Maple River IA 06-LSR-1581

Assessment Comments

Assessment is based on results of IDNR ambient monthly monitoring near Mapleton in 2000 & 2001.

Basis for Assessment

[Note:  For the 2002 report, the previous waterbody segment for the Maple River (IA 06-LSR-0070-0), which extended 45 miles from its mouth confluence with the Odebolt Creek at Ida Grove (Ida Co.), was split into two subsegments:  (1) mouth (Monona Co.) to confluence with an unnamed tributary 1 mile east of Danbury in Woodbury Co.  (IA 06-LSR-0070-1 - this one) and (2) unnamed tributary near Danbury to confluence with Odebolt Creek at Ida Grove (Ida Co.) (IA 06-LSR-0070-2).   See previous Section 305(b) assessments from this subsegment for assessments for the original 45-mile river reach.]

SUMMARY:  The Class B(WW) aquatic life uses are assessed as "fully supported."  Fish consumption uses remain "not assessed."  This assessment is based on results of IDNR monthly ambient monitoring conducted during the 2000-2001 biennial period at the Highway 141-175 bridge at Mapleton (station 10180001 (formerly station 911040)).   EXPLANATION:  Monitoring at the IDNR station at Mapleton showed no violations of Class B(WW) water quality criteria during the 2000-2001 biennial period for dissolved oxygen (minimum value = 6.9 mg/l), pH (range = 7.7 to 8.7 units), or ammonia-nitrogen (maximum value = 5.70) in the 24 samples analyzed.   The maximum value of ammonia-nitrogen (5.7 mg/l) occurred on March 6, 2001, and did not violate the pH/temperature-dependent Class B(WW) chronic criterion of 7.18 mg/l.   The next highest level of ammonia-nitrogen during the biennial period was 0.6 mg/l on February 6, 2001.   Levels of toxic metals in the four samples analyzed, and levels of pesticides in the six samples analyzed, were all below the analytical level of detection.   Despite the relatively high level of ammonia-nitrogen in the sample from March 6, 2001, no violations of Class B(WW) criteria occurred during the biennial period; thus, these results suggest "full support" of the Class B(WW) aquatic life uses.   Fish consumption uses remain "not assessed due to the lack of recent fish contaminant monitoring in this river reach.