Assessment Comments
Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, and (4) results of a fish kill investigation in March 2004.
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 clarity due mainly to non-algal turbidity, but also algal turbidity. Violations of the Class A1 criterion for pH also contribute to impairment at this lake. The Class B(LW) (aquatic life) uses are assessed (monitored) as “partially supported” due to violations of the Class B(LW) criterion for pH. A fish kill occurred at this lake in March 2004, which also suggests impairment of the Class B(LW) uses. The Class C (drinking water) uses are “not assessed” due to a lack of information on which to base an assessment. Fish consumption uses remain “not assessed.” Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, and (4) results of a fish kill investigation in March 2004.
Note: A TMDL for siltation at Orient Lake was prepared by IDNR and approved by EPA in 2001; thus, this waterbody was placed into IR Category 4a (TMDL approved) for the 2004 assessment/listing cycle. Because not all Section 303(d) impairments identified for the 2012 assessment/listing cycle (algae, pH) are addressed by the TMDL, this waterbody remains in category 5a (impaired, TMDL needed).
EXPLANTION: For the 2012 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Orient Lake are assessed “not supported” based on information from the ISU lake survey and UHL lake monitoring program. Using the median values from these surveys from 2006 through 2010 (approximately 22 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 70, 69, and 82 respectively for Orient Lake. According to Carlson (1977) the Secchi depth and total phosphorus values place Orient Lake in the hypereutrophic category, while the chlorophyll a value places Orient Lake in between the eutrophic and hypereutrophic categories. These values suggest high levels of chlorophyll a and suspended algae in the water, very poor water transparency, and extremely high levels of phosphorus in the water column.
Based on data from the ISU and UHL lake surveys, the level of inorganic suspended solids was very high at this lake and suggests that non-algal turbidity contributes to the impairment at this lake. The median inorganic suspended solids concentration at Orient Lake was 10.2 mg/L, which was the 19th highest of the 134 monitored lakes.
Data from the 2006-2010 ISU and UHL surveys suggest a large population of cyanobacteria exists at Orient Lake, which contributes to the aesthetically objectionable conditions at this lake. These data show that cyanobacteria comprised 65% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (31.0 mg/L) was the 46th highest of the 134 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed (monitored) as “partially supported” due to violations of the Class A1,B(LW) criterion for pH. High levels of nutrients, non-algal turbidity, and siltation impacts also suggest a potential impairment at this lake. Results of the ISU and UHL lake surveys from 2006 through 2010 show there was one violation of the Class B(LW) criterion for ammonia in 22 samples (5%), and one violation of the Class B(LW) criterion for dissolved oxygen in 22 samples (5%). Based on IDNR's assessment methodology these violations are not significantly greater than 10% of the samples and therefore do not suggest impairment of the Class B(LW) uses at Orient Lake. Data for pH, however, show 6 violations of the Class A1,B(LW) criterion for pH in 22 samples (27%). Based on IDNR’s assessment methodology these violations are significantly greater than 10% of the samples and therefore suggest impairment (partial support/monitored) of the Class A1 and B(LW) uses of Orient Lake. The pH violations at Orient Lake likely reflect the excessive primary productivity at the lake and do not reflect the input of pollutants into this lake.
The occurrence of a fish kill at this lake in March 2004 is consistent with the assessment of the Class B(LW) uses as "partially supported." This kill occurred on or before March 2, 2004 and was attributed to natural causes (winterkill). An estimated 475 fish were killed with an estimated value of $7,125. Bluegill (75), crappie (150), and channel catfish (250) were observed killed. According to the investigation conducted by Adair County, the kill was caused by low oxygen conditions that developed during the winter. This lake has a maximum depth of eight feet and was approximately 3 feet low at the time of the investigation. This is the same assessment as that developed for the 2008 and 2010 assessment/listing cycle. This impairment remains appropriate for Category 2b of Iowa's 2012 Integrated Report. 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 was not identified during the IDNR investigation, or if the kill was attributed to non-pollutant causes (e.g., winterkill), the assessment type will be considered “evaluated” and will be placed in IR subcategories 2b or 3b and will be added to the state list of waters in need of further investigation. Thus, this impairment will remain in Category 2b of Iowa’s 2012 Integrated Report.
Drinking water uses are "not assessed" due to a lack of relevant water quality information upon which to base an assessment. The only parameter collected as part of the ISU and UHL lake surveys relevant to support of Class C (drinking water) uses is nitrate. While the results of the ISU survey from 2006-10 show that nitrate levels are low at this lake (maximum value = 10.6 mg/l; median = 1.8 mg/l) relative to the MCL (10 mg/L), these data are not sufficient for developing a valid assessment of support of the Class C uses.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake.
