Rudd Lake IA 02-CED-6497

Assessment Comments

Assessment is based on monitoring results from the 2011-2012 ISU lakes survey.

Basis for Assessment

SUMMARY: This lake is not classified for Class A1 (primary contact recreation) uses or Class B(LW) (aquatic life) uses.  General Class HH uses are assessed (evaluated) as "fully supported." This assessment is based on monitoring results collected as a part of the ISU lake survey conducted in 2011-2012.  According to IDNR methodology, 9 samples from the most recent assessment period (2008-2012) are required to constitute a "monitored" assessment.  As only 6 samples were collected during the 2014 assessment period, this assessment will be considered "evaluated." This is the first assessment for this segment.    

EXPLANATION: Results from the ISU lake survey suggests that the Class HH uses at Rudd Lake are “fully supported.”  Using the median values from these surveys from 2011-2012 (approximately 6 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 49, 40, and 48 respectively for Rudd Lake.    According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Rudd Lake in the mesotrophic category.    These values suggest extremely low levels of chlorophyll a and suspended algae in the water, exceptional water transparency, and and extremely low levels of phosphorus in the water column.    

The level of inorganic suspended solids is relatively low at this lake and does not suggest an impairment due to high non-algal turbidity.    The median inorganic suspended solids concentration at Rudd Lake was 2.5 mg/L, and ranked 42nd of the 134 monitored lakes.  

Data from the 2011-2012 ISU and UHL surveys suggest a relatively small population of cyanobacteria exists at Rudd Lake, which does not contribute to impairment at this lake.    These data show that cyanobacteria comprised 90% of the phytoplankton wet mass at this lake.    The median cyanobacteria wet mass (8.2 mg/L) and ranked 17th of the 134 lakes sampled.    

The ISU lake survey also suggesst relatively good chemical water quality at Rudd Lake.    Data from this survey shows that during 2011-2012 show there were no violations of the Class B(LW) criterion for ammonia in 6 samples, dissolved oxygen in 6 samples, or pH in 6 samples.    These results suggest "full support" of the Class HH uses.  

Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake.