Assessment Comments
Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted in 2006 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2006 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, (4) results of a fish kill investigation in August of 2006, and (5) results of U.S. EPA/IDNR fish contaminant monitoring in 2000, 2002, 2004, and 2006.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to aesthetically objectionable conditions caused by poor water transparency due to algal blooms and high levels of inorganic turbidity. The Class B(LW) (aquatic life) uses are assessed (monitored) as “not supported” due to a fish kill in 2006 and excessive nutrient loading, nuisance blooms of algae, siltation and organic enrichment. Fish consumption uses are assessed (monitored) as “fully supporting” due to the removal of the fish consumption advisory at this lake. Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted in 2006 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2006 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, (4) results of a fish kill investigation in August of 2006, and (5) results of U.S. EPA/IDNR fish contaminant monitoring in 2000, 2002, 2004, and 2006.
Note: A TMDL for algae, turbidity, and chlordane at Ottumwa Lagoon was prepared by IDNR and approved by EPA in 2005; thus, this waterbody was placed in Category 4a of Iowa's 2006 Integrated Report. Because the fish kill-related impairment is not covered by this TMDL, this waterbody is placed in Category 5b of Iowa's 2012 Integrated Report.
EXPLANATION: NOTE: Ottumwa Lagoon was not sampled by ISU or UHL in 2007, 2008, 2009, or 2010 because it was not accessible by boat. Because there is only one year of data upon which to base an assessment, this assessment is considered "evaluated" (of lower confidence) rather than "monitored." Results from the ISU and UHL lake surveys suggest that the Class A1 uses at Ottumwa Lagoon are assessed (evaluated) as “not supported.” Using the median values from these surveys from 2006 (approximately 6 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 77, 79, and 89 respectively for Ottumwa Lagoon. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Ottumwa Lagoon in the hypereutrophic category. These values suggest extremely high levels of chlorophyll a and suspended algae in the water, extremely poor water transparency, and extremely high levels of phosphorus in the water column.
The level of inorganic suspended solids is extremely high at this lake and suggests impairment due to high non-algal turbidity. The median inorganic suspended solids concentration at Ottumwa Lagoon was 22.0 mg/L, which was the 3rd highest of the 134 monitored lakes.
Data from the 2006 ISU and UHL surveys suggest a relatively large population of cyanobacteria exists at Ottumwa Lagoon, which contributes to impairment at this lake. These data show that cyanobacteria comprised 98% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (49.3 mg/L) was also the 26th highest of the 134 lakes sampled. This median is in the worst 25% of the 134 lakes sampled. The presence of a large population of cyanobacteria at this lake suggests a potential violation of Iowa’s narrative water quality standard protecting against the occurrence of nuisance aquatic life. This assessment is based strictly on the distribution of the lake-specific median cyanobacteria values for the 2006-2010 period. Median levels greater than the 75th percentile of this distribution were arbitrarily considered to represent potential impairment. No other criteria exist, however, upon which to base a more accurate identification of impairments due to cyanobacteria. The assessment category for assessments based on level of cyanobacteria will be considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence) to account for this lower level of confidence.
The Class B(LW) (aquatic life) uses are assessed (monitored) as “not supported” based on information from the IDNR Fisheries Bureau, results of a fish kill investigation, and results from the ISU and UHL lake surveys. A fish kill occurred on August 17, 2006 at Ottumwa Lagoon. The fish kill was attributed to a spill of petroleum products due to pumping of a local gas station that had been contaminated by fuel (pollutant/human). The number and type of fish killed was not reported. At the time of this assessment there are no records that IDNR sought/received restitution for this fish kill.
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 (2008-2011) 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. Fish kills attributed to a pollutant, but where a source of the pollutant was not identified and/or where enforcement actions were not taken against the responsible party, will be placed into Integrated Report subcategory 5b. The intent of placing these waterbodies into Category 5 is not to necessarily require a TMDL but to keep the impairment highlighted due to the potential for similar future kills from the unaddressed causes and/or sources. For previous assessment/listing cycles, IDNR had considered fish kill-impaired (IR 5b) waters with no subsequent kills in the three year subsequent to the kill as appropriate for de-listing and for movement to IR categories 2b or 3b (i.e., Iowa’s list of waters in need of further investigation). Due, however, to EPA uncertainty regarding the full recovery of the aquatic life following the kill, any existing fish kill (5b) impairment will remain in IR Category 5b until more recent monitoring has shown full recovery of the aquatic communities affected by the kill. Thus, this assessment segment will remain in Category 5b of Iowa’s 2012 Integrated Report.
Results of the ISU and UHL lake surveys show that during 2006 there was one violation of the Class B(LW) criterion for ammonia in 6 samples (17%). Based on IDNR’s assessment methodology one violation of the ammonia criterion does not suggest impairment of the Class B(LW) uses due to ammonia. There was one violation of the Class B(LW) criterion for dissolved oxygen in 6 samples (17%). Based on IDNR’s assessment methodology these dissolved oxygen violations were not significantly greater than 10% of the samples and therefore do not suggest impairment of the Class B(LW) uses. There were no violations of the Class A1,B(LW) criterion for pH in 6 samples. Based on IDNR’s assessment methodology these results do not suggest impairment of the Class B(LW) uses at Ottumwa Lagoon. However, information from the IDNR Fisheries Bureau suggests that Ottumwa Lagoon is not meeting its aquatic life uses due to siltation, a large population of rough fish, and frequent inputs from storm sewers. Thus, the fish kill and information from the IDNR Fisheries Bureau suggest impairment (nonsupport) of the Class B(LW) uses at Ottumwa Lagoon.
Fish consumption uses were assessed (monitored) as “fully supported” based on results of ongoing U.S. EPA/IDNR fish contaminant (RAFT) monitoring at Ottumwa Lagoon in 2000, 2002, 2004, and 2006. Recent fish contaminant monitoring (2004 and 2006) has shown that levels of contaminants are below IDNR/IDPH advisory trigger levels. 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. A fish consumption advisory had been in place at Ottumwa Lagoon since 2001. Levels of chlordane in channel catfish fillets had exceeded the trigger level for technical chlordane (0.6 ppm for a one meal per week advisory).
The level of technical chlordane in the composite sample of fillets from channel catfish collected for the 2000 RAFT program was 0.87 ppm; this level is greater than the IDPH/INDR trigger level of 0.6 ppm for a one meal per week consumption advisory. For the 2002 RAFT sampling, the composite samples of fillets from common carp and channel catfish had generally low levels of contaminants. Levels of primary contaminants in the composite common carp fillets were low and do not suggest a fish contaminant problems (mercury: 0.095 ppm; total PCBs: 0.106 ppm; and technical chlordane: 0.240 ppm). With the exception of chlordane, levels of primary contaminants in the composite sample of channel catfish fillets were also relatively low (mercury: 0.021 ppm; total PCBs: 0.143 ppm). The level of chlordane in the sample of channel catfish fillets (0.78 ppm), however, exceeded the IDNR/IDPH trigger level of 0.60 ppm for a one meal per week consumption advisory (this levels is well below the “do not eat” trigger level for chlordane of 5.0 ppm). Because the level of chlordane in the 2000 sample of channel catfish fillets (0.87 ppm) had also exceeded this trigger level, continuance of the existing advisory was justified. As per Iowa’s revised protocol, the type of advisory, however, was changed from a “do not eat” to a “one meal per week” advisory.
The 2004 RAFT follow-up sampling at Ottumwa Lagoon showed that levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: <0.0181 ppm; total PCBs: 0.12 ppm; and technical chlordane: 0.45 ppm. The level of chlordane in this sample of (0.45 ppm), however, was below the IDNR/IDPH trigger level of 0.60 ppm for a one meal per week consumption advisory. According to the IDNR/IDPH advisory protocol, if two consecutive samplings show that contaminant levels are below the trigger level in fillet samples, an existing consumption advisory can be removed. The 2006 RAFT follow-up sampling at Ottumwa Lagoon showed that levels of technical chlordane in channel catfish (0.3 ppm) were again below the IDNR/IDPH trigger level of 0.60 ppm for a one meal per week consumption advisory. The levels of PCBs in channel catfish (0.133 ppm) were also below the IDNR/IDPH trigger level. Therefore, the one meal per week consumption advisory for Ottumwa Lagoon was removed and the fish consumption uses are assessed as “fully supported” for the 2010 assessment/listing cycle.
