Assessment Comments
Assessment is based on (1) results of the statewide survey of Iowa lakes conducted from 2004 through 2007 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 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 “not supported” due to poor water transparency caused by algae blooms. The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” 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 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 2004 through 2007 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 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 2010 assessment/listing cycle (algae), however, are addressed in the TMDL. Thus, this waterbody remains in IR Category 5a (impaired; TMDL required) for the 2010 assessment/listing cycle.
EXPLANATION: For the 2008 reporting cycle, the Class A1 (primary contact recreation) uses for Arrowhead Pond are assessed (monitored) as “not 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 2004 through 2008 (approximately 19 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 70, 67, and 75 respectively for Arrowhead Pond. According to Carlson (1977) the Secchi depth and total phosphorus values place Arrowhead Pond in the hypereutrophic category, while the chlorophyll a value places the lake 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 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 (3.0 mg/L) was the 42nd lowest of all 132 lakes sampled by ISU and UHL.
Data from the 2004-2008 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 only comprised 55% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (14.0 mg/L) was equal to the median for the 132 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 suggest "full support" of the aquatic life uses. The ISU and UHL lake surveys data from 2004-2008 show no violations of the Class B(LW) criteria for ammonia in 19 samples, and one violation of the criterion for dissolved oxygen in 19 samples. The one violation of the dissolved oxygen criterion is not significantly greater than 10% of the samples and therefore based on IDNR's assessment methodology does not suggest an impairment of the aquatic life uses. None of the 19 pH samples exceeded the Class A1,B(LW) criterion for pH. Arrowhead Pond was assessed as “partially supporting” in the 2006 assessment/listing cycle due to significant violations of the pH criteria. Based on IDNR’s assessment methodology 2 consecutive assessment/listing cycles without significantly greater than 10% of the samples violating the criterion are necessary to propose delisting based on pH violations. Because violations of the pH criteria were not significantly greater than 10% for the 2008 assessment/listing cycle, and there were no violations of the pH criteria for the current (2010) assessment/listing cycle, the pH impairment for Arrowhead Pond is suggested for delisting. The past pH violations at Arrowhead Pond likely reflect the excessive primary productivity at the lake and do not reflect the input of pollutants into this lake.
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 2008 assessment/listing cycle. The continuance of the IR Category 2b listing is based on IDNR's 2010 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 (2006-2009) 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, the fish kill related impairment will remain in Category 2b of Iowa’s 2010 Integrated Report.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this lake.
