 4.8 mg/l of dissolved oxygen, and the sample from June 23, 2004 contained 4.5 mg/l; both samples 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.
During the 1998-1999 biennial period, five of 43 reservoir samples (12%) violated the criterion for dissolved oxygen (see assessment for the 2000 report). The somewhat lower frequency of violations during the 2000-2002 and 2002-2004 assessment periods may suggest improving water quality conditions or may indicate a continuing water quality problem. Regardless, problems with low levels of dissolved oxygen at this reservoir remain a concern. One of 67 samples (2%) collected for the ACOE program during the 2002-04 assessment period exceeded the Class B(LW) criterion for pH of 9.0 pH units (maximum value = 10.0; minimum value = 6.6 pH units).
The 2000-04 ISU lake survey data show three violations of the Class B(WW) criterion for dissolved oxygen in the 13 samples collected. All three violations occurred in 2000; no violations of the dissolved oxygen criterion were recorded during ISU monitoring from 2001 through 2004. 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. None of the 14 samples collected as part of ISU monitoring exceeded Class A,B(WW) criteria for pH.
Fish consumption uses were assessed (monitored) as "fully supporting." Fish contaminant monitoring conducted in Coralville Reservoir in 2003 and 2004 as part of the Coralville Reservoir Water Quality Study showed that levels of organochlorine contaminants (chlordane, dieldrin, and heptachlor epoxide) in composite samples of whole-fish carp were very low. 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 2002 or 2003 ACOE fish contaminant monitoring conducted at Coralville Reservoir: the levels of contaminants do not exceed any of the new (2006) advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody. Analysis of fish tissue for the ACOE monitoring program, however, does not include analysis for mercury or PCBs.
