Assessment Comments
Assessment is based on (1) results of the statewide survey of Iowa lakes conducted from 2009 through 2012 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted in 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, and (4) results of a fish kill investigation in July 2005.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” (IR 5a) due to poor water transparency and algae blooms. The Class B(LW) (aquatic life) uses remain assessed (evaluated) as “partially supported” (IR 2b) due to a fish kill that occurred in July 2005. Sediment, nutrients, turbidity, and algae are also concerns at this lake. Fish consumption uses are “not assessed” due (IR 3a) to a lack of fish contaminant monitoring at this lake. Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2009 through 2012 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted in 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, and (4) results of a fish kill investigation in July 2005.
Note: A TMDL for siltation at Arrowhead Pond was prepared by IDNR and approved by EPA in 2001. Not all Section 303(d) impairments identified for the 2014 assessment/listing cycle (algae), however, are addressed in the TMDL. Thus, this waterbody remains in IR Category 5a (impaired; TMDL required) for the 2014 assessment/listing cycle.
EXPLANATION: For the 2014 reporting cycle, the Class A1 (primary contact recreation) uses for Arrowhead Pond are assessed (monitored) as “partially supported” based on results from the ISU statewide survey of lakes and the UHL ambient lake monitoring program. Using the median values from these surveys from 2008 through 2012 (approximately 14 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 67, 67, and 70 respectively for Arrowhead Pond. According to Carlson (1977) the Secchi depth and chlorophyll a values place Arrowhead Pond in between the eutrophic and the hypereutrophic categories, while the total phosphorus value places the lake in the hypereutrophic category. These values suggest high levels of chlorophyll a and suspended algae in the water, poor water transparency, and very high levels of phosphorus in the water column.
The levels of inorganic suspended solids at this lake were relatively low and do not suggest an additional impairment due to non-algal turbidity. The median level of inorganic suspended solids in Arrowhead Pond (6.4 mg/L) and ranked 91st among the 134 lakes monitored.
Data from the 2008-2012 ISU and UHL surveys suggest a moderate population of cyanobacteria exists at Arrowhead Pond, which does not cause an additional impairment due to nuisance aquatic life at this lake. These data show that cyanobacteria comprised 83% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (20.3 mg/L) was slightly greater than the median (18.4 mg/L) for the 134 lakes sampled.
The poor water transparency and high levels of chlorophyll a, however, indicate impairment to the Class A1 (primary contact) use through the presence of algae blooms that violate Iowa’s narrative water quality standard protecting against aesthetically objectionable conditions.
The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” based on information from the IDNR Fisheries Bureau, results from the ISU and UHL lake surveys and the occurrence of a fish kill in July 2005. Information from the IDNR Fisheries Bureau suggests that algae remains a problem at this lake.
Results of the ISU and UHL lake surveys, however, suggest "full support" of the aquatic life uses. The ISU and UHL lake surveys data from 2008-2012 show no violations of the Class B(LW) criteria for ammonia in 14 samples, no violations of the Class B(LW) criteria for dissolved oxygen in 14 samples, and no violations of the Class A1/B(LW) criteria for pH in 14 samples. These results suggest "full support" of the Class B(LW) aquatic life uses.
A fish kill that occurred in this lake on July 26, 2005, however suggests "impairment" of the Class B(LW) uses. The kill was identified as a summer kill due to low levels of dissolved oxygen related to an algal die-off. According to the IDNR investigation, approximately 500 bluegill, 1,500 yellow bass, and 600 channel catfish (including all cage catfish at this lake) were killed. The estimated value of the fish killed was $39,000. This is the same assessment as that developed for the 2010 and 2012 assessment/listing cycles. The continuance of the IR Category 2b listing is based on IDNR's 2012 assessment methodology that states the following: 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 (2010-2013) 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 assessment segment will remain in Category 2b of Iowa’s 2014 Integrated Report.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this lake.
