Assessment Comments
Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, (4) results of the IDNR-county voluntary beach monitoring program, (5) results of a fish kill investigation in June 2005, and (6) results of IDNR/U.S. EPA fish tissue monitoring (RAFT) in 2005.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (evaluated) as “not supported” due to levels of indicator bacteria that exceed Iowa’s water quality standard. The Class B(LW) (aquatic life) uses are assessed (monitored) as “partially supported” due to a fish kill in 2005. Fish consumption uses are assessed (monitored) as “fully supported.” Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, (4) results of the IDNR-county voluntary beach monitoring program, (5) results of a fish kill investigation in June 2005, and (6) results of IDNR/U.S. EPA fish tissue monitoring (RAFT) in 2005.
EXPLANATION: Results of IDNR county beach monitoring from 2004 through 2005 suggest that the Class A1 uses are assessed (evaluated) as "partially supported." Levels of indicator bacteria at Briggs Woods Lake beach were monitored approximately once per week during the primary contact recreation seasons (May through August) of 2004 (22 samples) and 2005 (23 samples) as part of the IDNR county beach monitoring program. Because only two years of data were collected as part of this program these data are considered not sufficient to accurately characterize current water quality conditions, therefore the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). 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 Briggs Woods Lake beach, the geometric mean of 1 thirty-day period during the summer recreation seasons of 2004 and 2005 exceeded the Iowa water quality standard of 126 E. coli orgs/100 ml: 0 of 6 geometric means violated in 2004, and 1 of 12 geometric means violated in 2005. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was not significantly greater than 10% in either of the following recreation seasons: 2004: 14%, 2005: 13%. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest impairment (nonsupport/evaluated) of the Class A1 (primary contact recreation) uses.
Results from the ISU and UHL lake surveys, however, suggest that the Class A1 uses at Briggs Woods Lake are assessed as “fully supported.” Using the median values from these surveys from 2002 through 2006 (approximately 19 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 50, 64, and 61 respectively for Briggs Woods Lake. According to Carlson (1977) the Secchi depth index value places Briggs Woods Lake at the lower end of the eutrophic category. The index values for chlorophyll a and total phosphorus place Briggs Woods Lake in between the eutrophic and hypereutrophic categories. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, very good water transparency, and moderately high levels of phosphorus in the water column.
The levels of inorganic suspended solids at this lake were low and do not suggest problems due to non-algal turbidity. The median level of inorganic suspended solids in Briggs Woods Lake (2.0 mg/L) was the 18th lowest median of the 132 lakes sampled by the ISU and UHL surveys.
Data from the 2002-2006 ISU and UHL surveys also suggest that a small population of cyanobacteria exists at Briggs Woods Lake. These data show that cyanobacteria comprised only 46% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (5.7 mg/L) was also the 22nd lowest of the 132 lakes sampled.
The Class B(LW) (aquatic life) uses for Briggs Woods Lake are assessed (monitored) as “partially supported” due to a fish kill in 2005. A fish kill occurred on June 1, 2005 and was attributed to low levels of dissolved oxygen related to the excessive growth of submergent aquatic vegetation in the lake. An estimated 1,000 bluegill of a variety of sizes were killed. Because the kill affected immature as well as adult fish, the kill was attributed to an oxygen sag rather than spawning stress. This was only a partial kill: many live fish were observed and anglers were catching fish during the IDNR investigation. According to IDNR’s assessment/listing methodology, the occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or waterbody reach during the most recent assessment period (2004-2007) indicates a severe stress to the aquatic community and suggests that the aquatic life uses should be assessed as “impaired.” If a cause of the kill is identified, and the cause is either known, or suspected, to be a “pollutant”, the assessment type is considered “monitored” and the affected waterbody is a candidate for Section 303(d) listing.
Results from the ISU and UHL lake surveys, however, suggest good chemicalwater quality at Briggs Woods Lake. The ISU and UHL lake surveys data from 2002-2006 show no violations of the Class B(LW) criterion for ammonia in 13 samples, dissolved oxygen in 18 samples, or pH in 19 samples.
Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring at Briggs Woods Lake in 2005. 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: 0.0194 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: 0.0568 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 2005 RAFT sampling conducted at Briggs Woods 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.
