Assessment Comments
Assessment is based on limited chemical/physical monitoring conducted in August 2006 as part of IDNR/UHL TMDL-related monitoring near Lanesboro (STORET station 11140003; TMDL site MaB2) and on 2007 IDNR/UHL biological monitoring data; FIBI = 57 (good), BMIBI = 24 (poor). Non-riffle FIBI BIC = 32; BMIBI BIC = 62.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was classified only for general uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), this segment is now presumptively designated for Class A1 (primary contact recreation) uses and for Class B(WW1) aquatic life uses. According to the Iowa Water Quality Standards, all perennial rivers and streams and all intermittent streams with perennial pools that are not specifically listed in the Iowa surface water classification are designated as Class A1 and Class B(WW1) waters. Thus, for the current (2010) assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW1) water quality criteria. This waterbody was not assessed for Section 305(b)/303(d) purposes prior to the current (2008) assessment/listing cycle.]
SUMMARY: The presumptive Class A1 primary contact recreation uses are assessed (evaluated) as “not supported” due to high levels of indicator bacteria. The presumptive Class B(WW1) aquatic life uses are assessed (evaluated) as “partially supported” based on the combine results of IDNR/UHL TMDL-related chemical/physical water quality monitoring during 2006 and 2007 IDNR/UHL biological monitoring data. The source of data for this assessment is the limited chemical/physical monitoring conducted in August 2006 as part of IDNR/UHL TMDL-related monitoring near Lanesboro (STORET station 11140003; TMDL site MaB2). This amount of data (two samples) does not meet IDNR guidelines for Clean Water Act assessment and listing that require at least 10 samples be collected over a three-year period. Nonetheless, the limited data do suggest some directions in water quality that may be useful for interpreting results of monitoring in the downstream segment of Marrowbone Creek (IA 04-RAC-0123_0) that is Section 303(d) impaired.
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses remain assessed (evaluated) as “not supporting” due to the high levels of indicator bacteria (E. coli) in the two available samples. The samples collected from this stream segment on August 15 and August 23, 2006, contained 250 and 2,800 orgs/100 ml, respectively. These data values are high relative to both Iowa’s geometric mean criterion (126 E. coli orgs/100 ml) and Iowa’s single sample maximum criterion of 235orgs/100 ml. While two few data are available to adequately demonstrate an impairment of the Class A1 uses, these moderately high levels do suggest at least the potential for impairment. Such assessments are appropriate for IR Categories 2b or 3b and are appropriate for addition to Iowa’s list of waters in need of further investigation.
The presumptive Class B(WW1) aquatic life uses were assessed (evaluated) as “fully supported” based on results of IDNR/UHL TMDL-related water quality monitoring conducted in August 2006 at station 11140003. Results of this monitoring show no violations of Class B(WW1) water quality criteria for conventional parameters dissolved oxygen or pH) or for ammonia in the two samples collected on August 15 and August 23, 2006. The number of samples collected at this station (two) is low and does not meet IDNR guidelines for developing a “monitored” (higher confidence) assessment (i.e., at least 10 samples collected over a three-year period). Thus, the assessment type is considered “evaluated” (lower confidence). The occurrence of much stronger levels of dissolved oxygen in this upstream (formerly, general use) segment of Marrowbone Creek (8.0 and 9.1 mg/l) is interesting given that levels of dissolved oxygen in the downstream segment on these same two dates were 0.2 and 0.0 mg/l, respectively.
However, the assessment of the presumptive Class B(WW1) aquatic life uses based on 2007 biological data suggest partial impairment of the aquatic life uses. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species that were collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2007 FIBI score was 57 (good) and the 2007 BMIBI score was 24 (poor). The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The non-riffle habitat FIBI BIC for this ecoregion is 32 and the BMIBI BIC is 62. Even though this site passed the FIBI BIC and failed to meet the BMIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it is a small headwater stream and doesn’t fall in the calibrated watershed size.
This assessment is considered “evaluated” (of lower confidence) due to the lack of a biological assessment protocol for general use-only streams. IDNR’s existing protocol has been calibrated to aquatic life reference conditions in wadeable Class B(LR) and Class B(WW) streams. The aquatic environment of most general use streams is one of extremes in water quality. Consequently, general use-only streams tend to have biological diversity that is low relative to more stable aquatic environments of Class B(LR) and Class B(WW) streams. Thus, the use of biological assessment methods developed for the ecologically more stable and diverse Class B(LR) streams to assess general use reaches will likely overstate the existence of impairment. For these reasons, general use-only stream reaches that show a failure to meet regional expectations for aquatic biota (fish or aquatic macroinvertebrates) of Class B(LR) streams, will not be added to Iowa’s Section 303(d) list of impaired waters (Category 5 of the Integrated Report). The assessment type for these waters will be considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to “monitored" (indicating an assessment with relatively high confidence). Such waters will be placed in either Category 2b or 3b of the IR and thus will be added to the state’s list of “waters in need of further investigation”.
