Ventura Marsh IA 02-WIN-844

Results of water quality monitoring conducted at Ventura Marsh 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. This assessment is considered "evaluated" because only 5 samples were collected in 2014 during the current assessment period (2012-2014). Based on IDNR's assessment methodology, 9 samples within the most recent three year period are necessary to accurately characterize water quality for the purposes of identifying impaired waters. During the 2014 assessment cycle this lake was listed (monitored) as "not supported", therefor, this lake will remain listed as "not supported" due to high levels of algae and suspended solids 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 2012 through 2014 (approximately 5 samples), the median growing season total suspended solids concentration was 3 mg/L; this median value is well below the UMRCC guideline and suggests "full support" of the aquatic life uses. 

In addition, the level of algae also suggests "full support" of the aquatic life uses at Ventura Marsh. The Carlson’s (1977) trophic state index value for chlorophyll a was 57. According to Carlson (1977), the index value for chlorophyll a places Ventura Marsh in the eutrophic category.  This value suggests relatively low levels of chlorophyll a and suspended algae in the water and "full support" of the aquatic life uses.

NOTE:  The TSI value for Secchi depth is not used to evaluate the attainment of aquatic life goals 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 instance, water clarity may be sufficient to support the Class B(LW) uses, but the index value is limited by the depth of the lake.   Thus the combination of total suspended solids and chlorophyll a will be used to determine whether or not the Class B(LW) uses are impaired in these shallow systems.

Note:  A TMDL for algae and turbidity at Ventura Marsh was prepared and approved by EPA in 2010.    Because all of the Section 303(d) impairments identified for the 2014 assessment/listing cycle are addressed by the TMDL, this waterbody is moved to IR Category 4a (impaired; TMDL approved) for the 2014 assessment/listing cycles.   

Additional monitoring of fish and aquatic vegetation populations at Ventura Marsh 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."  

Fish consumption uses remain "not assessed" due to the lack of data for levels of fish contaminants upon which to base an assessment.   In general, Iowa wetlands are not managed for recreational fisheries; thus, fish contaminant monitoring is not typically conducted at these waterbodies.