ADBNet

Data Sources:

Class BLW - Lake TSI's

The TSI value for Secchi depth is not used to evaluate the attainment of the aquatic life use in shallow lakes. Due to the depth of these shallow lakes, TSI values for Secchi depth can be misleading. In some instances, the Secchi disk remains visible at the bottom of the lake and the depth of the lake is recorded as the Secchi depth. In these instances, water clarity may be sufficient to support the Class BLW use, but the index value is limited by the depth of the lake. Thus, the combination of total suspended solids and chlorophyll a was used to determine whether or not the Class BLW use was impaired in these shallow systems.

Class BLW - Binomial Parameters:

Dan Greene Slough was assessed as "not supported" for the 2022 assessment/listing cycle due to frequent violations of the state Class BLW criterion for pH. Based on DNR’s assessment methodology the current assessment/listing cycles must have fewer violations of the criterion based on the minimum required by the 10% Rule to propose delisting pH There were less than 10% of the samples exceeding the single-sample maximum criterion for the 2026assessment/listing cycle. Therefore, the impairment for pH is suggested for delisting for the 2026 assessment/listing cycle.

Dan Greene Slough was assessed as "not supported" for the 2022 assessment/listing cycle based on Dissolved Oxygen. Based on DNR’s assessment methodology the current assessment/listing cycles must have fewer violations of the criterion based on the minimum required by the 10% Rule to propose delisting. There were less than 10% of the samples exceeding the single-sample maximum criterion for the current assessment listing cycle. Therefore, the impairment for Dissolved Oxygen is suggested for delisting for the 2026 assessment/listing cycle.

Class BLW - Protection of Submerged Aquatic Vegetation:

Guidelines for wetland assessment from the Upper Mississippi River Conservation Committee’s Water Quality Technical Section (2003) state that a median 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 (SAV) in wetlands and shallow lakes. High levels of total suspended solids impede the growth of SAV. SAV 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.

Class BLW - Toxic Parameters:

Class HH - No Data

Additional Notes:

Monitoring of fish and aquatic vegetation populations at Dan Greene Slough by DNR staff also suggests that the water quality has improved in this wetland. These results further indicate that the aquatic life uses of this wetland should be assessed as "fully supported." Dan Greene Slough was drawn down and rough fish removed between 2008 and 2010.