Assessment Comments
Assessment remains based on results of water quality, aquatic vegetation, and fish monitoring conducted by the IDNR shallow lakes and wetlands monitoring program from 2008 through 2009 and information from the IDNR Wildlife Bureau.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (evaluated) as "not supported" due to high levels of algae that cause aesthetically objectionable conditions. The Class B(LW) aquatic life uses are assessed (evaluated) as "not supported" due to high levels of total suspended solids that leads to an impairment of the narrative criteria protecting against undesirable or nuisance aquatic life. High levels of algae at this wetland also suggest impairment. The fish consumption uses remain "not assessed" due to the lack of water quality information upon which to base an assessment. Sources of data for this assessment include results of water quality, aquatic vegetation, and fish monitoring conducted by the IDNR shallow lakes and wetlands monitoring program from 2008 through 2009 and information from the IDNR Wildlife Bureau. This assessment is considered "evaluated." Based on IDNR's methodology, 9 samples collected during the most recent assessment period (2010-2012) are required for a "monitored" assessment.
EXPLANATION: The Class A (primary contact recreation) uses are assessed (evaluated) as "not supported" due to high levels of algae that create aesthetically objectionable conditions. The Carlson’s (1977) trophic state index value for chlorophyll a was 78. According to Carlson (1977), the index value for chlorophyll a places Pickerel Lake in the hypereutrophic category and suggests extremely high levels of chlorophyll a and suspended algae in the water.
Results of water quality monitoring conducted at Pickerel Lake indicate that the aquatic life uses should be assessed (evaluated) as "not supported" due to high levels of total suspended solids and algae at this lake. Guidelines for wetland assessment from the Upper Mississippi River Conservation Committee’s Water Quality Technical Section (2003) state that an average total suspended solids concentration during the growing season of less than 30 mg/L is necessary to provide sufficient water clarity to support the growth of submersed aquatic vegetation in wetlands and shallow lakes. High levels of total suspended solids impede the growth of submersed aquatic vegetation (SAV). Submersed aquatic vegetation is critical to the health of wetland and shallow lake ecosystems. The elimination of SAV can degrade habitat quality such that undesirable aquatic species such as cyanobacteria, common carp and fathead minnows dominate. As such, the suppression of SAV constitutes a violation of Iowa’s narrative water quality criteria protecting against undesirable or nuisance aquatic life.
Using the overall median values from the IDNR shallow lakes and wetlands monitoring program from 2008 through 2009 (approximately 12 samples), the median growing season total suspended solids concentration was 47 mg/L; this median value exceeds the UMRCC guideline. Thus, based on (1) suppression of SAV growth, (2) the resultant production of undesirable aquatic life, and (3) IDNR’s assessment and listing methodology, the aquatic life uses at Pickerel are assessed as “not supported” due to high levels of total suspended solids.
Additional monitoring of fish and aquatic vegetation populations at Pickerel Lake by IDNR staff also suggests that the high levels of total suspended solids and algae have adverse effects on fish populations and limit the production of rooted aquatic vegetation in this wetland. These results further indicate that the aquatic life uses of this wetland should be assessed as "not supported."
