Green Castle Lake IA 02-IOW-643

Marshall County S8T82NR17W 1 mi. S of Ferguson.

Open Data Collection Period Modal

For purposes of developing stream/river water quality assessments for integrated reporting, three years of water quality data are typically used for both conventional pollutant parameters (e.g., indicator bacteria) and the less frequently monitored toxic parameters (e.g., toxic metals). Since the 2004 IR cycle, DNR has used a three-year data gathering period for streams, rivers, and beaches. For most assessments, the use of three years of data increases the number of samples upon which the decision on use support is based and helps address the problem of weather-related year-to-year fluctuations in water quality.

Due to the lower sampling frequency in Iowa’s ambient lake, biological, fish kill, and fish tissue monitoring programs, five years of data are used for developing IR assessments and for identifying Section 303(d) listings.

Data Type	Data Timeframe
Beach Sampling Data	CY 2012 - 2014
Stream/River Water Quality Data	CY 2012 - 2014
Lake Water Quality Data	CY 2010 - 2014
Biological Sampling Data	CY 2010 - 2014*
Fish Kill Data	CY 2010 - 2014
Fish Tissue Sampling Data	CY 2010 - 2014
Continuous Dissolved Oxygen Sampling Data	CY 2010 - 2014
*Biological sites sampled in both 2009 and 2013 were also assessed.

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Cycle: 2016
Release Status: Final
Overall IR: 3 - Insufficient data exist to determine whether any designated uses are met.
Trophic: Eutrophic
Trend: Unknown
Created: 5/26/2016 11:30:40 AM
Updated: 8/1/2016 2:17:13 PM

Use Support

Class A1

Recreation - Primary contact

WINOFI

Turbidity: Secchi Disk Transparency

Support Level

Further Investigation Needed

Impairment Code

3b - Use potentially impaired based on an evaluated assessment.

Cause Magnitude

Slight

Status

New

Source

Other: Sediment Resuspension

Source Confidence

Low

Cycle Added

2016

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

Class BLW

Aquatic Life - Lakes and wetlands

Fully Supported

Class HH

Human Health -

Not Assessed

General Use

General Use water -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 (primary contact recreation) uses are assessed (evaluated) as "partially supported" due to poor water transparency. The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported.” Fish consumption uses remain “not assessed.” Note: For the 2010 assessment/listing cycle, Green Castle Lake was listed as "partially supporting" due to high levels of pH that violated the state criterion. Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2010 through 2014 by Iowa State University (ISU), and (2) information from the IDNR Fisheries Bureau.

Assessment Explanation

For the 2016 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Green Castle Lake are assessed (evaluated) as "partially supported" due to poor water transparency based on information from the ISU lake survey. Using the median values from these surveys from 2010-2012 (approximately 9 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 67, 63, and 61 respectively for Green Castle Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Green Castle Lake in the Eutrophic category. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, poor water transparency, and moderately high levels of phosphorus in the water column. The data show no violations of the Class A1 criterion for pH in 9 samples. This assessment of "evaluated/partially supported" is due to the lack of data during this assessment cycle to justify an impairment. The lake was drawn down during this assessment cycle.

The level of inorganic suspended solids was moderately high at Green Castle Lake, and does suggest that non-algal turbidity may contribute to the impairment at this lake. The median level of inorganic suspended solids in Green Castle Lake (6 mg/L) was ranked 95th among the 138 lakes by the ISU lake survey.

Data from the 2010-2012 ISU lake survey suggest a moderate population of cyanobacteria exists at Green Castle Lake. These data show that cyanobacteria comprised 83% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (13.3 mg/L) was ranked 41st of the 138 lakes sampled.

The Class B(LW) (aquatic life) uses are assessed (evaluated) as "fully supported." Results of the ISU lake survey from 2010-2012 show there were no violations of the criterion for ammonia in 9 samples(0%), no violations of the criterion for dissolved oxygen in 9 samples(0%), and no violations of the criterion for pH in 9 samples(0%). Based on IDNR's assessment methodology these violations are not significantly greater than 10% of the samples and therefore suggest (fully supported/evaluated) of the Class B(LW) uses of Green Castle Lake.

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

Note: Green Castle Lake was drained in 2013. Common carp and silt were removed from the lake and fish habitat improvements were made. Improvements in water clarity were observed in 2015 sampling season after the lake refilled.

Monitoring and Methods

Assessment Key Dates

6/21/2010

Fixed Monitoring Start Date

9/19/2012

Fixed Monitoring End Date

Methods

120

Surveys of fish and game biologists/other professionals

222

Non-fixed-station monitoring (conventional during key seasons and flows)

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)