Assessment Comments
Assessment is based on: (1) results of the IDNR-UHL beach monitoring program in the summers of 2004, 2005, and 2006, (2) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), (4) information from the IDNR Fisheries Bureau, and (5) results of EPA/DNR fish contaminant (RAFT) monitoring in 2004.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to violations of the state water quality criteria for indicator bacteria. The Class B(WW-1) (aquatic life) uses are assessed (monitored) as “fully supported.” Fish consumption uses remain assessed (monitored) as “fully supported.” Sources of data for this assessment include (1) results of the IDNR-UHL beach monitoring program in the summers of 2004, 2005, and 2006, (2) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), (4) information from the IDNR Fisheries Bureau, and (5) results of EPA/DNR fish contaminant (RAFT) monitoring in 2004.
EXPLANATION: Results of IDNR beach monitoring from 2004 through 2006 suggest that the Class A1 uses are "not supported." Levels of indicator bacteria at Big Creek Lake beach were monitored once per week during the primary contact recreation seasons (May through September) of 2004 (22 samples), 2005 (23 samples), and 2006 (28 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 A1 (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 A1 uses should be assessed as “not supported.” Also, if significantly 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 A1 uses should be assessed as “partially supported.” This assessment approach is based on U.S. EPA guidelines (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
At Big Creek Lake beach, the geometric means of 6 thirty-day periods during the summer recreation season of 2004 exceeded the Iowa water quality standard of 126 E. coli orgs/100 ml. No geometric means violated this standard in 2005 or 2006. Also, the percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was significantly greater than 10% in 2004 (23%). Less than 10% of the samples exceeded the single-sample maximum standard during the recreational seasons of 2005 (0%) and 2006 (4%). According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest impairment (nonsupport) of the Class A1 (primary contact recreation) uses of Big Creek Lake.
Results from the ISU and UHL lake surveys suggest full support of the Class A1 uses of Big Creek Lake. Using the median values from these surveys from 2002 through 2006 (approximately 23 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 48, 51, and 57 respectively for Big Creek Lake. According to Carlson (1977) the Secchi depth value places Big Creek Lake at the upper end of the mesotrophic category, while the value for chlorophyll a is at the low end of the eutrophic category. The index value for total phosphorus places Big Creek Lake at the upper end of the eutrophic category. These values suggest low levels of chlorophyll a and suspended algae in the water, exceptional water transparency, and relatively low levels of phosphorus in the water column.
The level of inorganic suspended solids was low at this lake and does not suggest water quality problems due to non-algal turbidity. The median level of inorganic suspended solids in Big Creek Lake (2.0 mg/L) was the 17th lowest median concentration among the 132 lakes sampled by the ISU and UHL lake surveys.
Data from the 2002-2006 ISU and UHL surveys suggest a small population of cyanobacteria exists at Big Creek Lake, which does not suggest an impairment at this lake. These data show that cyanobacteria comprised 74% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (9.8 mg/L) was also the 31st lowest of the 132 lakes sampled.
The Class B(WW-1) (aquatic life) uses are assessed (monitored) as “fully supported” based on information from the IDNR Fisheries Bureau, results from the ISU and UHL lake surveys, and physical and chemical results associated with IDNR’s beach monitoring program. The ISU and UHL lake survey results show good chemical water quality at Big Creek Lake. During 2002-2006 there were no violations of the Class B(WW-1) criterion for ammonia (16 samples), or dissolved oxygen (23 samples), and only one violation in 20 samples of the pH criterion. Based on IDNR’s assessment methodology, the one violation of the pH criterion does not constitute an impairment at Big Creek Lake. The physical/chemical data associated with the beach monitoring data from 2004 through 2006 show no violations of the Class B(WW-1) criteria for dissolved oxygen (70 samples) or pH (71 samples).
Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring at Big Creek Lake in 2004. The composite samples of fillets from channel catfish and largemouth bass had low levels of contaminants. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: <0.0181 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm. Levels of primary contaminants in the composite sample of largemouth bass fillets were as follows: mercury: 0.043 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm. 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. The fish contaminant data generated from the 2004 RAFT sampling conducted at this lake show that the levels of contaminants do not exceed any of the advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.
