Assessment Comments
Assessment is based on results of (1) results of monitoring for indicator bacteria conducted from April 2008 through October 2010 as part of the Upper Iowa River Watershed project, (2) results of monitoring at one site for the 1998-99 statewide assessment of freshwater mussels in Iowa streams, (3) IDNR/UHL stream REMAP biological sampling near Decorah in 2006, and (4) U.S. EPA/IDNR fish tissue (RAFT) monitoring in 2005, 2006 and 2008 near Decorah. An additional mussel survey was conducted in this segment in August 2012.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated for Class A1 (primary contact recreation) uses and B(WW) aquatic life uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, this segment remains designated for primary contact recreation uses (still termed Class A1) and for aquatic life uses (now termed Class B(WW1). In addition, this assessment segment remains designated for fish consumption uses (now termed Class HH (human health/fish consumption uses).]
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to high levels of indicator bacteria. The Class B(WW1) aquatic life uses remain assessed (evaluated/impaired) as "not supported" based on results of a 1998-99 statewide assessment of freshwater mussels in Iowa streams (results of recent (2012) mussel surveys confirm this impairment). Contrary to the mussel findings, results of monitoring of the fish and benthic macroinvertebrate communities in 2006 indicate "full support" of Class B(WW1) aquatic life uses. Fish consumption uses are assessed as “partially supported” based on results of fish contaminant monitoring in 2002, 2005, 2006, and 2008. Sources of data for this assessment include (1) results of monitoring for indicator bacteria conducted at UIRW Site 17 near Freeport (STORET No. NEIARCD 191910010) from April 2008 through October 2010 as part of the Upper Iowa River Watershed project, (2) results of monitoring at one site for the 1998-99 statewide assessment of freshwater mussels in Iowa streams (Arbuckle et al. 2000), (3) 2006 IDNR/UHL stream REMAP sampling, and (4) U.S. EPA/IDNR fish tissue (RAFT) monitoring in 2002, 2005, 2006, and 2008 near Decorah.
EXPLANATION: The Class A1 (primary contact recreation) uses are assessed as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric mean of indicator bacteria (E. coli) in the 20 samples collected during the recreational seasons of 2008 through 2010 at the Upper Iowa River Watershed monitoring station 17 slightly exceeded the Iowa water quality criterion to protect primary contact recreation uses. Recreation season (March-November) geometric means based on the these 20 samples were above Iowa’s Class A1 water quality criterion of 126 orgs/100 ml: the 2008 geometric mean was 271 orgs/100 ml, and the 2010 geometric mean was 262 orgs/100 ml. The 2009 recreation season geometric mean, however, was 66 orgs/100 ml as was below the Class A1 criterion. Six of the 20 samples (30%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if a recreation season geometric mean is greater than 126 orgs/100 ml., the primary contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
The Class B(WW1) uses remain assessed as "not supported" based on information from the 1998-99 statewide survey of freshwater mussels (Arbuckle et al. 2000). The data upon which this assessment is based are now more than 10 years old. Thus, the level of confidence in the assessment is low as water quality conditions may have changed over the 10-plus years since this most recent sampling occurred. Regardless of the age of the data, however, the Class B(WW1) aquatic life uses of this stream segment remain Section 303(d) impaired due to a decline in the freshwater mussel community. Results from this survey suggest a potential impairment to the aquatic life uses of this stream segment. As part of this study, sampling results from 1998 and 1999 (Arbuckle et al. 2000) were compared to results from stream sites surveyed in 1984 and 1985 by Frest (1987). On a statewide basis, this comparison showed sharp declines in the numbers of mussel species ("species richness") in Iowa’s streams and rivers from the mid-1980s to the late 1990s. Results of this comparison were used by staff of the Iowa DNR to assess the degree to which the aquatic life uses of the sampled stream segments are supported. For purposes of Section 303(d) listing, this assessment was based on the percent change in the number of species of freshwater mussels found in the 1984-85 survey versus the 1998-99 survey. Greater than a 50% decline in species richness from the 1984-85period to the 1998-99 period suggests an impairment of the aquatic life uses. Species richness of freshwater mussels at the one sample site in this stream segment was 6 in the 1984-85 period and was 0 in the 1998-99 period for a percent change of minus 100%. Based on these results, the aquatic life use are assessed as "not supported" for purposes of both Section 303(d) listing and Section 305(b) reporting. As presented by Arbuckle et al. (2000), the potential causes of declines in species richness of Iowa's freshwater mussels include siltation, destabilization of stream substrate, stream flow instability, and high in-stream levels of nutrients (phosphorus and nitrogen). Their study also suggested the importance of stream shading provided by riparian vegetation to mussel species richness. Additional monitoring is needed to better define the biological status of this stream segment as well as the site-specific causes and sources of impairment of these uses that may exist. Because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). Despite this change in assessment type, this waterbody remains in IR Category 5b.
Note: Surveys of freshwater mussels were conducted by Iowa DNR staff at one site (Site 48) in this assessment segment in August 2012.
--Number of freshwater mussel species from surveys conducted in 1984 (Frest (1987), in 1998 (Arbuckle et al. 2000), and IDNR Watershed Improvement Section staff (J. Kurth) in 2012:
1984 1998 2012
Site 48: 6 0 1
The results of this monitoring suggest that the decline in the number of species at Site 48 remains, with only one mussel species collected compared to six species in 1984. These result suggest continuing impairment of the Class B(WW1) aquatic life uses.
Contrary to the mussel findings in the late 1990s, the fish and other benthic macroinvertebrate communities appear to be healthy. This evaluated biological assessment was based on data collected in 2006 as part of the IDNR/UHL stream REMAP project. A series of biological metrics that 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 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 2006 FIBI score was 81 (excellent) and the BMIBI score was 75 (good). The aquatic life use support was assessed (evaluated) as fully supporting (=FS), 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 FIBI BIC for this ecoregion is 52 and the BMIBI BIC for this ecoregion is 61. This assessment is considered evaluated because the drainage area (584 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. Even though this site passed both the FIBI and BMIBI BICs, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it doesn’t fall in the calibrated watershed size.
Fish consumption uses are assessed (monitored) as “partially supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring upstream from Decorah in 2005, 2006 and 2008 and on the issuance of a fish consumption advisory in 2006. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses.
For the 2005 RAFT sampling, levels of primary contaminants in the composite sample of common carp fillets were as follows: mercury: 0.036 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. Levels of primary contaminants in the composite sample of smallmouth bass fillets were as follows: mercury: 0.334 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. Similar to the 2002 sampling, the level of mercury in the smallmouth bass fillets at this site exceeded the IDNR/IDPH trigger level of 0.3 ppm.
The 2006 RAFT sampling produced similar results. The composite sample of smallmouth bass fillets contained 0.32 ppm of mercury. The sample of golden redhorse (Moxostoma erythrurum) fillets contained 0.567 ppm of mercury. Both of these levels were above the 0.3 one-meal/week advisory trigger level.
For the 2008 RAFT sampling levels of primary contaminants in the composite sample of golden redhorse fillets were as follows: mercury: 0.351 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm. Similar to the 2005 and 2006 sampling, the level of mercury in the golden redhorse fillets at this site exceeded the IDNR/IDPH trigger level of 0.3 ppm.
According to the IDNR/IDPH advisory protocol, if two consecutive samplings show that contaminant levels are above the trigger level in fillet samples, issuance of a consumption advisory is justified. Because the levels of mercury in samples of smallmouth bass and golden redhorse fillets from this river segment consistently have been at or above the advisory trigger level, a one-meal/week advisory was issued by IDNR and IDPH in January 2006. This advisory originally covered the reach of the Upper Iowa River from the Lower Dam in eastern Winneshiek County to the county road bridge approximately 5.5 miles upriver (northwest) from Decorah. Additional fish contaminant (RAFT) monitoring in 2006 resulted in extending this advisory downriver from the Lower Dam to state highway 76. The existence of a fish consumption advisory at this river segment suggests that the fish consumption uses be assessed as "partially supporting."
