Middle Fork Little Maquoketa River IA 01-TRK-138

The assessment of the Class B(CW1) aquatic life uses was based on data collected in 2012 and 2016 as part of the DNR/SHL cold water stream sampling project. A series of biological metrics which reflect coldwater stream water quality and habitat integrity were calculated from the biological sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa that were collected in the stream sampling reach. The biological metrics were combined to make a coldwater benthic index (CBI). The index ranks the biological integrity of a coldwater stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2012 CBI scores were 35 and 42.The 2016 CBI scores were 45 and 49.The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the CBI scores with biological impairment criteria (BIC) established for the 2012 Section 305(b) report.The biological impairment criteria were determined from a statistical analysis of data collected at coldwater stream reference sites from 1994-2011.The CW BIC is 60 and this segment passed the CW BIC 0/4 times in the last five years (2012-2016).

This aquatic life assessment is now considered "monitored" based on a change in the 2010 DNR assessment methodology. DNR now requires a segment have two or more biological samples collected from the segment in multiple years in a recent five-year period to be considered “monitored”. This segment had a multiple samples collected in the last five years (2012-2016).

Results of continuous dissolved oxygen (DO) and temperature monitoring in 2012 for the DNR/SHL coldwater stream sampling project suggest impairment of Class B(CW1) aquatic life uses. The lowest DO concentration recorded in 55 days of continuous monitoring was 5.7 mg/L. The daily DO minimum concentration failed to meet the 24-hour DO criterion (5 mg/L) in 0 of 55 days. The percentage exceeding (0%) was less than (passing) the 10% impairment threshold used to assess conventional water quality parameters. The associated statistical analysis confidence level was high (>90%). In contrast, the 16-hour DO criterion (7 mg/L) was exceeded in 10 of 55 days. The percentage exceeding (18%) was greater than (failing) the 10% threshold with high statistical confidence (>90%). The maximum stream temperature recorded during the sensor deployment period was 22.8 degrees (C). The B(CW1) temperature criterion of 20 (C) was exceeded in 22 of 55 days. The percentage exceeding (40%) was greater than (failing) the 10% impairment threshold with high statistical confidence (>90%). Based on these data, the B(CW1) aquatic life use is assessed as impaired due to DO and temperature. The assessment type is “evaluated” because it is based on data collected from a single year within the current data assessment period. In order to meet the requirements for a “monitored” assessment, the DNR’s continuous monitoring assessment methodology requires monitoring data from two or more years within the assessment period.

In contrast to the water quality and benthic macroinvertebrate data, an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in January 2019 suggests that the Class B(CW1) uses should be assessed as "fully supported". According to the updated summary, Middle Fork Little Maquoketa River (a.k.a. Bankston Cr.) is in the group of Iowa coldwater streams that support natural reproduction of trout. Based on results of surveys by the DNR Fisheries Bureau, the upper portion of this stream (~ 1 mile) is placed in the category of Iowa trout streams that exhibit consistent natural reproduction and maintain a wild population of Brown Trout without any stocking (Category I stream).