Green Belt Lake IA 02-CED-548

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 2007 by University Hygienic Laboratory (UHL), and (3) information from the IDNR Fisheries Bureau. NOTE: Green Belt Lake was not sampled in 2008 because it was inaccessible due to flooding.

Basis for Assessment

SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “fully supported.”  The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported.”  Fish consumption uses remain “not assessed.”  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 2007 by University Hygienic Laboratory (UHL), and (3) information from the IDNR Fisheries Bureau.   NOTE: Green Belt Lake was not sampled in 2008 because it was inaccessible due to flooding.

EXPLANATION:  For the 2010 reporting cycle, the Class A1 (primary contact recreation) uses for Green Belt Lake are assessed (monitored) as “fully supported.”  Results from the ISU lake survey and UHL ambient monitoring program suggest good water quality at Green Belt Lake.   Using the median values from these surveys from 2004 through 2007 (approximately 23 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 56, 55, and 54 respectively for Green Belt Lake.   According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Green Belt Lake in the eutrophic category.   These values suggest relatively low levels of chlorophyll a and suspended algae in the water, relatively good water transparency, and low levels of phosphorus in the water column.  

The levels of inorganic suspended solids at this lake were low and do not suggest that non-algal turbidity causes an impairment at this lake.   The median level of inorganic suspended solids in Green Belt Lake (1.5 mg/L) was the 11th lowest median of the 132 lakes sampled by the ISU and UHL programs.

Data from the 2004-2007 ISU and UHL surveys suggest a relatively small population of cyanobacteria exists at Green Belt Lake.   These data show that cyanobacteria comprised 81% of the phytoplankton wet mass at this lake.   The median cyanobacteria wet mass (10.4 mg/L) was the 47th lowest of the 132 lakes sampled.  

The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported.”  Results from the ISU and UHL lake surveys from 2004-2007 show no violations of the Class B(LW) criteria for ammonia in 23 samples, or dissolved oxygen in 23 samples.   The pH data show 4 violations of the Class B(LW) criterion for pH in 23 samples (17%).   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 Green Belt Lake.

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