Green Belt Lake IA 02-CED-548

Assessment Comments

Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), and (3) information from the IDNR Fisheries Bureau.

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 2002 through 2006 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), and (3) information from the IDNR Fisheries Bureau.

EXPLANATION:  For the 2008 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 2002 through 2006 (approximately 23 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 57, 59, and 56 respectively for Green Belt Lake.   According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Green Belt Lake at the upper end of the eutrophic category.   These values suggest relatively low levels of chlorophyll a and suspended algae in the water, relatively good water transparency, and relatively 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 5th lowest median of the 132 lakes sampled by the ISU and UHL programs.

Data from the 2002-2006 ISU and UHL surveys suggest a relatively small population of cyanobacteria exists at Green Belt Lake.   These data show that cyanobacteria comprised 91% of the phytoplankton wet mass at this lake.   The median cyanobacteria wet mass (10.3 mg/L) was the 36th 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 2002-2006 show no violations of the Class B(LW) criteria for ammonia in 17 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.